Department of Chemical and Environmental Engineering, University of Toledo, 3048 Nitschke Hall, 1650 N. Westwood Ave., Toledo, Ohio 43606, USA.
Langmuir. 2011 Sep 6;27(17):10392-9. doi: 10.1021/la201194a. Epub 2011 Jul 27.
Chitosan micro- and nanoparticles are routinely prepared through ionotropic gelation, where sodium tripolyphosphate (TPP) is added as a cross-linker to dilute chitosan solutions. Despite the wide use of these gel-like particles, their preparation currently relies on trial and error. To address this, we used isothermal titration calorimetry (ITC), dynamic light scattering (DLS), transmission electron microscopy (TEM), and ζ-potential measurements to investigate how the formation, structure, and colloidal stability of chitosan microgels are linked to the molecular interactions that underlie their self-assembly. The strength of the chitosan/TPP interactions was systematically varied through the addition of monovalent salt (NaCl). Remarkably, and contrary to other colloidal systems, this revealed that moderate amounts of NaCl (e.g., 150 mM) enhance the colloidal stability of chitosan/TPP microgels during their formation. This stems from the weakened chitosan/TPP binding, which apparently inhibits the bridging of the newly formed microgels by TPP. The enhanced colloidal stability during the ionic cross-linking process yields microgels with dramatically narrower size distributions, which hitherto have typically required the deacetylation and fractionation of the parent chitosan. Conversely, at high ionic strengths (ca. 500 mM) the chitosan/TPP binding is weakened to the point that the microgels cease to form, thus suggesting the existence of an optimal ionic strength for ionotropic microgel preparation.
壳聚糖微球和纳米颗粒通常通过离子凝胶法制备，其中三聚磷酸钠（TPP）被添加为交联剂来稀释壳聚糖溶液。尽管这些凝胶状颗粒被广泛使用，但它们的制备目前仍依赖于反复试验。为了解决这个问题，我们使用等温热滴定法（ITC）、动态光散射（DLS）、透射电子显微镜（TEM）和ζ-电势测量来研究壳聚糖微凝胶的形成、结构和胶体稳定性如何与其自组装的分子相互作用相关联。通过添加单价盐（NaCl），系统地改变壳聚糖/TPP 相互作用的强度。值得注意的是，与其他胶体系统相反，这表明适量的 NaCl（例如 150 mM）可在壳聚糖/TPP 微凝胶形成过程中增强其胶体稳定性。这源于壳聚糖/TPP 结合的减弱，这显然抑制了 TPP 对新形成的微凝胶的桥接。在离子交联过程中增强的胶体稳定性导致微凝胶具有明显更窄的粒径分布，迄今为止，这通常需要对母体壳聚糖进行脱乙酰化和分级。相反，在高离子强度（约 500 mM）下，壳聚糖/TPP 结合被削弱到微凝胶不再形成的程度，因此表明存在最佳的离子强度来制备离子凝胶微球。
