Extraction of collagen from bovine tannery solid waste preserving original conformation via radical initiation and hydrogen bond reformation†

Abstract

Tannery solid waste (TSW) contains 70–90% collagen by weight. The rapid extraction of collagen while preserving its original and unique triple-helical conformation has proved challenging. In this paper, an ionic liquid-synergistic dissolution and regeneration (IL-SDR) method was developed based on a TBAH/DMSO/H₂O ternary (TDH) solvent for the rapid recovery of collagen from TSW under mild conditions. A solubility of 10.25% TSW and a collagen recovery yield of 51.2% were achieved in 30 minutes at room temperature. The original triplet helical conformation and the molecular weight of the collagen product were retained, confirmed via FT-IR, circular dichroism, and matrix-assisted laser desorption/ionization time-of-flight analysis. SEM was used to verify that dense and uniform pores could be formed within collagen by adjusting the DMSO content, and cytotoxicity and moisture retention tests demonstrated that the collagen produced via the IL-SDR process is comparable to natural collagen used in cosmetic and skincare applications. Moreover, the TDH solvent demonstrated excellent reproducibility across five cycles, achieving consistent solubility varying from 9.71% to 11.04%. EPR and ¹H NMR showed that the OH^– in TBAH induced the generation of DMSO˙ free radicals in the TDH solvent, and these radicals were indispensable for the dissolution of TSW. The DMSO content was positively correlated with the concentration of free radicals. A synergistic dissolution mechanism was proposed: DMSO˙ free radicals preferentially cleaved the terminal peptide chains, causing the collagen molecules to be exposed to DMSO. Subsequently, DMSO disrupted the original hydrogen bond network within the collagen molecules. Then, TBAH and DMSO formed hydrogen bonds with the collagen molecules, stabilizing the dissolved collagen and preventing the reformation of the hydrogen bond network between collagen molecules. This work provides an avenue for low-temperature and rapid dissolution of TSW, and reveals an in-depth, atypical dissolution mechanism for collagen-based materials during the IL-SDR process.