Effect of aqueous ethanol on the triple helical structure of collagen

Collagen, the most abundant protein in mammals, is widely used for making biomaterials. Recently, organic solvents have been used to fabricate collagen-based biomaterials for biological applications. It is therefore necessary to understand the behavior of collagen in the presence of organic solvents at low (≤50%, v/v) and high (≥90%, v/v) concentrations. This study was conducted to examine how collagen reacts when exposed to low and high concentrations of ethanol, one of the solvents used to make collagen-based biomaterials. Solubility testing indicated that collagen remains in solution at low concentrations (≤50%, v/v) of ethanol but precipitates (gel-like) thereafter, irrespective of the method of addition of ethanol (single shot or gradual addition); this behavior is different from that observed recently with acetonitrile. Collagen retains its triple helix in the presence of ethanol but becomes thermodynamically unstable, with substantially reduced melting temperature, with increasing concentration of ethanol. It was also found that the CD ellipticity at 222 nm, characteristic of the triple-helical structure, does not correlate with the thermal stability of collagen. Time-dependent experiments reveal that the collagen triple helix is kinetically stable in the presence of 0-40% (v/v) ethanol at low temperature (5 °C) but highly unstable in the presence of ethanol at elevated temperature (~34 °C). These results indicate that when ethanol is used to process collagen-based biomaterials, such factors as temperature and duration should be done taking into account, to prevent extensive damage to the triple-helical structure of collagen.