Elgersma Scott V, Ha Michelle, Yang Jung-Lynn Jonathan, Michaelis Vladimir K, Unsworth Larry D
Department of Chemical and Materials Engineering, Faculty of Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada.
National Research Council, National Institute for Nanotechnology, Edmonton, AB T6G 2M9, Canada.
Materials (Basel). 2019 Mar 12;12(5):832. doi: 10.3390/ma12050832.
Self-assembling peptides are a promising class of biomaterials with desirable biocompatibility and versatility. In particular, the oligopeptide (RADA)₄, consisting of arginine (R), alanine (A), and aspartic acid (D), self-assembles into nanofibers that develop into a three-dimensional hydrogel of up to 99.5% (w/v) water; yet, the organization of water within the hydrogel matrix is poorly understood. Importantly, peptide concentration and polarity are hypothesized to control the internal water structure. Using variable temperature deuterium solid-state nuclear magnetic resonance (²H NMR) spectroscopy, we measured the amount of bound water in (RADA)₄-based hydrogels, quantified as the non-frozen water content. To investigate how peptide polarity affects water structure, five lysine (K) moieties were appended to (RADA)₄ to generate (RADA)₄K₅. Hydrogels at 1 and 5% total peptide concentration were prepared from a 75:25 (w/w) blend of (RADA)₄:(RADA)₄K₅ and similarly analyzed by ²H NMR. Interestingly, at 5% peptide concentration, there was lower mobile water content in the lysinated versus the pristine (RADA)₄ hydrogel. Regardless of the presence of lysine, the 5% peptide concentration had higher non-frozen water content at temperatures as low as 217 ± 1.0 K, suggesting that bound water increases with peptide concentration. The bound water, though non-frozen, may be strongly bound to the charged lysine moiety to appear as immobilized water. Further understanding of the factors controlling water structure within hydrogels is important for tuning the transport properties of bioactive solutes in the hydrogel matrix when designing for biomedical applications.
自组装肽是一类很有前景的生物材料，具有理想的生物相容性和多功能性。特别是由精氨酸（R）、丙氨酸（A）和天冬氨酸（D）组成的寡肽（RADA）₄会自组装成纳米纤维，进而形成含水量高达99.5%（w/v）的三维水凝胶；然而，人们对水凝胶基质内水的组织情况了解甚少。重要的是，据推测肽浓度和极性可控制内部水结构。我们使用可变温度氘固态核磁共振（²H NMR）光谱法测量了基于（RADA）₄的水凝胶中结合水的量，将其量化为非冷冻水含量。为了研究肽极性如何影响水结构，在（RADA）₄上连接了五个赖氨酸（K）基团以生成（RADA）₄K₅。由75:25（w/w）的（RADA）₄与（RADA）₄K₅混合物制备了总肽浓度为1%和5%的水凝胶，并同样通过²H NMR进行分析。有趣的是，在肽浓度为5%时，与原始的（RADA）₄水凝胶相比，赖氨酸化水凝胶中的可移动水含量更低。无论赖氨酸是否存在，在低至217±1.0 K的温度下，5%的肽浓度都具有更高的非冷冻水含量，这表明结合水随肽浓度增加。尽管结合水未冻结，但可能与带电荷的赖氨酸基团紧密结合，从而表现为固定水。在设计生物医学应用时，进一步了解控制水凝胶内水结构的因素对于调节生物活性溶质在水凝胶基质中的传输特性非常重要。
