The Pivotal Step of Structure Formation and Oil-Binding Capacity of Polyglucosamine

For decades, polyglucosamine (PGA), also known as chitosan, has been used as an active ingredient in medical devices intended for body weight reduction and the control of blood lipid levels in obese patients, even though the exact mechanism of lipid binding still remains unclear. The binding capability of polyglucosamines towards dietary lipids is well documented in the literature and has been studied in-depth with respect to the physicochemical properties of the biopolymer. However, only a limited number of reliable correlations between the oil-binding capacity and material properties have been reported. In contrast, the morphology and structural nature of oil-polyglucosamine sponges have not received much attention and have been investigated only rudimentarily. Our work closes this gap and shines light on the pivotal step of structure formation and morphology in relation to oil-binding capacity. After the characterization of three batches of polyglucosamine via elemental and thermal analysis, infrared spectroscopy, and size exclusion chromatography, the oil binding capacity was determined over a range of oil-to-PGA ratios for one selected batch PGA ₂₁ (M _w = 251.6 kDa, D _A = 4.3%). From the resulting oil-binding capacity, which turned out to be as high as 3,750 g_oil/g, a combination of variables C ₁₀₀ and C _max was derived for more reliable material characterization. Furthermore, the prepared sponges were subjected to morphology investigations. Mild electron microscopy techniques, as well as confocal microscopy, were utilized to resolve the native three-dimensional network of polyglucosamine embedded in the oil matrix. After oil removal using a tailored solvent-exchange method, we were successful in resolving a highly porous, sponge-like structure featuring nanofibrils as the structural subunit. This delicate structure offered a high surface area, resulting in increased oil-binding capacity. From these findings, we derived that an interplay of morphological characteristics and molecular interactions leads to the ultra-high and structurally rigid oil-binding capacity of polyglucosamine.