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PubMed1989

Structural control of poly(2-hydroxyethyl methacrylate)-graft-polyamine copolymers for differential retention of rat lymphocyte subpopulations.

Poly(2-hydroxyethyl methacrylate)-graft-polyamine copolymers (HA copolymers) of varying composition and chain length of the polyamine graft were prepared by radical copolymerization of 2-hydroxyethyl methacrylate with a given quantity of polyamine macromonomer having a controlled molecular weight, and their interaction with lymphocyte subpopulations (B and T cells) was estimated using a column method. From these results, it was revealed that the most suitable molecular structure of HA copolymers for separating lymphocyte subpopulations is that of an HA copolymer with 13 wt% of polyamine graft with a chain length 3000-6600 in molecular weight. It is concluded that the retention process of lymphocytes on the HA graft copolymers is driven primarily by ionic interactions between the protonated amino groups and the cells. However, the mode of the polyamine microdomain structure, that is the distribution of protonated amino groups, and the conformation of the polyamine chains, which varies with the chain length of the HA copolymer, are also important factors in determining differential lymphocyte retention.

Animals↗
PubMed1978

Experimental scleral buckling with a soft xerogel implant. I. Properties of poly(hydroxyethyl acrylate) compared with gelatin and other swelling implants.

Scleral buckling can be obtained with insoluble hydrophilic polymers that are implanted in the dry state (xerogels, which then expand to a predetermined size by imbibing tissue fluids. Absorbable gelatin, nonabsorbable poly(hydroxyethyl methacrylate) (PHEMA), and poly(glyceryl methacrylate) (PGMA), have been implanted as xerogels in scleral buckling procedures. Gelatin, PHEMA, and PGMA are soft when hydrated, but are hard and brittle in the dehydrated state. However, poly(hydroxyethyl acrylate) (PHEA) is soft not only in the dehydrated state. However, poly(hydroxyethyl acrylate) (PHEA) is soft only when hydrated but also when dehydrated. Dry PHEA can be carved easily to shape and size, and because it is soft it could be very useful for operations on thin, weakened sclera. We have implanted PHEA intrasclerally and suprasclerally in rabbit eyes. Tolerance of PHEA appears to be as good as that of other materials in clinical use. We have impregnated PHEA and gelatin implants with antibiotics to achieve prolonged antibiotic delivery to the surgical site. When dried impregnated gels were assayed for antibiotic activity in agar plates with Sarcina lutea, both gels displayed high but rapidly decreasing activity.

Acrylic Resins↗
PubMed2006

Effect of gamma-irradiation on the structure of poly(ethyl acrylate-co-hydroxyethyl methacrylate) copolymer networks for biomedical applications.

The effect of the sterilization process by gamma-irradiation on the structure of poly(ethyl acrylate-co-hydroxyethyl methacrylate) copolymer networks, P(EA-co-HEMA) is studied for a broad dose range (7, 15, 25 and 50 kGy) and copolymer composition interval (0, 0.3, 0.5, 0.7 and 1 weight fraction of HEMA in the copolymer). gamma-irradiation promotes chain scission in PHEMA homopolymer but induces new crosslinking points in PEA homopolymer. Both effects are present in the copolymers, with a net result that depends on composition. For copolymers with high HEMA fractions chain scission predominates, while, as the amount of EA in the copolymer increases, the situation changes and the net effect turns out to be an increase in the number of elastically active chains. Further, gamma-irradiation strengthens the gamma relaxation in PHEMA homopolymer, what suggest that the number of interchain hydrogen bonds decreases. FTIR spectroscopy reveals no oxidation as a consequence of the sterilization process.

Acrylic Resins↗
PubMed1994

Do hydrogels contain different classes of water?

In the first part of this article calorimetric studies on poly (hydroxy ethyl methacrylate) (PHEMA) are presented. In the past the irregular melting curves in this type of experiment have been interpreted as evidence for the existence of different types of water in these gels. The studies presented here demonstrate that the occurrence of a glass transition in the freezing hydrogels may be responsible for this irregular melting behavior, and that this behavior is not (necessarily) an indication for the existence of different types of water. In the second part results are shown of measurements of the mobility of water in hydrogels, made by relaxation NMR. These results indicate that very rapid interchange occurs between the water molecules, and they support the conclusion that the calorimetric data mentioned above are not indicative for the existence of different classes of water in hydrogels. These results are compared with data from other fields of science, especially from fundamental freeze drying studies, which support the alternative interpretation of the calorimetric measurements.

Biocompatible Materials↗
PubMed2003

Surface mechanical properties of pHEMA contact lenses: viscoelastic and adhesive property changes on exposure to controlled humidity.

The surface mechanical properties of poly(hydroxyethyl)methacrylate (pHEMA)-based contact lenses were monitored as a function of humidity by atomic force microscopy (AFM). Surface viscoelastic and adhesion values were extracted from AFM force versus distance interaction curves and were found to be strongly dependent on the bulk water content of the lens and on the relative humidity. At low relative humidity, 40-50%, the dehydration rate from the surface is faster than the hydration rate from the bulk, leading to a rigid surface region that has mechanical properties similar to those measured on totally dehydrated lenses. At relative humidity values > 60%, the dehydration rate from the lens surface rapidly decreases, leading to higher surface water content and a softer surface region. The results indicate that, in an ocular environment, although the bulk of the pHEMA contact lens is hydrated, the surface region may be in a transition between a dehydrated glassy state and a hydrated rubbery state.

Biocompatible Materials↗
PubMed1986

Hydrogels in endovascular embolization. I. Spherical particles of poly(2-hydroxyethyl methacrylate) and their medico-biological properties.

Spherical macroporous particles based on poly(2-hydroxyethyl methacrylate) with defined porosity, swelling and morphology have been developed, and are suitable for endovascular occlusion of various organs. Unlike cylindrical particles, spherical particles are specifically suited for transcatheteral introduction. The method chosen for the preparation of such particles was suspension radical polymerization, where the monomers were dissolved in a mixture of higher-boiling alcohols, and the solution dispersed in water. Physicochemical and medico-biological properties of spherical particles were examined. The residual amounts of monomers and other low-molecular compounds were checked; haematological analyses showed that the value 10(-5) g/g of the polymer was not toxic and contributed to an irreversible aggregation of thrombocytes. The occlusion effect in the vascular lumen was stable. The histomorphological results fully demonstrated the perfect biocompatibility of artificial spherical emboli. The latter met the requirements of application to clinical practice.

Animals↗
PubMed1989

Tissue reaction after silicone and poly(methyl methacrylate) intraocular lens implantation: a light and electron microscopy study in a rabbit model.

We describe the histopathologic results of extracapsular lens extraction and silicone and poly(methyl methacrylate) (PMMA) intraocular lens (IOL) implantation in 36 rabbit eyes. Phase-contrast microscopy was used to examine precipitates on IOL surfaces and posterior capsules. Semithin and ultrathin sections were taken from the central cornea, anterior uvea, capsular bag, and retina near the posterior pole. The follow-up was one to 16 weeks. Silicone IOLs did not cause significantly less precipitation than PMMA IOLs. Precipitates consisted of spindle-shaped fibroblast-like cells, various forms of inflammatory cells and multinucleated giant cells, single melanophages, and irregularly arranged birefringent collagen fibers. Corneal endothelial edema was slightly more prominent in PMMA IOL implanted eyes. Significant retinal edema in the posterior pole area was not observed with either of the two lens types. Severe precipitation in the form of large clusters of pigment cells and inflammatory reactions seemed to depend on mechanical trauma (iris capture and lens dislocation) and individual animal reactions, but not on the lens type used.

Animals↗
PubMed2005

[Biocompatibility of a special hydrogel orbital implant (PHEMA and MMA) in rabbits].

OBJECTIVE: To investigate the biocompatibility of a hydrogel orbital implant and its rate of vascularization in an experimental study. METHODS: The implant was made of copolymerization of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA). Thirty-two hydrogel orbital implants were implanted into the right orbit of 32 New Zealand albino rabbits. The rate of vascularization was examined by SPECT, immunohistochemistry and electron microscopy. RESULTS: Single Positron Emission Computerized Tomography (SPECT) examination showed that a radiotracer could be found locally concentrated on hydrogel orbital implants in vivo along with time. On light microscopy, implants fibro vascular tissue invade the pores of the hydrogel orbital implant after 2 weeks and gradually invaded the implant deeper and deeper from 4 to 8 weeks, almost all implants were fully vascularized after 12 weeks with a relatively spare inflammatory reaction. Only one case needed additional surgery. CONCLUSIONS: The hydrogel orbital implant has many advantages, such as well biocompatible, fast vascularization, simple operation and low complication of surgery. It is safe and applicable for clinical use as a new type of orbital implant material.

Animals↗
PubMed2004

Concanavalin a immobilized affinity adsorbents for reversible use in yeast invertase adsorption.

Concanavalin A (Con A) immobilized poly(2-hydroxyethyl methacrylate) (PHEMA) beads were investigated for specific adsorption of yeast invertase from aqueous solutions. PHEMA beads were prepared by a suspension polymerization technique with an average size of 150-200 microm, and activated by epichlorohydrin. Con A was then immobilized by covalent binding onto these beads. The maximum Con A immobilization was found to be 10 mg/g. The invertase-loading capability of the PHEMA/Con A beads was 107 mg/g. The maximum invertase adsorption capacity on the PHEMA/Con A adsorbents was observed at pH 5.0. The values of the Michaelis constant K(m) of invertase were significantly larger upon adsorption, indicating decreased affinity by the enzyme for its substrate, whereas V(max) was smaller for the adsorbed invertase. Adsorption improved the pH stability of the enzyme as well as its temperature stability. Thermal stability was found to increase with adsorption. The adsorbed enzyme activity was found to be quite stable in repeated experiments. Storage stability of adsorbed invertase.

Adsorption↗
PubMed1992

Invertase activity of Saccharomyces cerevisiae cells entrapped in poly (2-hydroxyethyl methacrylate) gels: kinetic and thermostability study in membrane reactors.

Films of poly (2-hydroxyethyl methacrylate) with entrapped yeast cells have been prepared and characterized in membrane reactors. Two concentrations, 5 and 10% w/w, of crosslinking agent ethylene dimethacrylate are used. The invertase activity is monitored between 30 and 55 degrees C in the range of sucrose concentration from 40 to 200 mM and during almost 600 h of operation. Comparison is also made with the behaviour of free cells and small size particles (less than 115 mesh) of poly-HEMA immobilized cells. The results show that the whole membrane volume is not involved in substrate permeation and a combined diffusion-reaction rate controlling mechanism holds. An unusual dependence of reaction rate on bulk pH is observed. In the range of pH from 4.0 to 6.0, invertase activity in films continuously increases while two distinctive maxima for free yeast cells (pH 4.75) and for small particles of poly-HEMA-immobilized yeast cells (pH 4.5) are observed.

Biotechnology↗
PubMed1985

Localization of periodate-Schiff reactive glycosaminoglycans in semi-thin sections embedded in GMA-Quetol 523-MMA--application of a method for correlative light and electron microscopy of identical sites.

A correlative light and electron microscope method in which semi-thin sections of embedded tissue were treated with periodate acid and Schiff's reagent (PAS) was used to determine the precise localization of PAS reactive substance. Small blocks of tissue specimens were fixed with aldehyde mixtures. After dehydration, the blocks were embedded in a modified mixture of glycol methacrylate (GMA), Quetol 523, methyl methacrylate (MMA) and QCU-1. Semi-thin sections, 0.2-0.3 micron thick, were stained by the PAS reaction, followed by counterstaining with hematoxylin if necessary. It was found that PAS reaction products representing the specific sites for glycosaminoglycans and glycoproteins were seen in both light and electron microscopy. In the control experiments the specificity of the reaction was confirmed. The granules of goblet cells were well stained and contrasted by the reaction materials. The basement membrane and the microvilli of the epithelial cells appeared as the staining layer. In the spermatocytes the reaction products were demonstrated in the Golgi apparatus, acrosomal vesicles and head cap. The results indicated that the PAS deposits became electron dense when the embedding matrix had a low electron scattering property. Using this method of preparing semi-thin sections, a comparative study of the localization of glycosaminoglycans was performed.

Animals↗
PubMedDate not supplied

Imaging of cell/substrate contacts on polymers by total internal reflection fluorescence microscopy.

A simplified model of total internal reflection fluorescence (TIRF) emission of fluorescently labeled cell membranes [Reichert, W. M.; Truskey, G. A. J. Cell Sci. 1990, 96, 219-230] was used to determine the topography of the cell membrane in apposition to a polymer-coated surface. The homopolymer substrates were spun cast films of hydrophilic poly(hydroxyethyl methacrylate) (polyHEMA) or hydrophobic poly(ethyl methacrylate) (polyEMA). Bovine aortic endothelial cells (BAEC) on preadsorbed fibronectin polymer substrates were either plated for 24 h, fixed, labeled, and examined by TIRF microscopy (TIRFM) and phase-contrast microscopy or plated for 2 h and tested for their adhesion strength in a parallel-plate flow chamber. BAEC attached to polyHEMA showed no evidence of focal contact formation. However, BAEC attached to polyEMA were well spread and showed an array of focal contacts. TIRFM data were transformed to construct a detailed topographical map of relative cell/substrate separation distances. Virtually all of the BAEC plated to polyHEMA were sheared from the surface when subjected to a 50 dyn/cm2 burst of laminar flow, whereas only 10% of the BAEC were sheared from the polyEMA surface. These data suggest that the polyHEMA and polyEMA surface properties (e.g., hydrophobicity) correlate with the presence of BAEC focal contacts and the BAEC attachment strength.

Animals↗
PubMed1995

Dual-analyte fiber-optic sensor for the simultaneous and continuous measurement of glucose and oxygen.

A fiber-optic sensor for the continuous and simultaneous determination of glucose and oxygen is described. The sensor is comprised of dual-analyte sensing sites in defined positions on the distal end of an imaging fiber (350 microns o.d.). Each sensing site is an individual polymer cone covalently attached to the activated fiber surface using localized photopolymerization. The oxygen sensor consists of a double-layer polymer cone. The inner polymer cone is a hydrophobic gas-permeable copolymer containing an oxygen-sensitive ruthenium dye, and the outer layer is a poly(hydroxyethyl methacrylate) (HEMA) polymer. The glucose sensor is an oxygen sensor with a poly-HEMA outer layer containing immobilized glucose oxidase. The fluorescence images of both sensing sites are captured with a CCD camera, and the measured fluorescence intensities are related to analyte concentrations. Oxygen quenching data for both sensing sites fit a two-site Stern-Volmer quenching model. The sensor has been used to simultaneously monitor independent changes in glucose and oxygen concentrations. Glucose calibration curves were obtained under varying oxygen tensions, and the detection limit is 0.6 mM glucose. The effect of fluctuations in oxygen partial pressure on the glucose response can be used to calibrate the sensor. The sensor response time varies from 9 to 28 s, depending on the different thicknesses of the enzyme layer. The sensor maintains the same sensitivity for 2 days. Multiple glucose sensing sites with different enzymatic activities can be immobilized on the distal end of the fiber, affording control of the linear range.

Fiber Optic Technology↗
PubMed1993

Hydrogels as an interface between bone and an implant.

The use of fully hydrated hydrogels in the body has been well established. The forces a hydrogel generates on swelling when it is placed in a constrained space were investigated with a view to providing a mechanism for fixing a prosthesis in the intramedullary cavity. A cross-linked poly(2-hydroxyethyl methacrylate) [p(HEMA)] hydrogel was investigated as a potential material. In vitro mechanical tests were carried out to determine the stresses generated in the p(HEMA) when it was placed in water and not allowed to swell. Pull out loads of up to 375 N indicated that the system could be used successfully in vivo. Consequently, the material was placed intraosseously at two sites in a rabbit animal model, in the mid-shaft (diaphysis) and the lower end (metaphysis) of the femur. Histological examination showed there was no adverse bone response; bone was growing from the endosteal surface up to and into the hydrogel in the diaphyseal implants and surrounded the hydrogel in the metaphysis. As a result of the shape and size variations in the rabbit femur, in vivo mechanical tests were found to give lower values than those obtained in vitro.

Animals↗
PubMedDate not supplied

HEMA/MMMA microcapsule implants in hemiparkinsonian rat brain: biocompatibility assessment using [3H]PK11195 as a marker for gliosis.

Microencapsulation of dopamine-secreting cells in biocompatible, semi-permeable polymer membranes has been proposed as an alternative strategy for dopamine replacement for Parkinson's disease. In order to assess the viability of this proposal, dopamine-secreting PC12 cells were immunoisolated via microencapsulation in a 75:25 2-hydroxyethyl methacrylate/methyl methacrylate (HEMA/MMA) copolymer. A submerged nozzle-liquid jet method was used to produce small diameter (400 microm) microcapsules, which were stereotaxically implanted in the denervated striatum of hemi-Parkinsonian rats. A 96% survival rate was associated with the implantation surgery and no deleterious side effects were apparent. Light microscopy revealed good biocompatibility between the HEMA/MMA copolymer and the host brain, as evidenced by the absence of gross tissue damage at the neuronal tissue/capsule interface. Autoradiographic analyses using [3H]PK11195 as marker for reactive astrocytes revealed a moderate inflammatory response, confined to the immediate vicinity of the injection tract. Quantitative analyses indicated that the local tissue response did not differ significantly between brains implanted with PC12-containing capsules and those implanted with vehicle-containing capsules. Taken together, these results support the biocompatibility of HEMA/MMA copolymer as well as the feasibility and safety of stereotaxic implantation of microcapsules.

Animals↗
PubMed2007

An active wound dressing for controlled convective mass transfer with the wound bed.

Conventional wound dressings-gauze, plastic films, foams, and gels-do not allow for spatial and temporal control of the soluble chemistry within the wound bed, and are thus limited to a passive role in wound healing. Here, we present an active wound dressing (AWD) designed to control convective mass transfer with the wound bed; this mass transfer provides a means to tailor and monitor the chemical state of a wound and, potentially, to aid the healing process. We form this AWD as a bilayer of porous poly(hydroxyethyl methacrylate) (pHEMA) and silicone; the pHEMA acts as the interface with the wound bed, and a layer of silicone provides a vapor barrier and a support for connecting to external reservoirs and pumps. We measure the convective permeability of the pHEMA sponge, and use this value to design a device with a spatially uniform flow profile. We quantify the global coefficient of mass transfer of the AWD on a dissolvable synthetic surface, and compare it to existing theories of mass transfer in porous media. We also operate the AWD on model wound beds made of calcium alginate gel to demonstrate extraction and delivery of low molecular weight solutes and a model protein. Using this system, we demonstrate both uniform mass transfer over the entire wound bed and patterned mass transfer in three spatially distinct regions. Finally, we discuss opportunities and challenges for the clinical application of this design of an AWD.

Alginates↗
PubMed1996

A novel MMC-loaded pHEMA drainage device for the treatment of glaucoma: in vitro and in vivo studies.

Administration of subconjunctival 5-fluorouracil (5-FU) and topical mitomycin-C (MMC) has been shown to improve the success rate of glaucoma-filtering surgery. However, corneal toxicity and administrative problems remain. To overcome this limitation, drainage devices for the sustained release of 5-FU and MMC were designed and tested in vitro and in vivo. This paper presents only the results of our studies which were carried out on MMC-loaded devices. Here, the drainage devices were prepared from MMC-loaded poly(hydroxyethyl methacrylate) (pHEMA) matrices in different cross-linking ratios and in different drug loading capacities, i.e. 0.2, 0.5, and 2.0 mg MMC per device. These devices released MMC at approximately 6.0-90.0 micrograms day-1 for over 2 months depending on cross-linking density and initial drug loading. The diffusional release of MMC from glassy and swollen copolymers showed that diffusion mechanism is Fickian in both cases. The usability of the pHEMA implants were investigated by in vivo experiments which were done on eight dog's eye. In the treatment eyes, intraocular pressures remained significantly lower than the control eyes throughout the experimental period (4 months). Subconjunctival implantations revealed no clinical and histological evidence for toxicity. The results of in vitro and in vivo studies indicate that an implantable release system delivering MMC for over 2 months can improve the prognosis for filtering surgery by preventing postoperative fibrosis.

Administration, Topical↗
PubMed2006

Poly(2-hydroxyethyl methacrylate) microspheres/liquid poly(dimethylsiloxane) composition for correction of small defects in face: histological evaluation in animal experiment.

Two kinds of composition based on commercial liquid poly(dimethylsiloxane) and laboratory-made poly(2-hydroxyethyl methacrylate) (PHEMA) microspheres of different size fractions (30-40 or 125-180 microm) were prepared. Tissue reaction on injection of the compositions, optimum microsphere size and morphology were investigated in the experiments on rats. The microspheres induced foreign body reaction characterized by an increased content of fibroblasts and mild infiltration of injection field by inflammatory cells. The 125-180 microm microspheres seemed to be well covered with poly(dimethylsiloxane) and more uniformly distributed in the tissue than the 30-40 microm ones. As a result, the extent of foreign body reaction induced by the former microspheres was somewhat lower than that induced by the latter. Moreover, time-dependent degradation of 30-40 microm PHEMA microspheres was more pronounced than that of 125-180 microm ones, which can affect duration of the aesthetic effect after prospective facioplasty. Results of histological investigations demonstrate a good prospect of the proposed composition for contour and bulk facioplasty of small soft tissue defects and skin wrinkles.

Animals↗