One-Step Preparation of Uniform Cane-Ball Shaped Water-Swellable Microgels Containing Poly(<i>N</i>-vinyl formamide)

In this study we report the preparation of a new family of core–shell microgels that are water-swellable and have a morphology that is controllable by particle composition. Here, nearly monodisperse core–shell PNVF-<i>x</i>GMA [poly­(<i>N</i>-vinylformamide-<i>co</i>-glycidyl methacrylate)] particles (where <i>x</i> is the weight fraction of GMA used) were prepared via nonaqueous dispersion (NAD) polymerization in one step. The shells were PGMA-rich and were cross-linked by reaction of epoxide groups (from GMA) with amide groups (from NVF). The core of the particles was PNVF-rich. A bifunctional cross-linking monomer was not required to prepare these new microgels. The particles had a remarkable “cane-ball”-like morphology with interconnected ridges, and this could be controlled by the value for <i>x</i>. The particle size was tunable over the range 0.8–1.8 μm. Alkaline hydrolysis was used to hydrolyze the PNVF segments to poly­(vinylamine), PVAM. The high swelling pressure of the cationic cores caused shell fragmentation and release of some of the core polymer when the hydrolyzed particles were dispersed in pure water. The extent to which this occurred was controllable by <i>x</i>. Remarkably, the PGMA-rich shells could be detached from the hydrolyzed particles by dispersion in water followed by drying. The hydrolyzed PNVF-0.4GMA particles contained both positively and negatively charged regions and the dispersions appeared to exhibit charge-patch aggregation at low ionic strengths. The new cross-linking strategy used here to prepare the PNVF-<i>x</i>GMA particles should be generally applicable for amide-containing monomers and may enable the preparation of a range of new water-swellable microgels

Injectable Doubly Cross-Linked Microgels for Improving the Mechanical Properties of Degenerated Intervertebral Discs

The use of injectable pH-responsive doubly cross-linked microgels (DX microgels) to improve the mechanical properties of degenerated intervertebral discs is demonstrated for the first time. The microgel comprised methyl methacrylate (MMA), methacrylic acid (MAA), ethyleneglycol dimethacrylate (EGD) and glycidyl methacrylate (GM) and was poly­(MMA/MAA/EGD)-GM. The GM facilitated covalent interparticle cross-linking. The DX microgels are shown to have tunable mechanical properties. Degeneration of model bovine intervertebral discs (IVDs) was induced using collagenase. When injected into degenerated IVDs the DX microgels were shown to improve the strain, modulus, toughness and resilience. The extent of mechanical property improvement was an increasing function of DX microgel concentration, suggesting tunability. Cytotoxicity studies showed that the DX microgel was biocompatible under the conditions investigated. The results of this study imply that injectable DX microgels have good potential as a future regenerative medicine strategy for restoring the mechanical properties of degenerated load-bearing soft tissue, such as IVDs

Hollow Colloidosomes Prepared Using Accelerated Solvent Evaporation

We demonstrate a new, scalable, simple, and generally applicable two-step method to prepare hollow colloidosomes. First, a high volume fraction oil-in-water emulsion was prepared. The oil phase consisted of CH₂Cl₂ containing a hydrophobic structural polymer, such as polycaprolactone (PCL) or polystyrene (PS), which was fed into the water phase. The water phase contained poly­(vinylalcohol), poly­(<i>N</i>-isopropylacrylamide), or a range of cationic graft copolymer surfactants. The emulsion was rotary evaporated to rapidly remove CH₂Cl₂. This caused precipitation of PCL or PS particles which became kinetically trapped at the periphery of the droplets and formed the shell of the hollow colloidosomes. Interestingly, the PCL colloidosomes were birefringent. The colloidosome yield increased and the polydispersity decreased when the preparation scale was increased. One example colloidosome system consisted of hollow PCL colloidosomes stabilized by PVA. This system should have potential biomaterial applications due to the known biocompatibility of PCL and PVA

Responsive Nanogel Probe for Ratiometric Fluorescent Sensing of pH and Strain in Hydrogels

In this study a new pH-responsive nanogel probe containing a complementary nonradiative resonance energy transfer (NRET) fluorophore pair is investigated and its ability to act as a versatile probe of network-related changes in three hydrogels demonstrated. Fluorescent sensing using NRET is a powerful method for studying relationships between Angstrom length-scale structure and macroscopic properties of soft matter. Unfortunately, inclusion of NRET fluorophores into such materials requires material-specific chemistry. Here, low concentrations of preformed nanogel probes were included into hydrogel hosts. Ratiometric photoluminescence (PL) data for the gels labeled with the nanogel probes enabled pH-triggered swelling and deswelling to be studied as well as Ca²⁺-triggered collapse and solute release. PL measurements during compression of a nanogel probe-labeled nanocomposite gel demonstrated mechanochromic behavior and strain sensing. The new nanogel probes have excellent potential for investigating the internal structures of gels and provide a versatile ratiometric fluorescent platform for studying pH and strain