Two Laponite clays, of general formula [M n+ ] x/n [Li x Mg 6-x Si 8 O 20 F y (OH) 4-y ], were prepared with different Li + levels (0.57 and 0.70% w/w) and Flevels (9.5 and 9.9% w/w). The clays were characterized by measurements of nitrogen adsorption isotherms, cation exchange capacity, and conductometric titration data. The clay with higher Li + and Flevels had a higher (more negative) face charge and a lower (less negative) edge charge. Small-angle X-ray scattering (SAXS) data obtained from dilute aqueous dispersions indicate that both clays are of similar particle size (diameter ca. 40 nm and thickness ca. 3.5 nm). Experimental structure factors for concentrated Laponite dispersions were calculated using the ratio of scattered X-ray intensities from concentrated and dilute dispersions. Maxima in the experimental structure factors were observed at scattering angles of 0.14-0.2 nm -1 under favorable solution conditions (pH g 9 and ionic strength ca. 5 × 10 -3 mol dm -3 ) for one of the Laponite clays. These results are interpreted in terms of an ordered, aligned structure where the particles' face and edge electrical double layers are expanded and negative in sign. This is in contrast to a "house-of-cards" structure which results when particle aggregation is promoted by lower pH, higher ionic strength, or a lower particle edge charge.

An interesting, and potentially important, challenge for colloid scientists is to design injectable dispersions that enable repair of damaged and degenerated tissue. This work presents a study of the ability of pH-responsive microgel particles to restore the mechanical properties of loadbearing soft tissue. Microgel particles are cross-linked polymer colloid particles that are swollen with solvent. The first part of the study consists of an investigation of the pH-triggered swelling of poly(EA/MAA/BDDA) (ethylacrylate, methacrylic acid and 1,4-butanediol diacrylate) microgel particles using photon correlation spectroscopy (PCS) measurements. The concentrated dispersions exhibit a strong fluid-to-gel transition when the pH is increased to above 6.0, i.e., above this pH they form gelled microgel dispersions. The swelling data are used to aid interpretation of the pH-triggered changes in the gel modulus, as probed using dynamic rheology. The second part of the study involves an investigation of the mechanical properties of artificially degenerated, model intervertebral discs (IVDs) containing gelled microgel dispersions. High concentration microgel dispersions were injected as fluids into the interior of degenerated IVDs and the pH increased by subsequent alkaline solution injection to cause particle swelling and dispersion gelation. Uniaxial compression data measured for the IVDs containing injected microgel dispersions indicate that the pH-induced particle swelling of the microgel restores the mechanical properties of degenerated IVDs to values similar to those measured for normal, non-degenerated, IVDs.

Nanogels are crosslinked polymer particles with a swollen size between 1 and 100 nm. They are of major interest for advanced surface coatings, drug delivery, diagnostics and biomaterials. Synthesising polyacid nanogels that show triggered swelling using a scalable approach is a key objective of polymer colloid chemistry. Inspired by the ability of polar surfaces to enhance nanoparticle stabilisation, we report the first examples of pH-responsive polyacid nanogels containing high -COOH contents prepared by a simple, scalable, aqueous method. To demonstrate their functionalisation potential, glycidyl methacrylate was reacted with the -COOH chemical handles and the nanogels were converted to macro-crosslinkers. The concentrated (functionalised) nanogel dispersions retained their pH-responsiveness, were shear-thinning and formed physical gels at pH 7.4. The nanogels were covalently interlinked via free-radical coupling at 37 °C to form transparent, ductile, hydrogels. Mixing of the functionalised nanogels with polymer dots enabled covalent assembly of fluorescent hydrogels.

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