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PubMed1986

Fluorinated oils as experimental vitreous substitutes.

Two kinds of fluorinated oils (a fluorosilicone oil and a perfluoroether [Freon E15]) that have a higher density than water were evaluated as long-term vitreous substitutes. Vitreous compression using perfluoropropane gas was performed to create a space for the vitreous substitute in rabbit eyes. Two fluorosilicone oils (1000 and 10 000 centistokes) induced edema of the inner retinal layers and occasionally of the outer retinal layers regardless of viscosity or period of observation up to six months, but they were well tolerated clinically. Control eyes injected with silicone oils of comparable viscosities showed similar histopathologic findings. Freon E15 induced formation of bubbles and precipitates by one month after injection, and retinal disorganization, formation of preretinal membranes, and tractional retinal detachment by six months. Thus, Freon E15 proved to be unsuitable, but fluorosilicone oil is a possible high-density vitreous substitute.

Animals↗
PubMed1986

The effect of liquid silicone on the rabbit retina. Histologic and ultrastructural study.

Silicone oil was injected into 23 rabbit eyes, which had undergone vitrectomy and which were then examined in the electron microscope six weeks later. Retinal lesions were observed in the outer plexiform layer. They consisted mainly of a subtotal disappearance of the processes of horizontal and bipolar cells and of the synaptic terminals of the photoreceptors. The lesions were seen only in areas of the retina that had been in permanent contact with the oil bubble. They did not depend on the purity of the silicone oil injected.

Animals↗
PubMed1986

The effect of intraocular silicone oil on anterior chamber oxygen pressure in cats.

Intraocular silicone oil has been observed to lessen the incidence of neovascular glaucoma in patients with a high risk of anterior segment neovascularization. In order to test the hypothesis that the presence of silicone oil in the vitreous cavity acts as a diffusion/convection barrier to oxygen and prevents the decrease in anterior chamber oxygen tension that occurs after lensectomy and vitrectomy, we measured anterior chamber oxygen pressure in six cats that had undergone lensectomy-vitrectomy in one eye and lensectomy-vitrectomy with silicone oil placement in the other eye ten to 21 days previously. The anterior chamber oxygen tension was 17.8 +/- 6.9 mm Hg (mean +/- SD) in the eyes that had undergone lensectomy-vitrectomy and 34.8 +/- 3.5 mm Hg in the silicone oil-treated eyes (P less than .001). Silicone oil does appear to act as a diffusion/convection barrier to oxygen and may alter the stimulus for anterior segment neovascularization.

Animals↗
PubMed2000

Internal support of tissue-engineered cartilage.

BACKGROUND: Auricles previously created by tissue engineering in nude mice used a biodegradable internal scaffold to maintain the desired shape of an ear. However, the biodegradable scaffold incited a compromising inflammatory response in subsequent experiments in immunocompetent animals. OBJECTIVE: To test the hypothesis that tissue-engineered autologous cartilage can be bioincorporated with a nonreactive, permanent endoskeletal scaffold. MATERIALS AND METHODS: Auricular elastic cartilage was harvested from Yorkshire swine. The chondrocytes were isolated and suspended into a hydrogel (Pluronic F-127) at a cell concentration of 5 x 10(7) cells/mL. Nonbiodegradable endoskeletal scaffolds were formed with 1 of 5 polymers: (1) high-density polyethylene, (2) soft acrylic, (3) polymethylmethacrylate, (4) extrapurified Silastic, and (5) conventional Silastic. Three groups were studied: (1) a control group using only the 5 polymers, (2) the 5 polymers enveloped by Pluronic F-127 only, and (3) the implants coated with Pluronic F-127 seeded with chondrocytes. All constructs were implanted subdermally; implants containing cells were implanted into the same animal from which the cells had been islolated. The implants were harvested after 8 weeks of in vivo culture and histologically analyzed. RESULTS: Only implants coated by hydrogel plus cells generated healthy new cartilage. With 3 polymers (high-density polyethylene, acrylic, and extrapurified Silastic), the coverage was nearly complete by elastic cartilage, with minimal fibrocartilage and minimal to no inflammatory reaction. The Food and Drug Administration-approved conventional Silastic implants resulted in fragments of fibrous tissue mixed with elastic cartilage plus evidence of chronic inflammation. The polymethylmethacrylate implant was intermediate in the amount of cartilage formed and degree of inflammation. CONCLUSIONS: This pilot technique combining tissue-engineered autologous elastic cartilage with a permanent biocompatible endoskeleton demonstrated success in limiting the inflammatory response to the scaffold, especially to high-density polyethylene, acrylic, and extrapurified Silastic. This model facilitates the potential to generate tissue of intricate shape, such as the human ear, by internal support. Arch Otolaryngol Head Neck Surg. 2000;126:1448-1452

Animals↗
PubMed2004

Abdominal wall closure with a silastic patch after repair of congenital diaphragmatic hernia.

HYPOTHESIS: Newborns with congenital diaphragmatic hernia (CDH) have a high risk of mortality, ranging from 50% to 70%. Tensioned closure of the narrowed abdominal cavity is detrimental. PATIENTS AND METHODS: Twelve high-risk newborns underwent operation for CDH. To achieve tension-free closure of the abdominal wall, a Silastic patch was used. The Silastic patch was sutured intermittently to the edges of the abdominal wall fascia with absorbable sutures and left open to the air. The skin was not closed above the Silastic patch, which was lubricated with 1% gentamicin sulfate ointment. RESULTS: Eleven patients (91.6%) survived. No local or systemic septic complication occurred. The abdominal wall was gradually closed, and total closure was achieved within 4 to 6 weeks (mean, 4.9 weeks). CONCLUSION: Because of the high survival rate and the complication-free rapid healing of the abdominal wall, the technique can be used in any case of CHD in which tension-free closure of the abdominal wall cannot be achieved by other methods.

Abdominal Muscles↗
PubMed1996

Fabrication and selective surface modification of 3-dimensionally textured biomedical polymers from etched silicon substrates.

A new method is described for producing biomedically relevant polymers with precisely defined micron scale surface texture in the x, y, and z planes. Patterned Si templates were fabricated using photolithography to create a relief pattern in photoresist with lateral dimensions as small as 1 micron. Electroless Ni was selectively deposited in the trenches of the patterned substrate. The Ni served as a resilient mask for transferring the patterns onto the Si substrate to depths of up to 8.5 microns by anisotropic reactive ion etching with a fluorine-based plasma. The 3-dimensional (3-D) textured silicon substrates were used as robust, reusable molds for pattern transfer onto poly (dimethyl siloxane), low density poly (ethylene), poly (L-lactide), and poly (glycolide) by either casting or injection molding. The fidelity of the pattern transfer from the silicon substrates to the polymers was 90 to 95% in all three planes for all polymers for more than 60 transfers from a single wafer, as determined by scanning electron microscopy and atomic force microscopy. Further, the 3-D textured polymers were selectively modified to coat proteins either in the trenches or on the mesas by capillary modification or selective coating techniques. These selectively patterned 3-D polymer substrates may be useful for a variety of biomaterial applications.

Biocompatible Materials↗
PubMed1997

Theoretical analysis of hydrolysis of polydimethylsiloxane (PDMS).

Silicones (polydimethylsiloxane, PDMS) are the materials currently used in most breast implants. ICP and FTIR analysis of the tissue capsule around aged breast implants and in vitro models show that Si-containing material is leaking from the PDMS implants. In this study, the hydrolysis of PDMS has been theoretically modeled using a semiempirical quantum mechanical method called AM1. The activation barrier for removing a methanol monomer was found to be +82 Kcal/mol while the removal of a methane monomer was +41 Kcal/mol. Using the same AM1 method, hydrolysis of the identical to Si-O-Si identical to bond also has been modeled for pentasilicic acid and, in this study, for 1,1,3,3,-fetramethyldisiloxane-1,3-diol. The barrier to the removal of a silicon-containing tetrahedron for both studies was found to be +27 Kcal/mol. This is approximately one and a half times smaller than the energy of that needed to remove a methyl group. The pentacoordinated silicon-activated transition state for hydrolysis of PDMS may provide an energetically favorable pathway for development of a surface that will enhance chemisorption of charged protein molecules, and such a pathway may show up in NMR studies of the hydrolysis of PDMS.

Breast Implants↗
PubMed1999

Improved wettability of an experimental silicone rubber denture soft lining material.

The purpose of this study was to improve the wettability of an experimental silicone rubber soft lining material (Sildent) to increase patient comfort. Sildent was modified by the addition of polyalkylene oxide poly(dimethylsiloxane) surfactants. The various surfactants were added directly to the polymeric matrix in the quantities 5, 10, 20% w/w. The surfactants were also added to a one part silicone sealant, which was then painted onto the surface of already cured Sildent. Contact angle measurements were made on samples using a dynamic contact angle analyzer. Results showed that incorporation of surfactants A (Silwet L7600) and B (Silwet L7607) effectively improved the wettability of Sildent. This improvement was still evident after 6 months storage in distilled water at 37 degrees C suggesting retention of the surfactants matrix via physio-chemical bonding. Formulations with surfactants added directly to the matrix showed unacceptable water absorption after 2 months in distilled water. Samples with surfactant charged sealant painted on the surface showed a lower water absorption. In conclusion, Sildent formulations modified with polyalkylene silicone surfactants showed improved wettability compared to unmodified Sildent. Further work is needed to reduce water uptake and determine the effect on key mechanical properties.

Catalysis↗
PubMed1999

Flow cytometric study of in vitro neutrophil activation by biomaterials.

Neutrophil activation for adherent and nonadherent cells, as measured by flow cytometry, was not strongly dependent on material surface chemistry. We had hypothesized that material-induced neutrophil activation was an important parameter associated with material failure. All materials tested [cellophane, an acrylonitrile copolymer (AN69), Pellethane, nylon, polyethylene terephthalate, low density polyethylene, and polydimethylsiloxane] activated isolated human neutrophils, which were resuspended in plasma or serum, to similar extents based on L-selectin shedding, CD11b upregulation, and stimulation of the oxidative burst after 30-min exposure. Inhibition of complement activation by sCR1 unexpectedly had little effect if any on nonadherent neutrophils. However, neutrophil adhesion, but not the level of activation of the adherent cells, was strongly dependent on complement activation. Pretreatment with albumin did not inhibit adhesion or reduce neutrophil activation, but plasma pretreatment resulted in increased activation for nonadherent and adherent cells. More adhesion and a higher level of activation of adherent cells was observed following pretreatment with fibrinogen, a ligand of CD11b. Taken together these results suggest that upon contact with a material, neutrophil activation may occur though mechanisms that are not mediated by complement. For example, the presence of plasma proteins such as fibrinogen at the interface may trigger activation and the release of other activating agents. Although the material differences are small, the extent of activation may be significant and warrant further study of the mechanism and consequences of that activation.

Acrylic Resins↗
PubMed1999

Fibrinogen adsorbs from aqueous media to microscopic droplets of poly(dimethylsiloxane) and remains coagulable.

Fibrinogen binds from aqueous media containing it to droplets of linear trimethylsilyl-terminated poly(dimethylsiloxane) (PDMS) dispersed in those same media. Once bound, fibrinogen elutes from emulsified droplets of PDMS only very slowly, even when incubated in buffer that contains a physiologic concentration of the protein. The bound fibrinogen is coagulable, as indicated by the thrombin-dependent agglutination of droplets. Thus fibrinogen bound to droplets of PDMS renders an adhesive potential to the surface of the droplets, a potential that may have relevance to the biologic processing of the polymer in vivo.

Adhesiveness↗
PubMedDate not supplied

Comparative studies on the interaction of proteins with a polydimethylsiloxane elastomer. I. Monolayer protein capture capacity (PCC) as a function of protein pl, buffer pH and buffer ionic strength.

Polydimethylsiloxane (PEP) is widely used in medical prostheses and therefore is in contact with plasma and secretory proteins. Two pair of globular proteins, lactoferrin (Lf) and transferrin (Trf), and bovine IgG1 and IgG2a, which differ substantially between pair members in their pl, were used to study the interaction of a PEP widely used in breast implants and soluble protein. Studies were done using iodinated proteins over a concentration range that resulted in an apparent protein monolayer. Secondary incubations with dilute protein solutions were needed to form the monolayer on PEP, possibly as a consequence of micro air bubbles trapped on its highly textured surface as shown by atomic force microscopy. Immunoassay quality polystyrene microtiter wells were used as controls. Adsorption studies were routinely performed at pH 4, 7 and 10 and at ionic strengths corresponding to 0.95, 9.5 and 90.0 mS. The protein capture capacity (PCC) of PEP for Lf and Trf was optimal at physiological pH and ionic strength and comparable under these conditions to that of Immulon 2 (Imm 2) microtiter wells. While increasing the ionic strength and pH further increases the PCC of Imm 2 for Lf and Trf, this markedly lowered the PCC of PEP for these proteins suggesting that initial polar interactions may precede subsequent hydrophobic bonding to PEP. This was tested using a hydrophilic variant of PEP, which when tested in a 90.0 mS buffer, showed a > five-fold lower PCC at neutral and alkaline pH. The greatly reduced PCC of the hydrophilic variant might also suggest that hydrophilic variants of silicone would be more biocompatible than those currently used. The PCC of PEP for the IgGs was less than that of Imm 2 but still optimal at physiological conditions. Consistent with the data on Lf/Trf, PCC progressively decreased with increasing ionic strength at alkaline pH. Differences in pl between the protein pairs had only a marginal effect on the PCC of PEP. Monolayer adsorption on both PEP and Imm 2 was slowly reversible and greater in the presence of free ligand (< 2% in 16 h) suggesting that the process follows Mass Law principles. However, even in the presence of non-ionic detergent and free ligand, 85-90% remained bound on either surface. Thus, desorption of proteins in the monolayer should not complicate subsequent immunochemical studies conducted on adsorbed monolayers.

Adsorption↗
PubMedDate not supplied

Comparative studies on the interaction of proteins with a polydimethylsiloxane elastomer. II. The comparative antigenicity of primary and secondarily adsorbed IgG1 and IgG2a and their non-adsorbed counterparts.

The antigenicity of bovine IgG1 and IgG2a adsorbed on a polydimethysiloxane (PEP) elastomer, on a widely used polystyrene (Imm 2, Dynatech) or immobilized as biotinylated proteins to streptavidin covalently bound to polystyrene (SA-PS) was compared using various monoclonal (mAbs) and polyclonal antibodies (pAb) to bovine IgG. The IgGs were either adsorbed as native proteins or pre-denatured with 6M Guanidine-HCl (Gu-HCl) or 6 M Gu-HCl/0.1% 2-mercaptoethanol. In special situations, bovine and human IgG was immobilized by secondary adsorption to an albumin monolayer adsorbed on either PEP or Imm 2. Results indicate that pre-denaturation of IgGs with 6 M Gu-HCl/2-mercaptoethanol destroys all antigenicity whereas those IgGs pretreated with 6 M-GuHCl are indistinguishable in their antigenicity from the IgGs adsorbed to either PEP or Imm 2 without such treatment. When immobilized on SA-PS, Gu-HCl-treated IgGs were significantly less detectable, especially when tested using mAbs. In general, IgGs adsorbed on PEP or Imm 2 were less antigenic than when immobilized on SA-PS. However, two monoclonals specific for the IgG2a(A2) allotypic variant, favored the adsorbed protein and one polyclonal best recognized the IgG2a(A1) variant adsorbed on Imm 2 rather than when adsorbed on PEP or immobilized on SA-PS. Both IgG1 and IgG2a, bound by apparent protein-protein interactions to an albumin monolayer, were significantly more detectable than when directly adsorbed on either Imm 2 or PEP. Using 125I-antibody or its Fab fragment to reduce steric hindrance in detection, we observed the same differences in detectability as when measured by enzyme-linked immunosorbent assay. Failure to identify a steric hindrance effect and the preference of some antibodies for adsorbed allotypic variants, support the concept of adsorption-induced conformational change (AICC). We conclude that proteins adsorbed as a monolayer on the PEP elastomer used to form the envelope of silicone breast implants are conformationally altered, but not necessarily to the same extent or the same manner as when adsorbed on polystyrene. The significantly great antigenicity of secondarily adsorbed IgG suggests that it may be present in near native conformation.

Adsorption↗
PubMed2000

Limits of detection of polydimethylsiloxane in (29)Si NMR spectroscopy.

Limits of detection for neat poly(dimethylsiloxane) (PDMS), as detected via (29)Si NMR spectroscopy, were determined by the IUPAC, graphical, and propagation of errors methods from calibration curves obtained using a 7.05 Tesla superconducting magnet equipped with a magic angle spinning (MAS) NMR probe. Under conditions permitting full relaxation of the nuclear spins (recycle time >150 sec), the limit of detection with 128 transients was 1.7, 2.2, and 3.7 mg PDMS (23, 30, and 50 micromoles elemental Si) for the IUPAC, graphical, and propagation of errors methods, respectively. A higher limit of detection results when additional sources of uncertainty are considered. From the strict dependence of the limit of detection on the inverse of the square root of the number of transients signal-averaged, it is possible to extrapolate to a limit of detection of 183 microg PDMS (2.47 micromoles elemental Si) for a 24-hr signal averaging period. This limit of detection is 3 orders of magnitude higher than silicon levels found in human blood.

Biocompatible Materials↗
PubMed2000

Electrokinetic control of fluid flow in native poly(dimethylsiloxane) capillary electrophoresis devices.

Capillary zone electrophoresis (CZE) devices fabricated in poly(dimethylsiloxane) (PDMS) require continuous voltage control of all intersecting channels in the fluidic network in order to avoid catastrophic leakage at the intersections. This contrasts with the behavior of similar flow channel designs fabricated in glass substrates. When the injection plugs are shaped by voltage control and leakage from side channels is controlled by the application of pushback voltages during separation, fluorescein samples give 64 200 theoretical plates (7000 V separation voltage, E = 1340 V/cm). Native PDMS devices exhibit stable retention times (+/- 8.6% RSD) over a period of five days when filled with water. Contact angles were unchanged (+/- 1.9% RSD) over a period of 16 weeks of dry storage, in contrast to the known behavior of plasma-oxidized PDMS surfaces. Electroosmotic flow (EOF) was observed in the direction of the cathode for the buffer systems studied (phosphate, pH 3-10.5), in the presence or absence of hydrophobic ions such as tetrabutylammonium or dodecyl sulfate. Electroosmotic mobilities of 1.49 x 10(-5) and 5.84 x 10(-4) cm2/Vs were observed on average at pH 3 and 10.5, respectively, the variation strongly suggesting that silica fillers in the polymer dominate the zeta potential of the material. Hydrophobic compounds such as dodecyl sulfate and BODIPY 493/503 adsorbed strongly to the PDMS, indicating the hydrophobicity of the channel walls is clearly problematic for CZE analysis of hydrophobic analytes. A method to stack multiple channel layers in PDMS is also described.

Animals↗
PubMed2000

Fabrication of microfluidic systems in poly(dimethylsiloxane).

Microfluidic devices are finding increasing application as analytical systems, biomedical devices, tools for chemistry and biochemistry, and systems for fundamental research. Conventional methods of fabricating microfluidic devices have centered on etching in glass and silicon. Fabrication of microfluidic devices in poly(dimethylsiloxane) (PDMS) by soft lithography provides faster, less expensive routes than these conventional methods to devices that handle aqueous solutions. These soft-lithographic methods are based on rapid prototyping and replica molding and are more accessible to chemists and biologists working under benchtop conditions than are the microelectronics-derived methods because, in soft lithography, devices do not need to be fabricated in a cleanroom. This paper describes devices fabricated in PDMS for separations, patterning of biological and nonbiological material, and components for integrated systems.

Animals↗