*2.6. Thermal Characterization*

Thermal properties of PLA and PLA/PBSA blends were investigated by calorimetric analysis (Q200 TA- DSC). Nitrogen, set at 50 mL/min, was used as purge gas for all measurements. Indium was used as a standard for temperature and enthalpy calibration of DSC. The materials used for DSC analysis have been cut from the ISO 5271-A dog-bone injection mold specimens. In order to evaluate if an eventual crystallization occurred during the specimen injection molding (affecting the mechanical behavior of the materials), the thermal properties were evaluated considering only the first DSC heating run. The sampling was carried out taking the material in the same region of the specimens to avoid differences ascribable to different cooling rates in the specimen thickness. The samples, with mass between 11.5 and 15 mg, were sealed inside aluminum pans before measurement. PBS granules were also analyzed in order to better understand how its thermal properties could affect the thermograms of the binary blends.

The samples were quickly cooled from room temperature to −50 ◦C and kept at this temperature for 1 min. Then the samples were heated at 10 ◦C/min to 200 ◦C to delete the thermal history then a second cooling scan from −70 ◦C to 190 ◦C, at 10 ◦C/min, was carried out. Melting temperature (Tm) and cold crystallization temperature (Tcc) of the blends were recorded at the maximum of the melting peak and at the minimum of the cold crystallization peak, respectively. The enthalpies of melting and cold crystallization were determined from the corresponding peak areas in the thermograms. Where possible the PLA and PBSA crystallinity were calculated according the following Equation:

$$X\_{\text{cc, PLA}(or \text{ PBSA})} = \frac{\Delta H\_{\text{m, PLA} \text{ (or } \text{PBSA})} - \Delta H\_{\text{cc, PLA} \text{ (or } \text{PBSA})}}{\Delta H^{\text{\text{\textdegree}}\_{\text{m, PLA} \text{ (or } \text{PBSA})} \cdot \text{wt. \text{\textquotesingle}} \text{ PLA} \text{ (or } \text{PBSA})} \tag{8}$$

where *Xcc*, is the crystallinity fraction of PLA or PBSA, Δ*Hm* and Δ*Hcc* are the melting and cold crystallization enthalpies respectively, while Δ*H*◦ *m* is the theoretical melting heat of 100% crystalline polymer. For PLA a Δ*H*◦ *m* value of 93 J/g [71] and for PBSA a Δ*H*◦ *m* value of 142 J/g were considered [8].

The heat deflection temperature or heat distortion temperature (HDT) corresponds to the temperature at which the polymeric material deforms under a specified load. This property is fundamental during the design and production of thermoplastic components. The HDT is also strictly correlated to the polymer crystallinity, in fact it is noteworthy that a highly crystalline polymer has an HDT value higher than its amorphous counterpart [72]. For this purpose, the determination of the deflection temperature under load (HDT) was carried out on a CEAST HV 3 (INSTRON, Canton, MA, USA) in accordance with ISO 75 (method A). A flexural stress of 1.81 MPa and a bath heating rate of 120 ◦C/h were used. The sample size was 80 mm × 10 mm × 4 mm. When the sample bar deflects by 0.34 mm, the corresponding bath temperature represents the HDT (Type A) value. At least five measurements were carried out and the average value was reported.


**1. Introduction**

It was in the 15th century that anatomy (still undistinguished from physiology) started to strongly develop. It was part of the core of the European society developments, upon the development of the Late Middle Ages, the Early Renaissance, and the early Modern period, the melting pot for important medical developments, announcing the "European miracle" of the following centuries [1]. But for all practical purposes, physiology was considered to be born in the 17th century, most likely upon the publication of William Harvey's book on the circulation of the blood, in 1628 (**Figure 1A**) [2].

It was on Harvey's work that for the first time traditional (and unquestionable) beliefs about the heart and the circulation (dating back to Galen, 1500 years earlier) have been dethroned. Harvey declined to consider uncritically what he had been taught and insisted on relying on his own scientific observations. This approach is considered to be one of the most revolutionary ideas in science in the 17th century, and Harvey's greatest contribution to science [3].

#### **Figure 1.**

*A: Title page of William Harvey's De Motu Cordis (1698) to the left and demonstration of blood flow in the veins of the forearm to the right. B: Above; Malpighi's drawing of the pulmonary capillaries and alveoli: 2 lungs with the alveoli on the left and the capillaries on the right. Below; pulmonary capillaries in a diagram of an alveolus that has been opened up.*

However, this was not without controversy. Many have initially opposed to the concept of physiology however great names such as Marcello Malpighi (**Figure 1B**) and Antoni van Leeuwenhoek have supported the thoughts on human function, joining efforts in developing modern physiology.

Following the initial scientific developments, a halt followed between 1750 and 1850 throughout Europe with critical thinking of medicine as a science coming to a stop and being replaced by an artistic view of medical science, resourcing to texts in Latin. This came to such an extent that the microscope was not made available to students in Leiden as was auscultation not included in the teaching curricula, albeit having been discovered in 1819 [4].

In the middle of the 1800's German doctors proposed the 'medicine equals science' concept and pointed towards the reintroduction of science in the curricula, motivated by Rudolf Virchow (cellular pathology) and by significant scientific advances at that time such as the periodic table (Dmitri Mendelejev) and upon the publication of the "Origin of Species" (Charles Darwin). Noteworthy, important technological advancements were also made at that time such as the development of steam locomotives and railroads, and the first steel steamship crossing the Atlantic. For the above, ideal conditions for the advancing of physiology has also occurred giving rise to physiologists like Carl F.W. Ludwig in Germany and Claude Bernard in France [5].

Specializations within general physiology also started, namely on gastrointestinal physiology (William Beaumont); pathology (Rudolf Virchow) and bacteriology (Louis Pasteur, Robert Koch), with scientific journals being written as the basis for solidification of these new physiology branches such as the "Archiv für Pathologische Anatomie und Physiologie und für klinische Medicin" (Virchow and Reinhardt; today called Virchows Archiv) and Pflügers Archiv (today called Pflügers Archiv - European Journal of Physiology), laying the basis for modern physiology in the 19th–20th century with names such as Pavlov (psychophysiology), Sherrington (neurophysiology), Mosso (ergograph, sphygmomanometer), Golgi (nervous system, malaria), and Ringer (Ringer's solution). This great evolution was supported (and recognized) with the creation of the Nobel Prize of Physiology or Medicine, first awarded in 1901 [5].

#### *Virtual Physiology: A Tool for the 21st Century DOI: http://dx.doi.org/10.5772/intechopen.99671*

The rapid changes observed in modern societies have caused higher level education providers (i.e. Higher Education) to face a variety of challenges in order to cope with today's demands [6]. This has, in all, lead to the training of more enthusiastic students in an array of interdisciplinary fields [7], generating effective pedagogical methods and strategies to the point that these are now recognized as one of the most important necessities of educational systems [8].

Physiology is today recognized as the bedrock of medical curriculum [9] and, as such, the preference for a particular content delivery method has been vastly investigated by to pass knowledge logically and strategically to students [10]. A greater focus has been given now on critical thinking skills in contrast to emphasis on the systems-based didactic lectures [11]. This has been done also due to the longstanding recognition of the Physiology Science as a challenging discipline for students to grasp, assimilate and employ in clinical sciences. Furthermore, as a core science in the disease process, its understanding is of the utmost importance for an integrated knowledge [12, 13].

As such, physiology educationists are making great efforts towards focusing on ways to obtain vertical and horizontal integration in the discipline of Physiology, exceeding the typical periodical assessment of the medical curriculum by further stimulating and introducing a myriad of new teaching and learning approaches to captivate and augment students' knowledge acquisition [14].


*2.2. Electron Thermal Conductivity*

The first process that influences the electron thermal conductivity is the electronphonon scatter. The process is described by the thermal resistance *W*e−p [10]:

$$\mathcal{W}\_{\text{e}-\text{P}}(\theta) = \frac{\rho\_{\text{el}|\text{F}\text{g}}(\theta)}{L(\theta) \cdot \theta}. \tag{10}$$

The ideal electric resistivity is the electric resistivity of pure iron *ρ*elFe(*ϑ*) in this application. The value can be calculated utilizing the following [8,13]:

$$\rho\_{\rm elFe}(\theta) = (-2.4 + 3.65 \times 10^{-2}/\text{K} \cdot \theta + 64 \times 10^{-9}/\text{K}^3 \cdot \theta^3) \text{μ}\Omega \,\text{cm.} \tag{11}$$

Please note that there seems to be a typo in the original source in [13] because the values do not match the measurement data presented in the publication. This typo is corrected in [8]. The values of [8] are used in this study and presented in Equation (11). The Lorenz number *L*0 = 2.443 × 10−8 WΩ/K2 is modified by a temperature-dependent therm [10] in Equation (10):

$$L(\theta) = L\_0 \cdot \left(1 - e^{-\theta/159.3 \text{ K}}\right). \tag{12}$$

The second considered electron scattering process is the electron–impurity scatter that is represented by *W*e−i:

$$\mathcal{W}\_{\text{e}-\text{i}}(\theta) = \frac{\rho\_{\text{el}\_0}(\theta)}{L\_0 \cdot \theta},\tag{13}$$

with the residual electrical resistivity *ρ*el0(*ϑ*) = *ρ*el(*ϑ*) − *ρ*elFe(*ϑ*) as a difference between the electric resistivity of the alloy *ρ*el(*ϑ*) and the electric resistivity of pure iron *ρ*elFe(*ϑ*). The electric resistivity of an alloy can be calculated utilizing Matthiessen's rule as follows:

$$\rho\_{\rm el}(\theta) = \rho\_{\rm el\_{\rm Fe}}(\theta) + \sum\_{i} \rho\_{\rm elj} \varepsilon\_{\rm a,i} \tag{14}$$

The calculated values utilizing this formula deviate from measurement results as discussed in [10], due to the independency of the electric resistivity *ρ*eli from the temperature. The authors [10] propose an improved formulation:

$$
\rho\_{\rm el}(\theta) = \rho\_{\rm el\_{\rm Fe}}(\theta) + \sum\_{i} \rho\_{\rm elj}(\theta) c\_{\rm a,i} \tag{15}
$$

The estimation of the necessity of utilizing the improved equation in comparison to the Matthiessen's rule is not possible for this application. The error estimation in [10] is based on values of the electric resistivity of the alloy at 4 K and based on Cr and Ni alloys. While Equation (14) is preferred, due to the simple availability of the electric resistivity of the alloy components *ρ*eli , Equation (15) seems to give more accurate results. Within this study, the electric resistivity of the alloys is measured over the temperature range and compared to the simplified equation. The final value of the electron thermal conductivity *k*e(*ϑ*) can be calculated with:

$$k\_{\rm c}(\vartheta) = \left(\frac{\rho\_{\rm el\,Fe}(\vartheta)}{L(\vartheta)\cdot\vartheta} + \frac{\rho\_{\rm el\,l\_0}(\vartheta)}{L\_0\cdot\vartheta}\right)^{-1}.\tag{16}$$