Development Of Controlled Release Vehicle And Related Survey Of Construction Of Functional Tissue Engineering Skin Equivalent

Bioactive compounds, especially the growth factors with multiple biological efficacies, play the vital role among the numerous research fields of tissue engineering. Bioactive compounds are polypeptide materials, which take the part of both informational deliverers between cells and growth regulator on cells. They can improve or suppress the cell proliferation, differentiation, immigration and gene expression during the different stages of cell growth. The considerable application of growth factors theses days makes for renovation and regeneration of tissues. However, due to the property of being protein, growth factors are subjected to external condition (such as temperature, pH and organic reagents); and the half-life period of growth factors is so short, that they diffused, denaturized and degraded quickly. Therefore, effective conservation and delivery of growth factors is urgent needs for the development of tissue engineering. The drug delivery system (DDS), which is an advanced technology today, provides the suitable vehicle of releasing the growth factors. Considering the particularity of tissue engineering products, the DDS in this study should be accord with the standards below: biocompatibility, absorbability of vehicle or degradation product, safety and asepsis, half- penetrated, suppression of pathological period, improved tissue renovation and regeneration and being the scaffolds of renewal tissue. The objective of this study is to design and construct the functional products based on tissue engineering and controlled release technology, which play the dual role of growth factor delivery vehicle and implantable scaffold, and to survey the characteristics, thus giving an indication of possible application as a promising candidate in tissue engineering. The study was composed of threesections as follows:1. Preparation and related characteristics survey of controlled release microspheres incorporated growth factors: Three kinds of solidification (chemical crosslinking, photo-crosslinking and thermo-crosslinking) were applied with improved emulsifying condense method to prepare the controlled release microspheres incorporated basic fibroblast growth factor (bFGF), the characteristics including morphology, diameter, degradation, drug content, encapsulation and bFGF releasing efficacy were surveyed, and the biocompatibility and their effects on fibroblasts were investigated to testify the security and bioactivity of growth factors. Conclusion:â‘ The microspheres incorporated bFGF, which were all rapid and accurate constructed by different methods, have excellent function and respective advantages, and they could control release bFGF through a long period.â‘¡The microspheres incorporated bFGF with low antigenicity and well biocompatibility can promote the proliferation of fibroblasts with time obviously. Due to the unique beneficial effects above, it could be hypothesized that the functional implantable microspheres incorporated bFGF might substantially be fundament for future study.2. Preparation and related characteristics survey of bilayer wound dressings containing bFGF- incorporated microspheres: The purpose of this study was to synthesize a novel wound dressing containing bFGF-loaded microspheres to provide an optimum healing milieu for promoting healing and tissue regeneration. For this purpose, a natural, nontoxic and biocompatible material, gelatin, was chosen as the underlying layer and the porous matrices in sponge form were prepared from gelatin by physical crosslinking technique. As the external layer, elastomeric polyurethane membranes were adhered. The composite dressings were characterized for structure, in vitro protein release and compatibility, and further tested via in vivo experiments on full-thickness skin defects created on york pigs. Conclusion:â‘ The full structure of a bilayer wound dressing is composed of a thin polyurethane film over which the gelatin sponge containing bFGF-loaded microspheres was attached. The two layers adhered firmly to each other; the gelatin sponges show the porous and inter-connected network structures, and the microspheres did not interfere with the pore structure of the sponge.â‘¡Fibroblasts grew and proliferated well on wound dressings and there were no immune rejection in the subdermal implantation. The wound dressings could induce the infiltration of host cells and the vascularization.â‘¢The application of these novel bilayer wound dressing containing bFGF-loaded microspheres provided an optimum healing milieu for regenerating tissues in pig's skin defect models.3. Preparation and related characteristics survey of multifunctional particle skin equivalents: The gelatin particles encapsulating bFGF based on thermo-crosslinking microspheres were prepared and modified by cryogenic freeze-drying treatment to develop the surface with three kinds of features on morphology during the post-preparation. The particles were characterized and their influence on fibroblasts has been assessed, and in vivo examinations have been made to observe guided dermal tissue regeneration after implantable particles transplantation. The multifunctional implantable particles might play a triple role as a culture substrate, protein transplantation vehicle, and biodegradable implant in this study. Conclusion:â‘ The features on morphology were smooth, gyrus-patterned and porous according to different experiment condition, and they expressed respective advantages;â‘¡The according results we present in the text indicate that the feasibility of multifunctional implantable particles(SGM-bFGF, GGM-bFGF, PGM-bFGF),especially PGM-bFGF as an excellent skin equivalent;â‘¢They could deliver cultured cells and bioactive molecules to correct dermal defects, thus giving an indication of a promising and novel candidate of skin equivalents.In summary, we present a series of functional tissue engineering products constructed with unique controlled release vehicle. As a beneficial drug delivery system, growth factors can be introduced to be responsible for cell growth onto polymer surfaces in cell culture and induce cell ingrowth and vascularization at the initial stages of wound healing. Specifically, basic fibroblast growth factor (bFGF) is a multifunctional protein that promotes angiogenesis and regulates many aspects of cellular activity, including cell proliferation, migration, and metabolism in a concentration-dependent manner, and the best way to retain the biological activity and enhance the efficacy of bFGF is to achieve sustained release and to maintain suitable concentration over an extended time period by controlled release vehicle. In the present study, we performed a overall evaluation of controlled release microspheres incorporated growth factors, bilayer wound dressings containing bFGF- incorporated microspheres, multifunctional particle skin equivalents. The according results we present in the text indicate that the feasibility of these products for skin regeneration, thus giving an indication of possible application as a promising candidate in tissue engineering.