Optimization of collagen-elastin-like polypeptide composite tissue engineering scaffolds using response surface methodology

The ability of a tissue-engineered scaffold to regenerate functional tissues depends on its mechanical and biochemical properties. Though the commonly used collagen scaffolds have good biochemical properties, they fail due to their poor mechanical and physical properties. We have reinforced the collagen matrix with elastin-like polypeptide (ELP) to improve the mechanical and physical properties and optimized the composite composition using a novel statistical method of response surface methodology (RSM). RSM used a central composite design to correlate the 2 input factor variables (collagen and ELP concentrations) and 3 output objectives (tensile strength, elastic modulus, and toughness) using a second order polynomial equation. Upon uniaxial tensile testing and subsequent RSM optimization, a composite prepared using 6 mg/mL collagen and 18 mg/mL ELP was identified as having an optimal combination of all the three tensile properties. Physical properties of the 6:18 mg/mL composite versus the 6:0 mg/mL collagen-only hydrogel characterized by swelling ratio, differential scanning calorimetry, and FTIR spectroscopy revealed that the addition of ELP reduced the residual water content in the composites and provided evidence of the presence of collagen-ELP interactions. Scanning electron microscopy images of the collagen-only hydrogel showed porous fibrillar and dense afibrillar collagenous microstructure, but the collagen-ELP composite showed a dense collagenous microstructure with characteristic ELP aggregates. We surmise that because of the low water content and dense microstructure, the 6:18 mg/mL collagen-ELP composite had improved mechanical properties. Taken together, the composites prepared in this research can form good quality, rigid porous structures required for tissue engineering applications.