The Manifold Varieties of Poly(2‐Hydroxyethyl Methacrylate) Hydrogels−IPNs

Abstract

Summary The interpenetrating network structure was used to control mechanical properties of hydrogels based on poly(2‐hydroxyethyl methacrylate) (PHEMA) (first network (A) or second network (B)) and poly(glycerol methacrylate) (PGMA) (network B). In order to understand the structure, mechanical and swelling properties of sequentially made IPN hydrogels, the swollen PHEMA network microstructure and its formation was investigated by means of swelling and SWAXS experiments. Visually clear and microscopically homogenous hydrogel networks based on poly(2‐hydroxyethyl methacrylate) revealed presence of domains of size 1–10 nm formed during polymerization in the presence of water. The study was carried out to understand conditions under which the hydrophobic interactions are operative and their effect on the microstructure as well as how they change when the double network structure is introduced. The morphologies of network A ranged from homogenous, non‐porous, and optically clear gels, to macroporous gels resulting from phase separation and offering fused‐sphere morphology. A cryogel characterized by large elongated and partially interconnected pores of tens to hundreds micrometers were another object for comparison. In most cases, an increase of tensile moduli and improvement of ultimate tensile properties was achieved. A surprisingly high increase in true strength (by a factor of 10 – 30) was achieved when the macroporous PHEMA network A was reinforced by weak PHEMA or PGMA networks B. All these weakly crosslinked IPN gels were optically clear.

Microscopic Structure of Swollen Hydrogels by Scanning Electron and Light Microscopies: Artifacts and Reality

“…For proper application in these fields, morphology of hydrogels must be precisely controlled. It can be done through varying the ratio of components in the reaction mixture [24]: for example, certain excess of diluent can trigger pore formation during polymerization by reaction induced phase separation [19]. For example, lightly crosslinked systems based on PHEMA undergo the phase separation above the critical amount of water about 40-45 vol.% [3,20,25].…”

Double‐networks based on interconnected amphiphilic “in–out” star first polymer conetworks prepared by RAFT polymerization

“…The original DN hydrogels comprised two interpenetrating, chemically cross‐linked hydrogels, the first of which was fragile and highly swollen because it was a rather densely cross‐linked polyelectrolyte, and the second was nonionic, ductile and loosely cross‐linked . Subsequently, however, the DN concept was expanded and proven to also hold when the order of the polyelectrolytic and nonionic components was reversed, when one or both networks were physically rather than chemically cross‐linked, and even when both networks were nonionic . In all cases, the mechanical properties (stress and strain at break, Young's modulus) of the final DN hydrogels were better than those of the two individual components separately.…”

“…6,11,12 Subsequently, however, the DN concept was expanded and proven to also hold when the order of the polyelectrolytic and nonionic components was reversed, when one or both networks were physically rather than chemically cross-linked, and even when both networks were nonionic. 13,14 In all cases, the mechanical properties (stress and strain at break, Young's modulus) of the final DN hydrogels were better than those of the two individual components separately. Furthermore, in most of the studies on DN hydrogels to date, the two constituting networks were poorly defined, as they were prepared via conventional free radical cross-linking copolymerization chemistries, employing photochemical or thermal initiation.…”

Poly(hexylacrylate)Core‐poly(ethyleneglycol methacrylate)Shell nanogels as fillers for poly(2‐hydroxyethyl methacrylate) nanocomposite hydrogels

“…One of the first hydrogels successfully applied as biomaterial is PHEMA . Initially, it was envisioned for contact lenses in the 60's and later for rhinoplasty .…”

“…The major improvements were achieved by introduction of 1%–2% BC; compared with neat gels, the storage shear modulus (G) increased by a factor of 4–5 in the case of PHEMA hydrogels. Dušková‐Smrčková et al used another strategy for the mechanical enhancement of PHEMA hydrogels, the preparation of interpenetrating polymer networks (IPN) of PHEMA of different porosities (network A) with poly(glycerol methacrylate) (network B) . Results showed that, in most cases, an increase of tensile moduli and improvement of ultimate tensile properties was achieved.…”