Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstraße 31, 93053, Regensburg, Germany.
JPK BioAFM Business, Bruker Nano GmbH, Am Studio 2D, 12489, Berlin, Germany.
J Mech Behav Biomed Mater. 2022 Oct;134:105397. doi: 10.1016/j.jmbbm.2022.105397. Epub 2022 Jul 31.
Anisotropic capillary hydrogels are formed by ionotropic gel formation of an aqueous sodium alginate solution during unidirectional diffusion and complexation with divalent cations. The type of cation used for gel formation dictates the size of the resulting capillary structure which might facilitate applications as biomaterial scaffolds in tissue engineering and regenerative medicine. Until now, such capillary hydrogel structures have not been characterized regarding their mechanical properties, and we hypothesise that both, the macroscopic capillary structure and the concentration of a chemical crosslinking agent, influence the mechanical properties and the stability of the hydrogels against degradation and dissolution in physiological environment. We prepared anisotropic gels with capillary sizes ranging between 12 and 100 μm using electrolyte solutions containing Ba, Sr, Zn or Ni cations. They were chemically crosslinked with hexamethylene diisocyanate in concentrations varying between 1 and 100 mmol L. Hydrogel properties were determined by swelling experiments, oscillatory rheometry and microindentation analysis and monitored during incubation in phosphate-buffered solution at 37 °C for up to three months. We found, that the mechanical strength generally decreases with increasing capillary diameter. The higher the concentration of the crosslinking agent, the higher is the mechanical strength. The resistance of the alginate hydrogels against degradation is positively correlated with the concentration of the crosslinking agent. Furthermore, microindentation experiments revealed a microscopic anisotropy of the mechanical properties resulting from a perpendicular orientation of the polymer fibres relative to the capillary axis.
各向异性毛细管水凝胶是通过在单向扩散过程中离子凝胶形成将海藻酸钠水溶液与二价阳离子进行络合而形成的。用于凝胶形成的阳离子类型决定了所得毛细管结构的大小，这可能有助于组织工程和再生医学中的生物材料支架的应用。到目前为止，尚未对这种毛细管水凝胶结构的机械性能进行表征，我们假设宏观毛细管结构和化学交联剂的浓度都会影响水凝胶的机械性能以及在生理环境中对抗降解和溶解的稳定性。我们使用含有 Ba、Sr、Zn 或 Ni 阳离子的电解质溶液制备了具有 12 至 100μm 大小毛细管的各向异性凝胶。它们用六亚甲基二异氰酸酯在 1 至 100mmol/L 的浓度下进行化学交联。通过溶胀实验、振荡流变学和微压痕分析来确定水凝胶的性能，并在 37°C 的磷酸盐缓冲溶液中孵育长达三个月进行监测。我们发现，机械强度通常随毛细管直径的增大而降低。交联剂浓度越高，机械强度越高。海藻酸钠水凝胶的抗降解能力与交联剂的浓度呈正相关。此外，微压痕实验揭示了机械性能的微观各向异性，这是由于聚合物纤维相对于毛细管轴垂直取向所致。
