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

Abstract

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.

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

“…The structure of polyvinyl hydrogels that contain silver and graphene materials should make a difference in the connective tissue response, so a well-formed capsule, signs of connective collagen production, and infiltration of leukocytes are expected here, according to Ratner's formula for biocompatibility assessment. 7,21,54 Macrophages are present in all observed time periods (7th, 15th, 30th, and 60th p.o.d.) and follow the stages of skin regeneration.…”

“…55 Collagenation, encapsulation, and magnification of tissue macrophages are indicators of a receding tissue reaction and its gradual recovery and healing. 54,56 The renewal of the matrix components (collagen), the restraint of the foreign body by encapsulation, and the increase in macrophages and giant cells number are an indicator of normal tissue defect regeneration. 43,48 Thus, an increase in the number of macrophages on the 15th and 30th day in our observation is an indicator of low to moderate tissue response at the implantation site, considering the gradations in the processing of TIRI.…”

“…In one of our previous research studies, we used immunohistochemistry to analyze and visualize skin regenerative processes after subcutaneous implantation of Ag/PVA and novel Ag/PVA/Gr hydrogels in an animal model. 54 The biocompatibility markers’ in vivo evaluation demonstrated tissue remodeling processes. We observed cellular and extracellular components such as laminins, vessel density and angiogenesis in the wound bed, collagenization, capsulation, fibroblast and keratinocyte migration, and proliferation on the 7th, 15th, 30th, and 60th p.o.d.…”

Maternal Subclinical and Clinical Hypothyroidism Effects on Rat Offspring: A Story of the Skin and its Derivatives

“…Proliferation and differentiation are essential for normal skin structure and homeostasis and they take place alternately, diffusely and they overlap in some epidermal layers [24,25]. Proliferation is more pronounced in the germinal layer, with differentiation in the higher ones, while apoptosis is diffusely present in all layers of the epidermis [24].…”

“…On the other hand, T3 is proven as a suppressor of Casp3 + activity and an important antiapoptotic factor [26]. The lack of T3 results in impaired synthesis of extracellular matrix proteins like laminin [23] and nuclear matrix proteins like PCNA, in charge for cell cycle control [27], both with a key role in connection, growth, proliferation and distribution of epithelial cells like keratinocytes [25]. Thus, the changes are understandably more pronounced in the pups from mothers with overt hypothyroidism (T0 and T7) where amplifi ed apoptosis and decreased proliferation result in reduced thickness of the non-cornifi ed layer.…”