Fabrication of highly concentrated collagens using cooled urea/HAc as novel binary solvent

Abstract

It is difficult to prepare homogeneous concentrated collagen with concentration > 40 mg/mL due to its extremely high viscosity. Herein, cooled (−12 °C) urea/HAc solutions was employed as novel solvent to prepare collagen samples with concentrations varied from 40 to 120 mg/mL. Fourier transform infrared spectroscopy and sodium dodecyl sulfonate-polyacrylamide gel electrophoresis demonstrated that the concentrated collagen maintained the intact triple-helical structure. As reflected by differential scanning calorimetry, collagen with acetic acid as solvent displayed two thermal transition peaks when concentration ≥ 60 mg/mL, which could be attributed to the denaturation of dissolved collagen and un-dissolved collagen. Whereas, collagen prepared in cooled urea/HAc just exhibited one thermal denaturation peak other than samples with concentration ≥ 100 mg/mL. Images from polarizing optical microscopy displayed that the cholesteric band grew more pronounced upon increasing collagen concentration. Field-emission scanning electron microscopy exhibited more aligned topographical features of the collagen sponges when increasing concentration from 10 to 100 mg/mL, nevertheless both of the aligned structure and anomalous structure could be captured when collagen concentration further reached 120 mg/mL. Rheological properties were found to be dependent on the collagen concentration, additionally, compared with collagen in acetic acid, a weaker entanglement network and lower viscosity for collagen with the same concentration using cooled urea/HAc as solvent could be reflected by the rheological measurements. Overall, this method presents a simple mean for generating homogeneous concentrated collagens, which can be applied to wider fields such as wet spin and biomimetic mineralization.