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At least 91 records · Page 5Linked to original sources
PubMed2002

Polymer hydrogels usable for nervous tissue repair.

The implantation of non-resorbable biocompatible polymer hydrogels into defects in the central nervous system can reduce glial scar formation, bridge the lesion and lead to tissue regeneration within the hydrogel. We implanted hydrogels based on crosslinked poly hydroxyethyl-methacrylate (pHEMA) and poly N-(2-hydroxypropyl)-methacrylamide (pHPMA) into the rat cortex and evaluated the cellular invasion into the hydrogels by means of immunohistochemical methods and tetramethylammonium diffusion measurements. Astrocytes and NF160-positive axons grew similarly into both types of hydrogels. We found no cell types other than astrocytes in the pHEMA hydrogels. In the pHPMA hydrogels, we found a massive ingrowth of connective tissue elements. These changes were accompanied by corresponding changes in the extracellular space volume fraction and tortuosity of the hydrogels.

Animals↗
PubMedDate not supplied

Hydrazide-functionalized poly(2-hydroxyethyl methacrylate) microspheres for immobilization of horseradish peroxidase.

Nonporous cross-linked poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) (poly(HEMA-co-EDMA)) microspheres were prepared by dispersion polymerization of HEMA and EDMA. The polymerization was performed in toluene/2-methylpropan-1-ol in the presence of cellulose acetate butyrate as a steric stabilizer and dibenzoyl peroxide initiator. The particle size may be increased by decreasing the toluene/2-methylpropan-1-ol ratio and by increasing polymerization temperature. Adipohydrazide was attached to the microspheres activated with 2,4,6-trichloro-1,3,5-triazine. After periodate oxidation of its carbohydrate moieties, horseradish peroxidase was coupled to the hydrazide-functionalized poly(HEMA-co-EDMA) microparticles up to 7.3 microgram of enzyme/g of carrier without a significant loss of its activity. Immobilized peroxidase was found to be stable, retaining more than 97% of its initial activity when stored for 23 days after the preparation.

Cross-Linking Reagents↗
PubMed2001

The ex vivo wettability of soft contact lenses.

PURPOSE: To investigate the ex vivo wettability of Etafilcon A contact lenses over an eight hour period of wear and observe the influence of surfactant pre-treatment. METHODS: Etafilcon A hydrogel lenses, comprising poly[2-hydroxyethyl methacrylate-co-methacrylic acid] and 58% water, were soaked for 12 hours in either 0.9% saline (control) or a 1% aqueous solution of poloxamine 1107 (treated). The advancing and receding contact angles were subsequently determined ex vivo after various periods of wear in six adapted contact lens wearers using a single-blind, randomised protocol. Contact angles were measured with a dynamic contact angle tensiometer, using the Wilhelmy plate technique. Patient comfort scores were recorded and the static surface tensions of the probe fluids assessed. RESULTS: Control lenses exhibited no change in wetting angles over time, indicating a lack of surface modification by components within the tear film. Treated lenses exhibited a significantly reduced advancing angle (p < 0.001) and hysteresis angle (p < 0.001) when compared with control lenses. In addition, treated lenses were consistently rated as being more comfortable than control lenses (p = 0.04). CONCLUSIONS: This study has shown clearly that new Etafilcon A lenses do not exhibit significant changes in wettability during the initial four hour wearing period. Pre-treatment of such lenses with a polymeric surfactant results in wetting of the lenses due to the adsorption of surfactant. The surfactant is retained by the lens for at least eight hours of wear, resulting in significant improvements in subjective comfort, especially over the first 30 minutes of wear.

Adolescent↗
PubMed2002

Comparison of bacterial and tissue cell initial adhesion on hydrophilic/hydrophobic biomaterials.

In this study, interactions of widely-used polymeric biomaterials, i.e. poly(hydroxyethyl methacrylate) (PHEMA) and its copolymer with dimethylaminoethyl methacrylate (PHEMA-20% DMAEMA), polyurethane (PU), polypropylene (PP), poly(vinyl chloride) (PVC), and poly(lactide-glycolide) (PLGA), with three pathogenic bacteria and one nonpathogen were investigated comparatively with the adhesion of two tissue cells in different morphologies, i.e. fibroblast-like baby hamster kidney (BHK 21) cells and epithelial Madine Darby kidney (MDBK) cells. Biomaterials were prepared in the membrane form by bulk polymerization or solvent casting. Surface characterization studies showed that these polymers have different surface free energies in the range of 26.9-63.1 erg cm(-2) and they have smooth surfaces. The bacteria used were; Escherichia coli ATCC 25922, Staphylococcus epidermidis ATCC 12228, Staphylococcus aureus, and Lactobacillus acidophilus B-13. Initial adhesion of bacteria to the polymeric surfaces was examined under static conditions and in a laminar flow cell. The adhesion behaviour of S. aureus and S. epidermidis was found independent of the polymeric surface hydrophobicity. However, the percentage of attached E. coli decreased when increasing the surface free energy of the polymer, while L. acidophilus showed just the opposite behaviour. The comparative results indicated that the adhesion of BHK and MDBK cell was lowest on the most hydrophilic PHEMA surface and highest on the most hydrophobic PP surface. In contrast to the case of bacterial adhesion, no relationship was found between polymer hydrophobicity and mammalian cell adherence.

Animals↗
PubMed1992

Staining of semithin tissue sections embedded in HPMA, quetol 523 and MMA.

Various tissues fixed in a mixture of formaldehyde and glutaraldehyde, and embedded in an improved 2-hydroxypropyl methacrylate mixture were employed for studying the fine structures of cells and tissues by light microscopy. The embedding mixture contained Quetol 523 and methyl methacrylate as a plasticizer without a cross-linker. The catalyst was QCU-1. The mixture had a low viscosity, was easy to handle and penetrated readily and completely into the specimen, producing a homogeneous block from which it was easy to cut sections of 1-2 microns in thickness. A wide variety of stains have been employed with such sections and those reported here are hematoxylin-eosin, Azan and PAS. There was excellent preservation of alkaline phosphatase activity. A method of poststaining immunoperoxidase labeling was also applied to the mouse pancreas and examples of staining with insulin are included.

Aminosalicylic Acid↗
PubMed1991

Early deposition trends on group I (Polymacon and Tetrafilcon A) and group III (Bufilcon A) materials.

One of the problems with hydrophilic contact lenses is that they are susceptible to spoilage. This study investigated the degree of spoilage associate with lenses of various surface changes during the early stages of wear and the effect of surfactant cleaning of lenses at this stage. Ten patients wore a control HEMA lens on one eye and either an ionic (Bufilcon A) or non-ionic (Tetrafilcon A) lens on the other for one week and used a peroxide system for disinfection. The lenses were then replaced with identical lenses, which were also worn for 1 week, with surfactant cleaning added to the care regimen. The lenses then were examined by fluorescence spectroscopy in order that the extent of lipid and protein deposition could be assessed. The results indicate that protein accumulation is highly material dependent, whereas lipid deposition is primarily patient dependent. Also the term "ionic" does not necessarily indicate equally enhanced deposition in all lenses so termed. Surfactant cleaning appears to be of little benefit in reducing deposits during the early stages of wear, its benefit in the long-term being of much greater significance.

Adult↗
PubMed2005

Acrylic scaffolds with interconnected spherical pores and controlled hydrophilicity for tissue engineering.

Polymer scaffolds are obtained in which the geometric characteristics (pore size, connectivity, porosity) and the physico-chemical properties of the resulting material can be controlled in an independent way. The interconnected porous structure was obtained using a template of sintered PMMA microspheres of controlled size. Copolymerization of hydrophobic ethyl acrylate and hydrophilic hydroxyethyl methacrylate comonomers took place in the free space of the template, different comonomer ratio gave rise to different hydrophilicity degrees of the material keeping the same pore architecture. The morphology of the resulting scaffolds was investigated by scanning electron microscopy (SEM), the porosity of the material calculated, and the mechanical properties compared with those of the bulk (non porous) material of the same composition.

Absorption↗
PubMed1993

Acid-base properties of adhesive dental polymers.

The surface energetics of three resins (polymethylmethacrylate, polyhydroxyethylmethacrylate, and Bis-GMA/triethyleneglycoldimethacrylate) commonly used in adhesive interactions with tooth hard tissues were evaluated according to the Fowkes acid-base theory of interfacial interactions. From the measurement of the contact angle of test acidic and basic liquids on the sample surfaces, the acid-base contribution to the work of adhesion was evaluated. Results show that polyhydroxyethylmethacrylate is a comparatively strong Lewis base, a finding that can explain the important role played by this material in the formulation of dentin adhesive.

Adhesiveness↗
PubMed2006

Imprinted soft contact lenses as norfloxacin delivery systems.

Soft contact lenses are receiving an increasing attention not only for correcting mild ametropia but also as drug delivery devices. To provide poly(hydroxyethyl methacrylate), PHEMA, lenses with the ability to load norfloxacin (NRF) and to control its release, functional monomers were carefully chosen and then spatially ordered applying the molecular imprinting technology. Isothermal titration calorimetry (ITC) studies revealed that maximum binding interaction between NRF and acrylic acid (AA) occurs at a 1:1, and that the process saturates at 1:4 molar ratio. Hydrogels were synthesized using different NRF:AA molar ratios (1:2 to 1:16), at two fix AA total concentrations (100 and 200 mM), and using moulds of different thicknesses (0.4 and 0.9 mm). The cross-linker molar concentration was 1.6 times that of AA. Control (non-imprinted) hydrogels were prepared similarly but with the omission of NRF. All hydrogels showed a similar degree of swelling (55%) and, once hydrated, presented adequate optical and viscoelastic properties. After immersion in 0.025, 0.050 and 0.10 mM drug solutions, imprinted hydrogels loaded greater amounts of NRF than the non-imprinted ones. Imprinted hydrogels synthesized using NRF:AA 1:3 and 1:4 molar ratios showed the greatest ability to control the release process, sustaining it for more than 24 h. These results prove that ITC is a useful tool for the optimization of the structure of the imprinted cavities in order to obtain efficient therapeutic soft contact lenses.

Acrylates↗
PubMed1997

Composite poly(2-hydroxyethyl methacrylate) membranes as rate-controlling barriers for transdermal applications.

Composite membranes were prepared by casting a linear poly(2-hydroxyethyl methacrylate) (pHEMA) solution onto polyester non-woven supports, and then the supported pHEMA within the membranes was cross-linked by a diisocyanate cross-linking agent to form a network structure. The swelling and permeation properties of these membranes were evaluated, with a system of nitroglycerin and aqueous ethanol solution, for potential application in transdermal drug delivery. The degree of swelling of these membranes in water and aqueous ethanol decreases as the cross-linker content is increased and increases slightly with an increase in the original molecular weight of the linear pHEMA. The permeation rates of both nitroglycerin and ethanol increase as the cross-linker content is reduced, the polymer molecular weight increases, and the concentration of the casting solution or membrane thickness decreases. Depending on the preparation conditions, the membranes can be tailored to give a permeation flux ranging from 4 to 68 micrograms cm-2 h-1 for nitroglycerin.

Administration, Cutaneous↗
PubMed2004

Tethered protein/peptide-surface-modified hydrogels.

We investigated a wet chemistry method to covalently bond polyethylene glycol (PEG)-tethered extracellular matrix (ECM) proteins (laminin and fibronectin) or peptide (fibronectin-adhesion-peptide sequence) onto the surface of a poly(2-hydroxylethyl methacrylate-co-methylacrylic acid) (PHEMA/MAA) hydrogel that could potentially be used as a replacement for corneal tissue in the eye. An essential requirement for the success of such a surface in the biological environment is its ability to support the growth and attachment of corneal epithelial cells; ECM proteins are known to promote cellular attachment and growth. We hypothesized that the use of tethers or long hydrophilic chains would allow the attached ECM protein/peptide molecules to move two-dimensionally in space, thereby increasing their ability to bind with epithelial cell membranes. Additionally, the tethers would prevent the specifically added growth-enhancing factors from being obscured by any non-specific protein binding occurring on the hydrogel surface. In this surface-modification study, carbodiimidazole (CDI) was used to activate the carboxylic groups (-COOH) on the hydrogel surface in anhydrous dimethylsulfoxide (DMSO) before addition of the PEGylated proteins/peptide. The resulting tethered protein/peptide surface-modified hydrogels were analyzed in terms of percent grafting efficiency, biological activity and mechanical properties. X-ray photoelectron spectroscopy (XPS) and 125I radioactive labeling demonstrated the successful covalent bonding between the moieties and the hydrogel surface. Radiolabeling and enzyme-linked immunosorbent assay (ELISA) studies indicated that the tethered proteins attached to the hydrogel surface at a concentration of approx. 0.1 microg/cm2. ELISA testing further showed that tethered proteins remained biologically active. However, mechanical tensile testing indicated that the mechanical properties of these chemically modified hydrogels were somewhat altered in comparison with the unmodified hydrogel. Future studies will evaluate the cellular response to these surface-modified materials in vitro and in vivo.

Biocompatible Materials↗
PubMed1993

Release behavior of bioactive agents from pH-sensitive hydrogels.

Controlled release systems of theophylline, proxyphylline and oxprenolol.HCl exhibiting modulated drug delivery were prepared by using pH-sensitive anionic copolymers of 2-hydroxyethyl methacrylate with acrylic acid or methacrylic acid. Drug release studies were carried out in simulated biological fluids. The initial drug release rates and the drug release mechanisms were dependent upon the pH and ionic strength of the buffer solution as well as its salt composition. Initial drug diffusion coefficients in these swelling-controlled release systems were calculated from the release curves; they were of the order of 10(-7) cm2/s and were dependent upon the degree of swelling. The drug release mechanism was non-Fickian in all the dissolution media studied. Lowest release rates were observed for drug release from nonionized polymer networks in agreement with the relationship between ionization, swelling and drug release.

Acrylic Resins↗
PubMed1998

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.

Biocompatible Materials↗
PubMed1999

Inhibition of fibroblast cell adhesion on substrate by coating with 2-methacryloyloxyethyl phosphorylcholine polymers.

Fibroblast adhesion and growth behavior were examined on various polymers coated on a poly(ethylene telephthalate) (PET) substrate. The polymers are poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylatel copolymer (PMB)s with different MPC unit compositions, and poly(2-hydroxyethyl methacrylate). Surface analysis by dynamic contact angle measurement revealed that the mobility of the polymer chain on the PET substrate depended on the MPC unit composition, but there was no significant difference between the PMBs with 3-10 mol% MPC units and poly(HEMA). Fibronectin adsorption on the polymer surface from a cell culture medium was determined by immunoassay. The adsorbed fibronection was evenly distrubuted in every polymer, however, the amount was reduced with an increase in the MPC unit composition in the PMB. This result suggested that the MPC unit could weaken the interaction between the polymer surface and proteins. When fibroblast L-929 cells, were cultured on the polymers, the cells adhered and the number of cells increased on not only the hydrophobic poly(BMA) but also on the hydrophilic poly(HEMA). However, the number of cells that adhered on the PMB surface decreased with an increase in the MPC unit composition. This was a result of the fibronectin adsorption behavior. Thus, it could be concluded that since the PMB could suppress cell adhesion proteins e.g. fibronectin, the PMB showed excellent cell adhesive resistance properties.

Adsorption↗
PubMed2000

Hydrogel lens monomer constituents modulate protein sorption.

PURPOSE: To examine the effect of hydrogel lens monomer constituents on protein sorption. METHODS: A series of hydroxyethylmethacrylate (HEMA)-based hydrogels with various amounts of methacrylic acid (MAA) or N-vinyl pyrrolidone (NVP) were synthesized. A radiolabel tracer technique was used to measure the amount of protein adsorbed on or penetrating into the hydrogels. Penetration of fluorescence-labeled proteins in the hydrogels was studied by laser scanning confocal microscopy. Single-protein solutions of human serum albumin (HSA) and hen egg lysozyme were studied. RESULTS: Inclusion of the comonomers MAA or NVP in hydrogels resulted in an increase in water content and also had a strong impact on protein sorption. An increase in the amount of MAA in the poly(HEMA-co-MAA) hydrogels increased lysozyme adsorption and penetration but reduced HSA adsorption. However, the amount of protein adsorbed for both HSA and lysozyme increased with the amount of NVP in the poly(HEMA-co-NVP) hydrogels. In contrast to the marked effect of MAA on protein sorption, in particular, on lysozyme sorption, NVP had little influence on protein sorption. When a hydrogel contains both MAA and NVP, MAA has the dominant effect on protein sorption-in particular, on lysozyme sorption. Furthermore, a large difference was observed in the amount of lysozyme adsorbed on the hydrogels that had similar water contents but little variation in adsorption of HSA. CONCLUSIONS: Negatively charged carboxyl groups of the MAA constituent may influence lysozyme sorption in two ways: by electrostatic attraction and by increasing the possibility for the small lysozyme molecule to penetrate the hydrogels. Interactions of the surface lactam groups of NVP with proteins may be attributable to the attraction of proteins to NVP. Water content is not a primary factor in determining protein adsorption. It appears that the monomer constituents, such as MAA or NVP, control protein adsorption.

Adsorption↗
PubMed1990

Suspension polymerization of 2-hydroxyethyl methacrylate in the presence of polymeric diluents: a novel route to spherical highly porous beads for biomedical applications.

Spherical, highly porous beads of poly(2-hydroxyethyl methacrylate) (PHEMA) cross-linked with ethylene glycol dimethacrylate (EGDM) were prepared by suspension polymerization of HEMA in concentrated NaCl solutions in presence of toluene, poly(methyl methacrylate) (PMMA) in toluene, and poly(tetramethylene glycol) (PTMG). Magnesium hydroxide prepared in situ in the dispersion medium gave the best stabilization effect for the monomer droplets. In the presence of PTMG, beads having nearly 1.0 mm in diameter could be prepared, while toluene alone as the diluent produced beads of very small size. Removal of PMMA or PTMG from the beads after polymerization using suitable solvents gave rise to highly porous PHEMA microspsheres. Polymerization in the presence of PTMG produced microspsheres with better spherical geometry as compared to those generated in the presence of PMMA. The effect of various factors such as NaCl concentration, concentration of Mg(OH)2, and the concentration of PMMA or PTMG in the monomer phase on the stability of the suspension and the particle size distribution was investigated.

Cross-Linking Reagents↗
PubMed2004

Architecture and solution properties of AB-type brush-block-brush amphiphilic copolymers via ATRP techniques.

Atom transfer radical polymerization (ATRP) was applied to the synthesis of AB-type brush-block-brush amphiphilic copolymers. The procedure included the following steps: (1). ATRP of methacryloyl-terminated poly(ethylene glycol methylether) macromonomer (PEG-MC) gave well-defined PEG brush macroinitiator, (2). subsequent ATRP of 2-hydroxyethyl methacrylate (HEMA) with this brush macroinitiator provided PEG brush-block-PHEMA (brush-block-coil) diblock copolymers, (3). esterification of the pendant hydroxy groups of PHEMA block with 2-bromoisobutyryl bromide yielded a block-type polyinitiator, brush-block-poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) (PBIEM), (4). ATRP of HEMA using brush-block-PBIEM as polyinitiator provided AB-type brush-block-brush amphiphilic copolymers. Dilute-solution properties of such AB-type copolymer brushes were investigated by static and dynamic light scatterings. As a result, this copolymer exhibited a slightly ellipsoidal shape, i.e., Janus-type structure, in solution.

Anisotropy↗