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At least 487 records · Page 27Linked to original sources
PubMed1992

Human gingival tissue response to HTR polymer.

Biopsies secured during reentry surgical evaluation of previously treated periodontal osseous defects were examined for gingival tissue response to HTR polymer. Eleven patients provided biopsies of HTR grafted sites 6-7 months after initial implantation. Minimal inflammation and infrequent foreign body giant cells were found. Bone was present in about half of the samples and osteogenesis associated with the HTR graft material was seen in about 20% of the biopsies. Serendipitously, biopsies of other graft materials or debridement only sites from 6-30 months post-treatment were also available for analysis and comparison, and showed similar tissue response. The results of this study suggest that HTR polymer (and other graft materials) is very biocompatible and elicits no untoward gingival tissue responses when placed in periodontal osseous defects.

Adult↗
PubMed1992

Morphological assessment of hepatoma cells (HepG2) microencapsulated in a HEMA-MMA copolymer with and without Matrigel.

Hepatoma cells (HepG2), an anchorage-dependent cell line, were microencapsulated in a HEMA-MMA polyacrylate membrane to which the cells do not adhere. This environment was altered by the coencapsulation of Matrigel, a reconstituted extracellular matrix derived from the Engelbreth-Holm-Swarm (EHS) mouse tumor basement membrane, to provide sites for cell attachment. The effect on the cells of these two capsule microenvironments during a 2-week in vitro culture period was assessed by examining the spatial arrangement, morphology, and viability of the cells using light microscopy and scanning electron microscopy (SEM). In preparation for microscopy, dissolution of the polymer was prevented by the use of frozen sections embedded in a water-soluble compound. Similarly, freeze cleavage of conductively stained capsules permitted SEM observation of the capsule interior along with ultrastructural detail of the cells. In the absence of Matrigel, cells in HEMA-MMA capsules were found to form aggregates in intracapsular pockets with central necrosis occurring at day 7 in large aggregates. The coencapsulation of HepG2 cells with Matrigel, resulted in an initially uniform distribution of essentially individual cells with aggregates appearing later within the Matrigel. Many cells within these capsules had remained viable when examined up to day 14 with only limited cellular necrosis, implying a favorable environment for microencapsulated HepG2 cells.

Biocompatible Materials↗
PubMed1992

Changes in fibrinogen adsorbed to segmented polyurethanes and hydroxyethylmethacrylate-ethylmethacrylate copolymers.

Fibrinogen adsorption from blood to biomaterials may regulate platelet adhesion and thrombus formation because of fibrinogen's central role in the coagulation cascade and its ability to bind specifically to the platelet membrane glycoprotein (GP) IIb-IIIa. Adsorption of fibrinogen from blood plasma to many materials exhibits a maximum with respect to plasma dilution and exposure time (the Vroman effect). In this study fibrinogen adsorption to several polymers was examined to ascertain the influence of controlled changes in surface chemistry on the Vroman effect. The materials included hydroxyethylmethacrylate-ethylmethacrylate (HEMA/EMA) copolymers, Biomer, and a series of segmented polyurethanes (PEUs), two of which contained fluorinated chain extenders. Each material exhibited maximal adsorption of fibrinogen at intermediate plasma concentrations. Little effect of soft-segment type or molecular weight was observed and no significant differences in fibrinogen adsorption to the fluorinated PEUs were seen. Changes in the strength of fibrinogen attachment to these materials with time after adsorption were also assessed. Fibrinogen adsorbed for 1 min was displaced more readily by blood plasma than that adsorbed for 1 h, regardless of the material. The more hydrophobic polymers exhibited greater retention of adsorbed fibrinogen. In addition, the fraction of fibrinogen retained by polyethylene depended on the amount of fibrinogen adsorbed to the surface, being greatest when the surface loading was the least. These studies indicate that spreading or transition of adsorbed fibrinogen molecules from a weakly to tightly bound state is a general consequence of protein adsorption to solid surfaces.

Adsorption↗
PubMed1995

Surface field of forces and protein adsorption behavior of poly(hydroxyethylmethacrylate) films deposited from plasma.

Polymeric films were deposited from hydroxyethylmethacrylate (HEMA) plasma on non-woven poly(butyleneterephtalate) (PBT) filter materials. To test the effect of deposition conditions on surface properties, film were deposited using a constant monomer flow rate and a discharge power ranging from 40-100 W. Surface composition and surface energetics were evaluated by Electron Spectroscopy for Chemical Analysis (ESCA) and contact angle measurement, respectively. Albumin (Alb) and fibrinogen (Fg) adsorption from single protein solutions to the plasma-coated filters was measured. Results illustrate the marked effects of the deposition condition on the surface composition, the surface field of forces, and the protein adsorption behavior. The latter is modeled by the application of the Good-van Oss-Chaudhury theory of Lewis acid-base contribution to interfacial energetics. Materials endowed with widely different properties are obtained from the same monomer and different deposition conditions, a result that must be taken into account both in the production step, to assure constant quality, and in the development of specifically tailored materials.

Adsorption↗
PubMed2004

Immobilized concentration gradients of nerve growth factor guide neurite outgrowth.

Axons are guided to their targets by a combination of haptotactic and chemotactic cues. We previously demonstrated that soluble neurotrophic factor concentration gradients guide axons in a model system. In an attempt to translate this model system to a device for implantation, our goal was to immobilize a stable neurotrophic concentration gradient for axonal (or neurite) guidance. Nerve growth factor (NGF) was immobilized within poly(2-hydroxyethylmethacrylate) [p(HEMA)] microporous gels using a gradient maker. The NGF was stably immobilized, with only approximately 0.05% of the amount originally incorporated into the gel released over an 8-day period. Immobilized NGF was bioactive: the percent of PC12 cells extending neurites on NGF-immobilized p(HEMA) gels was 16 +/- 2%, which was statistically the same as those exposed to soluble NGF (22 +/- 6%). We were able to predict and reproducibly create stable NGF concentration gradients in the gel. At an NGF concentration gradient of 357 ng/mL/mm, PC12 cell neurites were guided up the gradient. The facile, flexible, and reproducible nature of this method allowed us to translate soluble growth factor gradient models to stable growth factor gradient devices that may ultimately enhance axonal guidance and regeneration in vivo.

Animals↗
PubMed2004

Enhancing the biological activity of immobilized osteopontin using a type-1 collagen affinity coating.

The covalent attachment of biomolecules onto surfaces represents a step toward the improvement of biomaterial properties by providing relevant biological signals of interest to the cell culture or tissue environment. The chemistries involved, however, often attach proteins to the surface in a random fashion, rather than the conformation or orientation most easily recognized by cells and other proteins both in vitro and in vivo. An alternative approach is to take advantage of natural interactions to both bind and orient a biomolecule "naturally," thereby enhancing its biological activity. Type 1 collagen has been shown to bind to osteopontin (OPN), a protein implicated in processes such as wound healing, endothelial cell survival, and angiogenesis. This study seeks to characterize, quantify, and exploit this interaction in order to present a more naturally recognized form of OPN to the environment surrounding a biomaterial. Binding of OPN to type 1 collagen was confirmed using Surface Plasmon Resonance (SPR). Radio-iodination of OPN showed that binding to collagen was dose-dependent and maximal in basic conditions. Principal component analysis of Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) data identified differences in OPN immobilized via different techniques. Adhesion of bovine aortic endothelial cells on OPN immobilized using the affinity coating was also significantly enhanced compared to controls. Investigation into the in vivo relevance of this immobilization method is currently underway.

Animals↗
PubMed2007

A biodegradable copolymer for the slow release of growth hormone expedites scarring in diabetic rats.

In many diseases wound healing is impaired. This study was designed to establish whether the healing process in diabetes could be improved using a site-specific polymer delivery system containing hGH. The system was first optimized in in vitro experiments performed on cultured fibroblasts taken from healthy and diabetic rats and then tested in an incisional wound model created in the diabetic Wistar rat. In the in vitro experiments using cultured fibroblasts, cell viability, growth, and proliferation were determined, along with polymer degradation, hormone release rates and the expression of TGFbeta1 in the culture medium. For the in vivo experiments, polymer discs with/without GH were inserted through 3 cm incisions made on the backs of the animals. Wound specimens were obtained 7 and 30 days after surgery to evaluate inflammatory/apoptotic cells, metalloprotease expression and neoangiogenesis using microscopy and immunohistochemical techniques. The local administration of GH using a polymer delivery system did not affect the normal wound healing process. Conversely, when used in diabetic animals, epidermal and dermal repair was expedited. Our findings indicate that GH induces cell proliferation, enhances CD4(+) infiltration; increases extracellular matrix protein deposition; stimulates angiogenesis; and diminishes apoptosis at the diabetic wound site. These effects give rise to a comparable wound healing process to that observed in healthy animals.

Animals↗
PubMed1981

Adhesive substrates for fibronectin.

In order to promote cell attachment, fibronectin must first undergo activation by a suitable substrate. In this study, 52 materials have been surveyed for their ability a) to bind fibronectin, b) to activate the cell-adhesive property of fibronectin, and c) to support the growth of cells. Many plastics, polysaccharides, metals, and ceramics were found to support cell growth as well as the fibronectin-dependent attachment of cells. Several other substrates have been identified that were inactive in promoting either cell attachment or growth. Hydrophobic substrates were found to be active in fibronectin activation, whereas hydrophilic substrates were found to be inactive. Since fibronectin binds to substrata of extremely varied chemical composition, it is clear that the binding of fibronectin to such substrata is nonspecific in nature. Since protein pretreatment of all substrata, except collagen and poly(L-lysine), abolished the physical binding of fibronectin, the binding of fibronectin to artificial substrata is probably ascribable to a nonspecific hydrophobic protein-substratum interaction. In contrast, several lines of evidence indicate that the interaction between fibronectin and collagen displays biological specificity. Poly(hydroxyethylmethacrylate)(poly(HEMA)), which has previously been shown to be nonadhesive for cells, is demonstrated here to be unique in its inability to bind fibronectin. Addition of one part per million of an adhesive polymer to poly(HEMA) permits fibronectin binding to occur.

Animals↗
PubMed1998

Focal adhesion kinase pp125FAK and the beta 1 integrin subunit are constitutively complexed in HaCaT cells.

Binding of integrins to the extracellular matrix (ECM) activates various signal transduction pathways and regulates gene expression in many cell types. Integrin-dependent cytoplasmic protein/protein interactions are necessary for activation of those signal transduction cascades. In our studies we investigated a possible association of pp125FAK, an adhesion involved tyrosine kinase, with the integrin beta 1 subunit. Further we wanted to know to which extent protein tyrosine phosphorylation affects cell adhesion to the ECM and the possible beta 1 integrin/pp125FAK complex. We were able to show that in HaCaT cells (a human keratinocyte derived cell line) the integrin beta 1 subunit is associated with tyrosine kinase pp125FAK. This association was observed in ECM-adherent cells and nonadherent cells and is independent of tyrosine phosphorylation. However, cell adhesion of HaCaT cells to specific substrates requires tyrosine phosphorylation since genistein treatment that blocks phosphorylation of many cellular proteins as pp125FAK led to a reduced substrate adhesion.

Carcinoma, Squamous Cell↗
PubMed1992

Biologically modified PHEMA beads for hemoperfusion: preliminary studies.

Polyhydroxyethylmethacrylate (PHEMA) beads were prepared by phase separation polymerization. Hydroxyl groups on PHEMA beads were activated with CNBr at alkaline pH. Adsorption of heparin, blood proteins (i.e. albumin, fibrinogen and gamma-globulin), protein A, HIgG and DNA on these beads were studied. Preparation and activation procedures are given here. The preliminary results of these studies are also reported.

Adsorption↗
PubMedDate not supplied

Melanoma cells growing in aggregates on a non-adhesive poly(HEMA) substrate exhibit polykaryocytosis but do not develop an increased metastatic capability.

B16-F1 melanoma cells were plated onto plastic tissue-culture dishes rendered non-adhesive for cells by coating with 0.12 per cent poly(2-hydroxyethyl methylacrylate), poly(HEMA). These growth conditions caused the normally flat, adherent B16-F1 cells to grow as single cells in suspension. Within 24 hours, the rounded cells formed aggregates and grew at a slower rate than control cells grown at the same density on untreated plastic dishes. Microscopic observations provided evidence that polykaryocytosis was occurring among the aggregates. Following replating onto standard adhesive tissue-culture plastic, 20-30 per cent of the aggregates were observed to contain varying numbers of multinucleated giant cells (polykaryocytes). The study has revealed a previously undescribed propensity of certain B16-F1 cells cultivated as aggregates in suspension to develop into polykaryocytes, most probably as a result of spontaneous tumor cell-tumor cell fusion. The possible relevance of this behavior in vitro to events in tumor progression is discussed. This study, however, does not support the findings of others that the metastatic capability of B16-F1 cells is increased by such non-adherent culture conditions. No increase in metastatic potential was observed for B16-F1 cells, or for a low metastatic clone (F1-7) derived from it, grown for 72 or 96 hours in a spherical configuration compared to control cells grown in a flat, adherent monolayer.

Animals↗
PubMed1991

A new method for selective localization of flavan-3-ols in plant tissues involving glycolmethacrylate embedding and microwave irradiation.

A method for selective staining of flavan-3-ols in plant tissues fixed with glutaraldehyde is given. The use of glycolmethacrylate as embedding medium allows the sulphuric acid-containing staining solution to be heated without destroying the fine structure of the tissue. The distribution of flavan-3-ols and proanthocyanidins in different plant tissues is discussed.

Anthocyanins↗
PubMedDate not supplied

HTR polymer facial implants: a five-year clinical experience.

Forty-three patients at two different international sites underwent onlay facial augmentation of the malar, paranasal, and chin regions using 61 HTR polymer preformed implants. All implants were placed intraorally and rigidly fixed with a titanium screw. Over postoperative periods ranging from two to five years, one implant was removed because of infection. Two other implants in patients with rheumatic and connective tissue disease were removed because of persistent pain and erythema. Another peri-implant infection was treated successfully without removal. One-year postoperative radiographs in patients with chin implants demonstrated no underlying bone resorption. This porous polymeric material appears to offer clinical results comparable to other alloplastic materials for onlay facial skeletal augmentation.

Adolescent↗
PubMed1994

The influence of the incision length on the early postoperative intraocular pressure following cataract surgery.

In a prospective study we recorded the early postoperative intraocular pressure of 60 eyes following phacoemulsification and posterior chamber lens implantation. In 30 patients each the implantation either of a folded polyHema intraocular lens through a 3.5 mm incision or of a polymethylmetacrylate intraocular lens through a 7 mm incision was performed. Healon was used in all eyes and thoroughly evacuated from the capsular bag behind the implanted lens and the anterior chamber. For intraoperative miosis 0.5 ml acetylcholine chloride was injected into the anterior chamber after wound closure. Intraocular pressure was measured preoperatively as well as six hours, 18 hours, one week and two months postoperatively without the influence of antiglaucomatous medication. We found no statistically significant change of intraocular pressure at any measurement time in the 3.5 mm group (Student's t-test, p > 0.1). In the 7 mm group only the rise of intraocular pressure at 18 hours was statistically significant (p < 0.05, student's t-test). The comparison of the changes of intraocular pressure from preoperative values between both groups revealed a statistically significant difference at 18 hours (p < 0.05, student's t-test) but not at any other time recorded. Intraocular pressure exceeding 22 mmHg was found at 6 hours in 4 (13.3%) patients of both groups and at 18 hours in 3 (10%) eyes of the 3.5 mm group and 5 (16%) eyes of the 7 mm group (p > 0.1, Fisher's Exact Test). From these results we conclude that 1) regardless of the wound size the pressure rising effect of Healon is successfully counteracted by the aspiration technique described, and 2) with small-incision cataract surgery statistically significant less changes of intraocular pressure are observed in the early postoperative period.

Acetylcholine↗
PubMedDate not supplied

Changes in adhesive properties of tumor cells do not necessarily influence metastasizing capacity.

BSp6S and BSp73AS are two rat tumors which grow locally after intra-footpad (ifp) application. BSp73ASML and BSp6AS are variants, which metastasize via the lymphatics. Both variants have lost adherence properties, as shown by in vitro culture on plastic surfaces, suggesting that loss of adherence may be accompanied by increased metastasizing capacity. However, after growth of BSp6S and BSp73AS in vitro on poly(2-hydroxyethylmethacrylate) (polyHEMA)-coated plates, which resulted in loss of adherence and spreading, and subsequent intravenous (iv) or ifp injection of non-adherent tumor cells into syngeneic rats, metastasizing capacity was not increased. It is concluded that loss of adherence may facilitate metastatic spread, but certainly is not sufficient for initiation.

Animals↗