**4. Results**

#### **4.1 Differences in psychosocial development by criminal justice involvement**

Results in **Figure 2** show differences in levels of psychosocial development across groups in adolescence (Wave 1). Subscripts indicate significant differences between groups at p < .05 level. Non-delinquent adolescents report significantly higher levels of temperance self-control than delinquent youth (non-confined or confined) (2.65 vs. 2.25 and 2.12, respectively) and future-orientation perspective (4.43 vs. 4.27 and 4.26, respectively). Non-delinquent youth have significantly higher baseline levels of responsibility and social-temporal perspective than delinquent confined youth (4.11 vs. 3.99 and 1.99 vs. 1.86, respectively). Delinquent nonconfined and delinquent confined groups are statistically similar on all measures of psychosocial development except responsibility. Thus, prior to subsequent detention, delinquent youth are fairly similar in their levels of psychosocial development.

**Figure 3** shows differences in psychosocial development as youth enter early adulthood (Wave 3). Here all delinquent youth (non-confined and confined) report lower levels of perspective – believing they will live to age 35 than non-delinquent youth (4.56 and 4.32 vs. 4.66, respectively). Youth who were incarcerated during adolescence report significantly lower levels than either non-delinquent or delinquent non-confined youth, or both on all dimensions except social-temporal perspective. Confined youth report significantly lower levels of responsibility (3.38 vs. 3.96 for both other groups), temperance (3.18 vs. 3.57 for non-delinquent youth), and perspective – future orientation (3.40 vs. 3.94 for non-delinquent youth). It appears juvenile correctional confinement depresses delinquent youths' levels of responsibility and outlook for their future.

We assess the robustness of these descriptive results in a multivariate model regressing psychosocial development in young adulthood on our sociodemographic

**Figure 2.** *Wave 1 psychosocial maturity.*

#### **Figure 3.**

```
Wave 3 psychosocial development. Superscripts indicate significant differences between reference groups,
p < .05.
```
controls, controlling for our lagged dependent variable (the baseline measures of psychosocial development). Results (not shown) indicate that youth who are incarcerated exhibit decreased responsibility and future-orientation relative to nondelinquent youth, and confined youth report significantly lower hopes of living to age 35 than both non-delinquent you and non-confined delinquent youth, controlling for any baseline differences in psychosocial development.

#### **4.2 Confinement and adult transitions**

**Figure 4** presents odds ratios for two full regression models for each of six adult transitions by criminal justice involvement. Net of demographic controls for age, gender, race, parental education, family structure, and residential location,

#### **Figure 4.**

*Odds ratios of effects of juvenile arrest and detention on young adult outcomes. Significant differences between reference group and non-delinquent group.\*\*\*p < 0.001, \*\*p < 0.01, \*p < 0.05, † p < 0.1.*

and psychosocial development, adolescent criminal justice involvement (arrest or confinement) reduces the odds of attainment in young adulthood. Young adults who were confined as youth report significantly lower odds of full-time employment in their late 20s than youth who were arrested before age 18 but did not serve time in a juvenile correctional facility. Among those who work, delinquency is associated with reduced (though not significantly) odds of being in career-type work. Criminal justice involvement in adolescence increases the risk of high school non-completion and reduces the odds of college completion; for those who were confined as adolescents, odds of on-time college completion (by the late 20s) are reduced almost to zero (OR = 0.04). Finally, juvenile delinquency (arrest but not confinement) reduces the odds of marriage by the late 20s and any criminal justice involvement (arrest or confinement) increase the odds of cohabitation relative nondelinquent youth. We discuss the implications of these findings below.

### **5. Discussion, implications, and future direction**

This research explored the effects of the impact of juvenile confinement on the development of psychosocial maturity and the transition to adulthood. Qualitative research suggests that individuals reentering society from a period of confinement struggle in many facets of their life related to relationships, friendships, education, employment and chemical and mental health issues [60–62]. However, it is wrong to assume that juveniles recidivate simply as a product of what [60] terms "poor choices." Fader's work uncovered the complexity between incarceration and psychosocial maturity that ultimately made it difficult for young offenders to meet the demands and expectations of adulthood upon release. Our quantitative findings suggest that not only confinement, but also formal criminal justice involvement (arrest) negatively impact outcomes for youth compared to youth who never experience confinement.

Importantly, prior to confinement, youth with similar levels of delinquency had roughly equal levels of psychosocial development. However, post-criminal justice

involvement (confinement or arrest), delinquent youth lag behind their non-delinquent peers on the psychosocial development measures of temperance (impulsivity and control) and perspective (believing they will live to 35). But, confined youth have significantly lower development of responsibility and perspective compared to delinquent youth who are not confined. Therefore, as youth exit correctional facilities and struggle to transition to the community, they are lagging further behind other youth in their self-clarity, self-esteem, decision-making, and future orientation. This results in reduced likelihood of working full-time and dismal college completion rates by their late 20s. Despite hopes that a period of confinement can be the turning point leading youth out of future offending behavior, the barriers produced by the context of confinement have real consequences for psychosocial development and attainment in adulthood. Comparing these findings with the adult desistance literature, confined youth struggle to achieve success in the exact areas shown to promote desistance from crime in adulthood—employment and education (see [1, 63]).

The most robust finding in our analysis relates to educational outcomes for individuals in their late twenties and early thirties. Confined youth are four times more likely to not complete high school even when we control for psychosocial development. Thus, the combination of confinement with the decreased development of perspective leads to significantly lower levels of educational attainment. The decrease in the likelihood of high school completion also leads to a shocking reduction (96% reduction) in the likelihood of college completion for confined youth, net of all controls including parents' educational attainment and psychosocial development. This finding is particularly interesting considering that 92.8% of confined youth in the SYRP data report that they attend school in the facility [26]. Thus, it appears the increased risk of not completing high school and the decreased odds of college completion are not from lack of educational access in juvenile correctional facilities but rather it appears the conditions of confinement, along with the decreased development of perspective and future orientation during this time, have long-term impacts post-confinement. Overall, as shown in **Figure 5**, the effects of criminal justice interventions in adolescence have far-reaching effects across multiple domains in the transition to adulthood. These are magnified when youth are placed in out-of-home settings.

This study is not without limitations. First, Add Health does not include information on the type or security of placement for confined youth; however it is likely that confined youth in the Add Health data were in detention or training facilities because on average, 65.1% of youth confined during 1997 (two years post Wave 1 collection and around the time many Add Health respondents would have been confined) resided in one of these two types of facilities [58]. We have attempted to mitigate some of this limitation by using the SYRP to provide a picture of adolescent confinement in general terms. Second, Add Health survey items and questions change slightly across waves and thus the measures of psychosocial development in Waves 1 and 3 are not consistent, though we have attempted to replicate measures across waves. Third, because the Add Health data does not allow researchers to directly match each offense reported to a specific outcome, the study does not include measures of offense severity for youth arrested and confined. However, prior research by [64, 65] suggests that this might not matter.

Findings in this chapter point to a few interventions for practitioners and juvenile correction administrators. First, formal criminal justice interventions, particularly confinement of youth, should be used as a last resort. It is important to point out here that our study uncovered that not only confined youth, but also arrestees (our delinquent non-confined sample) have poorer outcomes in the transition to adulthood. This suggests that it is not just delinquency (as we controlled for general

**Figure 5.** *The far-reaching effects of criminal justice interventions in adolescence.*

self-reported delinquency) but rather formal juvenile justice intervention that leads to negative outcomes, an outcome surprising given this is the very system intervening on the "best interests of the child" ([66]; p. 971). Therefore, even short-term stays in confinement can affect psychosocial development and success in adulthood. Although the United States national Juvenile Detention Alternatives Initiative (JDAI) has decreased the use of detention and increased the used of communitybased alternatives, there continues to be just over 107,000 youth admitted to detention annually in the United States [67]. We must continue to divert youth not only from confinement but from any formal justice involvement.

Second, our findings suggest that practitioners and juvenile correction administrators change the conditions of confinement to promote greater psychosocial development, particularly related to the development of perspective. Research shows that delinquent youths' fears about their future exceed their hopes and long-term expectations for success [37]. Thus, even though a correctional facility may offer programs related to "events" that promote positive change, the context and ability for young adults to exercise developmental skills necessary to mature and subsequently translate these skills into successful outcomes in young adulthood is imperative for capitalizing on positive turning points [7, 18]. At the facility level, this could mean implementing a step-down process in the level of control over juveniles, particularly through transitional housing for confined youth. In the transitional housing structure, youth could investigate educational or vocational career paths in the community, while also allowing room for youth to fail and use this failure as an opportunity for development rather than a technical violation that sends them deeper into the justice system. For the "typical" adolescent, the transition to adulthood is marked with trial and error (e.g., loss of a job, romantic

breakups, oversleeping for school) yet youth in highly regulated confinement environments experience few opportunities for developmental failure. This begs the question: how can one expect that confined youth understand failure as a developmental process rather than a projection of future outcomes? Programming in juvenile correctional facilities should allow room for autonomy and failure and subsequent teach youth to build on failure as a natural part of development.

We are not suggesting there is not a place for juvenile correctional facilities in society, but if and when the juvenile court deems confinement is required, it is necessary to revise the physical and programmatic structure of juvenile correctional facilities. For example, the Missouri Model replaces secure confinement facilities with smaller facilities with a group-home-like structure. This emphasizes the ability to integrate community-based interventions, closer proximity to family, independent decision-making, and wrap-around services for youth. Although preliminary findings examining the Missouri Model's outcomes do not explicitly test the development of psychosocial maturity over time, the reduced recidivism and increased attainment of education and employment for youth in Missouri suggests that the restructured conditions of confinement may allow more room for development, and in turn have positive outcomes as youth transition to the community and adulthood [68].

Future work in this area should explicitly consider the developmental process for confined youth. First, research should explore of the effects of psychosocial development and criminal justice involvement on attainment in young adulthood across demographic groups. While we have controlled for many demographic factors, this research does not break down outcomes by race, gender, or socioeconomic status; as with other developmental processes, the mechanisms at work here may very well differ across demographic lines. Second, qualitative research should seek to understand how the correctional context leads to lower levels of responsibility and perspective for confined youth. Third, given the important role of future orientation in attainment in adulthood, future research might explore the relationship between expectations for the future and actual outcomes in a longitudinal context. Finally, understanding the relationship between confinement, psychosocial development, and desistance from crime is an important next step for research in this area.


*2.4. Test Contents and Methods*

## 2.4.1. Dry Density

In order to save the engineering cost, foamed concrete needs to be of good expansibility, and dry density was chosen as the evaluation index of the expansibility, which is convenient for measurement. The standard cylindrical samples of 50 mm × 100 mm were selected, put into a constant temperature vacuum drying oven (see Figure 2), adjusted to 80 ± 5 ◦C for 24 h, and then the temperature adjusted to 120 ◦C until gaining the constant weight *M*. The diameter and height of the sample were measured, and its volume was calculated *V*. Then the dry density ρ of the concrete material can be obtained by the formula:

$$
\rho = \frac{M}{V} \times 1000\tag{1}
$$

where, ρ is the dry density of the sample, kg/m3; *M* is the mass of the sample after drying, g; *V* is the volume of the sample, cm3.

**Figure 2.** Constant temperature vacuum drying oven.


*5.6. Human THP-1 Pre-Monocyte Differentiation into THP-1 Macrophages*

Human pre-monocytes were differentiated into macrophages using Phorbol 12- Myristate 13-Acetate (PMA, Sigma Aldrich, St. Louis, MO, USA), according to protocol described by Daigneault and colleagues (2010) [33]. Briefly, live cells were transferred to 24 culture wells plates containing 1 mL/well of supplemented RPMI medium containing PMA (100 ng/mL) at a density of 2 × 105 cells/well. The cell was incubated at 37 ◦C in an atmosphere containing 5% CO2 during 72 h. After the fourth day, PMA-containing medium was replaced by medium without PMA (2 mL/well), and the cells were kept at rest for 4 more days. At the end of the rest period, macrophage adhesion was visualized under a phase contrast microscope (Leica DM2500, Wetzlar, Germany) and photographed.


**1. Introduction: a historical contextualization**

Education has faced in the second half of the twentieth century a heavy crisis, which is not finished yet. It is the correspondent crisis society and culture have met in the same period. It was a real epochal transition, from an Evo that lasted less than 2 s to one that, perhaps, was not yet started.

This crisis involves major social issues such as family and, conceptually before it, the couple and genres. We may adopt in this regard the inclusive concept of 'system' that was introduced in Italy since the 1968 dispute [1] to indicate the whole of sociocultural phenomenon. 'The system' had a profound crisis and owing to it, we understood how and to what extent the system was relying on a peculiar way of raising a family, of living partnership, on a particular construction of genders (i.e., polarized to their extreme extent, functional to the entire system, besides being the very root of it).

The basic features of this crisis were represented, quite obviously, by the dizzying acceleration of the evolutionary rhythms, by the evident extension of the explicit lifelong education, by the multiplication of access to and dissemination of information, by the generalization of mobility, until the current globalization took place.

In times, chronologically not too far away, although culturally remote, one could at least suggest an education consisting of the replication of some set of patterns. In order that it might actually work, an explicit kind of family education limited to a relatively short period of human life, about a dozen years, and an evolutionary rhythm not too high was necessary. In other words, what we will call 'a quasi-static hypothesis' with a transfer from thermodynamics would have shown its value: that is to say, becoming a process that could be strictly treated as if 'the system' were in every moment of its evolution in a static equilibrium. For these reasons, evolution need not happen according to frantic rhythms, as it would have happened sooner or later, but effectively along those centuries. In addition, the gaps were not to be too long, in compliance with an explicit education that began in childhood and ended, as it was claimed, in adolescence.

### **2. A social revolution: new paradigms of couple and family required**

The evolution that occurred includes a profound *shift* of *paradigm* with a Kuhnian meaning [2]. We are facing a '*scientific revolution,*' which was born more or less around the 1960s or shortly before, and whose problematic content is a big part of our dealing today, and for the next decades. The educational problems posed are direct and mainly dwell on a specific professional sector.

We are problematically leaving a historical age that lasted about two centuries, or less, which properly came after the one that was historiography called 'Modern Age'. The term 'Postmodern' introduced by Jean-François Lyotard [3] was impressive, and effective, to appoint the end of the previous age. The term "post" resulted totally inappropriate and misleading when applied to the history and the humanities. It could have a partial success as well as ephemeral in the domains for which it was coined, that is, in literature and architecture, but had no plausibility in the human sciences and in pedagogy in particular.

The Postmodern Age, put properly next to the 'Modern' one, so-called by history and culture (sixteenth-seventeenth-eighteenth century, about), had its roots in the Enlightenment, the Industrial Revolution and the bourgeois revolutions of the late eighteenth century: in a definite set of ideas and orientations, economic and social upheavals, and spread in the West during the following century. In this specific regard, Der Wiener Kongress formed an unrealistic restoration of political regimes specifically 'modern,' that is to say absolute, which no longer had any cultural, economic and social coherence.

The nineteenth-twentieth century society had as its primary cell a peculiar type of family called by Durkheim "*famille conjugale*" [4, 5] and by Le Play "*famille nucleaire*" [6]. Its acceptance, with all the heavy sacrifices which involved especially the woman, went hand in hand with the claim that it was the kind of family that 'existed since the ancient times' (or 'natural'), 'traditional' or 'the result of millennia of civilization,' apparently powerful and mutually contradictory and that therefore could only have had a rhetorical function of persuasion and compliance. In fact, it was an absolutely dated and contextualized phenomenon, with its specificity: this paradigm of family completely peculiar and absolutely original has taken the place of the two pre-existing paradigms that remained in the West for many centuries: that is, the *noble* and *patriarchal* paradigm.

**155**

*Pedagogist as Social Professional: Sozialpädagogik and Professional Pedagogy*

The paradigm of nuclear family postulated (and required) a particular type of couple, the so-called overlapping couple, built through polarization of the genders pushed to the extreme, enhanced by a target education in line with its goals.

The dominant educational paradigm in the short Evo XIX-XX was transmissive and consisted of the replication from one generation to another of strict and fixed idealized models, that the teacher had first received and made his own, in such an integral way to feel unconditionally committed to replicate them as closely and impersonally as possible with her/his pupils. Moreover, she/he was considered uncritically entitled to use any tool she/he considered fit for the purpose.

The current information and mobility would be enough to explain the practical impossibility of a transmissive education, especially if focused on fixed models, and this is because these would have lost soon every plausibility and would have proved outdated, overcome by some others as time went by, at least before the end of a dozen years or slightly more. In addition, the longest lifespan of the 'explicit' education in a reality characterized by an increasingly frantic and quick evolutionary rhythm would make obsolete any model or fixed principle, despite its primal validity and soundness, to be checked by information and interpersonal mobility

**4. The new social need of the professional at the top of the pedagogical**

This particular crisis today is clearly a problematic situation for pedagogy: we refer to a pedagogy that, properly and by its very nature, cannot have any form of detachment, just like, for example, the separation of the historian or what has been

In cases like these, it is manifested more clearly than elsewhere in the application framework that is its true essence, not reducible to merely speculative, philosophical or 'theoretical' thought, but inseparable from taking charge and care of whosoever is going to be educated, in any interpersonal relationship and as a social requirement, and from the organic relationship with the experience of the object of

This, among other things, is more consistent with the etymology of a term [7] that is present and common in Romance languages, as well as in German and Slavic languages and also in Hungarian, Finnish, Basque or Albanian, while it is still facing difficulties in English. We should not forget that the same term has appeared in the

This means that pedagogy is characterized more clearly today than it was in the past, as a domain of study that can be called upon to express its own profession: an upper intellectual profession, working in the social and in all of its instances, whose most proper name is "Pedagogist" (Pädagoge, paedagogist…not to be confused with

Strictly speaking, the profession of the pedagogist has emerged (or better, reemerged) as a social profession only in the twentieth century. This can be compared to the professions of the psychologist, sociologist, psychotherapist, and in some respect to other intellectual occupations such as the accountant or the social worker. For all these professions, and others, a wide methodological framework is to be found in the previous century, mostly *in Mitteleuropa*, in the central European world German-speaking, or in its immediate vicinities. For example, a psychologist would refer to Wundt, Weber, Fechner, Helmholtz, Mach; a sociologist to Auguste

*DOI: http://dx.doi.org/10.5772/intechopen.91335*

**3. The XIX-XX paradigm of education**

like in our days with no ancestors in human history.

attributed to clinical physicians for a long time.

**culture**

its study and intervention.

West in 1495, as a mold from Latin [8].

the educator, l'éducateur or die Erziehrer).


*Article* **Sunflower Honey—Evaluation of Quality and Stability during Storage**

**Milica Živkov Baloš, Nenad Popov, Sandra Jakši´c, Željko Mihaljev, Miloš Peli´c, Radomir Ratajac and Dragana Ljubojevi´c Peli´c \***

> Scientific Veterinary Institute "Novi Sad", 21000 Novi Sad, Serbia **\*** Correspondence<EMAIL_ADDRESS>
**Abstract:** Honey's unique qualities should last for several years when properly stored. Therefore, it is up to manufacturers to choose the right shelf life for their product while also considering the product's nature. Physicochemical parameters (water content, electrical conductivity, free acidity, pH, ash, water-insoluble matter, hydroxymethylfurfural (HMF), sugar content and composition, and diastase activity) were analyzed in 24 samples of sunflower honey collected from several localities in Vojvodina, Serbia. Crystallization indices were also calculated. Furthermore, the impact of eighteen months of room temperature storage (22 ± 2 ◦C) in a dark place on selected physicochemical parameters (water, HMF, diastase activity, pH value, and free acidity) was investigated. The results of the initial test indicated that the tested samples of sunflower honey from Vojvodina is of good quality because the parameters under examination revealed results that were within the legal bounds of both national and European legislations. Eighteen months of storage at room temperature reduced diastase activity by 2 times, increased HMF content by about 17 times, and decreased the pH value of honey from a mean value of 3.66 to 3.56. The water content was relatively stable at 17.01% before storage and 16.29% after storage. The storage of sunflower honey did not have an impact on the free acidity.

**Keywords:** sunflower honey; physicochemical properties; storage; shelf life


*3.2. The 2003 and 2015 Heat Waves in the Context of Climate Change*

In the context of climate change, the number of heat waves is very likely to increase in the next decades [4]. In the following, we quantify the probability for heat waves comparable to the ones of 2003 and 2015 in the near and far future using RCM simulations.

RCM data is usually not available in a temporal resolution higher than daily means. Therefore, the analysis shown in Figure 3 was repeated using the daily mean HUMIDEX (Figure 4a). This approach led to very comparable results. The heat wave of 2003 was now characterized by 8 consecutive days above the 95th percentile, while for 2015, 5 consecutive days were found. To generalize these findings, we assessed the change in heat wave frequencies for all events where the daily mean HUMIDEX exceeds the 95th percentile for 3 to 10 consecutive days. Therefore, we calculated the 95th temperature percentile for each model separately to reduce the influence of model biases on the analysis [33]. The 95th temperature percentile was calculated using the reference period 1971–2000.

First, the RCM's capability to simulate these heat waves was assessed (Figure 4b). In the reference period the RCMs tend to overestimate the average number of heat waves per year for all durations. Heat waves with a duration of three days, for instance, occured on average every second summer in the observations (0.5 events/yr), while the multi model ensemble median suggest a frequency of about 0.6 events/yr. While for most durations at least a few models simulate frequencies comparable to the observations, the medium-length durations of 5 and 6 days are clearly overestimated by the models. This overestimation of the heat wave persistence in the CORDEX simulations has been discussed earlier [33] and may be attributed to a misrepresentation of land-atmosphere feedbacks (e.g, soil moisture, surface energy fluxes).

The projected changes are calculated separately for each model with respect to the model mean value of the reference period, to reduce some effect of the overestimated persistence. In the near future (2021–2050) and under RCP4.5, a clear increase in the frequency is found for all durations. Short term events (3 days) already increase by 0.9 events/yr (multi-model median). Furthermore, the very strong 10 day events increase by about one event per decade (0.1 events/yr) in comparison to less than one event in 30 yrs in the reference period (multi-model median 0.03 events/yr). No pronounced differences are found between RCP4.5 and RCP8.5 for the near future. Increases are in general slightly larger in RCP8.5, but much smaller than the differences between the models. On this time scale, differences in the emission scenarios have no systematic effect on the heat wave frequencies.

In the far future (2070–2099), however, the differences between the scenarios emerge. For RCP4.5 a further increase is found for all classes. However, at least for the shorter events, a weakening of the trend is found, i.e., the changes 1971–2000 to 2021–2050 are larger than the changes from 2021–2050 to 2070–2099. The three day heat waves, for instance, increase by 1.5 events/yr relative to the reference period (0.6 relative to 2021–2050). In case of the extreme long-lasting heat waves, changes are still small, but nevertheless pronounced. 10 day events may increase by 0.3 events/yr, suggesting one additional extreme heat wave every third summer.

**Figure 4.** (**a**) Similar to Figure 3 but for the daily mean HUMIDEX; (**b**) Boxplot statistics for number of heat waves per year in the RCM simulations. Heat waves are defined by 3 to 10 consecutive days with a daily mean HUMIDEX above the 95th percentile. Dots resemble the results from the individual simulations; colored squares denote the number of events per year derived from observations. The events of 2003 (8 consecutive days) and 2015 (5 consecutive days) are highlighted by the red and green color; (**c**) Boxplot statistics for the change of heat waves frequencies with a duration between 3 and 10 days in the near (2021–2050) and far (2070–2099) future for the RCP4.5 scenario relative to the model mean value for 1971–2000. Dots resemble the individual RCM simulations; (**d**) Same as (**c**), but for RCP8.5.

Still, in comparison to the RCP8.5 the changes found for RCP4.5 are moderate. For all duration the intensification is always larger than the changes from 1971–2000 to 2021–2050. 3 day heat waves increase by 3.5 events/yr, the 2015-like events with 5 day duration increase by 2.2 events/yr (two additional 2015-like heat waves in every summer), and a 2003-like event is also likely to take place once a summer (multi-model median increase by 1.2 events/yr). The strongest 10 day heat wave, finally, increases by 0.9 events/yr until the end of the 21th century.


*2.2. MTT Assay*

MDA-MB-231 cells were seeded in 96-well plates (2.5 × 103 cells/well) and treated with ISL (Sigma-Aldrich, St. Louis, MO, USA) for 24, 48, and 72 h. The cell survival rate was analyzed using an MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide; Abcam, Cambridge, MA, USA) assay. At the end of incubation, serum-free DMEM medium with 0.5 mg/mL of MTT was substituted for conditional medium and incubated for an additional 3 h; subsequently, the media were removed. Crystal formazan was dissolved in 100 μL/well dimethyl sulfoxide (DMSO; ECHO Chemical Co. Ltd., Taipei, Taiwan). The optical density was measured by using a VERSA Max microplate reader (Molecular Devices, San Jose, CA, USA) at 570 and 630 nm as reference wavelengths.

#### *2.3. Lactate Dehydrogenase (LDH) Assay*

MDA-MB-231 cells were seeded in 96-well plates (2 × 104 cells/well) and treated with ISL for 24, 48, and 72 h. The medium LDH activity was detected using the LDH Cytotoxicity Assay Kit (Cayman Chemical Company, Ann Arbor, MI, USA). The procedure was performed according to the manufacturer's protocols. The absorbance was read at 450 nm with a VERSA Max microplate reader (Molecular Devices, San Jose, CA, USA).


**1. Introduction**

Due to a combination of the high electrical and thermal conductivity of Cu [1] with the light weight of Al [2–6], Cu/Al bimetallic composites [7–14] were widely used in the electric power transportation industry. Cu/Al composite materials can replace copper materials in generators and aluminum materials in external power grids, as well as the contact surfaces between the two, thereby reducing the use of copper resources and reducing the accident rate in power generation and supply. Although the compound casting method has exhibited great superiority in fabricating irregular shapes of Cu/Al bimetallic composites, it still has some drawbacks in the aspects of the rapid growth of intermetallic compounds and the oxidation of the solid Cu substrate. The hard and brittle transition zone was formed at the interface of the Cu/Al bimetallic composite, which reduced the mechanical properties of the material. Therefore, optimization of the transition zone has become a hot topic in the research and development of Cu/Al bimetallic composite.

It was widely reported that the transition zone played an important role in the microstructure and mechanical properties of Cu/Al bimetallic composites [15]. There have been extensive studies on the formation mechanism of the transition zone. For example, Wang et al. [16] used synchrotron X-ray technology to study the interfacial diffusion behavior and microstructure evolution of Cu/Al bimetals. Cu and Al first diffuse to each other and then form α-Al dendrites and intermetallic compounds (IMCs) between the matrix.

**Citation:** Wu, Z.; Zuo, L.; Zhang, H.; He, Y.; Liu, C.; Yu, H.; Wang, Y.; Feng, W. Effect of Liquid-Solid Volume Ratio and Surface Treatment on Microstructure and Properties of Cu/Al Bimetallic Composite. *Crystals* **2023**, *13*, 794.

https://doi.org/10.3390/ cryst13050794

Academic Editors: Andrea Di Schino and Claudio Testani

Received: 27 March 2023 Revised: 7 May 2023 Accepted: 8 May 2023 Published: 9 May 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/).

The liquid–solid ratio was one of the key factors for the formation of the transition zone in the preparation of bimetallic composite by gravity casting. For example, it has been found that the bonding quality of AZ91 and AZ31 alloys was better when the liquid–solid ratio was larger [17]. Other studies have shown the preparation of high chromium cast iron and medium carbon steel bimetals by gravity casting. With the increase of liquid–solid product ratio, the diffusion activity of elements increased, leading to the increase of the interfacial transition zone width and shear strength [18]. It has been reported that the transition zone consisted of the intermetallic compounds and the remelting zone, and the cooling rate influenced the thickness of intermetallic compounds, the microstructure of the remelting zone, and the morphology of the remelting zone/Al interface [19]. Tavasoli et al. [20] reported the effect of pouring temperature on the transition zone, and the results showed that an increase in Al melting temperature resulted in a gradual increase in the thickness of intermetallic compounds and interfaces. Chen et al. [21] found that pouring temperature, cooling mode of Cu plate surface, and starting time of forced cooling after pouring had no effect on the microstructure species of the transition zone.

In addition, during the preparation of the Cu/Al bimetallic composite by gravity casting, an oxidation reaction occurred on the surface of Cu during preheating [22], and the formation of an oxide film reduced the metallurgical bonding property of the interface between Cu and Al. Therefore, it was particularly important to cover the surface of the copper with a protective film to prevent oxidation [23]. A suitable protective film can not only prevent the surface oxidation of Cu, but also promote the metallurgical bonding between Cu and Al. Boucherit et al. [24] achieved friction stir welding of Cu/Al using a zinc interlayer and found that Zn can significantly reduce the formation of intermetallic compounds such as Al2Cu and Al4Cu9, thereby improving the shear lap tensile strength of the joint. Ye et al. [25] adopted a new Zn-Al-Si filler metal to braze Cu/Al and found that Si could inhibit the growth of intermetallic compounds, thus significantly improving the corrosion resistance of Cu/Al bimetallic materials. Breedis et al. [26] found that adding a certain amount of Ni to copper alloys can inhibit the growth rate of Cu/Al intermetallic compounds, effectively reduce the content of intermetallic compounds, improve the microstructure of copper alloys, and effectively improve its properties. It was found that by depositing Ni-P coating on a copper substrate by electroless plating, the intermediate coating acted as a protective film, which could reduce the rate of intermetallic compound generation [27]. If Ni was used as the intermediate layer during the pouring process of Al and Cu, it can be seen from the Cu-Ni binary phase diagram that due to the infinite solubility of Cu and Ni, intermetallic compounds will not be generated and copper matrix oxidation can be prevented. Liu et al. [28] reported that a uniform Ni protective layer on the electroplating of the copper matrix can prevent the surface oxidation of the copper matrix, and the Ni layer dissolved during the interfacial reaction during the pouring process, promoting the metallurgical combination of copper and aluminum.

At present, the research on interface processing of Cu/Al composite materials mainly focuses on coating materials and coating methods, while there are few studies on the effect of coating thickness on the microstructure and properties of Cu/Al composite materials. In this study, the fabrication of Cu/Al bimetallic composite was achieved by gravity casting, and the effect of liquid–solid ratio and coating thickness on the microstructure and properties of Cu/Al bimetallic composites was discussed. The appropriate thickness of the transition zone will significantly improve the mechanical properties of the Cu/Al bimetallic composites.

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

The Cu/Al bimetallic composite was fabricated by pure copper rods and aluminum rods. In order to prevent oxidation of the copper while being kept at elevated temperature, a layer of nickel was plated on the surface of the copper rods before casting. The electroplating solution consisted of 840 g Ni2SO4, 100 g NiCl2·6H2O, and 3 L deionized water. The nickelplating voltage was 4V, and the nickel-plating time was 10, 25, and 40 min, respectively. The electroplating device was shown in Figure 1. Both the casting mold and nickel-plated copper rod were kept at 500 ◦C with the resistance furnace at the beginning of the test. The pure aluminum rod was melted and refined in a steel crucible at approximately 740 ◦C. The melt was left to stand at 720 ◦C for about 10 min to ensure the equilibrium temperature after the refining slag was skimmed. Then, the aluminum melt was cast into the steel mold equipped with the nickel-plated copper rod, and after waiting until it had completely cooled and solidified, it was removed from the mold.

**Figure 1.** Electroplating Operation Console.

The metallographic specimen was first polished on different grit sandpaper, then with a combination of mechanical polishing and hand polishing on a velvet polish cloth with a solution of 0.5 μm aqueous magnesium oxide. The microstructure of Cu/Al bimetallic composite was observed by AXIO-type metallographic microscopy (OM). The Ultima IV X-ray diffraction (XRD) was used to analyze to the types of intermetallic compounds in the transition zone of materials, with a voltage of 35 kV and a scanning speed of 10◦/min; diffraction angle range was 10◦ ≤ θ ≤ 45◦. Jade 6.0 software was then used to perform phase calibration on the acquired dates. The sampling locations of hardness and shear samples were shown in Figure 2. The hardness (HV) of the Cu/Al bimetallic composite were tested on the HXD-1000TM digital microhardness tester with a load of 200 g and loading time of 15 s. The cylindrical shear specimen with diameter of 16 mm and height of 6 mm was fabricated by the electric spark machine. The shear specimen was performed on HXD-1000TM electronic universal material testing machine with the speed of 1.0mm/s. Then, the FEI Scios-2 HiVac scanning electron microscopy (SEM) was used to analyze the shear surface of the Cu/Al bimetallic composite.

**Figure 2.** Casting mold drawing and shear material: (**a**) casting mold diagram; (**b**) Cu/Al bimetallic composite; (**c**) schematic diagram of shear strength test.


**3. Discussion**

In the present study, both of the synthesis methods proposed using sodium citrate or sodium borohydride as reducing agents, led to the anchorage between the silver nanoparticles and calcium glycerophosphate (Figure 2). Besides, in general, the nanocomposites (AgCaGP) were effective against reference strains of *Candida albicans* and *Streptococcus mutans*. Notably, CaGP substantively increased the antimicrobial effectiveness of silver in the AgCaGP, reducing up to a quarter their minimum inhibitory concentration when compared to the respective AgNP controls (Tables 1 and 2).

Although the CaGP has been previously nanoparticulated before the Ag-CaGP synthesis, in our study it was not characterized as being in nanoparticulated form when associated with silver. It might be happen due to the poor solubility of calcium at pH = 7 [29], even when using the same dispersant (NH-PM), as preconized by Miranda et al., whom synthesized AgNP with hydroxyapatite. A pastier bulk was particularly noted in micrographics of Ag-CaGP when water was used as solvent instead of isopropanol (Figure 2c–f), regardless of the reducing agent that was used in the reaction. Although there has not been difference between micro and nanoparticulated-CaGP in the SEM images, its form influenced the amount of silver ions in the compounds (Table 1). In addition, our results showed the antimicrobial effectiveness against *C. albicans* and *S. mutans* for the samples of group C, and it could be explained by the highest amount of silver ions that are present in those compounds [4,30–35].

This expressive difference in the quantity of silver ions between groups B and C would be related to the characteristics of the reducing agents used, being sodium borohydride considered a stronger reducing agent than sodium citrate [33]. Although silver ions are effective to kill several pathogenic microorganisms, they are easily dispersed, which quickly decreases its local concentration to levels of low effectivity. Moreover, ambient light reduces ionic silver forming typical black spots on skin or on any surface of contact [36]. This process causes aesthetic problems and it has potential to injure healthy living tissues. Silver nanoparticles, contrary to ionic silver, induce the production of reactive oxygen species (ROS), which is the primary antimicrobial mechanism [37]. However, AgNP tend to form aggregates in the absence of any support, reducing their efficacy. Therefore, substrates decorated with immobilized AgNP exhibits enhanced antimicrobial activity for longer periods, reducing the undesirable secondary effects that are associated to free ionic silver [38]. Although the difficult to separate the impact of free ionic silver from the AgNP antimicrobial action, differences that were observed in minimum inhibitory concentrations (MIC), as shown in Table 1, for *C. albicans* and *S. mutans* suggests the influence of their respective metabolism on the efficacy of silver against each microorganism.

Furthermore, other factors may influence the antimicrobial potential of AgNP [34]. For instance, how the compound containing silver interacts with the microorganisms would dependent on the characteristics of the AgNP formed, as well as the chemical and physical changes that may occur when they are added to the medium of interest [33]. In general, for the synthesis of AgNP, AgNO3 is used as source of silver, water or ethanol as solvent, and sodium borohydride or sodium citrate as reducing agent [39]. Fabricated under similar conditions, the AgNP would have a negative surface charge [33,40], and this fact is noteworthy to elucidate the lower effectiveness of the compounds against *S. mutans*. Bacteria have a negative outer membrane charge [41] and the electrostatic attraction may have been hampered, and hence the action of the AgNP associated or not with CaGP on the *S. mutans*

was diminished. On the other hand, apart from fungi present a neutral surface charge [41] and might enhance the attraction of AgNP, the presence of phospholipid components, which contain phosphate groups, may have improved the antimicrobial activity of silver by targeting these sites [42,43]. Indeed, the control of AgNP reduced by sodium citrate showed a lower amount of ions (107.2 μg Ag+/mL) than the control that was produced using sodium borohydride (576.2 μg Ag+/mL), and it was more effective against *C. albicans*, suggesting an antifungal potential of AgNP by itself, which may have afforded the disruption of the *C. albicans* cell membrane by damaging the inner layers of the cell wall, increasing their permeabilization and then allowing for the passage of these particles to into the cell.

On the contrary, against *S. mutans* plaktonic cells, Ag+ may have played a preponderant role, particularly in view of the MIC values that are found for AgNO3 (21.2 μg/mL) when compared to those for AgNP, regardless of the reducing agent that is used in the reaction (250 and 125 μg/mL, respectively, for AgNP (Na3C6H5O7) and AgNP (NaBH4)). Noteworthy was the effect that was produced against *S. mutans* when CaGP was associated with AgNP (Table 1). CaGP afforded an increment in the silver activity and it could be related to the acidogenic and acidic characteristic of *S. mutans*, acting CaGP probably as a buffer, and hence might have prevented the proliferation of the cells in the medium [44–46]. So that, the CaGP buffer activity and the highest amount of Ag+ ions could account for the better effectiveness of the samples of C group against that gram positive bacteria tested.

#### **4. Materials and Methods**

#### *4.1. Synthesis of Silver-Calcium Glycerophosphate (Ag/CaGP) Nanocomposites*

Ag/CaGP nanocomposites were synthesized at the Interdisciplinary Laboratory of Electrochemistry and Ceramics of the Chemistry Department in Federal University of São Carlos. Initially, the commercial form of calcium glycerophosphate (80% β-isomer and 20% rac-α-isomer, CAS 58409-70-4, Sigma-Aldrich Chemical Co., St. Louis, MO, USA) was acquired and was nanoparticulated using a ball mill for 24 h at 120 rpm, obtaining nanoparticles of approximately 10 nm. Then, two chemistry methods were employed for the synthesis. The first method was employed using sodium borohydride as reducing agent (NaBH4, Sigma-Aldrich Chemical Co., St. Louis, MO, USA) and was based on the methodology that was proposed by Miranda et al. [29]. The synthesis was carried out in an alcoholic medium (isopropanol) or deionized water. For this, suspensions containing 5 g of CaGP and silver nitrate (AgNO3 Merck KGaA, Darmstadt, Hessen, Germany) at 0.85 or 0.085 g were prepared in the presence of 0.5 mL of a surfactant (ammonium salt of polymethacrylic acid (NH-PM), Polysciences Inc., Warrington, PA, USA) (Table 1). Then, NaBH4 (0.015 g) was added to each suspension, which caused the reduction of Ag+ to metallic silver nanoparticles in the presence of CaGP. The molar stoichiometric ratio between Ag+ and NaBH4 was 1:1.26, respectively. The second method was based on that proposed by Turkevich et al. [47] and Gorup et al. [48] (2011, p. 355). The reducing agent of AgNO3 was sodium citrate (Na3C6H5O7, Merck KGaA) and the stoichiometric ratio of each compound was, respectively, 1:3. Thus, in a flask containing 100 mL of deionized H2O 5 g of CaGP was added following of 0.5 mL NH-PM and 1.4 g of Na3C6H5O7. This mixture was kept under magnetic stirring and heating. After reaching 95 ◦C temperature, AgNO3 was added and this suspension was maintained stirring for 30 min until occurring the color change, which qualitatively indicated the formation of AgNP. Controls containing only the reducing agents and surfactant, and AgNP produced by both reducing were also prepared.

#### *4.2. Characterization of Ag-CaGP Nanocomposites*

In order to demonstrate the presence of AgNP and CaGP in the compounds, the UV-Vis absorption spectroscopy was employed. The measure is based on the phenomenon of plasmon resonance band, as observed in metallic nanoparticles. Thus, UV-Vis spectra of Ag-CaGP nanocomposites were obtained from aqueous solutions poured out in a commercial quartz cuvette with 1 cm optical path using a spectrophotometer (Shimadzu MultSpec-1501 spectrophotometer; Shimadzu Corporation, Tokyo, Japan) at 300 to 800 nm. Water was used as blank.

After a drying step, the resulting powder, Ag-CaGP, was subjected to X-ray diffraction (XRD) phase characterization using Cu K α radiation (λ = 1.5406 Å), generated at a voltage of 30 kV and a current of 30 mA with continuous sweep in the range of 5◦ < 2θ < 80◦, at a scan rate of 2◦/min (Diffractometer Rigaku DMax-2000PC, Rigaku Corporation, Tokyo, Japan). The particles morphology was also characterized by scanning electron microscopy (SEM) on a Zeiss Supra 35VP microscope (S-360 Microscope, Leo, Cambridge, MA, USA), with field emission gun electron effect (FEG-SEM) operating at 10 kV. A drop of each sample were added with a micropipette and deposited on silicon metal plate (111) and dried at 40 ◦C for 2 h. With this technique, we can identify in the synthesized biomaterials the presence of silver, oxygen, silicon, phosphate, and calcium, which were artificially colored (Figures 3 and 4).

#### *4.3. Minimum Inhibitory Concentration (MIC)*

The MIC values for each sample were determined through the microdilution method and followed the Clinical Laboratory Standards Institute guidelines (CLSI, documents M27-A2 and M07-A9). *Candida albicans* (ATCC 10231) was cultivated on Sabouraud Dextrose Agar (SDA, Difco, Le Pont de Claix, France) and *S. mutans* (ATCC 25175) on Brain Heart Infusion Agar (BHI, Difco, Le Pont de Claix, France). Inocula from 24 h cultures on the respective media were adjusted to a turbidity equivalent to a 0.5 McFarland standard in saline solution (0.85% NaCl). This suspension was diluted (1:5) in saline solution, and afterwards diluted (1:20) in RPMI 1640 or BHI. Initially, the Ag-CaGP nanocomposite was diluted in deionized water in a geometric progression, from 2 to 1024 times. Afterwards, each Ag-CaGP nanocomposite concentration obtained previously was diluted (1:5) in RPMI 1640 medium (Sigma-Aldrich) for *C. albicans* and in BHI for *S. mutans*. The final concentrations of Ag-CaGP nanocomposite in the dispersion ranged from 5 to 0.01 mg/mL. Each inoculum (100 μL) was added to the respective well of microtiter plates containing 100 μL of each specific concentration of the Ag-CaGP nanocomposite solution. The microtiter plates were incubated at 37 ◦C, and the MIC values were determined visually as the lowest concentration of Ag-CaGP with no microorganism growth after 48 h for *C. albicans* and 24 h for *S. mutans*. All of the assays were repeated in triplicate on three different occasions.

#### *4.4. Determination of Ag+ Concentration*

The evaluation of Ag+ concentration in Ag-CaGP and AgNP, as obtained by both reducing agents, was determined by a specific electrode 9616 BNWP (Thermo Scientific, Beverly, MA, USA) coupled to an ion analyzer (Orion 720 A+, Thermo Scientific, Beverly, MA, USA). A 1000 μg/mL silver standard was prepared placing 1.57 g of dried AgNO3 into a 1 L volumetric flask containing deionized water. This solution was stored in an opaque bottle in a dark location and diluted in deionized water at the moment of dosage in order to achieve the standard concentrations used. Thus, the combined electrode was calibrated with standards containing 6.25 to 100 μg Ag/mL at the same conditions of samples. A silver ionic strength adjuster solution (ISA, Cat. No. 940011) that provides a constant background ionic strength was used (1 mL of each sample/standard: 0.02 mL ISA).