Björn Atthoff

Synthesis and surface activation of synthetic biodegradable polymers as support for cell produced ECM

Introduction: For tissue engineering of small-diameter blood vessels, biodegradable, flexible and elastic porous tubular structures are most suited. The applicability of poly(trimethylene carbonate) (PTMC), random copolymers of TMC and e-caprolactone poly (TMC-CL), and networks based on these polymers as scaffolding materials was investigated. Methods: TMC-based (co)polymers were synthesized by ringopening polymerization. Tubular structures were prepared by dipping glass mandrels in polymer solutions containing dispersed, sieved sugar particles, followed by g-irradiation and cross-linking, and leaching. For mechanical- and biocompatibility tests, films of different thicknesses were prepared by compression molding, solvent casting, and spin-coating. Results and Discussion: PTMC and poly(TMC-CL) are flexible materials, with E-modulus values below 10 MPa and elongations at break higher than 500%. After g-irradiation in vacuo at 25– 100 kGy, networks with gel contents up to 73 wt% were obtained. The networks showed excellent creep resistance under static and dynamic loading conditions. Good cell attachment and proliferation behavior of mesenchymal stem cells, endothelial cells, and smooth muscle cells on polymer films and networks was observed. In lipase solutions, the films degraded substantially within one month by surface erosion. Porous tubular structures, with pore sizes in the range of 80 – 130 mm and a porosity of approximately 85%, could readily be prepared. A pulsatile bioreactor that allows mechanical stimulation of smooth muscle cells and endothelial cells seeded in the porous structures is being constructed. Conclusions: TMC-based (co)polymers and networks are flexible, elastic, biocompatible, and biodegradable. Porous tubular scaffolds based on these materials have much potential in tissue engineering of small diameter blood vessels.Our bodies are constantly exposed to different sorts of mechanical forces, from muscle tension to wound healing. Connective tissue adapts its extracellular matrix (ECM) to changes in mechanical load and the influence of mechanical stimulation on fibroblasts has been studied for a long time [1, 2]. When exposed to forces, fibroblasts are known to respond with expression and remodeling of ECM proteins, in particular collagen type I [3]. In this study the effect of dynamic culture conditions on human dermal fibroblasts was evaluated in terms of deposition and remodeling of ECM, with the aim of producing an ECM based scaffold. The fibroblasts were grown on compliant polymer supports either in a bioreactor with a pulsating flow or under static conditions. By applying dynamic culture conditions, the collagen deposition on the polymer supports increased fivefold. Scanning electron microscopy showed that polymer fibers were well integrated with cells and ECM and alignment along the polymer fibers was observed. Scaffold design should aim at creating structures that can help guiding the cells to form new, functional tissue. The presented system may present a new way of producing designed extracellular matrix based scaffolds for tissue engineering.Synthesis and surface activation of synthetic biodegradable polymers as support for cell produced ECMWe have previously demonstrated that porous poly-(epsiloncalprolactone) films with regularly spaced, controlled pore sizes provide adhesion and support for cultured dermal fibroblasts. We have determined the effects of applying various sized porous films (n¼3 for each treatment) on 4mm punch biopsy wounded mice to assess wounding response. Films with pores ranging in size from 3–20 microns, elicited a mild lymphocytic and foreign body perifollicular immune response, regardless of pore size but this treatment failed to significantly shorten wound healing time or increase the rate of wound closure. By 21 days after wounding the grafted porous films had become fully incorporated into or completely biodegraded in the wounded tissue. Finally, we assessed the proof of principle that live cultured fibroblasts can be delivered using porous films and sustained in model SCID mouse wounds. Human fibroblasts (30,000 cells) were subconfluently cultured on 5 micron porous films. These cell/film combinations were then transplanted onto wounded mice but failed to significantly affect wound healing. However, these transplanted fibroblast cells were readily detected using anti-human HLA antibodies in wounded SCID mice skin 21 days after treatment, when the wounds had completely healed. Taken together, these data demonstrate for the first time the feasibility of using porous films to deliver living human cells into skin wounds as part of our aim to use cell therapy to improve the wound healing response.The aim of this work is to develop an artificial artery for use in bypass surgery. The hybrid artery consists of a porous tubular scaffold made from a polyurethane elastomer. The surface of the polymer is then modified with recombinant proteins in order to encourage the growth of organised layers of vascular cells.