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At least 469 records · Page 26Linked to original sources
PubMed2005

Matrix inclusion within synthetic hydrogel guidance channels improves specific supraspinal and local axonal regeneration after complete spinal cord transection.

We have previously shown that a novel synthetic hydrogel channel composed of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (pHEMA-MMA) is biocompatible and supports axonal regeneration after spinal cord injury. Our goal was to improve the number and type of regenerated axons within the spinal cord through the addition of different matrices and growth factors incorporated within the lumen of the channel. After complete spinal cord transection at T8, pHEMA-MMA channels, having an elastic modulus of 263+/-13 kPa were implanted into adult Sprague Dawley rats. The channels were then filled with one of the following matrices: collagen, fibrin, Matrigel, methylcellulose, or smaller pHEMA-MMA tubes placed within a larger pHEMA-MMA channel (called tubes within channels, TWC). We also supplemented selected matrices (collagen and fibrin) with neurotrophic factors, fibroblast growth factor-1 (FGF-1) and neurotrophin-3 (NT-3). After channel implantation, fibrin glue was applied to the cord-channel interface, and a duraplasty was performed with an expanded polytetrafluoroethylene (ePTFE) membrane. Controls included animals that had either complete spinal cord transection and implantation of unfilled pHEMA-MMA channels or complete spinal cord transection. Regeneration was assessed by retrograde axonal tracing with Fluoro-Gold, and immunohistochemistry with NF-200 (for total axon counts) and calcitonin gene related peptide (CGRP, for sensory axon counts) after 8 weeks survival. Fibrin, Matrigel, methylcellulose, collagen with FGF-1, collagen with NT-3, fibrin with FGF-1, and fibrin with NT-3 increased the total axon density within the channel (ANOVA, p<0.05) compared to unfilled channel controls. Only fibrin with FGF-1 decreased the sensory axon density compared to unfilled channel controls (ANOVA, p<0.05). Fibrin promoted the greatest axonal regeneration from reticular neurons, and methylcellulose promoted the greatest regeneration from vestibular and red nucleus neurons. With Matrigel, there was no axonal regeneration from brainstem motor neurons. The addition of FGF-1 increased the axonal regeneration of vestibular neurons, and the addition of NT-3 decreased the total number of axons regenerating from brainstem neurons. The fibrin and TWC showed a consistent improvement in locomotor function at both 7 and 8 weeks. Thus, the present study shows that the presence and type of matrix contained within synthetic hydrogel guidance channels affects the quantity and origin of axons that regenerate after complete spinal cord transection, and can improve functional recovery. Determining the optimum matrices and growth factors for insertion into these guidance channels will improve regeneration of the injured spinal cord.

Animals↗
PubMed2004

Mechanical stability of microkeratome-assisted intracorneal keratoprosthesis implantation.

OBJECTIVE: To develop a laboratory model to study intracorneal keratoprosthesis implantation. METHODS: A combination microkeratome and artificial anterior chamber system was used to create a hinged lamellar keratectomy on 13 human corneas. After reflecting the flap, the posterior stroma was trephined at either 2.5 or 3.0 mm. A model keratoprosthesis was positioned in the bed. The flap was sutured closed. Intrachamber pressure was increased, and wound leak pressure was recorded. The anterior corneal lamella was trephined at either 3.0 or 3.5 mm to expose the keratoprosthesis. Leak pressure was again determined. RESULTS: After keratoprosthesis placement and prior to anterior trephination, all 13 corneas were watertight at maximum attainable intrachamber pressures. With posterior/anterior trephination combinations of 2.5/3.0 mm, 2.5/3.5 mm, or 3.0/3.5 mm, mean +/- SD wound leak pressure occurred at 95 +/- 12 mm Hg, 32 +/- 7 mm Hg, or 59 +/- 12 mm Hg, respectively (P<.01). CONCLUSIONS: With a posterior trephination of 2.5 mm, there is significant keratoprosthesis-cornea interface destabilization between a 3.0- and 3.5-mm anterior trephination. For an anterior trephination of 3.5 mm, interface destabilization improves by increasing the posterior trephination to 3.0 mm. CLINICAL RELEVANCE: An intracorneal keratoprosthesis may be implanted using microkeratome assistance. Our laboratory model provides a useful method for examining a range of posterior and anterior trephination diameters and their effects on the mechanical stability of intracorneal keratoprosthesis placement.

Adult↗
PubMed1995

Dystrophic calcification of an implanted hydroxyethylmethacrylate intraocular lens.

Hydroxyethylmethacrylate is a biomaterial still under clinical trial for use in foldable intraocular lenses. We observed a patient in whom a geographic opacification developed within an implanted hydroxyethylmethacrylate lens, together with granular deposits on the posterior lens capsule and in the scar of a paracentesis. The intraocular lens and posterior lens capsule were removed because of impaired visual acuity. Light and scanning electron microscopy disclosed nodular calcifications within the intraocular lens and granular, partially crystalline, calcifications on the posterior lens capsule. Energy-dispersive x-ray analysis and x-ray diffraction showed the deposits in the intraocular lens to consist of calcium hydroxyapatite. We presume this mineralization to be dystrophic, with calcium derived from lens remnants and phosphorus possibly derived from a thymoxamine solution used briefly during the cataract operation. Our observation suggests caution in the use of phosphated solutions together with hydroxyethylmethacrylate intraocular lenses and may warrant reconsideration of the suitability of hydroxyethylmethacrylate intraocular lenses, should additional similar cases be reported.

Aged↗
PubMed1999

Constitutive and conditional cadherin expression in cultured human ovarian surface epithelium: influence of family history of ovarian cancer.

Epithelial ovarian carcinomas arise in a simple mesothelium (ovarian surface epithelium, OSE) but exhibit properties of oviductal and endometrial epithelia. Thus, during malignant progression, their differentiation proceeds from simple to complex, in contrast to carcinomas in other tissues. Related changes in OSE of women with a history of familial ovarian cancer indicate that this aberrant differentiation is initiated very early in neoplastic progression. The mechanisms underlying this process are not understood. Because cadherins are known regulators of differentiation, we investigated the relationship of the cadherins E, N and P to OSE morphology, growth patterns and differentiation in cultures of normal and metaplastic OSE from women with (FH-OSE) and without (NFH-OSE) a family history of ovarian cancer and in the ovarian carcinoma lines OVCAR-3 and CaOV3. We used immunofluorescence, RT-PCR, in situ hybridization and Western blotting. Our results define N-cadherin as the constitutively expressed cadherin of normal and metaplastic OSE and indicate that P-cadherin is undetectable while E-cadherin expression is conditional and related to genotype, stage of neoplastic progression and growth pattern. The altered expression of E-cadherin in apparently normal OSE of women with hereditary ovarian cancer syndromes in conjunction with the known capacity of E-cadherin to induce epithelial characteristics implicates this adhesion molecule as a possible inducer of the aberrant Mullerian differentiation which characterizes epithelial ovarian carcinomas. Abnormal differentiation in such (pre)-neoplastic tissues may represent an early, irreversible, non-mutational step in ovarian epithelial neoplastic progression.

Adult↗
PubMed1996

Effect of fibronectin amount and conformation on the strength of endothelial cell adhesion to HEMA/EMA copolymers.

The effect of substrate surface hydrophobicity on fibronectin (Fn) adsorption and endothelial cell adhesion strength was studied. Bovine aortic endothelial cells (BAEC) were plated for 2 h with and without preadsorbed Fn on slides coated with homopolymers and copolymers of hydrophilic polyhydroxyethylmethacrylate (polyHEMA) and hydrophobic polyethylmethacrylate (polyEMA). The polarity of the substrate was determined by Wilhelmy plate contact angle. The amount of adsorbed Fn was determined using 125I-labeled Fn. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to detect gross conformational changes of adsorbed Fn on polyHEMA or polyEMA. BAEC were cultured in serum-free medium for 2 h and subjected to a brief exposure of laminar flow in a variable-height flow chamber that provided a range of shear stresses of 15-185 dynes/cm2. The critical shear stress to detach 50% of the cells increased with increasing EMA content to a maximum at 20% HEMA/80% EMA copolymer irrespective of the presence of preadsorbed Fn. However, the critical force increased even though there were similar amounts of Fn adsorbed on all substrates. ATR-FTIR spectroscopy showed only minor changes in beta-sheet structure of Fn adsorbed to polyHEMA and polyEMA. These results show that the force to detach cells did not increase solely with increasing amounts of adsorbed Fn; rather, these results indicate a more complex interplay involving both the amount and conformation of adsorbed Fn.

Animals↗
PubMed1998

Insulin-like growth factor-I-mediated survival from anoikis: role of cell aggregation and focal adhesion kinase.

Anoikis is a form of cell death that occurs when cells are denied attachment to the extra-cellular matrix. Using p6 cells, that are 3T3 cells overexpressing the type 1 insulin-like growth factor receptor (IGF-IR), we show that these cells undergo apoptosis when seeded on polyHEMA plates in serum-free medium (SFM). IGF-I protects p6 cells from anoikis, without inducing mitogenesis or DNA synthesis. In the surviving p6 cells in suspension cultures, the focal adhesion kinase (FAK) is tyrosyl phosphorylated by IGF-I, although this phosphorylation occurs only after several hours. The importance of FAK in protection from anoikis is confirmed by v-src-transformed R-cells, in which FAK is constitutively phosphorylated, that survive even in SFM. Surviving cells, whether p6 or v-src transformed, tend to form large cell aggregates, whose appearance precedes the phosphorylation of FAK. These and other findings suggest that FAK phosphorylation in the case of IGF-I is a mediated effect rather than a direct one. When p6 cells are plated on polyHEMA dishes, IGF-I induces cell aggregation and this aggregation correlates with survival and the eventual phosphorylation of FAK.

3T3 Cells↗
PubMed2001

Biocompatibility of NDGA-polymerized collagen fibers. II. Attachment, proliferation, and migration of tendon fibroblasts in vitro.

The material properties of collagen fibers polymerized with nordihydroguaiaretic acid (NDGA) are equivalent to native tendon, suggesting that NDGA crosslinking may provide a viable approach to stabilizing collagenous materials for use in repairing ruptured, lacerated, or surgically transected fibrous tissues, such as tendons and ligaments (Koob & Hernandez, Biomaterials, in press). The present study evaluated the biocompatibility of these fibers with cultured bovine tendon fibroblasts. Fibroblast attachment, migration, and proliferation on NDGA-crosslinked materials were compared to those on prepolymerized type I tendon collagen constructs as well as on tissue-culture-treated plastic. Fibroblast attachment on NDGA-crosslinked collagen fibrils was equivalent to attachment on plates coated with collagen alone. Over a period of 8 days in culture, attached fibroblasts proliferated on NDGA-crosslinked collagen at a rate identical to that of fibroblasts attached to native collagen. In order for the biomaterial effectively to bridge gaps in fibrous tissues, fibroblasts must be able to migrate and replicate on the bridging fiber. Control and crosslinked fibers were inserted in calf tendon explants, with a portion of the fiber extending out of the sectioned end of the tendon. Explants were cultured for 9 weeks, and the number of cells was measured at weekly intervals. Cells appeared on the fibers after 1 week of culture. By 2 weeks, cells had colonized the entire fiber. The number of cells continued to increase throughout the 9 weeks in culture, forming a layer several cells thick. Histologic analysis indicated that the fibroblasts populating the fibers appeared to originate in the epitenon. There was no difference in the rate of fibroblast migration and replication, nor in the ultimate number of colonizing cells, between control collagen fibers and NDGA-crosslinked fibers. NDGA-crosslinked fibers may provide a means of bridging gaps in ruptured, lacerated, or surgically transected tendons by providing a mechanically competent scaffold on which tendon fibroblasts can migrate, attach, and proliferate.

Animals↗
PubMed2001

Overexpression of lysosomal-type sialidase leads to suppression of metastasis associated with reversion of malignant phenotype in murine B16 melanoma cells.

Increased sialylation in cell surface glycoproteins is one characteristic feature of cancer cells, particularly related to their metastatic potential and invasiveness. Expression of lysosomal-type sialidase, which plays a major role in hydrolysis of such sialo-glycoproteins, is therefore considered to have a great influence on malignant properties of cancer cells. To investigate whether the sialidase expression level is linked to the malignant phenotype, we transfected B16-BL6 murine melanoma cells, a highly invasive and metastatic line, with an expression vector harboring a rat lysosomal sialidase cDNA; then clones were isolated and examined for changes in biological character. Sialidase-overexpressing cells showed suppression of experimental pulmonary metastasis and tumor progression. The transfectants exhibited diminished cell growth, anchorage-independent growth and increased sensitivity to apoptosis induced by suspension culture or serum depletion in vitro, but no significant alterations in invasiveness, cell motility and cell attachment to fibronectin, collagen IV and laminin. Flow cytometric analysis with either peanut agglutinin (PNA) or Ricinus communis agglutinin (RCA) lectin revealed that desialylated forms of glycoproteins on the cell surfaces were increased. In particular, a desialylated form of a cell surface glycoprotein of 83 kDa was prominent in the transfectants, as determined by galactose oxidase labeling. These observations indicate that sialidase expression is inversely associated with metastatic potential and tumor growth in cancer cells, probably through a regulation mechanism that suppresses cell growth and anchorage-independent growth and promotes apoptosis with deprivation of cell anchorage.

Animals↗
PubMed1982

Growth control and cell spreading: differential response in preneoplastic and in metastatic cell variants.

Growth control and sensitivity to changes in cell shape were studied in anchorage-dependent mouse fibroblasts (diploid fibroblasts, 3T3 and 3T6), in DNa tumor-virus-transformed mouse fibroblasts (SVPy 3T3), in four B16 melanoma and five uv-2237 fibrosarcoma cell variants that exhibit distinct metastatic properties. Differential adhesive conditions were established by precoating the plastic plates with poly (2-hydroxyethylmethacrylate) that allowed an accurate and reproducible control of cell shape, from flat to spherical. Mouse fibroblasts that form a continuum between rigorously controlled cells to fully anchorage-independent cells, display a direct correlation between degree of growth control and sensitivity to changes in cell spreading. In contrast, there is no apparent direct correlation between sensitivity of growth control to changes in cellular configuration and the metastatic potential of tumor cells.

Animals↗
PubMed1981

Poly(methyl acrylate-co-hydroxyethyl acrylate) hydrogel implant material of strength and softness.

The physiochemical properties of a hydrogel used as a scleral buckling implant for retinal detachment surgery are described. The new material was prepared by simultaneous polymerization and crosslinking of 2-hydroxyethyl acrylate with methyl acrylate and ethylene diacrylate, in the presence of an inert diluent, ethylene glycol. At equilibrium swelling, the hydrogen absorbed 17% water and had a durometer hardness (DH) of 15 (Shore Durometer A-2). A unique property of this material was its swelling hysteresis; when the gel swollen in 70% ethanol was placed in water, it retained a high level of hydration (75% water) and softness (DH 8), and most of its elasticity and strength as well. Then the swelling decreased very slowly so that the implant reached its ultimate size at equilibrium swelling in ca. 1 year. This property is especially useful in the scleral buckling procedure, in which a soft implant indents the sclera over the detached retina until reattachment is achieved. In addition to this advantage, this hydrogel is more elastic and stronger than available hydrogels of similar softness.

Biocompatible Materials↗
PubMed1985

Surface energies and the bone induction principle.

The macroscopic and histologic sequence of events in the induction of ectopic bone formation by porous demineralized bone and by synthetic porous sponges of poly-hydroxyethylmethacrylate (poly-HEMA) is described and reviewed. The observed relationship between the yield of new bone generated, and in vitro calcification, with the zeta potential, seems to parallel the connection between general adhesion in biologic systems and the critical surface tension. Consistent with experimental findings over the years, the bone induction principle (BIP) is probably associated with porous, mechanically suitable, hydrophilic materials with a high polar surface energy. It can be inferred that such surfaces are exposed when bone is suitably demineralized and treated, as has been reported. The discovery of noncollagenous proteins that are important to the BIP may be viewed in this light. Local heterogeneities on cellular surfaces are known to be important but are not detected by macroscopic techniques. It is suggested, following Lerchental, that induced stresses in the cell membranes cause a redistribution of surface charges that increases the local surface energy. This may lead therefore to an agglomeration and alignment of cells, as a response to the stress, accompanied by differentiation, as well.

Animals↗
PubMedDate not supplied

The kinetics of baboon fibrinogen adsorption to polymers: in vitro and in vivo studies.

Fibrinogen adsorption on polymers from blood may mediate or potentiate thrombosis because of its involvement in both the intrinsic clotting system and the formation of platelet aggregates. While the kinetics of fibrinogen adsorption from plasma in vitro have previously been found to be very different on polar and nonpolar surfaces [T. A Horbett, "The kinetics of adsorption of plasma proteins to a series of hydrophilic-hydrophobic copolymers," ACS Org. Coat. Plas. Chem. 40, 642-646 (1979)] the significance of this difference with respect to thrombogenesis in vivo has not been clarified. In this study, the kinetics of deposition of baboon 125I fibrinogen from plasma in vitro or from blood in vivo on a series of polymers was measured. The polymers chosen for this study had previously been found to have a large range in surface polarity and reactivity in the in vivo baboon shunt model. The kinetics of fibrinogen adsorption in vitro were observed to be of three types, depending on the polymer: high initial adsorption decreasing to a lower steady state value; constant throughout the time course; low initial adsorption rising steadily to a plateau value. In vivo, fibrinogen deposition kinetics were of two types: low, constant deposition throughout the time course, independent of heparinization; low deposition initially followed by a second phase of greatly increased deposition (probably as fibrin) which was prevented or greatly decreased by heparinizing the animals. Polymers for which fibrinogen adsorption increased to a plateau in vitro were found to have a heparin inhibitable second phase of enhanced in vivo fibrinogen deposition. These polymers also have been found in previous studies to enhance the rate of platelet destruction when used as in vivo shunts on baboons. Conversely, most polymers with high initial in vitro fibrinogen adsorption followed by a decrease had low fibrinogen deposition behavior in vivo and were also minimally destructive of platelets. The adsorption kinetics of fibrinogen to polymers from blood in vivo and in vitro and the consumption of platelets in vivo induced by the polymers all vary with polymer polarity. More polar polymers had in vitro fibrinogen kinetics characterized by a rise to a plateau, in vivo fibrinogen deposition characterized by a second stage of great increase inhibitable by heparin, and enhanced platelet consumption. The correlation of three separate indicators of surface thrombogenicity with surface polarity suggests that more polar materials may be more thrombogenic because of an influence on the way in which fibrinogen interacts with these surfaces.

Adsorption↗
PubMed1990

Hard tissue replacement (HTR) polymer as an implant material.

This study aimed to evaluate the effectiveness of a synthetic implant material Hard Tissue Replacement polymer (HTR) for: (1) compatibility with bone and soft tissues, (2) capacity to physically attach to bone and soft tissues, and (3) capacity for bone induction and metaplasia. HTR was implanted for a 3-week test period in femur bones, connective tissue, and skeletal muscle of 15 Sprague-Dawley descent rats for histological examination and implanted in bone in 6 rats for infrared absorption analyses to determine the presence of new bone. Compatibility (defined as absence of significant inflammation) was present in 13/14 (93%) bone sites, 7/9 (78%) connective tissue, and 4/4 (100%) muscle sites. Physical attachment of HTR occurred in 10/14 (71%) bone sites, 4/9 (44%) connective tissue, and 1/7 (14%) muscle sites. Density of new bone appeared to be greater with HTR than in controls. However, no metaplastic bone was formed in nonbony sites indicating that this material is nonosteogenic. These preliminary findings demonstrated the effectiveness of HTR as an implant material.

Animals↗