A.B. Clayton

Hydrophilic Sponges Based on 2‐Hydroxyethyl Methacrylate. III. Effect of Incorporating a Hydrophilic Crosslinking Agent on the Equilibrium Water Content and Pore Structure

The effect of using a hydrophilic crosslinking agent (divinyl glycol, DVG) on 2-hydroxyethyl methacrylate (HEMA) sponge swelling and pore morphology was evaluated. Concentrations of crosslinking agent, redox initiators and HEMA (75–90wt%) in the initial aqueous monomer mixture were varied. Anomalous sponge swelling behaviour, together with the formation of non-uniform stratified sponges was rationalised in terms of the assumed disparate free radical reactivities of DVG and HEMA. Environmental scanning electron microscopy indicated that the stratified sponges did not exhibit suitable porosity for biomedical use.

Hydrophilic sponges based on 2‐hydroxyethyl methacrylate. V. effect of crosslinking agent reactivity on mechanical properties

Tensile properties of poly(2-hydroxyethylmethacrylate) (PHEMA) sponges crosslinked with divinyl glycol (DVG) and ethylene glycol dimethacrylate (EDMA), two crosslinking agents having very different hydrophilicity and reactivity, were compared. Crosslinking agent concentrations were varied from 0·5 to 5·0 mol%, at a fixed water content of 80 wt% in the monomer mixture. The poorer tensile properties of EDMA-crosslinked sponges were attributed to network inhomogeneities, which were presumed to arise from the formation of rigid crosslinks within the phase-separated droplets. Comparison of the crosslinking efficiencies of DVG and EDMA via stress (compression)–strain measurements was not possible because of the non-linear response of the sponges to compressive strains. ©1997 SCI

Assessment of anticollagenase treatments after insertion of a keratoprosthetic material in the rabbit cornea

Purpose This study was performed to evaluate the enzyme production in response to implantation of the hydrogel material used in the experimental Chirila keratoprosthesis (KPro) and to assess the effects of five topical drugs on enzyme production and activity. KPros may be extruded from the cornea as a result of tissue melting, a process that involves excessive enzyme activity. To reduce the possibility of implant loss for the hydrogel Chirila KPro, a number of antiinflammatory drugs that have been used to treat other corneal melting conditions were investigated for their effect on initial collagenase activity after the implantation of KPro material into the rabbit cornea. Methods Poly(2-hydroxyethyl methacrylate) sponge pieces were implanted into rabbit corneas. Prednisolone, tetracycline, medroxyprogesterone, acetylcysteine, and sodium citrate were assessed for effects on gelatinolytic activity and stromal collagenase [matrix metalloprotease-1 (MMP-1)] production in vivo and in vitro by using zymography and Western blotting techniques. Results Whereas all five anticollagenase drugs were effective in reducing gelatinolytic activity in vitro, many were ineffective in vivo. However, medroxyprogesterone caused a reduction of gelatinolytic activity in vivo. The amount of MMP-1, as measured by immunoblotting, also was reduced by medroxyprogesterone treatment when compared with untreated controls. An increase in the apparent molecular weight of MMP-1 in operated corneas appears to be the result of the association of MMP-1 with collagen fragments resulting from the surgical trauma. Conclusion This study indicates that topical medroxyprogesterone may be a useful adjunctive therapy after prosthokeratoplasty.

The modulation of corneal keratocyte and epithelial cell responses to poly(2-hydroxyethyl methacrylate) hydrogel surfaces: phosphorylation decreases collagenase production in vitro.

We examined the regulation of collagenase production by rabbit keratocyte, epithelial and mixed keratocyte/epithelial cell cultures which were exposed to poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel surfaces with different chemistries and morphologies (sponge and homogeneous gels). Tissue culture modified polystyrene (TCP), used as a control surface, induced the maximum collagenase response with all cell culture types. Copolymer homogeneous gels containing 2-ethoxyethyl methacrylate (EEMA) or methyl methacrylate (MMA) induced a high response in keratocyte cultures, whilst PHEMA hydrogels induced a moderate response and the phosphorylated PHEMA (phos-PHEMA) hydrogel induced no response. Epithelial cells cultured on PHEMA, copolymer and phos-PHEMA hydrogels produced less collagenase activity than the keratocyte cells. The profile of collagenases produced by epithelial cells in response to phos-PHEMA was different to that for the other hydrogels. Co-cultured cells produced higher levels of collagenase (relative to the TCP) in response to hydrogels than did either the keratocytes or epithelial cells alone, but the response of phos-PHEMA was still the lowest. The overall enzyme response to the sponge hydrogels was lower than that to the homogeneous hydrogels, although this effect was less prominent in the keratocyte cultures. The markedly reduced and alternative collagenase responses to phosphorylated surfaces was not a consequence of cell death, and may be a phenomenon related to changes in cell surface charge and morphology.

Hydrophilic Sponges Based on 2-Hydroxyethyl Methacrylate. IV. Novel Synthetic Routes to Hydroxyl-Containing Crosslinking Agents and Their Effect on the Mechanical Strength of Sponges

Abstract The use of hydrophilic poly(2-hydroxyethyl methacrylate) sponges as biomaterials have diversified over recent years. Since the poor mechanical characteristics of these materials is a limiting factor to further development, an attempt was made in this study to improve the properties of sponges by using hydroxyl-containing crosslinking agents. Two such agents, 2-hydroxytrimethylene dimethacrylate (I) and 2,3-dihydroxytetramethylene dimethacrylate (II) were synthesized by novel procedures. Sponges were then produced using these agents and compared to sponges crosslinked with divinyl glycol (DVG), a hydrophilic but less reactive agent, and with ethylene dimethacrylate (EDMA), a hydrophobic but reactive agent. The use of I, II and DVG clearly improved the tensile characteristics of sponges, and tentative explanations were advanced.

The modulation of cellular responses to poly(2-hydroxyethyl methacrylate) hydrogel surfaces: phosphorylation decreases macrophage collagenase production in vitro

We examined the regulation of collagenase production by the monocyte/macrophage THP-1 cell line when these cells were exposed to poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel surfaces with different chemistries and morphologies. Tissue culture modified polystyrene (TCP), used as a control surface, induced the maximum collagenase response. Copolymer hydrogels containing 2-ethoxyethyl methacrylate (EMA) or methyl methacrylate (MMA) also induced a high response, while PHEMA hydrogels induced a low level response and the phosphorylated hydrogel induced no response. This pattern was altered when the morphology of the hydrogels was changed to that of a sponge. The overall enzyme response to the sponge hydrogels was lower than that to the homogeneous hydrogels. Sponges containing EMA and MMA produced low level response relative to the TCP control. PHEMA and phosphorylated sponges produced little and no response respectively. The dramatically reduced enzyme response to phosphorylated surfaces was not a consequence of cell death, and may be a phenomenon related to changes in cell surface charge.

Correlation of histological findings with gadolinium enhanced MRI scans during healing of a PHEMA orbital implant in rabbits

BACKGROUND/AIMS To investigate a poly(2-hydroxyethyl methacrylate) (PHEMA) orbital implant with a spongy anterior hemisphere and a smooth gel posterior hemisphere, by histology correlated with magnetic resonance images. METHODS Following enucleation, eight rabbits received PHEMA implants to which the muscles were directly sutured, and underwent gadolinium enhanced magnetic resonance imaging (MRI) from 3 to 52 weeks. After the rabbits were killed, the implants were removed, cut in a plane corresponding to the scan, and processed for light and electron microscopy. RESULTS All eight rabbits retained their implant to the end of the study period without complications. The scans demonstrated muscle attachment to the anterior half of the implant, and enhancement was seen on injection of gadolinium chelate. Histology confirmed muscle attachment, and cellular and vascular ingrowth. Over time, a transformation from reactive inflammatory to relatively non-vascular scar tissue was seen within the implant. Calcium deposits in one implant were detected by imaging and histology. CONCLUSION The implants are readily visualised on MRI. Muscle attachment and fibrovascular ingrowth into the anterior hemisphere are seen, while encapsulation of the posterior hemisphere is minimal. Histological findings confirm the progress of the healing response, with initial inflammation and marked vascularisation, developing later into quiescent scar tissue predominantly of fibroblasts.