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A Fiber-Reinforced, Large Vessel Chitosan Scaffold for Pediatric Applications

Irina Robu, Chemical Engineering, Wayne State University, 5050 Anthony Wayne Drive, Detroit, MI 48202, Henry L. Walters III, Children's Hospital of Michigan, 3901 Beaubien Blvd., Detroit, MI 48201, and Howard W. T. Matthew, Department of Chemical Engineering and Materials Science, Wayne State University, 5050 Anthony Wayne Drive, Detroit, MI 48202.

Congenital heart and large vessel defects are a significant cause of morbidity and mortality in pediatric patients. Current vessel replacement options lack the capacity to grow and remodel in response to patient needs. This limitation is a major problem for pediatric patients who may require multiple surgical procedures before reaching adulthood. In this study, we explored the prospect of a tissue engineered large vessel graft using polysaccharide biomaterials. Our scaffold design was based on the use of chitosan as the main structural biopolymer, with cell adhesion ligands provided by blending Type I collagen with the chitosan. In addition, we explored the effects of covalently grafting various glycosaminoglycans (GAGs) to the scaffold surfaces to promote binding and presentation of growth factors and extracellular matrix proteins.

Scaffold composition effects were studied under static conditions using chitosan-GAG and chitosan-collagen-GAG films in culture dishes. These studies indicated that incorporation of collagen increased aortic smooth muscle cell (ASMC) attachment and proliferation. In the presence of collagen, addition of covalently linked heparin further enhanced SMC proliferation.

Porous tubular constructs were fabricated from a blend of chitosan 1.5 wt% and 10 wt% collagen using controlled freezing and lyophilization.The graft dimensions were 12-13 mm inner diameter and 40-50 mm in length.Some constructs were reinforced by embedding random or spirally arranged chitosan fibers within the porous structure.The grafts were covalently linked with heparin.The elastic modulus and tensile strengths of the fiber-reinforced constructs in wet conditions were 36.43 kPa and 21.84 kPa respectively .

After initial cell seeding with 30 million porcine ASMC, the constructs were cultured dynamically for 3 days and were then transferred to a perfusion culture system with an initial flow rate of 150 ml/min. Fluorescence microscopy observation of excised scaffold samples using Calcein AM showed that cells within the scaffold grow, proliferate and elongate in a parallel orientation.Hematoxylin and Eosin staining show that cells penetrate within the scaffold in a homogenized fashion. Early results indicate that chitosan-collagen-heparin materials are suitable for engineering of large vessel constructs. Long term (30 day) perfusion cultures are underway and the results of these studies will be reported.