• Produced starch hydrogels through high temperature-pressure gelatinisation. • Employed a range of NMR methods to probe the molecular mobility and water dynamics. • Reported for the first time highly dynamic starch chains in the solvent phase of gels. • Correlated the degree of chain structural mobility with bulk properties. • Revealed a previously unknown level of molecular organisation in starch gels.

Targeted colonic drug delivery systems are needed for the treatment of endemic colorectal pathologies, such as Crohn's disease, ulcerative colitis, and colorectal cancer. These drug delivery vehicles are difficult to formulate, as they need to remain structurally intact whilst navigating a wide range of physiological conditions across the upper gastrointestinal tract. In this work we show how starch hydrogel bulk structural and molecular level parameters influence their properties as drug delivery platforms. The in vitro protocols mimic in vivo conditions, accounting for physiological concentrations of gastrointestinal hydrolytic enzymes and salts. The structural changes starch gels undergo along the entire length of the human gastrointestinal tract have been quantified, and related to the materials' drug release kinetics for three different drug molecules, and interactions with the large intestinal microbiota. It has been demonstrated how one can modify their choice of starch in order to fine tune its corresponding hydrogel's pharmacokinetic profile.

Bacterial cellulose consists of a complex three dimensional organization of ultrafine fibres which provides unique material properties such as softness, biocompatibility, and water retention ability, of key importance for biomedical applications. However, there is a poor understanding of the molecular features modulating the macroscopic properties of bacterial cellulose gels. We have examined chemically pure bacterial cellulose (BC) hydrogels and composites with arabinoxylan (BC AX), xyloglucan (BC XG) and high molecular weight mixed linkage glucan (BC MLG). Atomic force microscopy (AFM) showed that MLG greatly reduced the mechanical stiffness of BC gels, while XG and AX did not exert a significant effect. A combination of advanced solid state NMR methods allowed us to characterise the structure of BC ribbons at ultra-high resolution, and to monitor local mobility and water interactions. This has enabled us to unravel the effect of AX, XG and MLG on the short range order, mobility and hydration of BC fibers. Results show that BC XG hydrogels present BC fibrils of increased surface area, which allows BC XG gels to hold higher amounts of bound water. We report for the first time that the presence of high molecular weight MLG reduces the density of clusters of BC fibrils and increases dramatically water interactions to BC. Our data support two key molecular features determining the reduced stiffness of BC MLG hydrogels, i.e. (i) the adsorption of MLG on the surface of BC fibrils precluding the formation of a dense network, and (ii) the preorganization of bound water by MLG. Hence, we have produced and fully characterised BC MLG hydrogels with novel properties which could be potentially employed as renewable materials for applications requiring high water retention capacity (e.g. personal hygiene products).

A cellulose nanocrystal (CNC)-polyvinyl acetate (PVAc) self-healing composite film was fabricated using a grafting-from approach generating polyvinyl acetate (PVAc) chains on CNC macroinitiators. These grafted-to CNCs were then mixed with bulk PVAc polymer to form a composite. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance were used to demonstrate the presence of the grafted PVAc chains on the surface of the CNCs. Transmission electron microscopy images revealed the structure of the modified CNCs, which formed closely packed clusters due to the grafted PVAc chains. The thermal properties of the CNCs and their composite films were assessed by using differential scanning calorimetry, determining the appropriate temperature for the healing of the composite film. On this basis, the film was cut into two pieces and rejoined and healed in an oven heated at 40 °C for 6 h. The healed sample was viewed under an optical microscope and electron microscopy, demonstrating the efficacy of the healing process. An array of microindentation tests across the surface of the healed specimen was conducted to quantify stiffness, revealing no detectable differences between the healed and intact regions. This healing was found to only occur for the grafted-to samples and was not evident for the composites made of PVAc and ungrafted CNCs. This work demonstrates that grafting polymer chains onto CNCs and blending these with a bulk polymer are promising approaches for fabricating composite films capable of healing macroscopic fractures.