*3.3. X-ray Diffraction Analysis of the Powders*

Several XRD patterns gathered at various stages of MA are shown in Figure 5a. As can be seen at the early stage of MA (5 h), the microstructure was purely bcc, and the main Fe-bcc phase was accompanied by several reflections of Mn-bcc. After 5 h of milling, no significant change in microstructure occurred as compared to the initial powder mixture (Figure 5c), besides broadening of reflections, and Mn peaks were still present. Eventually, after 30 h of MA, Mn reflections vanished, suggesting that it was finally dissolved in the Fe matrix. At this point, the Mn-induced phase transformation process was obvious, as the bcc peak intensities dropped drastically and fcc peaks became dominant (Figure 5a,c). After 60 h of MA, the bcc reflections were nearly elusive, with the exception of the most prominent [110] Fe-bcc peak. Prolonged milling caused a further increase in the intensity of the Fe-fcc phase. The Fe-bcc [110] peak trace, however, was still detectable even after 150 h of MA (Figure 5d).

**Figure 5.** Microstructural evolution of Fe-18Cr-18Mn alloy: (**a**) overall comparison of XRD patterns after a certain MA time, (**b**) insight showing the vanishing of Fe-bcc peaks, (**c**) comparison of initial and after 5 h of MA patterns with emphasis on Mn-bcc reflections, (**d**) changes of the shape and intensity of most prominent Fe-bcc [110] and Fe-fcc [111] reflections during the MA course.

XRD patterns were fitted using the pseudo-Voigt function and the extracted data (peak 2*θ* position and FWHM) were processed in accordance with the MWH procedure, using the calculated contrast factor values for Fe-bcc and Fe-fcc phases, and regarding the instrumental broadening correction and proper background definition. The phase percentage was estimated by the ratio of integrated areas of peak profiles of Fe-bcc and Fe-fcc phases, respectively, as presented in Figure 6.

**Figure 6.** Phase percentage of Fe-fcc.

Extracting information from the experimental peak profiles, where multiple phases exist simultaneously, outlines the major problem concerning the traditional LPA methods—overlapping among peak profiles (especially within the region of Fe-bcc [110] and Fe-fcc [111] peaks). The most common solution to this difficulty is pattern decomposition—separating the individual contributions from different phases and subtracting the instrumental and background effects.

The main results of the MWH analysis are collated in Figure 7. The experimental values of *q*, which imply the edge/screw characters of dislocation, were evaluated using the methodology provided by Ungár et al. [18] (Figure 7a). The FWHM values were plotted according to the MWH relation (Figure 7b), where the intersection at *KC*1/2 = 0 gave the average crystallite size *d*. It is clear that the data points follow the linear trend in almost the exact manner and, therefore, were fitted using the linear function. It should be underlined that, due to the progressive bcc→fcc phase transformation over the MA time, the reliable determination of FWHM of Fe-bcc reflections was rather unobtainable after 30 h of MA, caused by the strong broadening and low intensity. Although after 30 h of MA, there were still three apparent Fe-bcc reflections present (Figure 5a), they were not enough to calculate *d* accurately using the MWH method.

As presented in Figure 7c, the domain size was reduced from ~20 nm to around 10 nm during the first 60 h of MA and saturates at this level until the end of milling. The slope of the MWH linear approximation is also plotted in Figure 7c, which can be related to the dislocation arrangement parameter *M* and the square root of dislocation density *ρ*. However, the *M* can be determined thoroughly only with the Fourier methods, such as WPPM. Consequently, the determination of *ρ* from the results obtained by MWH alone is improper and should be avoided [38]. Nevertheless, the inspection of the MWH slope provides some insight into the strain accumulation in the material, and it can be noticed that it mimics the trend of *d* in the opposite manner (Figure 7c). Finally, the dislocation character trend was plotted in the form of the edge dislocation fraction *fe* (Figure 7d). In general, the dislocation structure is in favor of screw dislocations over the whole MA process, which might be caused by the rotational nature of the ball milling process, promoting the formation of twists in crystals [39]. The *fe* value fluctuates in the 0.2–0.4 region and never exceeds the half edge–half screw line. This supports the other authors' conclusions that edge dislocations are unstable in fine Fe domains [24,40].

**Figure 7.** The principal result of the MWH analysis: (**a**) determination of experimental *q* values, (**b**) FWHM values plotted according to the MWH procedure, (**c**) evolution of crystallite size and MWH slope, (**d**) fraction of edge dislocations during MA.

The diffraction data were furtherly analyzed by the WPPM approach and the quality of fit can be perceived in Figure 8. Plots present the experimental data compared with model WPPM diffractograms, further decomposed into single analyzed phases (Mn-bcc, Fe-bcc, and Fe-fcc). A flat, nearly featureless residual line (the difference between experimental and calculated patterns) proves good quality of modeling. The graphical analysis is essential to determine the quality of fit and to ensure that the model is chemically plausible. The quality of WPPM fit, such as in other least-squares minimization methods, can also be defined by inspecting the discrepancy factors. In this study, the most straightforward discrepancy index, the weighted profile *R*-factor, *Rwp*, did not exceed 3.46%, which indicates a robust quality of fit, particularly considering the multiplicity of phases and overlapping peaks. Another marker, goodness of fit (GoF, related to the ratio between actual and expected *Rwp*) had a maximum of 1.52 (pattern after 5 h of MA) and a mean value of 1.21 (where unity indicates the flawless fit).

Unlike the MWH method, the pattern is not decomposed into individual line profiles, but the whole diffractogram is modeled by optimizing the value of several physical parameters. Figure 8a presents the pattern obtained after 5 h of MA, with a detailed view of multiple, minor Mn-bcc reflections, successfully refined using WPPM. Figure 8b–d magnify the most interesting, from the modeling viewpoint, 2*θ* region, where prominent Fe-bcc [110] and Fe-fcc [111] peaks extensively overlap. Additionally, inserts show the fit quality of the remaining reflections.

**Figure 8.** WPPM-refined experimental patterns gathered after: (**a**) 5 h of MA, (**b**) 30 h of MA, (**c**) 60 h of MA, (**d**) 150 h of MA. Legend: hollow dot—experimental data, red line—WPPM model, orange line—Mn-bcc phase, blue line—Fe-bcc phase, green line—Fe-fcc phase, black line—residual.

Basic results derived from WPPM refinement, in terms of size and strain evolution during MA, are revealed in Figure 9. It is a known fact that MA prompts the volume expansion of the unit cell, predominantly as a result of severe plastic deformation and persistent dissolution of alloying additives and various contaminants originating from the milling equipment into the matrix [28]. As depicted in Figure 9a, the lattice parameter *a f cc* of the Fe-fcc phase increases constantly up to 90 h of MA and then exhibits a sharp rise and sets around this value.

The domain size *d* decreases with the MA time, following a similar trend as using the MWH method, and so does the lognormal standard deviation (Figure 9b,c). However, the *d* values obtained with the WPPM method are roughly half of that calculated by MWH. Both methods confirm that grain refinement is effective only during the beginning of MA (up to 30 h), with little reduction achieved afterward. It is worth mentioning that real materials have distributions of domain sizes, so the trends of the size distributions should also be followed, as demonstrated in Figure 10, and the corresponding values of the standard deviation of lognormal distribution are plotted in Figure 9c. It is clear that mechanical treatment causes the shift of the domain size distribution curve to lower values, the standard deviation being reduced accordingly, especially in the early stage of MA (Figure 10a). Eventually, a microstructure consisting of very fine (*d* = 6 nm) and narrowly distributed (*σ* = 3 nm) crystalline domains is established. Similar crystallite sizes were previously reported for other ball-milled fcc alloys (e.g., [41,42]).

**Figure 9.** Basic microstructural data derived from WPPM refinement in terms of the progression of following the parameters during MA: (**a**) lattice parameter, (**b**) lognormal domain size, (**c**) lognormal standard deviation, (**d**) dislocation density. Error bars correspond to the estimated standard deviation of the WPPM fit.

**Figure 10.** Lognormal domain size distributions of crystalline domains: (**a**) up to 30 h of MA, (**b**) after 30 h of MA, in terms of probability density function (PDF).

It is also clear that ball milling generates a high density of dislocations due to severe plastic deformation of ground material, which can be followed in Figure 9d. In general, the accumulation of defects in the Fe-fcc phase follows a similar trend to lattice expansion, with the same sharp rise after 120 h of MA. This is foreseeable, given the fact that the

lattice inflation is caused not only by the dissolution of alloying additives but is directly caused by an increase in the dislocation density [43] and is further promoted by extrinsic dislocations pilling up at the grain boundaries [44]. Rawers and Cook suggested that the strain on the grain boundary could extend into the nanograin itself, expanding the lattice [45]. In this study, from the moment of appearing (30 h) up to 90 h of MA, the *ρ* of Fe-fcc phase oscillates around 2 × 1016/m2, then experiences a sharp rise and sets around 3.5 × 1016/m2, the effective outer cutoff radius *Re* being 6.24 nm. The final value of *Re* is around that of the mean crystallite size *d* (6.0 nm), and corresponds to an average of half the dislocation per crystalline domain (for *d* = 6.0 nm: *d*/ *πd*3/6 ∼ 5.3 × 1016/m2), which is plausible. This is in line with HRTEM observations of ball-milled FeMo alloy by Rebuffi et al. [24], which concluded that dislocations are rather unlikely to be present in every single crystalline domain. As the accumulation of defects in powders, subjected to serious mechanical treatment, is the principal cause of microhardness growth during MA (Figure 4), *ρ* and *HV* can be related, which is demonstrated in Figure 11.

**Figure 11.** Relationship between dislocation density *ρ* and powder microhardness *HV*. Dashed line is the linear fit of the data.

Regarding the mutual dependence of *ρ* and *Re* parameters in the Krivoglaz–Wilkens dislocation theory, Wilkens introduced the dimensionless parameter *M* = *Reρ*−1 = *Re*/*ld* called the Wilkens parameter. As can be noticed, *M* is also directly related to the average dislocation distance *ld*; therefore, it is used to determine the arrangements of dislocation arrangements in the strain fields [30]. The value of *M* much larger than unity (*M* 1) indicates that the dislocations are very weakly correlated and randomly arranged (weak dipole character). In contrast, *M* ≤ 1 signifies a distinctly correlated dislocation arrangement, accompanied by an intense screening of strain fields (*Re* < *ld*) (strong dipole character). In the present case, the decreasing value of *M* of the fcc phase to the value of ~1 with milling time (Figure 12) supports the hypothesis of gradual transformation from a dislocation cell structure with long-range strain fields into the nanocrystalline microstructure with a high density of dislocations, systematically distributed in grain boundaries.

**Figure 12.** Trend of the Wilkens parameter *M* in the function of milling time.

The WPPM modeling quality was good (mean GoF = 1.21) and hassle-free in almost all cases, except the problems encountered during refining the pattern obtained after 30 h of MA. In that case, during refinement of the Fe-bcc phase, *Re* constantly reached unrealistically small values (<1 nm), the lower limit of the continuum approach [46]. As a consequence, *ρ* rose to incredibly high levels a few times 1017/m2, accompanied with very low *M* (~0.35). When the dislocation density in material becomes sufficiently high (1016/m2), the strain field parameters (*ρ*, *Re*, *M*) can become uncertain in the sense that *Re* constantly approaches 0; this is a known intrinsic problem with the Krivoglaz–Wilkens theory caused by the strong reciprocal correlation of *Re* and *ρ* [47]. The simplest way to overcome this discrepancy is by imposing the arbitrary value of *Re* and keeping it fixed during refinement. Here, we assumed that *Re* was extended to the size of the entire crystalline domain (*Re* = *d*, ~6 nm), and with this constraint, *ρ* = 2.92 × 1016/m2 and *M* = 0.85 was obtained, which seemed perfectly reasonable.


*Article* **Novel Motion Sequences in Plant-Inspired Robotics: Combining Inspirations from Snap-Trapping in Two Plant Species into an Artificial Venus Flytrap Demonstrator**

**Falk J. Tauber 1,2,\* ,† , Philipp Auth 1,†, Joscha Teichmann 1 , Frank D. Scherag 2,3 and Thomas Speck 1,2,4**

**Abstract:** The field of plant-inspired robotics is based on principles underlying the movements and attachment and adaptability strategies of plants, which together with their materials systems serve as concept generators. The transference of the functions and underlying structural principles of plants thus enables the development of novel life-like technical materials systems. For example, principles involved in the hinge-less movements of carnivorous snap-trap plants and climbing plants can be used in technical applications. A combination of the snap-trap motion of two plant species (*Aldrovanda vesiculosa* and *Dionaea muscipula*) has led to the creation of a novel motion sequence for plant-inspired robotics in an artificial Venus flytrap system, the Venus Flyflap. The novel motion pattern of Venus Flyflap lobes has been characterized by using four state-of-the-art actuation systems. A kinematic analysis of the individual phases of the new motion cycle has been performed by utilizing precise pneumatic actuation. Contactless magnetic actuation augments lobe motion into energyefficient resonance-like oscillatory motion. The use of environmentally driven actuator materials has allowed autonomous motion generation via changes in environmental conditions. Measurement of the energy required for the differently actuated movements has shown that the Venus Flyflap is not only faster than the biological models in its closing movement, but also requires less energy in certain cases for the execution of this movement.

**Keywords:** plant-inspired robotics; artificial Venus flytrap; motion sequence; biomimetics; bioinspiration

### **1. Introduction**

Within the last decade, plant-inspired robotics has become established as a new emerging field of soft robotic science. One outstanding example is represented by the plant-inspired growing robots developed by the group at the Italian Institute of Technology; these robots have roots, tendrils, and leaves like their biological models and are able to grow, forage, and harvest energy from the environment [1–5]. A focus area within this field is the development of artificial systems with certain characteristics that are able (1) to exist autonomously, (2) to sense, adapt, and react to the environment, (3) to sustain their homeostasis by harvesting energy, (4) to sense damage, and (5) to possess self-repair functions. Such systems are currently still in their infancy but should revolutionize the technical world in the future.

The Venus flytrap (*Dionaea muscipula*) provides a suitable biological model for plantinspired robotics. These plants perceive their environment and adapt and react to it, all

**Citation:** Tauber, F.J.; Auth, P.; Teichmann, J.; Scherag, F.D.; Speck, T. Novel Motion Sequences in Plant-Inspired Robotics: Combining Inspirations from Snap-Trapping in Two Plant Species into an Artificial Venus Flytrap Demonstrator. *Biomimetics* **2022**, *7*, 99. https:// doi.org/10.3390/biomimetics7030099

Academic Editor: Jinyou Shao

Received: 15 June 2022 Accepted: 15 July 2022 Published: 22 July 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

of which are features required by robots. In addition, Venus flytraps carry out one of the most complex decentralized controlled process sequences in nature, namely a fast snap-buckling prey capture movement, which includes an upstream mechanical memory and several subsequent processes depending on successful prey capture [6]. The Venus flytrap can be considered as a bi-stable system, with the lobes being stable in a convex and concave configuration [6–8], changing through a snap-buckling motion similar to technical bistable systems [9–12]. The transference and combination of the basic principles of the Venus flytrap movement sequence has enabled the production of life-like artificial Venus flytraps (AVF) [13]. However, artificial Venus flytraps have so far been produced more as a by-product of the development of new actuation systems. AVFs have been used as suitable demonstrators of the capabilities of actuators in the development of novel pneumatic systems utilizing instabilities in elastic energy storage [14], magnetically driven bi-stable prepregs [15,16], ionic electroactive polymer metal composites (IPMCs) [17,18], light responsive liquid crystalline elastomers (LCEs) [19,20], and hygroscopic bistable systems (HBS) reacting to changes in humidity [21]. However, none of these AVF systems incorporates all the functions of the biological model *D. muscipula*. Most of them only exhibit a reasonably fast (sometimes without snapping) closure mechanism following an external stimulus, as Esser et al. [13] have shown in their review of the current state of AVFs. Nevertheless, a simple and low cost AVF with a novel motion pattern inspired by two carnivorous plants has been developed, inspired by those AVF systems: the Venus Flyflap (VFf). It uses various actuation modes and allows the investigation and characterization of the energy needed for actuation [22]. In addition, for the first time, this system combines motion features of two closely related snap-trapping carnivorous plants into one system, namely the snap-buckling of *D. muscipula* (Figure 1A,B) and the kinematic coupling and motion amplification of the Waterwheel plant (*Aldrovanda vesiculosa*) (Figure 1C,D) [6,7,23,24]. The trap closure movements based on these motion principles are among the fastest movements in the plant kingdom: *A. vesiculosa* needs 0.02 to 0.1 s [23] and *D. muscipula* 0.1 to 0.5 s [6] to close their trap lobes.

The compliant foil structure used in the VFf is based on a shape inspired by the biological models. A rectangle forms the base (analogous to the leaf midribs of *A. vesiculosa* and *D. muscipula*); attached to its long sides, two triangles represent the trap lobes, and two circles ('ears') at the short ends of the rectangle allow the actuation of the system through kinematic coupling (Figure 1E–G) [14]. A downwardly directed motion of the 'ears' results in motion amplification causing the fast closure of the system by a continuous motion, as found in *A. vesiculosa*. To be able to snap, the foil 'midrib' is reinforced with a plastic microscopic slide as a backbone. When force is applied centrally, the backbone changes its curvature, and the VFf opens its lobes in a fast snapping motion similar, but inverse in direction, to the snapping by curvature inversion in *D. muscipula*. Thus, a new motion sequence has been achieved by combining the motion principles of the two snap-trap plants into one artificial system. A fast (continuous) closing step, followed by a sudden release of the stored potential elastic energy in the system, causes a snap opening, as soon as the input energy exceeds a certain threshold.

The present study aims to answer the following questions. Is it possible to build a biomimetic system that combines and utilizes two movement principles in one cost-efficient structure, that mimics the biological models, and that can be triggered by environmental stimuli?

net varying the actuation speed is used to achieve and investigate a uniform energy-effective oscillation or resonance-like motion (Figure 1I). Concerning autonomous systems, the VFf can be also actuated by environmental stimuli such as heat and humidity or a combination of both, by using environmentally sensitive materials such as shape memory alloys and polymers in combination with hydrogels. Furthermore, a comparison of our system with the biological models and the state of the art in artificial Venus flytraps allows an

evaluation of its biomimetic potential.

**Figure 1.** After being triggered, the Venus flytrap (*Dionaea muscipula*) closes its lobes by inverting the curvature of the lobes from, as viewed from the outside, concave (**A**) to convex (**B**) through the **Figure 1.** After being triggered, the Venus flytrap (*Dionaea muscipula*) closes its lobes by inverting the curvature of the lobes from, as viewed from the outside, concave (**A**) to convex (**B**) through the release of stored elastic energy. In the waterwheel plant (*Aldrovanda vesiculosa*) (**C**), water displacement in turgescent cells lying along the midrib combined with the release of stored elastic energy results in bending of the midrib, which is kinematical amplified and causes trap closure (**D**). The compliant foil demonstrator, the Venus Flyflap (VFf) (**E**), combines both mechanisms to close and open its artificial lobes. When force is applied to the ears (**F**,**G**), the lobes close via a kinematic coupling mechanism. Force applied to the backbone triggers a fast-snapping opening movement similar to the closing movement of the Venus flytrap. These mechanisms have been incorporated into various actuation scenarios. Pneumatic cushions drive the motion and enable the characterization of each phase of the motion sequence (**H**). A resonance-like, rapidly oscillating, flapping motion is achieved by a magnet that is attached to the ears and that responds to a rotating magnetic field (**I**). The VFf can also be actuated by environmental stimuli, when fitted with shape memory alloy (SMA) springs (**J**) or a combination of environmentally sensitive materials such as SMA and polymers in combination with hydrogels reacting only to a change in humidity and temperature (**K**).

Direct actuation by means of pneumatic cushions enables the opening and closing movements of the VFf to be controlled in a targeted manner (Figure 1H). Thereby, specific aspects of the motion and system as a whole can be investigated separately. This should provide new insight into the motion behavior (closing and opening times and speeds), the kinematics, and the elastic energy storage of the system. Contactless actuation via a magnet varying the actuation speed is used to achieve and investigate a uniform energy-effective oscillation or resonance-like motion (Figure 1I). Concerning autonomous systems, the VFf can be also actuated by environmental stimuli such as heat and humidity or a combination of both, by using environmentally sensitive materials such as shape memory alloys and polymers in combination with hydrogels. Furthermore, a comparison of our system with the biological models and the state of the art in artificial Venus flytraps allows an evaluation of its biomimetic potential.

#### **2. Materials and Methods**

### *2.1. Setups for Movement Analysis of Dionaea Muscipula and the Artificial Venus Flyflap (VFf)*

In order to enable a valid comparison of the motion characteristics of the *D. muscipula* plant with the pneumatically and magnetically actuated VFf, a kinematic analysis was performed using a video chamber fitted with two 1000 fps high-speed cameras (Baumer matrix monochrome camera VCXU 13 M/Imaging Solutions Motion traveller 1000) (Figure 2A). Videos were recorded at a constant frame-rate of 1000 fps with a resolution of 512 × 512 pix, and the recordings were synchronized using NorPix-StreamPix <IP_ADDRESS> (x64) Software. During actuation, the path of motion, movement speed, and kinematic parameters (speed and acceleration) were tracked and analyzed using the open-source software Kinovea (version 0.9.1). During the testing period of three weeks, 28 traps from four different *D. muscipula* plants were tested repeatedly. The tests were performed on three different dates with one week of "rest" in between to minimize the stress for the plants. Tracking markers were applied to the lobe tips of the pneumatic VFf and the magnetic VFf and to the magnets. The video and picture-based analysis of the thermally driven VFf actuated with shape memory alloy (SMA) springs (Figure 2B) and of the hydrogel actuated VFf (Figure 2C) required only a lower framerate because of the lower motion speed. Therefore, a digital camera (Panasonic Lumix DMC-FZ1000, Figure 2(C3)) with a recording framerate of 25 fps was used. In the case of the thermally driven VFf, the lobe tips and the spring length were tracked. Statistical data analysis was performed with the open-source software RStudio (version 1.2.5042).

The setup of the actuator systems is described in detail in Esser et al. [14] and shown in Figure 1. Further information is provided in the supplementary material section "Materials and Methods: 2.1 Standardized production of the compliant foil demonstrators". *Biomimetics* **2022**, *7*, x FOR PEER REVIEW 5 of 27

**Figure 2.** *Cont*.

**Figure 2.** Characterization setups. High-speed videos were recorded in a specifically build recording chamber (**A**) with two highspeed cameras (**A1**) positioned at a 90◦ angle to each other. Light is provided by two high-power flicker-free LED light sources (**A2**) that point at the object of interest (**A3**). The Venus flytrap and the pneumatic and the magnetic demonstrators were recorded using this setup.The SMA actuated demonstrators were tested by placing them in a temperature chamber (**B1**). Three demonstrators were tested simultaneously (**B2**). The movement of the springs and the lobes of the demonstrator were recorded by two cameras (**B3**) for later analysis. For actuation of the hydrogelbased demonstrator (**C1**), a hot water vapour source (**C2**) provided enough humidity to unlock the demonstrator, which was filmed by a camera for kinematic analysis (**C3**). Force-displacement measurements were performed with specific test mounts by the Hegewald and Peschke Inspekt Table 5 (**D**). The output force for each SMA spring was measured (**E1**) at 63 ◦C. To mimic the actuation procedure, specific mounts were designed to apply pressure in the direction of actuation in the demonstrator (magnetic (**E2**) and pneumatic (**E3**)). An exemplary force displacement curve of an opening event of the pneumatic system is shown in (**F**). S1 and S2 indicate the lower and upper end, respectively, of the integral (green area) used for calculating the kinetic energy necessary to open the the two lobes (lobe openig indicated in the curve by the two sudden force reductions).

#### *2.2. Energy Measurements*

The energy consumption in each experiment was determined by measuring the amount of electricity that was required for actuation. The electricity consumption was determined with an energy-measuring device that was plugged into the socket before the actual electricity consumer, e.g., the pneumatic test bench, magnetic stirrer, temperature chamber, or steam source. Force-displacement measurements were performed for calculating the necessary work and kinetic energy to drive and trigger the closing and opening movements of the demonstrators (Figure 2F). A specific testing setup to apply force according to the actuation scenario was designed for each VFf system (Figure 2E). The pneumatic VFfs were fixed in an upside-down orientation in the testing machine, and the compression pistons applied force to the backbone through the casing openings for the pneumatic cushions (Figure 2(E3)). In the case of the magnetic VFf, a downward force was applied to the magnets until the lobes closed (Figure 2(E2)) Clamps for the tensile tests held the SMA spring of the thermal VFf inside the thermal chamber of the testing machine. The temperature was increased up to 65 ◦C, and the output force was measured. All measurements were performed with an Inspect universal testing machine (Hegewald and Peschke Meß-und Prüftechnik GmbH, Nossen, Germany). During all hysteresis measurements, the stroke was adjusted accordingly to achieve a full closing or opening movement. The movement of the machine caused further increasing forces after a complete opening, since the testing machine did not immediately change the direction of movement after opening. These measurement ranges were excluded from the kinetic energy calculations. Since the course of the force was not uniform, it had to be integrated over the entire path until the moment when both trap lobes opened (*s*2) (Figure 2F). The area under the force-displacement curve represents the work exerted on the moving object. By measuring the area, the work and thus the required kinetic energy can be calculated by:

$$\mathcal{W} = \int\_{s\_1}^{s\_2} \stackrel{\rightarrow}{F} \left( \stackrel{\rightarrow}{s} \right) \* d \stackrel{\rightarrow}{s} . \tag{1}$$

with *W* = work/kinetic energy; *F* = force; *s* = stroke; *s*1 and *s*2 indicate the lower and upper end of the integral, respectively. The efficiency calculation and corresponding equations are shown in the supplementary material section "Materials and Methods: 9. Actuation system efficiency calculation".

#### *2.3. Motion Analysis of Discrete Repetitive Motion Generation by Pneumatic Actuation*

Analysis of the complex motion pattern of the VFf was achieved by using directly driven pneumatic actuation of the opening and closing motions, which could be triggered separately. The foil-based VFf was attached to a 3D-printed (RigurTM; Stratasys Ltd., Eden Prairie, MN, USA) ridged case that housed three pneumatic cushions (EcoFlex 0030; KauPo Plankenhorn e.K., Spaichingen, Germany) (Figure S1). Pressurization of the two smaller outside cushions pushed the rigid backbone of the VFf upwards, because its ears were attached to the casing (Figure 1H). This closed the lobes via kinematic amplification, as seen in *A. vesiculosa*. To trigger the opening movement, the central cushion inflated, while the outside cushions deflated. This caused the backbone to bend, leading to a fast "snapping" opening movement accompanied by an inversion of the spatial curvature of the lobes, similar to the snap-buckling principle of *D. muscipula*. Pressurized air was supplied by a pneumatic test bench [25] that enabled measurement and manipulation of the pressure and pressurization time for the closing and opening motions, respectively (see Table S3 for actuation pattern). As pressurization inflated the cushions and actuated the system, we further refer to the duration of pressurization as the actuation time (AT). The actuation times chosen for the characterization were 200 ms, 300 ms, and 400 ms, as the closing time of the biological model was below 500 ms. During actuation, the valves opened depending on the AT pressurizing the cushions. The actuation pressure was determined to be 0.7 bar in preliminary tests. This was the maximum pressure at which complete closure was

guaranteed without the cushions bursting. The system pressure was adjusted accordingly to the AT in order to achieve a pressure of 0.7 bar within the actuators during each AT.

#### *2.4. Motion Analysis of Contactless Actuation of the Demonstrator by a Rotating Magnetic Field*

In the magnetic VFf, the foil demonstrator was directly attached to a 3D-printed casing without the rigid microscopy slide backbone. The casing in turn was attached to an aluminum profile in the video chamber (see Figures 1I and S2). A set of two round flat magnets (Neodymium, 15 × 2 mm, 30 g each, 6 kg holding force) was attached to one of the ears. The VFf was placed 20 mm above a magnetic stirrer (IKA RCT B 5000) with adjustable rotations per minute (rpm) ranging from 100 to 1500 rotations per minute. The rotating magnet pulled and pushed the VFfs magnets, resulting in upwards and downwards movements of the VFf ear, which in turn set the lobes into a flapping motion. To investigate the possibility of reaching the natural frequency and gaining a resonance effect in the oscillating flapping motion of the system, six different actuation speeds were investigated with 400, 700, 800, 900, 1000, and 1300 rpm, respectively. In preliminary tests, the rpm were steadily increased from 0 to 1500 and the behavior of the VFf was observed. From 400 rpm onwards, the first clear movements occurred, at 800 and 900 rpm a uniform movement behavior was observed and for frequencies above 1300 rpm only irregular behavior. Because of this, the focus of the experiments was on the range of 800 and 900 rpm, and additional frequencies 100 rpm higher and lower were investigated. In addition, the extremes of 400 rpm (first clear movements) and 1300 rpm (only irregular erratic motions) were investigated.

#### *2.5. Environmentally Triggerable Systems*

#### 2.5.1. Motion Analysis of Thermally Actuated VFf by Using SMA Springs

To introduce autonomy into the system, the VFf was equipped with a temperaturesensitive SMA spring (Nitinol). The critical temperature for the SMA springs to induce contraction was determined by placing five springs in the temperature chamber of the universal testing machine at increasing temperatures, starting at 22 ◦C, and the length was measured each time that the temperature rose by 2 ◦C (see Table S2 and Figure S4). An SMA spring was attached to the foil demonstrator by using rivets on each lobe (see Figure 1J). The spring was stretched to a fixed length of 115 mm and then attached to the VFf. Three VFf were tested simultaneously in a climate chamber (Environmental test chamber CTC256, Memmert GmbH + Co. KG) that allowed programmed temperature settings (Figure S5). Three different temperatures were tested (55 ◦C, 60 ◦C, 65 ◦C) (Figure S6). The rising ambient temperature induced a phase transformation in the spring material reversing the deformation of the spring, which then shortened and, hence pulled the ears downwards closing the VFf.


**8.1 Dosimetry in paediatric nuclear medicine: from acquisition to image processing, image gently**

The radiation burden in nuclear medicine depends principally on the administered radiopharmaceutical properties and the biological parameters-pharmacokinetics properties of the radiopharmaceutical within the patient. So,

To limit radiation exposure to children from diagnostic nuclear medicine procedures to the lowest levels with reliable qualitative imaging, a correlation of administered activity with weight-effective dose in radiopharmaceutical imaging is valued.

Administered activities in paediatric subjects are distributed over smaller volumes generating higher absorbed doses. In diagnostic examinations, fractions of adult administered amounts and formulae based on child's body parameters are used. Recommended activities could be obtained by EANM dosage-card or North American Guidelines—Paediatric dosage card.

Cumulated activity calculation from the time-activity curve will lead to a total number of disintegrations. Absorbed dose algorithms and image processing determine the radiation transport, energy deposition and the radiation burden of the subject; Advanced approaches such as Monte-Carlo modelling in nuclear medicine for imaging and dosimetry are successfully used.

For newborn subjects, it is necessary to apply the minimum dose, because the activity calculated according to newborn weight is less than the recommended minimum activity, resulting to worsen diagnostic imaging quality.

#### **8.2 Optimization—Conclusion**

Optimization in medical imaging is the balancing of the amount of ionizing radiation and image quality. The minimum radiation dose for the paediatric patient must assure that the image quality provides satisfactory information to meet the clinical requirement. Optimization involves both the imaging systems as testing and quality control as well as imaging body parameters and administered activity [25].

Optimal protocols, with improved image reconstruction methods and advanced instrumentation, facilitate the dosage reduction and provide the maximum image quality at a minimum effective dose. Optimization of imaging protocols and establishment of diagnostic reference levels achieve the goals of good quality images at reduced radiation doses. Standardized methods for performing dose calculations for radiopharmaceuticals by various steps in the process and models for calculating time– activity integrals as urinary bladder or intestines can be used [26].

In hybrid imaging PET/CT or SPECT/CT, deep learning-based reconstruction (DLR) may facilitate CT radiation dose reduction in children. Lower-dose DLR images were compared with standard-dose iterative reconstruction images. DLR use at 80-kVp results in substantial dose reduction with preserved or even improved image quality. So, the use of DLR allows greater dose reduction for paediatric CT than current image reconstruction techniques [27].

Clinical dosimetry in targeted radionuclide therapy in children supports the treatment decisions and should be a strong indication that treatment results are dependent on the absorbed dose delivered to the treated organ as well as to the critical organs.

### **Acknowledgments**

D.A. Verganelakis gratefully acknowledges all support provided by the 'ELPIDA' Association of Friends of Children with Cancer and the Oncology Clinic "Marianna V. Vardinoyiannis" at Children's hospital "Aghia Sophia" in Athens.

*Dosimetry*


**8. Immunotherapy**

The immune system recruitment may represent a powerful and innovative strategy in cancer therapy. Genetic mutations and alterations in regulatory processes of cancer cells lead to expression of various tumor-related antigens that can be presented to cytotoxic T-lymphocytes by antigen-presenting cells. A major understanding of immune activation, especially T-lymphocyte activation, has identified multiple co-stimulatory and co-inhibitory pathways regulating this process. The two most important targets of immunotherapy are co-inhibitory receptors, such as CTLA-4 (cytotoxic T-lymphocyte-associated antigen 4) and programmed cell death-1 (PD-1) receptor, expressed on the T-lymphocyte surface [26].

A molecule of IL-2 was first approved by the US FDA for immunotherapy of melanoma. It is of limited use due to the serious toxic side effect of this treatment [27]. The first approved checkpoint blocking antibody was ipilimumab.

 CTLA-4 is a key negative regulator of adaptive immune response and works as a brake on the immune response. Blocking immune response to anticancer leads to a longer and stronger activation of T-lymphocytes and, ideally, to an attack and destruction of the tumor tissue, resulting in long term remission for 15–20% of patients [28]. Although its effectiveness is tested with many carcinomas, the best results were achieved just in the treatment of melanoma [29]. Randomized clinical studies show that the treatment with ipilimumab leads to a significant extension of the survival of patients with metastatic melanoma. Side effects of ipilimumab are related to the mechanism of its action. Typical side effects are accompanied by diarrhea, skin rash, pruritus, enteritis, vitiligo, endocrinopathies and hepatotoxicity. Ipilimumab is approved in the USA for the treatment of patients with advanced melanoma and in Europe for patients with previously treated advanced melanoma.

dacarbazine is characterized with low overall response rates (approximately 10–15%) and there is no valid evidence of survival benefit [23]. Temozolomide is a monofunctional alkylating agent of the imidotetrazine class. It is stable at the acid pH of the stomach and adminis-

For years, the cornerstones of cancer treatment have been surgery, chemotherapy, and radiation therapy. Significant changes occurred in antitumor therapy for disseminated melanoma during the last decade. Detailed knowledge in the molecular biology of melanoma and immune response lead to the two directions: immunotherapy and targeted therapy. Before 2011, two approved drugs were used to treat patients with metastatic melanoma in the USA: dacarbazine and recombinant human interleukin-2 (IL-2) [24]. The treatment landscape for advanced stage melanoma was revolutionized in 2011 with the approval of ipilimumab and vemurafenib, both of which improved overall survival in phase III clinical trials. More recently, the targeted inhibitors dabrafenib and trametinib have demonstrated similar therapeutic profiles [25]. The latest approved (PD-1)-blocking antibody pembrolizumab is indi-

cated for the treatment of patients with unresectable or metastatic melanoma [26].

cell death-1 (PD-1) receptor, expressed on the T-lymphocyte surface [26].

checkpoint blocking antibody was ipilimumab.

The immune system recruitment may represent a powerful and innovative strategy in cancer therapy. Genetic mutations and alterations in regulatory processes of cancer cells lead to expression of various tumor-related antigens that can be presented to cytotoxic T-lymphocytes by antigen-presenting cells. A major understanding of immune activation, especially T-lymphocyte activation, has identified multiple co-stimulatory and co-inhibitory pathways regulating this process. The two most important targets of immunotherapy are co-inhibitory receptors, such as CTLA-4 (cytotoxic T-lymphocyte-associated antigen 4) and programmed

A molecule of IL-2 was first approved by the US FDA for immunotherapy of melanoma. It is of limited use due to the serious toxic side effect of this treatment [27]. The first approved

*Ipilimumab* (Yervoy®) is a human monoclonal IgG1 antibody that binds the human antigen CTLA-4 located on the surface of T-lymphocytes and blocks its interaction with molecule on the surface of antigen presenting cells. CTLA-4 is a key negative regulator of adaptive immune response and works as a brake on the immune response. Blocking immune response to anticancer leads to a longer and stronger activation of T-lymphocytes and, ideally, to an attack and destruction of the tumor tissue, resulting in long term remission for 15–20% of patients [28]. Although its effectiveness is tested with many carcinomas, the best results were achieved just in the treatment of melanoma [29]. Randomized clinical studies show that the treatment

tered orally with 100% bioavailability [22].

114 Human Skin Cancers - Pathways, Mechanisms, Targets and Treatments

**7. New approaches**

**8. Immunotherapy**

*Tremelimumab*, another drug of this group, is human therapeutic monoclonal antibody IgG2, with the same mechanism of action as ipilimumab. This antibody is currently in progress in phase II/III clinical study [30].

Ipilimumab, in combination with high dose IL-2, and tremelimumab, in combination with interferon alfa provide increased overall response rate, progression-free survival, or higher percentage of complete responses. *Interferon alfa* is FDA approved in adjuvant treatment for patients with high-risk melanoma and it has significant immunomodulatory effects [31–33]. Interferon alfa monotherapy has limited utility in the treatment of stage IV melanoma; therefore, its antitumor activity has led to profound investigation of its use in combination with other therapies [34].

Cancer immunotherapy can be achieved by inhibition of the PD-1/PD-Ll axes, which affect the overall survival in an important fraction of patients. PD-1 is an inhibitory receptor that is upregulated on activated lymphocytes. PD-1 has two known ligands, PD-L1 and PD-L2, which can be expressed on tumor and stromal cells; PD-L1 expression can be induced by cytokines produced by tumor-infiltrating lymphocytes [35].

*Pembrolizumab* (Keytruda®, Merck & Co) is the first anti-PD-1 immunotherapeutic agent approved by FDA. Keytruda® was granted FDA approval on September 4, 2014 for the treatment of patients with unresectable or metastatic melanoma. This molecule is a potent and highly selective humanized monoclonal antibody of IgG4-kappa isotype, designed to directly block the interaction between PD-1 receptor, expressed on T-cells, and its ligands, PD-L1 and PD-L2, without antibody-dependent cell-mediated or complement-dependent cytotoxicity. In practice, blocking PD-1 activity is believed to prevent inhibition of T-cell immune surveillance of tumors and, in some models, has resulted in decreased tumor growth [26]. The recommended dose of pembrolizumab is 2 mg/kg administered as an intravenous infusion over 30 min every 3 weeks until disease progression or unacceptable toxicity. Most common adverse reactions (reported in ≥20% of patients) included fatigue, cough, nausea, pruritus, rash, decreased appetite, constipation, arthralgia, and diarrhea [36].

Another approach, which has already been tested, is to combine anti-PD-1 and anti-CTLA-4 treatment and is represented by *nivolumab* (Opdivo®, Bristol-Meyers Squibb). Nivolumab is used alone or in combination with ipilimumab [37, 38]. Combination therapy with anti-CTLA-4 and anti-PD-1 monoclonal antibodies has recently led to remarkable antitumor effects, long-term survival and potential cures [39].

BRAF-mutant and BRAF-wild type patients, who progressed after ipilimumab therapy, were included into the Phase III study. One group of patients received nivolumab (3 mg/kg every 2 weeks), and in comparator group patients were treated with chemotherapy. Patients treated with nivolumab demonstrated higher response rate compared to the chemotherapy group—32% vs. 11% [40]. There was no statistical difference in two contemporary oncology median overall survivals between the study arm with nivolumab, 15.7 months, vs. the comparator group with chemotherapy, 14.4 months. The limitation of the clinical benefit of nivolumab could be related to the fact that control group patients (40%) received pembrolizumab, when progressed during chemotherapy. Furthermore, the number of patients with elevated lactate dehydrogenase levels and brain metastases was imbalanced, favoring the chemotherapy [41]. Adverse events are less frequent in patients treated with nivolumab than in those treated with ipilimumab or chemotherapy [4, 10]. The most frequently observed adverse events included fatigue, pruritus, diarrhea, rash, and nausea. The most commonly observed immune-related adverse events were pruritus, rash, diarrhea, vitiligo, hypothyroidism, and elevated aminotransferase activities [42].

Vaccines specific for cancer antigens exert antitumor effects by inducing cytotoxic T lymphocytes (CTLs) that recognize and attack antigenic cancer-derived peptides comprising 8–10 amino acid residues presented on major histocompatibility complex molecules on the cancer cell surface. Peptides, proteins, mRNA, DNA, and viral vectors can be used as cancer vaccines. Various peptides derived from Wilms' tumor gene-1, glycoprotein 100 (gp100), and melanoma-associated antigen 3 (MAGE-A3) have been used as vaccines

Possibilities for the Therapy of Melanoma: Current Knowledge and Future Directions

http://dx.doi.org/10.5772/intechopen.70368

117

Tumor antigen encoded by genes of the MAGE-A family, MAGE-A3 is of importance because they are expressed in a wide array of malignancies including melanoma, brain, breast, lung and ovarian cancer. Its ability to elicit spontaneous humoral and cellular immune responses has been shown in cancer patients. As antigen-specific immune responses can be stimulated by immunization with MAGE-A3, several clinical trials have used MAGE-A3 vaccines to observe clinical responses. The frequent expressions of this antigen in various tumors and its immunogenicity in cancer patients have led to application of this antigen in cancer immunotherapy. Indeed, the initial trials performed with MAGE-A3 peptides showed no significant toxicity [48]. Vaccination with a tumor-specific MAGE-A3 peptide, even without adjuvant, has been shown to induce a CTL response in a melanoma patient followed by reduction in tumor mass. MAGE-A3 protein produced by recombinant technology is more popular in clinical trials as a result of its potential to activate a wide range of T-cell responses as well as its potential application in a larger population of patients with MAGE-A3 expressing tumors [49]. As MAGE-A3 specific therapies have not reached their final goals to cause a significant improvement in the survival of patients. For future perspective of MAGE-A3 therapy, studies are needed to find the most effective vaccine formulations, the most immunogenic adjuvants

Over the past several years, oncolytic viruses for treating various cancers have been investigated. Oncolytic viruses play a role in cancer vaccination because antigen-specific immunity is effectively evoked against components released by destroyed cancer cells due to virusinduced production of type I interferon. The effects of oncolytic virus therapy are mediated not only by direct cell disruption, but also by indirect induction of cancer-specific immune

Oncolytic viruses selectively replicate within and lyse cancer cells without damaging normal cells. On October 27, the FDA approved the first oncolytic virus therapy, *talimogene laherparepvec (Imlygic™, T-VEC)*. The agency approved T-VEC for the treatment of some patients with unresectable cutaneous, subcutaneous, and nodal lesions in melanoma recurrent after initial surgery [50]. T-VEC is a modified herpes simplex virus, type 1 (HSV-1) that has undergone genetic modifications to promote selective tumor cell replication, while reducing viral pathogenicity and promoting immunogenicity. T-VEC improves overall response rate and durable response rate as a single agent, shows promise in combination therapy with immunotherapy, and is well tolerated. Ongoing trials will determine if T-VEC has a role in early

as well as the most applicable criteria for selection of patients.

**10. Oncolytic virus therapy**

responses [48].

against melanoma [47].

In the study of Pyo and Kang the effects of various immunotherapeutic agents and chemotherapy for unresected or metastatic melanomas were compared. They performed a network meta-analysis using a Bayesian statistical model to compare objective response rate of various immunotherapies from 12 randomized controlled studies. The estimated overall response rates of immunotherapy and chemotherapy were 0.224 and 0.108, respectively. The overall response rates of immunotherapy in untreated and pretreated patients were 0.279 and 0.176, respectively. In network meta-analysis, the odds ratios for overall response rate of nivolumab (1 mg/ kg)/ipilmumab (3 mg/kg), pembrolizumab (10 mg/kg) and nivolumab (3 mg/kg) were 8.54, 5.39 and 4.35, respectively, compared with chemotherapy alone. Their results showed that various immunotherapies had higher overall response rates rather than chemotherapy alone [43].

Except immunological checkpoint blockades the approach of *adoptive T cell therapy* seems to be a highly promising in use against cancer including melanoma. The ability of T cells to specifically lyse tumor cells and secrete cytokines to recruit and support immunity against cancer make them an attractive proposition for therapy. Since the first idea in 1989 to genetically redirect T cells, a lot of experiments have been performed. Recent methods of generating tumor-specific T cells include the genetic modification of patient's lymphocytes with receptors to endow them with tumor specificity. These T cells are then expanded *in vitro* followed by infusion of the patient in adoptive cell transfer protocols. Genes used to modify T cells include those encoding T-cell receptors and chimeric antigen receptors. Several trials with gene-modified T cells are ongoing and some remarkable responses have been reported [44]. In fact, current adoptive T cell therapy response rates are 80–90% for hematological malignancies and 30% for metastatic melanoma refractory to multiple lines of therapy. Although these results are encouraging, there is still much to be done to fulfill potential of adoptive T cell therapy, specifically with regard to improving clinical efficacy, expanding clinical indications and reducing toxicity [45].

## **9. Cancer vaccines**

Melanoma vaccines have the goal to induce long lasting immunity against melanoma to prevent the development of metastases. However, melanoma cells express many different tumorassociated antigens. Ideally, vaccines need to contain all these different tumor-associated antigens for antigen-presenting-cells (APC) to induce an adequate immune response [46].

Vaccines specific for cancer antigens exert antitumor effects by inducing cytotoxic T lymphocytes (CTLs) that recognize and attack antigenic cancer-derived peptides comprising 8–10 amino acid residues presented on major histocompatibility complex molecules on the cancer cell surface. Peptides, proteins, mRNA, DNA, and viral vectors can be used as cancer vaccines. Various peptides derived from Wilms' tumor gene-1, glycoprotein 100 (gp100), and melanoma-associated antigen 3 (MAGE-A3) have been used as vaccines against melanoma [47].

Tumor antigen encoded by genes of the MAGE-A family, MAGE-A3 is of importance because they are expressed in a wide array of malignancies including melanoma, brain, breast, lung and ovarian cancer. Its ability to elicit spontaneous humoral and cellular immune responses has been shown in cancer patients. As antigen-specific immune responses can be stimulated by immunization with MAGE-A3, several clinical trials have used MAGE-A3 vaccines to observe clinical responses. The frequent expressions of this antigen in various tumors and its immunogenicity in cancer patients have led to application of this antigen in cancer immunotherapy. Indeed, the initial trials performed with MAGE-A3 peptides showed no significant toxicity [48]. Vaccination with a tumor-specific MAGE-A3 peptide, even without adjuvant, has been shown to induce a CTL response in a melanoma patient followed by reduction in tumor mass. MAGE-A3 protein produced by recombinant technology is more popular in clinical trials as a result of its potential to activate a wide range of T-cell responses as well as its potential application in a larger population of patients with MAGE-A3 expressing tumors [49]. As MAGE-A3 specific therapies have not reached their final goals to cause a significant improvement in the survival of patients. For future perspective of MAGE-A3 therapy, studies are needed to find the most effective vaccine formulations, the most immunogenic adjuvants as well as the most applicable criteria for selection of patients.


**1. Introduction**

With their highly specific mechanical properties, carbon fibre-reinforced plastics (CFRP) are suitable for use in high-performance components such as crash- and impactloaded structures such as composite fan blades [1,2]. In addition, these materials have the advantage that the material properties and especially the failure behaviour can be adjusted. The focus is mostly on the adaption of the fibre orientation to the dominant stress in order to increase the stiffness and strength of the materials [3]. This approach often leads to a brittle failure behaviour of the corresponding structures so that on the one hand, the structural integrity is compromised, and on the other hand, the energy absorption capacity is not optimally utilised [4].

Besides the choice of fibre and matrix material as well as the textile architecture, there are essentially two approaches for increasing the energy absorption of fibre-reinforced plastics. Firstly, the fibre–matrix adhesion is specifically adjusted by influencing the boundary layer during manufacturing. Initial work on this goes back to [5], where the influence of the adhesion properties of an epoxy matrix to boron filaments and their influence on the

**Citation:** Kuhtz, M.; Richter, J.; Wiegand, J.; Langkamp, A.; Hornig, A.; Gude, M. Concepts for Increased Energy Dissipation in CFRP Composites Subjected to Impact Loading Conditions by Optimising Interlaminar Properties. *Aerospace* **2023**, *10*, 248. https://doi.org/ 10.3390/aerospace10030248

Academic Editors: Spiros Pantelakis, Andreas Strohmayer and Jordi Pons-Prats

Received: 30 January 2023 Revised: 16 February 2023 Accepted: 23 February 2023 Published: 3 March 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

fracture toughness of such composites is described. The work in [6] follows this approach and shows that the fracture toughness is further increased by alternating high and low fibre–matrix bonds along the fibres. Secondly, especially in multi-layered composites, suitable interlayers are inserted through the concept of controlled interlaminar bonding. In this methodology, primarily thermoplastic interlayers are inserted into layer-based thermoset composites. A good overview of methods that lead to an improvement of the interlaminar properties by interleaved layers on a thermoplastic basis, but also to a more brittle failure behaviour with lower energy absorption, is given in [7]. In contrast, methods with lower interlaminar properties generally result in significantly higher energy absorption with improved structural integrity and a moderate decrease in structural strength [8–10].

The mentioned studies are exclusively experimental, and their conclusions are based on purely empirical statements. The study presented here, however, introduces a simulation approach that can be used to identify, analyse, and target the phenomenology of the energy absorption mechanisms of impact-loaded composite structures. A methodology is presented that describes the interface modification of CFRP in the framework of finite element analysis (FEA) up to the structural scale. Thus, this approach can be used to extend the experimental database with virtual tests. Finally, it is shown how the interface modification approach can be adapted to an optimisation process [11,12]. Thus, it is possible to derive concepts with which the energy absorption behaviour of impact-loaded CFRP structures can be significantly increased.

#### **2. Materials and Methods**

Deformation, damage, and failure behaviour of interface-modified CFRP beams is investigated numerically based on the experimental data of [10]. An interfacial modification by means of perforated polytetrafluoroethylene (PTFE) foil is used (Figure 1a). Figure 1b shows the geometric dimensions of the perforated PTFE foil.

**Figure 1.** Modification concept. (**a**) Interface modification concept by inter-leaved perforated PTFE foils with quadratic holes; (**b**) geometry parameters of perforated PTFE foil: *a:* edge length of hole, *b*: distance between holes, *d*: edge length of unit cell [13].

As PTFE does not adhere to the composite material, the interface properties are influenced exclusively by the geometric (mesostructural) dimensions and can be adjusted by the so-called interlaminar contact area *κ*:

$$
\kappa = \frac{2}{d^2} \frac{a^2}{}.
\tag{1}
$$

In the experimental study, a constant value of 4 mm was chosen for the edge length of the perforation *a* [13]. Based of targeted interlaminar contact area *κ*, the distances between two perforations *b* and the length of the unit cell *d* are derived. The investigations are carried out using the example of a plain weave fabric composite based on a HexPly M49 200P prepreg semi-finished product from Hexcel. Consolidation is carried out in an autoclave process according to the manufacturer's specifications, resulting in an average fibre volume content of 55% [14]. Further details about the physical and mechanical properties are shown in Table A1 in Appendix A.


*<IP_ADDRESS> Socio-economic and policy-institution issues*

*Approaches to Improve Water Productivity and Livelihood Resilience in the Karkheh River… DOI: http://dx.doi.org/10.5772/intechopen.108720*

### *<IP_ADDRESS> Development of integrated watershed management (IWM) principles*

One of the project's important methodologies and outputs was the development of principles of integrated management of upstream watersheds in arid mountainous areas [15, 16]. The logic and hypothesis were that watershed management principles for tropical and temperate regions were well defined and documented. But mountainous areas with arid climates have their own characteristics in terms of climate, geomorphology, and the effects of water access on local communities' livelihood. Therefore, it is necessary to redefine and adapt these principles for the mentioned areas (such as upstream watersheds in the basins of Iran). The considered criteria and principles were developed under the following categories ([7, 15]): 1) issues and subjects of stakeholders and institutions, 2) issues and subjects of decision-making processes, 3) issues of stakeholder consultation and development of watershed management principles with the help of SWOT analysis, 4) issues of water scarcity and drought, 5) soil issues, 6) soil erosion/soil conservation issues, 7) issues of forest and rangeland ecosystems, 8) issues of areas with irrigated and rain-fed agriculture, 9) land use issues, 10) agronomic and crop selection issues, 11) on issues of participatory technology development, 12) policy matters, 13) livelihood issues, and 14) on gender issues.


**9. Research prospects of bamboo ascomycetes**

Currently, 1300 fungi have been recorded on bamboo substrates. These are including 150 basidiomycetes [3], 800 ascomycetous species, 240 hyphomycetous taxa, and 110 coelomycetous taxa. It provides large opportunities on the utilization of fungi on bamboo. For example, species in *Hypoxylon* Bull., which form large stromata, can be easier to see on bamboo culms. In the recent years, a new secondary metabolite named lenormandins, which are further representatives of the well-known azaphilones [66], was found from *Hypoxylon* spp. More than 18 species in *Hypoxylon* have been occurred so far on bamboo (**Figure 11**). There may be some other interesting unknown azaphilones in *Hypoxylon* species, which may still wait for extraction. Numerous fungi from bamboo were documented, and some pathogens were isolated as well, such as *Arthrinium phaeospermum* (Corda), M.B. Ellis, and *Phyllachora graminis* (Pers.) Fuckel. Approximately 300 bamboo fungal diseases were so far reported [5–7, 67], which provides the essential step to understand ecosystem communication [3]. It is showed that some bamboo ascomycetes have a high value in medical treatment, such as *Engleromyces goetzi*, *H. bambusae,* and *S. bambusicola*. However, their effective compounds can be only obtained from stromata, which cannot be cultivated successfully at the moment [68]. The phylogenic relationship between *H. bambusae* and *S. bambusicola* needs to be carried out to understand the reason why *H. bambusae* produces more hypocrellin than the latter. Many interesting and subsequent studies on bamboo ascomycetes are still awaiting and needs to be conducted, and large numbers of new ascomycetous taxa on bamboo are also still waiting for collection and isolation.

Scientific Research Foundation of Yunnan Provincial Department of Education (2017ZZX186), and the National Natural Science Foundation of China (Nos. NSFC 31760013, NSFC 31260087, NSFC 31460179, and NSFC 31460561). The authors would like to thank the Yunnan Province Universities of the Science and Technology Innovation Team for the exploitation and utiliza-

A Review of Bambusicolous Ascomycetes http://dx.doi.org/10.5772/intechopen.76463 179

Center for Yunnan Plateau Biological Resources Protection and Utilization, College of Biological Resource and Food Engineering, Qujing Normal University, Qujing, Yunnan,

[1] Janssen JJ. Mechanical Properties of Bamboo. Netherlands: Kluwer Academic Publishers;

[2] Opoku D, Ayarkwa J, Agyekum K.Alternative binders for increased sustainable construction in Ghana—A guide for building professionals. Materials Sciences & Applications.

[3] Hyde KD, Zhou DQ, Dalisayl T. Bambusicolous fungi: A review. Fungal Diversity.

[4] Hino I, Katumoto K. Illustrationes fungorum bambusicolorum VIII. Bulletin of the

[5] Mohanan C. Diseases of Bamboos in Asia: An Illustrated Manual India. Leiden: Brill

[6] Xu MQ, Dai YC, Fan SH, Jin LX, Lu Q, Tian GZ, Wang LF. Records of bamboo diseases and the taxonomy of their pathogens in China (I). Forest Research. 2006;**19**(6):692-699 [7] Xu MQ, Dai YC, Fan SH, Jin LX, Lu Q, Tian GZ, Wang LF. Records of bamboo diseases and the taxonomy of their pathogens in China (II). Forest Research. 2007;**20**(1):45-52 [8] Shen YX, Rong XG, Gao ZH. Studies on the chemical constituents of *Shiraia bambusicola*.

[9] Zhen JD, Lown JW. Hypocrellins and their use in photosensitization. Photochemistry

[10] Dougherty TJ, Gomer CJ, Henderson BW, Jori G, Kessel D, Korbelik M, Moan J, Peng Q. Photodynamic therapy. Journal of the National Cancer Institute. 1998;**90**(12):889-905

Faculty of Agriculture Yamaguti University. 1960;**11**:9-34

China Journal of Chinese Materia Medica. 2002;**27**(9):674-677

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and Photobiology. 1990;**52**(6):609-616

tion of endophytes for finance support.

Dong-Qin Dai, Li-Zhou Tang\* and Hai-Bo Wang

\*Address all correspondence to<EMAIL_ADDRESS>
**Author details**

People's Republic of China

1991. pp. 30-113

2013;**4**(12):20-28

2002;**9**(1):1-14

**References**


*2.3. Microstructure Analysis*

The morphology and element analysis of the SnS/C materials before and after cycling was examined using a Hitachi S-4800 (Hitachi, Chiyoda City, Japan) field emission scanning electron microscope (FESEM) and a Philips CM200-FEG (Philips, Amsterdam, The Netherland) transmission electron microscope (TEM); both were equipped with electron dispersive spectroscopy (EDS). After cycling, the cells were opened in a fume hood and the working electrode was dipped in a 1:1 by volume mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) for 30 s to remove electrolyte residue, and was then dried using argon. Powders were then scraped onto (i) a piece of conductive carbon tape that was placed on a standard FESEM sample holder, and (ii) a TEM carbon lacy grid, which was then placed in the TEM. X-ray diffraction (XRD) was performed using a Philips X'Pert MPD diffractometer (Philips, Amsterdam, The Netherland).