Structural changes in cartilage and collagen studied by high temperature Raman spectroscopy

Area of Science:

• Biomaterials Science
• Protein Chemistry
• Spectroscopy

Background:

• Understanding collagen's high-temperature behavior is crucial for surgical applications and biomaterials processing in food, pharmaceutical, and cosmetic industries.
• Collagen, a hierarchical material in connective tissues, undergoes thermal denaturation, involving polypeptide chain unfolding.

Purpose of the Study:

• To investigate the high-temperature behavior of collagen and proteoglycans in freeze-dried cartilage using Raman spectroscopy.
• To elucidate the role of residual water in collagen denaturation and structural changes at elevated temperatures.

Main Methods:

• High-temperature Raman spectroscopy was performed on freeze-dried cartilage, separated collagen, and proteoglycan fractions.
• Thermogravimetric analysis (TGA) was used to quantify residual water content.
• Spectra were analyzed for changes indicative of denaturation and peptide bond hydrolysis.

Main Results:

• Raman spectra showed increased fluorescence above 140°C, indicating collagen denaturation, associated with collagen rather than proteoglycans.
• New spectral features suggested peptide bond hydrolysis at high temperatures, implying retained molecular water (H₂O) within freeze-dried tissue.
• TGA confirmed 5-7 wt% residual H₂O in freeze-dried cartilage, released upon heating.
• Re-hydrated denatured collagen showed reduced water absorption capacity.

Conclusions:

• Bound water is present in freeze-dried collagenous connective tissue and plays a role in thermal denaturation.
• Denaturation may be accompanied or preceded by primary polypeptide structure breakdown (peptide bond hydrolysis).
• Findings are relevant for biomaterials processing and understanding collagen's thermal stability.