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PubMed1993

Poly(2-hydroxyethyl methacrylate) sponges as implant materials: in vivo and in vitro evaluation of cellular invasion.

The pore size and the in vivo behaviour of four poly(2-hydroxyethyl methacrylate) sponges were investigated. The sponges were synthesized by polymerization of monomer in 70, 80 and 90 wt% water, respectively. In one of the formulations, a high amount of initiator was added. The average pore diameter was calculated with Ferry's equation and the results compared to those obtained by examination of samples using environmental scanning electron microscopy. The use of the equation greatly underestimated the size of pores. We also showed that the pores in polymers obtained in 70 wt% water were not interconnected, whilst the pores in polymers obtained in 80 and 90 wt% water, respectively, were larger and interconnected throughout the polymer. When implanted subcutaneously in rabbits, only the latter polymers allowed invasion and proliferation of cells. Penetration and proliferation of cells in these sponges were also assessed by an in vitro method using cultured human fibroblasts. The procedure included the overlaying of a glass plate covered by confluent cultured cells on to the surface of polymer impregnated with collagen. The depth of migration and number of sections needed to be cut to count a fixed number of invading cells were measured after incubation for 2 wk and used as indicators in comparing the ability of various sponges to allow cellular invasion. The assay showed that more cells invaded a hydrogel sponge produced in 80 wt% water than one produced in 90 wt% water. It also showed that the cut polymer surfaces allowed a greater cellular invasion than the moulded ones.

Animals↗

PubMedDate not supplied

Immunoblot analysis of proteins associated with HEMA-MMA microcapsules: human serum proteins in vitro and rat proteins following implantation.

Human serum proteins and their fragments, associated with hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) copolymer microcapsules, were characterized using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot analysis. Capsules were incubated with serum for 1 week in vitro and then dissolved in ethanol to also precipitate the adsorbed protein. The precipitate was dissolved in 2% (w/v) SDS (the 'capsule eluate') to be assayed by electrophoresis. The majority of proteins probed for in the immunoblots were detected in the capsule eluates. These included fibronectin, plasminogen, IgG, vitronectin, Factor B, Factor H, Factor I, C3, but not beta-lipoprotein, fibrinogen, HMWK, or IgM. Complement activation fragments were detected in both the immunoblots of the capsule eluates and the medium containing serum without capsules. Thus, the adsorption of these fragments, formed independent of capsule presence, may be partially or completely responsible for the complement fragments associated with capsules. The prevention of complement activation by the addition of 5.8 mM EDTA, at the beginning of the week-long incubation, resulted in fewer low-molecular-weight C3 fragments associated with capsules. Rat proteins were also detected in immunoblots of the eluate of 'free-floating' capsules from the rat peritoneal cavity following implantation for 1 day using anti-human antibodies. Detected proteins included HMWK, fibrinogen, antithrombin III, transferrin, alpha1-antitrypsin, fibronectin, albumin, alpha2-macroglobulin, vitronectin, beta2-microglobulin, Factor B and Factor I. Rat fibrinogen, IgG, and complement C3 fragments were also detected in these immunoblots, but with monoclonal antibodies against the rat proteins.

Animals↗

PubMed2004

Controlling modulus and morphology of hydrogel tubes through surface modification.

Crosslinked, porous poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) tubes were prepared in cylindrical glass molds using a new centrifugal casting process developed in our group. The resulting hydrogel tubes have a bi-phasic wall structure, with a spongy inner layer and a gel-like outer layer, the latter of which provides mechanical strength to the tube. While many factors influence wall morphology and, thus, mechanical properties, we focused on the effect of the surface properties of the glass mold in which tubes are synthesized. Specifically, we investigated the impact of a diverse set of silane modifications of the glass mold on tube morphology, elastic modulus and mold release. We treated activated glass surfaces with one of three alkoxysilanes having either ethoxy, amine or fluorocarbon end-groups. Silane-modified glass surfaces were found to be more hydrophobic than the unmodified glass mold, with the most hydrophobic surface being that of the fluorocarbon-terminated silane. The presence of the silane layer on the mold was confirmed by X-ray photoelectron spectroscopy and the stability of this modification was confirmed by examining the surface chemistry of the hydrogel tubes. The biphasic hydrogel tube wall structure was observed for all tubes, yet those tubes synthesized in unmodified molds had a cracked outer morphology, whereas those synthesized in silane-modified molds had a smooth outer morphology. This influenced the mechanical properties of the tubes where tubes synthesized in silane-modified molds had a significantly greater elastic modulus than those tubes synthesized in unmodified molds. Release from the molds was easiest with ethoxy- and amine-functionalized silane mold modifications.

Biocompatible Materials↗

PubMed2000

Poly(2-hydroxy ethyl methacrylate)-alkaline phosphatase: a composite biomaterial allowing in vitro studies of bisphosphonates on the mineralization process.

We have immobilized the mineralizing agent alkaline phosphatase (AlkP) in a hydrophilic polymer: poly(2-hydroxy ethyl methacrylate) - (pHEMA) - in a copolymerization technique. Histochemical study on polymer sections revealed that AlkP has retained its enzymic activity. The image analysis of sections using a tessellation method showed a lognormal distribution of the area of the tiles surrounding AlkP particles, thus confirming a homogeneous distribution of the enzyme in the polymer. Pellets of pHEMA-AlkP were incubated with a synthetic body fluid containing organic phosphates (beta-glycerophosphate). Mineral deposits with a rounded shape (calcospherites) were obtained in about 17 days. We have investigated the effects of three bisphosphonic pharmacological compounds (etidronate, alendronate and tiludronate) on this system which mimics the mineralization process of cartilage and woven bone. Bisphosphonates at a concentration of 10(-2) M totally inhibited AlkP in solution at a concentration of 10(-4) mg/ml. Inhibition has been reported being due to the chelation of a metal cofactor (Zn2+). Etidronate and alendronate appeared to similarly inhibit the calcospherite deposition onto the pHEMA-AlkP material. Both bisphosphonates possess three sites for the mineral complexion by Ca chemisorbtion. On the other hand, tiludronate having only two sites, was associated with a reduced inhibitory effect on mineralization but larger crystals were obtained. The pHEMA-AlkP material contains an immobilized enzyme in a hydrogel and mimics the physiological conditions of matrix vesicles entrapped within the cartilage (or bone) matrix. It provides an interesting method to study the effects of pharmacological compounds on the mineralization process in bone and cartilage in a non cellular and protein-free model.

Alendronate↗

PubMed1982

Contact with specific surfaces stimulates the production of the second component of complement (C2) in human peripheral blood monocytes via a lymphocyte factor.

Whole mononuclear cells plated on surfaces coated with the polymer, poly (2-hydroxyethyl methacrylate) (poly-HEMA) produced significantly less C2 when compared to production by cells on tissue culture plastic dishes. The reduction in C2 production was dependent on the amount of poly-HEMA used to coat the dishes and was not due to nonspecific damage of the cells or effects of the poly-HEMA on the hemolytic activity of C2. T and B lymphocytes, but not monocytes, plated on tissue culture plastic produced a soluble factor that increased the production of C2 in freshly adherent monocytes. Lymphocytes plated on the poly-HEMA surface did not produce this soluble factor, which was termed surface-dependent factor (SDF). Whole mononuclear cells plated on poly-HEMA were able to respond to SDF by increasing C2 production by the same percentage as cells on the tissue culture plastic. This suggested that the primary basis for the decreased production of C2 by monocytes in the whole mononuclear cells plated on the poly-HEMA was decreased production of SDF by the lymphocytes. The effect of the poly-HEMA surface on C2 production was probably related to a generalized alteration in maturation of monocytes into macrophages, for SDF had the same type of effect on beta-glucosaminidase levels in monocytes as seen with C2, except that the magnitude of the effect was less. These studies suggest that interaction of lymphocytes with surfaces may modulate the function of the lymphocytes. In addition, interaction of lymphocytes with surfaces and the production of SDF in vivo may be responsible for enhancing maturation of monocytes in tissues.

B-Lymphocytes↗

PubMedDate not supplied

Rat peritoneal macrophage adhesion to hydroxyethyl methacrylate-ethyl methacrylate copolymers and hydroxystyrene-styrene copolymers.

Macrophage adhesion to a wide variety of substrates has been measured, but no systematic study of the influence of specific substrate chemical properties on adhesion is available. These studies were conducted using two series of materials, copolymers of hydroxyethyl methacrylate (HEMA) and ethyl methacrylate (EMA) and copolymers of hydroxystyrene and styrene, to determine the effect of a single chemical property, polar character, on adhesion. Rat peritoneal macrophages were allowed to contact polymer substrates for periods ranging from 1 to 240 min before being subjected to a shear stress of 60-120 dynes/cm2 in a thin-channel flow cell. Percentage adhesion was calculated from the number of cells that remained adherent to the substrate after 30 s of applied shear stress. Macrophages remained adherent to 100% EMA and all hydroxystyrene-styrene copolymer surfaces after only 1 min of contact. In copolymers of the HEMA-EMA series, the time required to attain peak adhesion levels increased with increasing substrate hydrophilicity (increasing HEMA content). Cells did not attach to the 20% EMA/80% HEMA copolymer and the 100% HEMA polymer. The results demonstrate that there is a time delay between contact and adhesion of the cells to surfaces of increasing hydrophilicity within the HEMA-EMA series and no time delay with the hydroxystyrene-styrene series. The time delay is thought to be a function of the excluded volume provided by polymers that are able to undergo significant chain rotation and or swelling in the solvent, water. Small excluded volumes present in copolymers of high EMA content and all hydroxystyrene-styrene copolymers offer little or no resistance to formation of adhesive bonds by macrophages, whereas copolymers with large excluded volumes (high HEMA content) prevent contact and/or adhesion. A mechanism based on the net excluded volumes of both the cell and substrate surface macromolecule is proposed to explain this phenomenon.

Animals↗

PubMed1994

Effects of environmental parameters and composition of poly(2-hydroxyethyl methacrylate)-graft-polyamine copolymers on the retention of rat lymphocyte subpopulations (B- and T-cells).

Retention behavior of rat lymphocyte subpopulations (B- and T-cells) was investigated on poly(2-hydroxyethyl methacrylate)-graft-polyamine (HA) copolymers with various copolymer compositions. Separation mechanism of B- and T-cells was then evaluated by focusing on several parameters, such as pH, temperature, and ionic strength. The interaction of lymphocytes with HA surfaces was mainly through the electrostatic force from their retention profile at varying ionic strengths of the medium. Temperature also has a crucial effect on the response of lymphocytes toward pH-induced phase transition of polyamine grafts at the polymer interface with aqueous milieu. At 4 degrees C, both B- and T-cells showed minimal retention on HA surfaces at pH 8. At this pH, polyamine grafts existed in a compact conformation with a low degree of protonation. However, at pHs below 8, at which polyamine grafts existed in extended conformation, the resolution of B- and T-cells was achieved. In contrast, at 23 degrees C, the phase transition of polyamine grafts significantly influenced T-cell retention, resulting in a decrease in the retention of T-cells on HA with polyamine in a compact conformation. Consequently, preferential retention of B-cells was achieved under this condition. The polyamine content was found to be another important factor affecting the retention behavior of lymphocyte subpopulations. On HA copolymers with low polyamine content (HA7, HA10), conformational transition of polyamine grafts showed a significant influence for B-cell retention, although the influence decreased with increasing polyamine content. From the study estimating the effect of neuraminidase treatment of lymphocytes on their retention to HA surfaces, sialic acid residues on the plasma membrane surface of lymphocytes are suggested as feasible anionic sites showing electrostatic interaction with polyamine grafts.

Amines↗

PubMed1996

Artificial cornea: surface modification of silicone rubber membrane by graft polymerization of pHEMA via glow discharge.

A method for producing various surfaces of silicone rubber membrane (SR) was developed in this study by grafting various amounts of poly(2-hydroxy ethyl methacrylate) (pHEMA) onto SR by plasma-induced grafted polymerization (PIP) as a homobifunctional membrane. The elemental composition and different carbon bindings on the surface of SR were examined by electron spectroscopy for chemical analysis with the amount of O1s/C1s being approximately 0.7 at 1 min, 60 W, 200 mTorr of Ar-plasma treatment. The peroxide group introduced on SR was measured via 1,1-diphenyl-2-picrylhydrazyl (DPPH) and the amount of 6.85 x 10(-8) mol cm-2 reached optimum value at 1 min of Ar-plasma treatment. After Ar-plasma treated SR, the peroxide group (33D peak) was introduced on the surface of SR by negative spectra of secondary ion mass spectroscopy analysis, whereas ester groups (72D peak) were observed for pHEMA-grafted SR. For the in vitro test, the influence of various surfaces of SR on attachment and growth of rabbit corneal epithelial cells (CEC) was studied by cell culture assay. These results indicated that 56-150 micrograms cm-2 of pHEMA grafted onto SR were suitable values for attachment and growth of CEC. On the contrary, the large grafted amounts (500-1650 micrograms cm-2) of pHEMA on SR were insufficient for attachment and growth of CEC. For the in vivo test, the migration of CEC from host cornea to implant was investigated by slit lamp microscopy. The experimental results indicated that SRs grafted with pHEMA were completely covered with CEC 3 weeks after implantation of the membranes into the host cornea. These results provide a valuable reference for developing an artificial cornea.

Animals↗

PubMed2005

Nerve guidance channels as drug delivery vehicles.

Nerve guidance channels (NGCs) have been shown to facilitate regeneration after transection injury to the peripheral nerve or spinal cord. Various therapeutic molecules, including neurotrophic factors, have improved regeneration and functional recovery after injury when combined with NGCs; however, their impact has not been maximized partly due to the lack of an appropriate drug delivery system. To address this limitation, nerve growth factor (NGF) was incorporated into NGCs of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate), P(HEMA-co-MMA). The NGCs were synthesized by a liquid-liquid centrifugal casting process and three different methods of protein incorporation were compared in terms of protein distribution and NGF release profile: (1) NGF was encapsulated (with BSA) in biodegradable poly(d,l-lactide-co-glycolide) 85/15 microspheres, which were combined with a PHEMA polymerization formulation and coated on the inside of pre-formed NGCs by a second liquid-liquid centrifugal casting technique; (2) pre-formed NGCs were imbibed with a solution of NGF/BSA and (3) NGF/BSA alone was combined with a PHEMA formulation and coated on the inside of pre-formed NGCs by a second liquid-liquid centrifugal casting technique. Using a fluorescently labelled model protein, the distribution of proteins in NGCs prepared with a coating of either protein-loaded microspheres or protein alone was found to be confined to the inner PHEMA layer. Sustained release of NGF was achieved from NGCs with either NGF-loaded microspheres or NGF alone incorporated into the inner layer, but not from channels imbibed with NGF. By day 28, NGCs with microspheres released a total of 220 pg NGF/cm of channel whereas those NGCs imbibed with NGF released 1040 pg/cm and those NGCs with NGF incorporated directly in a PHEMA layer released 8624 pg/cm. The release of NGF from NGCs with microspheres was limited by a slow-degrading microsphere formulation and by the maximum amount of microspheres that could be incorporated into the NGCs structure. Notwithstanding, the liquid-liquid centrifugal casting process is promising for localized and controlled release of multiple factors that are key to tissue regeneration.

Capsules↗

PubMed2002

Effects of negatively charged groups (carboxymethyl) on the calcification of poly(2-hydroxyethyl methacrylate).

Poly(2-hydroxyethyl methacrylate) (pHEMA) has potentially wide biomedical applications: it is biocompatible, allows immobilization of cells or bioactive molecules and has a hardness comparable to bone. We previously reported that immobilization of alkaline phosphatase (AlkP) in pHEMA can initiate mineralization in a manner that mimics the calcification of cartilage and woven bone. Because numerous proteins known to initiate mineralization possess acidic species, we have modified the neutral electrical surface of pHEMA by carboxymethylation (CM). We have studied the effects of these negative groups on the calcification process in vitro. Calibrated pellets of pHEMA were prepared and carboxymethylated by soaking with 0.5 M bromoacetic acid in 2 M NaOH. Pellets of pHEMA, pHEMA-AlkP and pHEMA-CM were incubated during 5, 10 and 15 days in two types of body fluid: normal (1X) and 1.5X concentration of ions. Nodules of hydroxyapatite developed on pHEMA-AlkP and pHEMA-CM but not on pHEMA. Hydroxyapatite crystals were dissolved in HCl allowing calcium to be dosed. CM significantly increased the amount of deposited Ca by 1.8 folds in the 1X fluid and 15.8 folds in the 1.5X fluid. The presence of AlkP considerably increased the amount of deposited Ca: 25.9 folds in 1X and 23.3 in 1.5X. ROS 17/2.8 osteoblast-like cells were seeded on the materials and examined by confocal microscopy after phalloidin staining. Cells grown on pHEMA alone appeared round, while cells grown on the crystals deposited on the pHEMA-CM or pHEMA-AlkP were flattened. The presence of AlkP favours the mineralization process more than the existence of surface negative groups on the polymer. Cells preferentially adhere to the polymer when hydroxyapatite crystals were developed.

Biocompatible Materials↗

PubMed2001

Clinical comparison of microporous biocompatible composite of PMMA, PHEMA and calcium hydroxide grafts and expanded polytetrafluoroethylene barrier membranes in human mandibular molar Class II furcations. A case series.

BACKGROUND: Class II furcations present difficult treatment problems. Several treatment approaches to obtain furcation fill have been used with varying success. METHODS: The response of mandibular Class II furcations to treatment with either a microporous biocompatible composite of PMMA (poly-methyl-methacrylate), PHEMA (poly-hydroxyl-ethyl methacrylate) and calcium hydroxide graft synthetic bone (HTR) replacement graft material; ePTFE barrier membrane; or a combination of the two was evaluated in trios of mandibular molars with Class II furcations in 8 patients with moderate to advanced periodontitis. Following initial preparation, full-thickness flaps were raised in the areas being treated, the bone and furcation defects debrided of granulomatous tissue, and the involved root surfaces mechanically prepared and chemically conditioned. By random allocation, HTR, ePTFE, or a combination of both was placed into and/or fitted over the furcations, packed and/or secured in place, and the host flap replaced or coronally positioned with sutures. Postsurgical deplaquing was performed every 10 days leading up to ePTFE removal at approximately 6 weeks. Continuing periodontal maintenance therapy was provided until surgical reentry at 6 months for documentation and any further necessary treatment. RESULTS: Direct clinical measurements demonstrated essentially similar clinical results with all 3 treatments for bone and soft tissue changes. There were no statistically or clinically significant differences except for better horizontal amount and percent defect fill with HTR alone. Four of 8 furcations became Class I clinically with HTR alone, 5 of 8 became Class I with ePTFE alone, and 5 of 8 with combination treatment. The only complete furcation closure occurred with HTR. CONCLUSION: The findings of this study suggest essentially equal clinical results with HTR bone replacement graft material alone, ePTFE barrier alone, and a combination of the two in mandibular molar Class II furcations. However, a real difference may not have been detected based on the small number of subjects in the study.

Biocompatible Materials↗

PubMed2002

Liquid 2-poly-hydroxyethyl-methacrylate embolization of experimental arteriovenous malformations: feasibility study.

BACKGROUND AND PURPOSE: We investigated the use of 2-poly-hydroxyethyl-methacrylate (2-P-HEMA) as an embolic agent in swine arteriovenous malformations (AVMs). METHODS: In seven mini swine, experimental AVMs were created surgically. The aim of treatment was complete embolization of the nidus compartment filled by the feeding artery, without brain embolization. Six animals received pure liquid 2-P-HEMA, and one, 50% 2-P-HEMA. For radiopacity, liquid 2-P-HEMA was mixed with tungsten powder. Six animals underwent angiographic follow-up within 5-8 mo (mean, 6.5 mo). Evaluation criteria were controllability, procedural reproducibility, and duration of the nidus occlusion. To detect complications, brain MR imaging and CT were performed. Histopathologic studies were performed to prove occlusion and assess histopathologic responses. RESULTS: 2-P-HEMA was easily injected through microcatheters, with a reproducible technique. Because of the radiopacity of the mixture, deep nidus penetration was controlled with fluoroscopy and confirmed with CT and histopathologic examination. In five AVMs embolized with pure 2-P-HEMA, feeder obliteration was long term. One animal had vasospasm during embolization, and complete obliteration of the main feeder was maintained for 3 mo, but partial recanalization developed 2 mo later. One animal receiving pure 2-P-HEMA had an infarction. In the animal embolized with 50% 2-P-HEMA, angiography and CT revealed embolic material in the circle of Willis; the animal died after embolization. No marked inflammatory reaction in the vessel wall or perivascular tissue was observed in the embolized AVMs. CONCLUSION: Experimental AVM embolization with pure 2-P-HEMA, made radiopaque with tungsten, is technically feasible in swine. Because of its properties, 2-P-HEMA has great potential as a therapeutic embolic agent.

Angiography, Digital Subtraction↗

PubMed1998

Cell viability and inflammatory response in hydrogel sponges implanted in the rabbit cornea.

In the quest for the development of a functional keratoprosthesis, the biocompatibility of the porous skirt material in the Chirila keratoprosthesis (KPro) was investigated. The population of live and dead cells within, and the inflammatory response to, a tissue-integrating poly(2-hydroxyethyl methacrylate) (PHEMA) sponge were studied. Samples of the hydrogel sponge were implanted in rabbit corneas and explanted at predetermined time points up to 12 weeks. The explanted sponges were subjected to cell viability assay using two types of fluoroprobes, 5-chloromethylfluorescein diacetate and ethidium homodimer-1. A semiquantitative analysis was performed to assess the number of dead cells within the sponge and in the area of corneal stroma proximal to the sponge. Five rabbits were used for each end point (2, 4 and 12 weeks). To investigate the inflammatory response to the sponge, immunocytochemistry, using specific antibodies to rabbit macrophages, enzyme histochemistry of chloroacetate esterase (to detect neutrophils) and transmission electron microscopy (TEM) were also employed at 24 h, 2, 4 and 12 weeks after implantation. Four weeks after implantation, fewer viable cells were observed in the sponge when compared to the 2-week implant. However, the proportion of viable cells increased dramatically by 12 weeks. The proportion of nonviable cells decreased gradually with time; central sponge contained 34+/-11 % dead cells after 2 weeks, and 15+/-4.3% after 12 weeks. The staining of inflammatory cells demonstrated the presence of macrophages and neutrophils up to 12 weeks after implantation. TEM confirmed the presence of these cell types and others. including eosinophils and myofibroblasts, as well as blood capillaries. The presence of a significant number of viable cells at each time point and the uniform reduction of the nonviable cell proportion with time suggests that the sponge is a conducive environment supporting a prolific, viable cellular colonization. Dead cells observed in the first instance indicate a normal injury pattern. However, the presence of a small but significant proportion of invading inflammatory cells 12 weeks after implantation confirms a characteristic pattern of wound healing within the sponges.

Animals↗

PubMed2004

In vitro drug-induced spoliation of a keratoprosthetic hydrogel.

PURPOSE: To investigate in vitro the effects of selected drugs on the spoliation of poly(2-hydroxyethyl methacrylate) (PHEMA), a synthetic acrylic hydrogel currently used for the manufacture of a keratoprosthesis, AlphaCor. The experiments were carried out both in the presence of simulated aqueous humor (SAH) and in its absence. METHODS: Disks of PHEMA were incubated and shaken with 9 commonly prescribed drugs at 37 degrees C in sterile conditions for 1 week. Samples were incubated either in SAH only (controls), in each drug preparation, or in each drug for 1 week followed by 1 week in SAH. The drugs selected for this study were steroids (prednisolone, dexamethasone, fluorometholone, medroxyprogesterone), antiglaucoma drugs (timolol maleate and pilocarpine), and antibiotics (chloramphenicol, cephazolin, and ciprofloxacin), as commercially available formulations. Following incubation, the PHEMA specimens were examined visually and then histologically, after staining with alizarin red for the presence of calcium in the spoliating sediments/deposits. RESULTS: Although only 5 of the drug formulations (dexamethasone as Maxidex, fluorometholone as FML, pilocarpine as Isopto Carpine, chloramphenicol as Chlorsig, and medroxyprogesterone as Depo-Ralovera) induced spoliation of the hydrogel in the absence of SAH, all drugs induced spoliation after postincubation in SAH, and calcium was detected in the majority of samples. The deposits on the hydrogel specimens incubated first in cephazolin (as Cefazolin-BC), pilocarpine (as Isopto Carpine), and chloramphenicol (as Chlorsig) and then in SAH did not contain calcium, despite its presence in SAH. CONCLUSIONS: The study appears to confirm our earlier clinical observations that topical medication may play a role in the spoliation of the hydrogel ophthalmic devices. Presence of calcium in the deposits seems to be correlated to the nature of drug. Although the incidence of spoliation in real clinical situations is much lower than suggested by this extreme-case in vitro simulation, topical therapy after implantation of AlphaCor should be carefully considered, kept to the minimum required, and additive-free where possible.

Anti-Bacterial Agents↗

PubMed1997

Six-year clinical evaluation of HTR synthetic bone grafts in human grade II molar furcations.

A biocompatible microporous composite of PMMA (poly-methyl-methacrylate), PHEMA (poly-hydroxy-ethyl-methacrylate) and calcium hydroxide bone replacement graft material (Bioplant HTR Synthetic Bone) was evaluated in 16 maxillary molar and 10 mandibular molar Grade II furcations in 13 patients. Following initial preparation, full thickness flaps were raised to gain access to the furcations; mechanical hand and ultrasonic root and defect debridement and chemical tetracycline root preparation were performed; furcation and adjacent osseous defects in each patient were grafted with HTR Synthetic Bone; and the host flaps replaced or slightly coronally positioned. Weekly, then monthly deplaquing was performed until surgical re-entry at 6-12 months. Patients were then followed on approximate 3-month recalls for > or = 6 yr. Evaluation of the primary clinical outcome of furcation grade change showed that in the maxilla 5/16 furcations were clinically closed, 9/16 were Grade I, and 2/16 remained Grade II; while in the mandible 3/10 were clinically closed, 5/10 were Grade I, and 2/10 remained Grade II. Other significant clinical changes included decrease in mean horizontal furcation probing attachment level from 4.4 mm at surgery to 2.2 mm at re-entry to 2.0 mm at 6 yr, decrease in probing pocket depth from 5.4 mm at surgery to 3.0 mm at re-entry to 3.2 mm at 6 yr, and improvement in vertical clinical probing attachment level from 5.4 mm at surgery to 4.2 mm at re-entry to 4.1 mm at 6 yr (all p < 0.05 from surgery to re-entry and surgery to 6 yr, n.s. from re-entry to 6 yr via ANOVA). These favorable results with HTR polymer are similar to several reports with other graft materials and with GTR barriers, and suggest that HTR polymer may have a beneficial effect in the clinical management of Grade II molar furcations.

Adult↗

PubMed1999

Synthesis, physical characterization, and biological performance of sequential homointerpenetrating polymer network sponges based on poly(2-hydroxyethyl methacrylate).

A limitation in the use of hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) sponges as implantable devices is their inherently poor mechanical strength. This precludes proper surgical manipulation, especially in the eye where the size of the implant is usually small. In this study a new method was developed to produce mechanically stronger PHEMA sponges. Sequential homointerpenetrating polymer network (homo-IPN) sponges were made by using HEMA as the precursor for generating both the first network and the successive interpenetrated networks. Following the formation of network I, the sponge was squeezed to remove the interstitial water, soaked in the second monomer (also HEMA), and squeezed again to remove the excess monomer from the pores before being subjected to the second polymerization leading to the formation of network II. Two two-component IPN sponges (K2 and K4) with increasing HEMA content in the network II and a three-component IPN sponge (K3) were produced, and their properties were compared to those of a homopolymer PHEMA sponge (control). Apart from elongation, the tensile properties were all significantly enhanced in the IPN sponges; the water content was the same as in the control sponge, except for sponge K4, which was lower. Light microscopy revealed similar pore morphologies of the control and IPN sponges K2 and K3, and the majority of the pores were around 25 microm. Sponge K4 displayed smaller pores of around 10 microm. Cellular invasion into the sponges was examined in vitro (incubation with 3T3 fibroblasts) and in vivo (implantation in rabbit corneas). Although the in vitro assay detected a change in the cell behavior in the early stage of invasion, which was probably due to the formation of IPNs, such changes were not reflected in the longer term in vivo experiment. There was a proper integration of sponges K2 and K3 with the corneal stroma, but much less cellular invasion and no neovascularization in sponge K4. We concluded that IPN formation is a valid method to enhance the strength of PHEMA sponges, provided that the content of HEMA in the successive networks is not too high.

Animals↗

PubMed1987

Steroidogenesis in adrenal tumor cells: influence of cell shape.

Y-1 adrenal tumor cells were grown on plastic, or plastic treated with poly(2-hydroxyethyl methacrylate) (polyHEMA) to produce concentration-dependent rounding (10(-5)-3 X 10(-4) M) of the cells or on plastic treated with poly-D-lysine (polylysine) to produce flat cells, in order to determine whether or not cell shape is correlated with steroid synthesis. The degree of rounding of cells was measured by determining mean cell height and longest cell diameter. Three measurements of steroid production were made: production of 20 alpha-dihydroprogesterone, transport of cholesterol to the inner mitochondrial membrane, and production of pregnenolone by isolated mitochondria. Cells grown on poly(HEMA) showed increase in mean cell height, decrease in longest diameter (i.e. rounding), and increase in all three measurements of steroidogenesis. In the case of synthesis of 20 alpha-dihydroprogesterone, the response was dependent on the concentration of poly(HEMA), being greater with higher concentrations (up to 10(-4) M), of this agent. Moreover the degree of rounding (cell height) was correlated with production of 20 alpha-dihydroprogesterone at three concentrations of poly(HEMA) (r = 0.93. ACTH at a supramaximal concentration produced increases in all of these responses to the poly(HEMA) surface. Polylysine produced flatter cells (lower mean height and greater longest diameter) than plastic and also inhibited all three steroidogenic responses to ACTH. (Bu)2cAMP exerted the same effects as ACTH. Growing cells on poly(HEMA) or polylysine did not affect production of cyclic AMP by the cells. Addition of poly(HEMA) or polylysine to the medium in which the cells were incubated, at the same concentrations as those used for influencing cell shape, was without effect on steroid synthesis or the response to ACTH. Cells grown on poly(HEMA) show decreased incorporation of [3H] thymidine into DNA. It is concluded that cell shape influences the delivery of cholesterol to inner mitochondrial membrane and in this way, increases the production of steroids by Y-1 cells and that the effects of poly(HEMA) on cell shape, cholesterol transport, and synthesis of DNA may involve microfilaments.

20-alpha-Dihydroprogesterone↗

PubMed2000

Calcification of poly(2-hydroxyethyl methacrylate) hydrogel sponges implanted in the rabbit cornea: a 3-month study.

Poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels have been used in the past as ocular implants. In a recent development, PHEMA sponges have shown suitable properties as materials for the peripheral component of an artificial cornea (keratoprosthesis). However, the propensity of PHEMA to calcify could threaten the long-term stability of the implanted devices. In an attempt to improve the understanding of the calcification mechanism, the dynamics, extent, and nature of calcified deposits within PHEMA sponges implanted in the cornea were investigated in this study, and the possible correlation between necrosis of cells and calcification was critically examined. Samples of a PHEMA sponge were implanted in rabbit corneas and explanted at predetermined time points (2, 4, and 12 weeks). The samples were examined by microscopy (light, transmission, scanning) and energy dispersive analysis of X-rays. Histological assessment and semiquantitative analysis of the amount of calcium deposited was performed using image analysis. An in vitro experiment was also performed by incubating sponge samples for 2 weeks in a solution of calcium and phosphate ions at a ratio similar to that in hydroxyapatite, in the absence of cells. Calcification was not seen in the 2- and 4-week explants, however, small deposits were detected in two of the 12-week explants, both within and on the sponge's constituent polymer particles. The deposit volumes represented 0.094% and 0.21%, respectively, of the total sponge volumes. Calcium deposits were present in large amounts both within the constituent polymer particles and on the surface of the sponges incubated in the abiotic calcifying solution. Cooperative mechanisms are suggested for the calcification of PHEMA sponges in vivo. The initial event may occur at a molecular level, when plasma proteins are adsorbed onto the polymer surface and bound through chelation to the calcium ions present in the medium. After their natural degradation, these structures may act as nucleation sites for calcium phosphate crystallization. Concurrently, the calcium ions can diffuse into the hydrogel particles and then the spontaneous precipitation of calcium phosphate may be caused by supersaturation due to the lower content of water in polymer, an effect which is likely predominant in vitro. The second event is the recruitment of phagocytic cells to clear calcium debris. Degeneration of these cells may then form nucleation sites for secondary calcification.

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