Jonathan V. M. Weaver

Synthesis of controlled-structure sulfate-based copolymers via atom transfer radical polymerisation and their use as crystal habit modifiers for BaSO4

Atom Transfer Radical Polymerisation (ATRP) has been used to polymerise ammonium 2-sulfatoethyl methacrylate (SEM) in aqueous media using various poly(ethylene glycol) (PEG) macro-initiators to give a range of controlled-structure, sulfate-based block copolymers. Such PEG–SEM diblock copolymers are effective crystal habit modifiers for the in situ precipitation of BaSO4 in dilute aqueous solution. In the presence of the PEG–SEM copolymer, near-monodisperse, lozenge-shaped BaSO4 particles were obtained, depending on the relative block lengths. X-Ray diffraction and thermogravimetric analysis of these particles demonstrated that they are polycrystalline in nature and contain around 8% copolymer by mass. This compares with the characteristic polydisperse rectangular platelets of single crystal BaSO4 obtained in the absence of the copolymer. Control experiments suggest that, while only the SEM block interacts directly with the particle surface, the PEG block also plays an important role in controlling the crystal growth. Independent variation of the PEG and SEM block lengths therefore provides a subtle mechanism for controlling the morphology, size distribution and crystalline structure of the inorganic phase.

Self-Healing, Self-Assembled β-Sheet Peptide–Poly(γ-glutamic acid) Hybrid Hydrogels

Self-assembled biomaterials are an important class of materials that can be injected and formed in situ. However, they often are not able to meet the mechanical properties necessary for many biological applications, losing mechanical properties at low strains. We synthesized hybrid hydrogels consisting of a poly(γ-glutamic acid) polymer network physically cross-linked via grafted self-assembling β-sheet peptides to provide non-covalent cross-linking through β-sheet assembly, reinforced with a polymer backbone to improve strain stability. By altering the β-sheet peptide graft density and concentration, we can tailor the mechanical properties of the hydrogels over an order of magnitude range of 10–200 kPa, which is in the region of many soft tissues. Also, due to the ability of the non-covalent β-sheet cross-links to reassemble, the hydrogels can self-heal after being strained to failure, in most cases recovering all of their original storage moduli. Using a combination of spectroscopic techniques, we were able to probe the secondary structure of the materials and verify the presence of β-sheets within the hybrid hydrogels. Since the polymer backbone requires less than a 15% functionalization of its repeating units with β-sheet peptides to form a hydrogel, it can easily be modified further to incorporate specific biological epitopes. This self-healing polymer−β-sheet peptide hybrid hydrogel with tailorable mechanical properties is a promising platform for future tissue-engineering scaffolds and biomedical applications.