Silkworm Protein-Hydroxyapatite Blend Films for Tissue Engineering Applications

A unique protein extracted from discarded silkworms was reinforced with hydroxyapatite (HA) and made into films for potential tissue engineering applications. After reeling of silk, the silkworms are treated as waste and disposed. However, the silkworms contain up to 25–30 % proteins, 40 % oil and 20–25 % carbohydrates and are inexpensive and a renewable resource for various biopolymers. Proteins extracted from silkworms had purity of 90 %, molecular weights of about 30 kDa and were soluble in a weak alkali. The proteins could be made into films using a simple compression molding technique. Hydroxyapatite (HA) was synthesized and added to the proteins to promote cell growth for tissue engineering applications. The changes in the structure, properties and enhancement in cell viability and growth due to the addition of HA were studied. The ability of the films to differentiate osteoblast cells was determined using ALP assay and calcium activity tests. Results showed that the addition of HA increased the tensile properties including the strength (3.5 to 5.5 MPa, elongation from 3.3 to 5.7 % and modulus from 153 to 242 MPa). However, no significant change was observed in terms of cell attachment, growth or viability. Yet, the inclusion of HA did not increase the cytotoxicity and hence, is considered to be beneficial to obtain silkworm protein-based films.