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PubMed1990

In vivo biocompatibility of collagen-poly(hydroxyethyl methacrylate) hydrogels.

Collagen-p(HEMA) hydrogels were subcutaneously implanted in rats for up to 6 month and the immediate short- and long-term tissue response to these implants was studied. Histopathological data indicated that the tissue reaction at the implant site progressed from an initial acute inflammatory response characterized by the presence of eosinophils and polymorphs to a chronic response marked by few macrophages, foreign body giant cells and fibroblasts. After one month a very thin fibrous capsule (approximately 11 microns thick) was observed around the implant. Even 6 month post-implantation, the capsule thickness was maintained at about 11-12 microns. No necrosis, calcification, tumorigenesis or infection was observed at the implant site up to 6 month. Fibrous capsule analysis showed that the collagen content and the capsule thickness were well within the threshold limits. The collagen-p(HEMA) hydrogels were found to be well-tolerated, non-toxic and highly biocompatible.

Animals↗
PubMed2005

Resin tissue microarrays: a universal format for immunohistochemistry.

Tissue microarray (TMA) technology allows the miniaturization and characterization of multiple tissue samples on a single slide and commonly uses formalin-fixed paraffin-embedded (FFPE) tissue or acetone-fixed frozen tissue. The former provides good morphology but can compromise antigenicity, whereas the latter provides compromised morphology with good antigenicity. Here, we report the development of TMAs in glycol methacrylate resin, which combine the advantages of both methods in one embedding format. Freshly collected tissue fixed in -20C acetone or 10% neutral buffered formaldehyde were cored and arrayed into an intermediary medium of 2% agarose before infiltration of the agarose array with glycol methacrylate resin. Acetone-fixed resin TMA demonstrated improved morphology over acetone-fixed frozen TMA, with no loss of antigenicity. Staining for extracellular, cell surface, and nuclear antigens could be realized with monoclonal and polyclonal antibodies as well as with monomeric single-chain Fv preparations. In addition, when compared with FFPE TMA, formalin-fixed tissue in a resin TMA gave enhanced morphology and subcellular detail. Therefore, resin provides a universal format for the construction of TMAs, providing improved tissue morphology while retaining antigenicity, allows thin-section preparation, and could be used to replace preparation of frozen and FFPE TMAs for freshly collected tissue.

Acetone↗
PubMed1982

Long-term in vivo studies of poly(2-hydroxyethyl methacrylate).

Poly(hydroxyethyl methacrylate) (PHEMA) was implanted subcutaneously in rats, hamsters, and guinea pigs for up to 24, 23, and 13 months, respectively. The tissue response and tumorigenesis caused by PHEMA were compared among the three species of the animals. Thick fibrous capsule formation and tumor production were noted only in rats, while no tumorigenesis and thin fibrous capsule formation were observed in hamsters and guinea pigs. These results support our previous hypothesis that animals producing a thick and avascular capsule tend to develop tumors at the implant site. PHEMA retrieved was characterized by scanning electron microscopy and x-ray energy dispersive analysis. Calcium and phosphorus were the main elements detected on the surface of PHEMA implants. PHEMA is suggested to be not suitable for long-term implant material.

Animals↗
PubMed2001

Mannosylerythritol lipid, a yeast extracellular glycolipid, shows high binding affinity towards human immunoglobulin G.

BACKGROUND: There have been many attempts to develop new materials with stability and high affinity towards immunoglobulins. Some of glycolipids such as gangliosides exhibit a high affinity toward immunoglobulins. However, it is considerably difficult to develop these glycolipids into the practical separation ligand due to their limited amounts. We thus focused our attention on the feasible use of "mannosylerythritol lipid A", a yeast glycolipid biosurfactant, as an alternative ligand for immunoglobulins, and undertook the investigation on the binding between mannosylerythritol lipid A (MEL-A) and human immunoglobulin G (HIgG). RESULTS: In ELISA assay, MEL-A showed nearly the same binding affinity towards HIgG as that of bovine ganglioside GM1. Fab of human IgG was considered to play a more important role than Fc in the binding of HIgG by MEL-A. The bound amount of HIgG increased depending on the attached amount of MEL-A onto poly (2-hydroxyethyl methacrylate) (polyHEMA) beads, whereas the amount of human serum albumin slightly decreased. Binding-amount and -selectivity of HIgG towards MEL-A were influenced by salt species, salt concentration and pH in the buffer solution. The composite of MEL-A and polyHEMA, exhibited a significant binding constant of 1.43 x 10(6) (M(-1)) for HIgG, which is approximately 4-fold greater than that of protein A reported. CONCLUSIONS: MEL-A shows high binding-affinity towards HIgG, and this is considered to be due to "multivalent effect" based on the binding molar ratio. This is the first report on the binding of a natural human antibody towards a yeast glycolipid.

Animals↗
PubMed2003

Characterization and analysis of osteopontin-immobilized poly(2-hydroxyethyl methacrylate) surfaces.

A wide array of technologies exist for the characterization and quantification of molecules present at surfaces. We have used several of these experimental and instrumental techniques for the analysis of a novel biomaterial surface. Osteopontin, an extracellular matrix molecule involved in wound-healing processes, has been chosen as a relevant model protein to immobilize onto poly(2-hydroxyethyl methacrylate) [poly(HEMA)]. Electron spectroscopy for chemical analysis and time-of-flight secondary ion mass spectrometry were used to verify the surface chemistry and the presence of protein. Iodination of osteopontin yielded quantitative data supportive of dose-dependent immobilization. Enzyme-linked immunosorbent assay was also used to investigate the presence of osteopontin on poly(HEMA). Finally, the cell adhesive properties of immobilized osteopontin were confirmed by using a bovine aortic endothelial cell adhesion assay. The use of multiple tools to characterize the many facets of a biomaterial surface will undoubtedly improve our understanding of the surface and facilitate the amelioration of in vivo performance.

Animals↗
PubMed1990

Laser-induced damage to transparent polymers: chemical effect of short-pulsed (Q-switched) Nd:YAG laser radiation on ophthalmic acrylic biomaterials. II. Study of monomer release from artificial intraocular lenses.

Commercial intraocular lenses and polymer specimens, both poly(methyl methacrylate) (PMMA) and poly(2-hydroxyethyl methacrylate) p(HEMA), were subjected to various levels of irradiation from a Q-switched Nd:YAG laser, and then to extraction and sample-enrichment techniques. The extracts were analysed by capillary gas chromatography. In PMMA samples, residual contents of 0.05-0.89% (wt) MMA were found and it appeared that the laser radiation did not cause a detectable increase of the monomer content. No residual HEMA could be found in p(HEMA) samples before or after laser bombardment. It is concluded that the accidental exposure of lenses to Nd:YAG laser cannot produce a significant release of monomers. Depolymerization induced by laser is a process unlikely to occur at the energy levels used in ophthalmic surgery.

Gas Chromatography-Mass Spectrometry↗
PubMed2005

Lysozyme interaction with poly(HEMA)-based hydrogel.

Lysozyme interaction with an acrylic-based hydrogel, poly(2-hydroxyethyl methacrylate) co-methacrylic acid (P(HEMA-MAA)), was investigated using a combination of quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR) and dual polarisation interferometry (DPI). This combination of techniques demonstrated that lysozyme initially absorbed into the hydrogel matrix and displaced water from the hydrogel while subsequent lysozyme additions were adsorbed onto the surface of the hydrogel material. QCM-D, being sensitive to bound water, showed an overall decrease in mass and stiffening of the layer after lysozyme addition. SPR, a water insensitive technique, showed a net mass increase after addition of lysozyme and buffer rinses. DPI showed that the first exposure of lysozyme to P(HEMA-MAA) was consistent with lysozyme absorption while subsequent lysozyme exposures were consistent with lysozyme adsorption.

Dose-Response Relationship, Drug↗
PubMed1988

Microencapsulation of mammalian cells in a hydroxyethyl methacrylate-methyl methacrylate copolymer: preliminary development.

Erythrocytes were microencapsulated in a thermoplastic copolymer of poly-2-hydroxyethyl methacrylate (79% mole%) - co-methyl methacrylate (21 mole %) with little apparent initial cell lysis. Droplets of cell suspension and polymer solution were blown from the tip of a coaxial needle assembly into a receiving bath of hexadecane over phosphate buffered saline (PBS) containing a low concentration of nonionic surfactant. Capsules were trapped at the hexadecane/PBS interface where they were cured by the removal of polymer solvent to precipitate a polymer coating around the cell suspension. Important principles which were considered in the development of the successful process, included the need to prevent intermixing of polymer solution and cell suspension, to fully surround the cells with polymer solution prior to precipitation, and to prevent direct mixing of the curing bath with the polymer solution.

Artificial Organs↗
PubMed1985

The structure of highly crosslinked poly(2-hydroxyethyl methacrylate) hydrogels.

Films were prepared by reaction of HEMA monomer with the crosslinking agent ethyleneglycol dimethacrylate (EGDMA) at crosslinking ratios, X, of 0.005, 0.01, 0.0128, 0.025, and 0.050 mol EGDMA/mol HEMA in the presence of 40 wt.% water at 60 degrees C for 12 h. These membranes were subsequently swollen in water at 37 degrees C and their structure analyzed using a modified Gaussian distribution equation of equilibrium swelling. The calculated values of Mc varied between 800 and 3700 daltons, which corresponded to a correlation length of the mesh size xi of 16.2 to 35.6 A. The structural analysis and diffusive studies of PHEMA membranes indicate that the recent determinations of Mc for PHEMA by Migliaresi et al. (C. Migliaresi, L. Nicodemo, L. Nicolais, and P. Passerini, "Physical characterization of PHEMA gels," J. Biomed. Mater. Res., 15, 307 (1981). and others are not accurate. The methods presented can also be used for analysis of any highly crosslinked polymer network produced by simultaneous polymerization and crosslinking reactions.

Chemical Phenomena↗
PubMed1987

Immobilization of glucose oxidase in poly(2-hydroxyethyl methacrylate) membranes.

Glucose oxidase (GOD) was immobilized in a poly(2-hydroxyethyl methacrylate) (HEMA) membrane through matrix entrapment in order to investigate the effect of various parameters (e.g. concentration of ingredients, temperature, repeated interaction with glucose and shelf storage) on the activity of the enzyme. Permeability of the membrane to a model permeant was tested and SEMs were obtained. It was observed that upon immobilization the affinity of GOD towards glucose was substantially decreased, and increasing the GOD content of the membrane adversely affected the activity. Membranes with the highest enzyme activity were also found to be the most permeable. Changes were detected in the pH and temperature where GOD is most active. Membrane permeability was observed to increase when crosslinker, and/or HEMA concentrations were low. The same parameters were also found to alter the morphology of the membrane as observed under SEM.

Enzyme Stability↗
PubMedDate not supplied

Glucose biosensors with enzyme entrapped in polymer coating.

The pursuit of reliable biosensors for measuring glucose levels has been ongoing for decades. Their importance lies partly in the development of the implantable artificial pancrease, which can be used to deliver insulin to diabetics without the need to test glucose levels externally, with automatic delivery based on physiologic demand. Glucose sensors can also be used in short-term monitoring of glucose levels in hospitals and clinical laboratories. Three types of glucose biosensors were studied. All were based on a two-electrode system: an insulated platinum wire as a hydrogen peroxide electrode, and a silver wire twisted around the platinum wire as both a reference and a counter electrode. Each was coated with the enzyme glucose oxidase entrapped in a polymer matrix of cellulose acetate (CA) or poly 2-hydroxyethyl methacrylate (HEMA), then dip-coated by an additional polymer coating of polyvinylchloride (PVC), polyurethane (PU), or HEMA. The experiments were designed mainly to study the effectiveness of polymer coatings as diffusion-limiting membranes. The effect of each coating on the linear response to glucose concentration was examined. It was shown that additional (multiple) coatings can increase the linearity of the sensor response. The best results were obtained when the sensor was PVC-dip-coated three times. This preparation had a linear response up to 600 mg/DL glucose concentration. The sensors coated with PU and HEMA have linearity up to 280 and 240 mg/DL glucose concentrations, respectively. It was also shown that the coatings reduce interference from certain body chemicals.

Biocompatible Materials↗
PubMed1992

Use of poly(2-hydroxyethyl methacrylate) for endovascular occlusion in pediatric surgery.

Embolization using poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel particles, of cylindrical spherical form, was successfully achieved in 42 children treated for non-operable haemangiomas of the liver, and angiodysplasias. Spherical PHEMA hydrogels appeared to be the only possibility for the treatment of 26 children suffering from extensive cavernous haemangiomas of face and neck. Particles were able to cover the tumour, stop its growth and allow the use of local hyperthermia with the electromagnetic field. A partial two-stage embolization using beaded PHEMA was also used as part of the multistage treatment for curing the spleen in 28 children suffering from haemolytic spherocytic anaemia, thrombocytopenic purpura and portal hypertension.

Adolescent↗
PubMed2005

The effect of charged groups on protein interactions with poly(HEMA) hydrogels.

Proteins, lipids and other biomolecules interact strongly with the acrylic-based biomaterials used for contact lenses. Although hydrogels are nominally resistant to protein fouling, many studies have reported considerable amounts of protein bound to poly(2-hydroxyethylmethacrylate) (PHEMA) lenses. This study examined the binding of a series of biomolecules (tear protein analogues, mucin and cholesterol) to poly(methylmethacrylate) (PMMA) and three HEMA-based hydrogels (PHEMA, HEMA plus methacrylic acid (P(HEMA-MAA)), HEMA plus methacrylic acid plus N-vinylpyrrolidone (P(HEMA-MAA-NVP))) by use of a quartz crystal microbalance with dissipation (QCM-D) monitoring. The QCM-D estimates changes in the mass and viscous constant for the adsorbed layer through measurements of frequency and dissipation. Protein interaction with each of the test materials caused a net increase in mass of the material indicating protein binding except for lysozyme interacting with P(HEMA-MAA). A net decrease in mass was observed for lysozyme interacting with P(HEMA-MAA) which may be ascribed to lysozyme collapsing the hydrogel by expelling water. A net mass decrease was observed for cholesterol interacting with each of the hydrogel materials, while a mass increase was observed on PMMA.

Adsorption↗
PubMed1991

Histochemical demonstration of heavy metals in the hippocampal formation embedded in Quetol 523M.

To facilitate improvement of investigations on the distribution of mossy fibers in the hippocampal formation, a method is described using Timm's stained preparations after methacrylate embedding with the hydrophilic resin, Quetol 523M. Fixation with a mixture of formaldehyde and glutaraldehyde yielded satisfactory staining results and good structural preservation. During the course of histochemical experiments employing Timm's staining, examinations revealed that sulfide silver reaction products were consistently present in both the mossy fibers themselves and their terminals associated with the dendrites of pyramidal cells in tissue sections of 1-2 microns in thickness. The results obtained also revealed that variations of the mossy fiber system occurred in the neurological mutant mouse dreher (dr). The bundles of mossy fibers forming the intrapyramidal synaptic field may be considered to reflect genotype-dependent differences in the mutation. The present method is adequate for allowing the histochemical demonstration of mossy fibers and their giant boutons by light microscopy.

Animals↗
PubMed2005

The electrochemical behaviour of ferrocene in a photocurable poly(methyl methacrylate-co-2-hydroxylethyl methacrylate) film for a glucose biosensor.

A single-step fabrication of a glucose biosensor with simultaneous immobilization of both ferrocene mediator and glucose oxidase in a photocurable methacrylic film consisting of poly(methyl methacrylate-co-2-hydroxylethyl methacrylate) was reported. The entrapped ferrocene showed reversible redox behaviour in the photocured film and no significant leaching of both entrapped ferrocene and enzyme glucose oxidase was observed because of the low water absorption properties of the co-polymer films. From electrochemical studies, ferrocene entrapped in the co-polymer film demonstrated slow diffusion properties. A linear glucose response range of 2-11 mM was obtained at low applied potential of +0.25 V. The glucose biosensor fabricated by this photocuring method yielded sensor reproducibility and repeatability with relative standard deviation of <10% and long-term stability of up to 14 days. The main advantage of the use of photocurable procedure is that biosensor membrane fabrication can be performed in a single step without any lengthy chemical immobilization of enzyme.

Biosensing Techniques↗
PubMedDate not supplied

Conformal coating of mammalian cells immobilized onto magnetically driven beads.

A novel cell bead system, comprising a magnetic core, a spherical annulus of agarose-immobilized cells, all conformally coated within a synthetic polymer, is proposed as a means of immunoisolating mammalian cells in a system that provides a balance between low total implant volume, retrievability, and diffusion limitations. A successful immunoisolation system could be used to transplant cells without eliciting an inappropriate host response. Chinese hamster ovary (CHO) cells were immobilized at the periphery of large (approximately 2 mm) agarose beads containing inert magnetic cores (< or = 1 mm) and coated in a hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) copolymer by interfacial precipitation. The beads were coated in liquid gradients containing polyethylene glycol 200 (PEG) or bromooctane. Although many cells were adversely affected by the coating process, the cells that did survive (30-50% of those loaded into the beads) remained viable for a period of at least 2 weeks. This viability was much higher than achieved previously because of a number of factors, such as the aqueous agarose, the hydrophobic bromooctane intermediate layer, and faster coating times that minimize the exposure of the cells to organic solvents. Also, a mathematical model was used to describe oxygen transport within the annular agarose beads. These results provide evidence that the proposed geometry and the fabrication approach may be useful for a variety of applications that involve cell encapsulation.

Animals↗
PubMed2004

Ophthalmic drug delivery through contact lenses.

PURPOSE: Currently available ophthalmic drug delivery systems are inefficient and may lead to side effects. To increase efficiency and reduce side effects, the authors propose disposable particle-laden soft contact lenses for ophthalmic drug delivery. METHODS: The essential idea is to encapsulate the ophthalmic drug formulations in nanoparticles and to disperse these drug-laden particles in the lens material, such as poly-2-hydroxyethyl methacrylate (p-HEMA) hydrogels. The drug-laden p-HEMA hydrogels were synthesized by free radical solution polymerization of the monomers in presence of nanoparticles. The particle-laden hydrogels were characterized by light-transmission and electron microscopy studies. Release profiles of lidocaine, a model hydrophobic drug, were measured by UV-Vis spectrophotometry. RESULTS: Microemulsions of hexadecane in water stabilized with a silica shell around the particles produced transparent hydrogels. Contact lenses made with particle-laden hydrogels released therapeutic levels of drug for a few days. CONCLUSIONS: Particle-laden hydrogels are promising candidates for ophthalmic drug delivery. They are transparent and can release drugs for extended periods. The drug delivery rates can be controlled by varying the loading of nanoparticles in the gel.

Anesthetics, Local↗
PubMed2002

Construction of an acetylcholinesterase-choline oxidase biosensor for aldicarb determination.

In this study, acetylcholinesterase and choline oxidase were co-immobilized on poly(2-hydroxyethyl methacrylate) membranes and the change in oxygen consumption upon aldicarb introduction was measured. Immobilization of the enzymes was achieved either by entrapment or by surface attachment via a hybrid immobilization method including epichlorohydrin and Cibacron Blue F36A activation. Immobilized enzymes had a long-storage stability (only 15% activity decrease in 2 months in wet storage and no activity loss in dry storage). Aldicarb detection studies showed that a linear working range of 10-500 and 10-250 ppb aldicarb could be achieved by entrapped and surface immobilized enzymes, respectively. Enzymes immobilized on membrane surfaces responded to aldicarb presence more quickly than entrapped enzymes. Aldicarb concentrations as low as 23 and 12 ppb could be detected by entrapped and surface immobilized enzymes, respectively, in 25 min.

Acetylcholinesterase↗