Silica Particles-pHEMA

Schiraldi et al. [64] have developed this kind of material by combining silica particles and pHEMA. pHEMA is a biocompatible hydrogel that has been widely studied in the past decades due to its chemical-physical structure and mechanical properties. It has been widely used in ophthalmic prostheses (contact or intraocular lenses), vascular prostheses, drug delivery systems and soft-tissue replacement [65]. These authors have shown that by incorporating silica nanoparticles, the resulting hybrid material is highly biocompatible and promotes bone cell adhesion and proliferation of bone cells seeded on it.1  

In the specific case of silica nanoparticles-pH EMA hybrid materials, the synthesis relies on obtaining a fine dispersion of silica nanoparticles (with a mean diameter of 7nm) in HEMA monomers (liquid phase). When a homogeneous solution is obtained, a free radical initiator is added at a concentration based on the weight of the monomer mixture. After the initiator dissolution, the solution can be poured into molds or between two glass plates to obtain monoliths or uniform films, respectively, after being cured at temperatures around 60-85 °C for several hours. 

---

Besides styrene, MMA, BA, or their copolymers, and also less commonly used polymers such as poly(styrenesulfonic acid) (PSSA), poly (hydroxyethylmethacrylate) (PHEMA), poly(aminoethylmethacrylate) PAEMA [111], polyethylene (PE) [112], or polyamides [113], were used for the encapsulation of the silica, as reported in the literature. Polyethylene [112] could also be obtained as encapsulating polymer if a nickel-based catalyst which is dispersed in the aqueous continuous phase is used. Here, lentil-shaped hybrid particles with semicrystalline polyethylene or isotropic hybrid particles with amorphous polyethylene are detected. Silica/polyamide hybrid nanoparticles were synthesized by miniemulsifying a dispersion consisting of 3-aminopropyl triethoxysilane (APS) modified silica particles and sebacoylchloride [113] in an aqueous continuous phase where hexamethylene diamine is dropwise added. 

The hybrid PU-PHEMA semi-IPNs were prepared as described previously [169]. To prepare the nanocomposites, fumed silica nanoparticles were introduced into the polymer system at the stage of PU synthesis. The silica particles were used (1) without special functionalization of their surface with initial surface silanol groups ( -OH cover ), (2) after their functionalization by... 

Fig. 64 Creep rate spectra obtained at tensile stress of 0.3 MPa in the temperature region of PHEMA glass transition for the 83PU-17PHEMA network and nanocomposites based thereon, containing 0.25 wt% (a) or 3 wt% silica particles (b) with different functional groups at their surface [268]...

Contrary to the majority of papers on polymer-silica nanocomposites, the very low content of 3D nanosilica particles in the polymer matrix in this work resulted in average inter-particle distance L larger by an order of magnitude than the radius of gyration Rq of PHEMA. In spite of that, a considerable impact of small 3D silica additives on matrix dynamics was found due to double PU/PHEMA and silica/matrix hybridization. 

---