Raman microspectroscopic and dynamic vapor sorption characterization of hydration in collagen and dermal tissue

Water is an integral part of collagen's triple helical and higher order structure. Studies of model triple helical peptides have revealed the presence of repetitive intrachain, interchain, and intermolecular water bridges (Bella et al., Structure 1995, 15, 893–906). In addition, an extended cylinder of hydration is thought to be responsible for collagen fiber assembly. Confocal Raman spectroscopy and dynamic vapor sorption (DVS) measurements of human Type I collagen and pigskin dermis were performed to probe relative humidity (RH)‐dependent differences in the nature and level of collagen hydration. Raman spectra were also acquired as a function of time for both Type I collagen and pigskin dermis samples upon exchange of a 100% RH H2O to deuterium oxide (D2O) environment. Alterations in Amide I and III modes were consistent with anticipated changes in hydrogen bonding strength as RH increased and upon H → D exchange. Of note is the identification of a Raman spectral marker (band at 938 cm−1) which appears to be sensitive to alterations in collagen‐bound water. Analysis of DVS isotherms provided a quantitative measure of adsorbed and absorbed water vapor consistent with the Raman results. The development of a Raman spectral marker of collagen hydration in intact tissue is relevant to diverse fields of study ranging from the evaluation of therapeutics for wound healing to hydration of aging skin. © 2011 Wiley Periodicals, Inc. Biopolymers 95: 607–615, 2011.