Abstract
Collagen and hyaluronic acid are two major components of intervertebral disc (IVD). They give resistance and hydration to Nucleus Pulposus. In this study, we assessed the impact of Collagen (COLL) and Hyaluronic acid-Tyramine (THA) contents on the mechanical properties and the structure of composite hydrogels. For this purpose, a range of composites were obtained using a 4 mg/mL collagen concentration and different COLL/THA ratios from 8:1 to 1:5 (w/w). Composite gelling was performed by pH increase, triggering collagen fibrillogenesis and oxidative coupling of tyramine moieties in THA catalyzed by H2O2 and horseradish peroxidase (HRP). To modulate the THA gelling kinetic, different HRP concentrations (0.05; 0.1 and 0.5 U/mL) were used. Composites with a low THA content exhibited a fibrillar structure and possessed mechanical properties close to those of pure collagen hydrogels (200 Pa). From the ratio 1:1, the storage modulus increased to reach c.a 1200 Pa for the ratio 1:5. From the ratio 1:2, the fibrillar structure disappeared and sheets, characteristic of THA hydrogels, were observed. The HRP activity dramatically impacted the physical properties. A rapid THA gelling associated with a high THA content tended to destabilize collagen fibrils and promoted the formation of covalent bond between collagen and THA. On the opposite a slow gelling kinetic favored collagen fibril formation up to the COLL/THA ratio 1:2. Taken together, these results show that a slow gelling and an 8 mg/mL THA concentration are the appropriate conditions to obtain biomimetic biomaterials for the treatment of Nucleus Pulposus.
