Ploypailin Milin Saengdet

The repair of critical bone defects remains a substantial clinical challenge. A regenerative material must support osteogenesis, provide appropriate mechanical function, and degrade at a rate compatible with tissue formation. Hydroxyapatite (HA) is osteoconductive and chemically similar to bone mineral, but its brittleness and slow resorption limit its use as a stand-alone load-bearing material. Silsesquioxanes, particularly polyhedral oligomeric silsesquioxanes (POSS), provide molecularly defined silicon–oxygen frameworks with modifiable organic substituents. These can be incorporated as fillers or covalent network components. This review critically evaluates silsesquioxane-based biomaterials for bone regeneration. It distinguishes direct evidence from HA-containing systems from mechanistic analogues. These analogues include silicate-substituted HA, bioactive glass, dental POSS composites, and related polymer–POSS materials. Sol–gel processing, in situ mineralisation, particle incorporation, surface grafting, and network formation are assessed in relation to interfacial bonding, apatite nucleation, mechanical behaviour, and degradation. Current evidence indicates that reinforcement depends on cage functionality, dispersion, loading, matrix chemistry, and interfacial integration. Direct evidence that implanted HA–POSS systems release orthosilicic acid at biologically active concentrations remains unavailable. Cross-system comparisons further show that reported mechanical values cannot be ranked without accounting for physical form, porosity, test mode, and environmental conditions. The principal translational barriers are (i) the scarcity of load-bearing in vivo studies, (ii) uncertain degradation-product fate, and (iii) sterilisation sensitivity in some POSS-modified polymers. Further barriers are (iv) limited manufacturing standardisation and (v) the absence of clinically validated HA–POSS implants. The most defensible rationale for these hybrids is therefore their capacity for multifunctional interfacial design rather than universal mechanical superiority.

Hydrogels are widely studied for their stimuli‐responsive properties. They adapt to external stimuli, including physical, chemical and biological ones. To enhance adaptability in complex environments, multi‐responsive hydrogels have been developed, which either react to multiple stimuli independently or cooperatively (multistimuli‐response) or exhibit multiple responses triggered by single or multiple stimuli (multi‐response). Their properties depend on polymer type, molecular weight, cross‐linking, and water content, which affect mechanical behavior and response. To address their inherent fragility, polymer‐inorganic nanocomposite hydrogels integrate the advantages of both components, yielding enhanced functionalities. Among various nanofillers, smectites have been extensively studied for improving mechanical strength and responsiveness. Polymer‐smectite nanocomposite hydrogels exhibit enhanced elasticity, toughness, thermal stability, gas barrier properties, and responsiveness to external stimuli, expanding their applications in biomedical engineering, environmental remediation, and smart materials. This review discusses the fundamentals of polymer‐smectite nanocomposite hydrogels, their design strategies, and the role of smectite in enabling multi‐responsive behavior. The classification based on the site of responsiveness (polymer network and smectite) is presented, highlighting the important role of smectite in controlling the response and potential applications. Finally, challenges are addressed, emphasizing smectite's role in advancing next‐generation smart materials.

Monodispersed gelatin hydrogel beads containing smectite with adsorbed cyanine dye exhibit chromotropic responses to compression and swelling/deswelling by solvent. Photoluminescence color of the beads changes by swelling in water (blue) and deswelling in ethanol (purple) reversibly. The forces generated by swelling/deswelling are thought to induce the transition between the J-aggregate and the monomer of cyanine dye adsorbed on smectite, giving the photoluminescent color changes.

Smectite clay nanosheets were incorporated into cross-linked gelatin hydrogel to impart luminescence mechanochromism induced by the stretching as a result of the aggregation/de-aggregation of cyanine adsorbed on the nanosheets.

Well-defined belt-shaped particles of octacalcium phosphate were prepared by mixing aqueous solutions of calcium acetate and that of sodium phosphate monobasic with the aid of a micro-flow reactor. Higher crystallinity and narrower particle size distribution were achieved by the micro-flow reactor if compared with the results of the batch reaction using the same solutions. The width of the belt was controlled by the mixing temperature (0.8 and 2.3 μm for the preparation at 50 and 70 °C, respectively). Post mixing aging at 50 °C, resulted in the directional growth of belt-shaped particles to obtain particles with the length of 17 μm (aspect ratio of 53). XRD and TEM analysis indicated that the micro-flow reactor could separate nucleation and growth allowing preferential growth along the a-direction.