In Vivo Investigation of Soft Tissue Response of Novel Silver/Poly(Vinyl Alcohol)/ Graphene and Silver/Poly(Vinyl Alcohol)/Chitosan/Graphene Hydrogels Aimed for Medical Applications – The First Experience

Application of Biological Composite Materials in the Regeneration of Subchondral Defects and Articular Cartilage in a Synovial Joint: An Experimental Model

Objective: Since the benefits of Nano-material usage have been well documented in orthopedic surgery, this study was conducted to explore the effect of polyvinyl alcohol/nano-hydroxyapatite/polyamide 66 (PVA/n-HA/P66) on repairing of traumatic cartilage defects in rabbit knee joint. Methods: New Zealand white rabbits were used to make a rabbit knee traumatic cartilage defect animal model. All rabbits were randomly located in three groups. Group-A (PVA/n-HA+PA66 implanted in cartilage defects); Group-B (HA nanospheres implanted in cartilage defects)/Gelatin sponge composite scaffold); Group-C (only cartilage defect without implant). The repairment of articular cartilage defects and the general observation were studied by using pathological staining and gene expression of collagen using RT-PCR after 12 weeks. Results: After 12 weeks, we observed a small amount of fibrous tissue growth in group C without soft cell filling. The repaired tissue in group B was stained with immunohistochemical and toluidine blue staining for collagen and type II collagen is positive, but chondrocyte structure is more visible. The relative mRNA expression of type II collagen was higher in group B in comparison to other groups. The results of the Wakitani score were 5.50±2.59 for group A, 8.83±2.79 for group B, 11.50±1.05 for group C. Results showed no significant difference between group B and C; however, significant differences were found in the scoring results between groups A and B, and between-group A and C. Conclusion: This study showed the high effectiveness of PVA/n-HA+PA66 in the treatment of cartilage defects through increasing the expression of type II collagen.

Macrophages, the main marker in biocompatibility evaluation of new hydrogels after subcutaneous implantation in rats

Biocompatibility of materials is one of the most important conditions for their successful application in tissue regeneration and repair. Cell-surface interactions stimulate adhesion and activation of macrophages whose acquaintance can assist in designing novel biomaterials that promote favorable macrophage-biomaterial surface interactions for clinical application. This study is designed to determine the distribution and number of macrophages as a means of biocompatibility evaluation of two newly synthesized materials [silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) nanocomposite hydrogels] in vivo, with approval of the Ethics Committee of the Faculty of Veterinary Medicine, University of Belgrade. Macrophages and giant cells were analyzed in tissue sections stained by routine H&E and immunohistochemical methods (CD68⁺). Statistical relevance was determined in the statistical software package SPSS 20 (IBM corp). The results of the study in terms of the number of giant cells localized around the implant showed that their number was highest on the seventh postoperative day (p.o.d.) in the group implanted with Ag/PVA hydrogels, and on the 30th p.o.d. in the group implanted with Ag/PVA/Gr. Interestingly, the number of macrophages measured in the capsular and pericapsular space was highest in the group implanted with the commercial Suprasorb^© material. The increased macrophage number, registered around the Ag/PVA/Gr implant on 60th p.o.d. indicates that the addition of graphene can, in a specific way, modulate different biological responses of tissues in the process of wound healing, regeneration, and integration.

Evaluation of Soft Tissue Regenerative Processes After Subcutaneous Implantation of Silver/ Poly(Vinyl Alcohol) and Novel Silver/Poly(Vinyl Alcohol)/Graphene Hydrogels in an Animal Model

A newly produced biomaterial is necessarily subject of standards, which are performed in vivo on animal models. For the evaluation of soft tissue regenerative possibilities after subcutaneous implantation of biomaterials – silver/poly(vinyl alcohol) (Ag/PVA) and novel silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) provided for clinical use, sixteen rats were used, according to the instructions of international standards, ISO 10993-6, 2007. Histological sections were observed 7, 15, 30 and 60 days after grafting. These hydrogels were produced by in situ electrochemical synthesis of silver nanoparticles in the polymer matrices, which enabled obtaining completely safe and biocompatible materials, free from any additional toxic chemical reducing agents. Surgical implantation of hydrogels was done according to the permission of the Ethical Committee of the Faculty of Veterinary Medicine, University of Belgrade. Immunohistochemical (IHC) studies included the assessment of smooth muscle expression actin in blood vessels (α-SMA), the expression of laminin and type I and type III collagen in the skin structures, and, the determination of cell proliferation marker expression (Ki-67) keratinocytes. The results were assessed in a semiquantitative manner. The data were analyzed in the statistical software package IBM SPSS 20. The conclusions indicated that Ag/PVA/Gr might be used as wound dressings to enhance the tissue healing potential and established faster integration and shorter retention in the tissue.

Animal models in bicompatibility assessments of implants in soft and hard tissues

The ethical dilemmas of using animals as in vivo models in preclinical and clinical examinations have been increasingly present in recent decades. Small laboratory animals (rats, rabbits) will continue to be used because they are cost-effective and permit the formation of statistically testable cohort groups; a task that, for financial, maintenance and care reasons, is almost prohibitive for larger animals. Technological advances in the production of new biomaterials for clinical use are enormous, but screening tests and methods used to assess biocompatibility lag behind these advances. The assessment of biological responses is slow and based on millennial recovery mechanisms in eukaryotic organisms. Therefore, the goal of researchers in this field is to re-evaluate old methods of biocompatibility assessment and introduce new methods of evaluation, especially for in vivo testing. In that sense, a revision of the ISO standards was planned and conducted in 2017, which insisted on cytotoxicity testing in cell lines and produced concrete proposals on how biocompatibility should be quantified. In vivo biocompatibility evaluation of biomaterials used for soft tissue recovery commonly utilises rats. Rabbits are recommended for implants used for hard tissues, because of the rabbit?s size, the possibility of implanting the biomaterials on a larger bone surface, and because of the peculiarities of rabbit bone tissue that favours rapid recovery after bone defects and enables easy reading of the results.