Preparation and Characterization of Poly (ε-caprolactone) PCL Scaffolds for Tissue Engineering Applications

The field of Tissue Engineering has developed in response to the shortcomings associated to the replacement of tissues lost to disease or trauma: donor tissue rejection, chronic inflammation, and donor tissue shortages. The driving force behind Tissue Engineering is to avoid these problems by creating biological substitutes capable of replacing the damaged tissue. This is done by combining scaffolds, cells and signals in order to create living, physiological, three-dimensional tissues. Scaffolds are porous biodegradable structures that are meant to be colonized by cells and degrade in time with tissue generation. Scaffold design and development is mainly an engineering challenge, and is the goal of this thesis. The main aim of this thesis is to develop and characterize scaffolds for Tissue Engineering applications. Specifically, its objectives are: To study scaffold processing method: Phase Separation. This is done by experiment design analysis. To characterize the behavior of the scaffolds produced. The scaffolds are prepared using a biodegradable polymer polycaprolactone by thermally induced phase separation technique using solid-liquid phase separation. The porosity, crystallinity and pore size was characterized using scanning electron microscopy (SEM), differential scanning calorimeter (DSC), Mercury porosimeter, and X-ray diffraction (XRD). The parameters that found to influence the architecture of the scaffolds were freezing temperature, freezing medium and polymer concentration. The freezing temperature was found to have a profound effect on the pore size and final morphology of the porous structures. The degree of crystallinity determined using XRD was comparable with that of the as received PCL. The porosity of the structures was found to be 90-97%. The porosity of the PCL structures can be controlled by the concentration of the polymer solution used. Micrographs of the samples from the SEM revealed that the pore size was smaller when the polymer solution was quenched to lower temperatures (-200C). Mercury porosimeter resulted in a pore size distribution from 50-100μm which makes them suitable for tissue engineering applications. PCL scaffolds therefore may have considerable potential as scaffold for tissue engineering

Zirconium, calcium, and strontium contents in magnesium based biodegradable alloys modulate the efficiency of implant-induced osseointegration

Development of new biodegradable implants and devices is necessary to meet the increasing needs of regenerative orthopedic procedures. An important consideration while formulating new implant materials is that they should physicochemically and biologically mimic bone-like properties. In earlier studies, we have developed and characterized magnesium based biodegradable alloys, in particular magnesium-zirconium (Mg-Zr) alloys. Here we have reported the biological properties of four Mg-Zr alloys containing different quantities of strontium or calcium. The alloys were implanted in small cavities made in femur bones of New Zealand White rabbits, and the quantitative and qualitative assessments of newly induced bone tissue were carried out. A total of 30 experimental animals, three for each implant type, were studied, and bone induction was assessed by histological, immunohistochemical and radiological methods; cavities in the femurs with no implants and observed for the same period of time were kept as controls. Our results showed that Mg-Zr alloys containing appropriate quantities of strontium were more efficient in inducing good quality mineralized bone than other alloys. Our results have been discussed in the context of physicochemical and biological properties of the alloys, and they could be very useful in determining the nature of future generations of biodegradable orthopedic implants

Mg-Zr-Sr alloys as biodegradable implant materials

Novel Mg&ndash;Zr&ndash;Sr alloys have recently been developed for use as biodegradable implant materials. The Mg&ndash;Zr&ndash;Sr alloys were prepared by diluting Mg&ndash;Zr and Mg&ndash;Sr master alloys with pure Mg. The impact of Zr and Sr on the mechanical and biological properties has been thoroughly examined. The microstructures and mechanical properties of the alloys were characterized using optical microscopy, X-ray diffraction and compressive tests. The corrosion resistance was evaluated by electrochemical analysis and hydrogen evolution measurement. The in vitro biocompatibility was assessed using osteoblast-like SaOS2 cells and MTS and haemolysis tests. In vivo bone formation and biodegradability were studied in a rabbit model. The results indicated that both Zr and Sr are excellent candidates for Mg alloying elements in manufacturing biodegradable Mg alloy implants. Zr addition refined the grain size, improved the ductility, smoothed the grain boundaries and enhanced the corrosion resistance of Mg alloys. Sr addition led to an increase in compressive strength, better in vitro biocompatibility, and significantly higher bone formation in vivo. This study demonstrated that Mg&ndash;xZr&ndash;ySr alloys with x and y ⩽5 wt.% would make excellent biodegradable implant materials for load-bearing applications.<br /

Strontium content and collagen-I coating of Magnesium-Zirconia-Strontium implants influence osteogenesis and bone resorption

Objective: Our objective was to study the role of Collagen type-I (Col-I) coating on Magnesium&#8211;Zirconia (Mg&#8211;Zr) alloys, containing different quantities of Strontium (Sr), in enhancing the in vitro bioactivity and in vivo bone-forming and mineralisation properties of the implants. Materials and methods: MC3T3-E1 osteoblast cell line was used to analyse the in vitro properties of Col-I coated and uncoated alloys. Cell viability analysis was performed by MTT assay; cell attachment on alloy surfaces was studied by scanning electron microscopy (SEM); and gene profiling of bone-specific markers in cells plated on uncoated alloys was performed by Quantitative RT-PCR. In vivo studies were performed by implanting 2-mm-sized cylindrical pins of uncoated and coated alloys in male New Zealand white rabbits (n = 33). Bone formation and mineralisation was studied by Dual Energy X-ray Absorptiometry (DXA) and histological analysis at one and three months post-implantation. Results: Our results clearly showed that Sr content and Col-I coating of Mg&#8211;Zr&#8211;Sr alloys significantly improved their bone inducing activity in vitro and in vivo. Osteoblasts on coated alloys showed better viability and surface binding than those on uncoated alloys. Sr inclusion in the alloys enhanced their bone-specific gene expression. The in vivo activity of implants with higher Sr and Col-I coating was superior to uncoated and other coated alloys as they showed faster bone induction and higher mineral content in the newly formed bone. Conclusion: Our results indicate that bone-forming and mineralising activity of Mg&#8211;Zr&#8211;Sr implants can be significantly improved by controlling their Sr content and coating their surface with Col-I