Exploiting the role of nanoparticle shape in enhancing hydrogel adhesive and mechanical properties.

The ability to control nanostructure shape and dimensions presents opportunities to design materials in which their macroscopic properties are dependent upon the nature of the nanoparticle. Although particle morphology has been recognized as a crucial parameter, the exploitation of the potential shape-dependent properties has, to date, been limited. Herein, we demonstrate that nanoparticle shape is a critical consideration in the determination of nanocomposite hydrogel properties. Using translationally relevant calcium-alginate hydrogels, we show that the use of poly(L-lactide)-based nanoparticles with platelet morphology as an adhesive results in a significant enhancement of adhesion over nanoparticle glues comprised of spherical or cylindrical micelles. Furthermore, gel nanocomposites containing platelets showed an enhanced resistance to breaking under strain compared to their spherical and cylindrical counterparts. This study opens the doors to a change in direction in the field of gel nanocomposites, where nanoparticle shape plays an important role in tuning mechanical properties.

Self-healing, stretchable and robust interpenetrating network hydrogels.

A self-healable stretchable hydrogel system that can be readily synthesized while also possessing robust compressive strength has immense potential for regenerative medicine. Herein, we have explored the addition of commercially available unfunctionalized polysaccharides as a route to synthesize self-healing, stretchable poly(ethylene glycol) (PEG) interpenetrating networks (IPNs) as extracellular matrix (ECM) mimics. The introduction of self-healing and stretchable properties has been achieved while maintaining the robust mechanical strength of the orginal, single network PEG-only hydrogels (ultimate compressive stress up to 2.4 MPa). This has been accomplished without the need for complicated and expensive functionalization of the natural polymers, enhancing the translational applicability of these new biomaterials.

Controlling the Size of Two-Dimensional Polymer Platelets for Water-in-Water Emulsifiers.

A wide range of biorelevant applications, particularly in pharmaceutical formulations and the food and cosmetic industries, require the stabilization of two water-soluble blended components which would otherwise form incompatible biphasic mixtures. Such water-in-water emulsions can be achieved using Pickering stabilization, where two-dimensional (2D) nanomaterials are particularly effective due to their high surface area. However, control over the shape and size of the 2D nanomaterials is challenging, where it has not yet been possible to examine chemically identical nanostructures with the same thickness but different surface areas to probe the size-effect on emulsion stabilization ability. Hence, the rationale design and realization of the full potential of Pickering water-in-water emulsion stabilization have not yet been achieved. Herein, we report for the first time 2D poly(lactide) platelets with tunable sizes (with varying coronal chemistry) and of uniform shape using a crystallization-driven self-assembly methodology. We have used this series of nanostructures to explore the effect of 2D platelet size and chemistry on the stabilization of a water-in-water emulsion of a poly(ethylene glycol) (PEG)/dextran mixture. We have demonstrated that cationic, zwitterionic, and neutral large platelets (ca. 3.7 × 106 nm2) all attain smaller droplet sizes and more stable emulsions than their respective smaller platelets (ca. 1.2 × 105 nm2). This series of 2D platelets of controlled dimensions provides an excellent exemplar system for the investigation of the effect of just the surface area on the potential effectiveness in a particular application.

1D vs. 2D shape selectivity in the crystallization-driven self-assembly of polylactide block copolymers.

2D materials such as graphene, LAPONITE® clays or molybdenum disulfide nanosheets are of extremely high interest to the materials community as a result of their high surface area and controllable surface properties. While several methods to access 2D inorganic materials are known, the investigation of 2D organic nanomaterials is less well developed on account of the lack of ready synthetic accessibility. Crystallization-driven self-assembly (CDSA) has become a powerful method to access a wide range of complex but precisely-defined nanostructures. The preparation of 2D structures, however, particularly those aimed towards biomedical applications, is limited, with few offering biocompatible and biodegradable characteristics as well as control over self-assembly in two dimensions. Herein, in contrast to conventional self-assembly rules, we show that the solubility of polylactide (PLLA)-based amphiphiles in alcohols results in unprecedented shape selectivity based on unimer solubility. We use log Poct analysis to drive solvent selection for the formation of large uniform 2D diamond-shaped platelets, up to several microns in size, using long, soluble coronal blocks. By contrast, less soluble PLLA-containing block copolymers yield cylindrical micelles and mixed morphologies. The methods developed in this work provide a simple and consistently reproducible protocol for the preparation of well-defined 2D organic nanomaterials, whose size and morphology are expected to facilitate potential applications in drug delivery, tissue engineering and in nanocomposites.

Precision Epitaxy for Aqueous 1D and 2D Poly(ε-caprolactone) Assemblies.

The fabrication of monodisperse nanostructures of highly controlled size and morphology with spatially distinct functional regions is a current area of high interest in materials science. Achieving this control directly in a biologically relevant solvent, without affecting cell viability, opens the door to a wide range of biomedical applications, yet this remains a significant challenge. Herein, we report the preparation of biocompatible and biodegradable poly(ε-caprolactone) 1D (cylindrical) and 2D (platelet) micelles in water and alcoholic solvents via crystallization-driven self-assembly. Using epitaxial growth in an alcoholic solvent, we show exquisite control over the dimensions and dispersity of these nanostructures, allowing access to uniform morphologies and predictable dimensions based on the unimer-to-seed ratio. Furthermore, for the first time, we report epitaxial growth in aqueous solvent, achieving precise control over 1D nanostructures in water, an essential feature for any relevant biological application. Exploiting this further, a strong, biocompatible and fluorescent hydrogel was obtained as a result of living epitaxial growth in aqueous solvent and cell culture medium. MC3T3 and A549 cells were successfully encapsulated, demonstrating high viability (>95% after 4 days) in these novel hydrogel materials.

Core functionalization of semi-crystalline polymeric cylindrical nanoparticles using photo-initiated thiol-ene radical reactions.

Sequential ring-opening and reversible addition-fragmentation chain transfer (RAFT) polymerization was used to form a triblock copolymer of tetrahydropyran acrylate (THPA), 5-methyl-5-allyloxycarbonyl-1,3-dioxan-2-one (MAC) and l-lactide. Concurrent deprotection of the THPA block and crystallization-driven self-assembly (CDSA) was undertaken and allowed for the formation of cylindrical micelles bearing allyl handles in a short outer core segment. These handles were further functionalized by different thiols using photo-initiated thiol-ene radical reactions to demonstrate that the incorporation of an amorphous PMAC block within the core does not disrupt CDSA and can be used to load the cylindrical nanoparticles with cargo.