Multilayered, Self-Assembled Polycaprolactone and Gelatin-Chitosan Scaffold for Congenital Heart Defect Repair
Seokwon Pok1, Jeffrey G. Jacot1,2
1Rice University, department of Bioengineering; 2Texas Children’s Hospital Division, of Congenital Heart Surgery
Introduction: Surgical repair of a ventricular septal defect (VSD) involves placement of a patch or baffle across the defect. Currently, surgeons use various forms of knitted polyester (most commonly Dacron), expanded polytetrafluoroethylene (such as Gore Tex) and autologous or bovine pericardium for VSD repair. However, these materials have significant drawbacks, including the inability to grow with the patient’s heart, loss of mechanical strength over time and little ability to remodel, or regenerate as well as an increased risk of infection and aneurysm (Mirensky and Breuer 2008).
We have recently reported a novel process of generating flat PCL matrices in aqueous medium, which decreased hydrophobic surface properties and maintained high mechanical strength (Pok, Wallace et al. 2010), though hydrophobicity remained too high for effective cell attachment. While gelatin has excellent biocompatibility and bioresorbability and induced fibrous tissue in-growth in the right ventricular outflow tract of rats (Gelfoam, Pharmacia & Upjohn Co, Kalamazoo, Mich), it is too fragile for repair of VSD (DeLeon, LoCicero et al. 1986). One study demonstrated the feasibility of using a chitosan scaffold for the creation of contractile cardiac tissue constructs for use as a cardiac patch. However, the chitosan scaffolds did not promote the binding of cardiomyocytes (CMs) (Blan and Birla 2008). In this study, we developed a method of synthesizing flat, self-assembled PCL with immobilized natural polymers gelatin and chitosan, in order to promote functional interaction with primary cardiac cells, while maintaining sufficient mechanical properties to ensure feasible surgical handing, and function.
Methods and Preliminary Results: 10% (wt/v) PCL (80 kDa) solution was prepared in glacial acetic acid, and matrices formed by self-assembled method in aqueous media. Ratios of chitosan containing gelatin were also prepared. 1 M of glacial acetic acid was added to the gelatin-chitosan solution to enable immobilization with acetic acid based PCL matrices. A multilayered hydrogel was formed successfully using a previously described procedure with modifications (Madihally and Matthew 1999). Briefly, formed PCL matrices were submerged into a gelatin-chitosan solution for pre-conditioning during one hour. Gelatin-chitosan solution poured into custom made Teflon well plates, and then pre-conditioned PCL matrices were sandwiched with the gelatin-chitosan solution then frozen immediately using dry ice. Samples were lyophilized overnight at – 30°C. Formed hydrogels showed no layer separation during re-hydration and neutralization process. Different MW of PCL were used to find optimal porous and degradation characteristics for neonatal rat cardiomyocytes (CMs). Blending with low MW of PCL (50:50 of 80 and 10 kDa) showed an increase in pore size and degradation rate compared to pure 80 kDa PCL. In addition, tensile stress and elastic modulus were decreased by a presence of 10 kDa PCL, but still showed strong mechanical properties (~1.5 MPa of tensile stress and ~2.0 MPa of elastic modulus). Cellular activity analysis of neonatal rat CMs on novel synthetic patches include colonization, survivability and in-growth are ongoing. In summary, mechanical properties of hydrogels were improved by a presence of self assembled PLC matrices. We highly expected that multilayered PCL matrices with gelatin-chitosan will have strong mechanical properties due to presence of PCL layer, and also they will have improved cellular activity due to gelatin-chitosan layer. Hence, this multilayered self assembled PCL with gelatin-chitosan hydrogels have significant potential in design of synthetic cardiac patch for VSD repair.