Effect of surface tension on alveolar surface area.
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At fixed lung volume (VL), alterations in surface tension change alveolar surface area (S) and lung recoil (PL). Wilson (26), using data from fixed lungs (1, 9), quantified the isovolume change in S with PL. We reexamined this question in fresh excised rabbit lungs, with two important differences. First, we measured fractional changes in S by using diffuse light scattering, avoiding the potential upset of the balance of tissue and surface forces during fixation. Second, we altered surface tension by ventilating the lungs with nebulized polydimethylsiloxane, with much less residual fluid compared with lavage. We found that S decreased at low and mid VL (treatment surface tension > control) by about half of Wilson's estimates and was nearly unaffected by treatment at high VL. This suggests that with increased surface tension there is 1) greater septal retraction in lungs fixed by vascular perfusion compared with unfixed lungs and 2) a greater increase in PL and less loss of S than would have been predicted. (+info)
Gradients of substrate-bound laminin orient axonal specification of neurons.
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Little is known about the influence of substrate-bound gradients on neuronal development, since it has been difficult to fabricate gradients over the distances typically required for biological studies (a few hundred micrometers). This article demonstrates a generally applicable technique for the fabrication of substrate-bound gradients of proteins with complex shapes, using laminar flows in microchannels. Gradients that range from pure laminin to pure BSA were formed in solution by using a network of microchannels, and these proteins were allowed to adsorb onto a homogeneous layer of poly-l-lysine. Rat hippocampal neurons were cultivated on these substrate-bound gradients. Analysis of optical images of these neurons showed that axon specification is oriented in the direction of increasing surface density of laminin. Linear gradients in laminin adsorbed from a gradient in solution having a slope of nabla [laminin] > about 0.06 microg (ml.microm)(-1) (defined by dividing the change of concentration of laminin in solution over the distance of the gradient) orient axon specification, whereas those with nabla [laminin] < about 0.06 microg (ml.microm)(-1) have no effect. (+info)
Microfluidic large-scale integration.
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We developed high-density microfluidic chips that contain plumbing networks with thousands of micromechanical valves and hundreds of individually addressable chambers. These fluidic devices are analogous to electronic integrated circuits fabricated using large-scale integration. A key component of these networks is the fluidic multiplexor, which is a combinatorial array of binary valve patterns that exponentially increases the processing power of a network by allowing complex fluid manipulations with a minimal number of inputs. We used these integrated microfluidic networks to construct the microfluidic analog of a comparator array and a microfluidic memory storage device whose behavior resembles random-access memory. (+info)
Serum as a factor influencing adhesion of Enterococcus faecalis to glass and silicone.
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The purpose of this work was to analyze the effect of serum on the physicochemical surface properties and adhesion to glass and silicone of Enterococcus faecalis ATCC 29212 at 37 degrees C. As is presented using thermodynamics analysis, serum minimizes the interaction of cells with water, which correlates well with the increase in hydrophobicity and in bacterial adhesion to glass and silicone. (+info)
Can interposition of a silicone implant after sapheno-femoral ligation prevent recurrent varicose veins?
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OBJECTIVES: To investigate whether a silicone implant at the sapheno-femoral ligation site could prevent recurrent varicosities. MATERIALS AND METHODS: Two non-randomised groups of patients were studied prospectively. In group A 173 patients and 212 limbs had sapheno-femoral ligation, while 172 patients and 210 limbs additionally had a piece (2x3cm) of silicone sheet sutured to the saphenous stump to cover the anterior half of the common femoral vein. The implant was fixed in apposition to the deep vein by carefully closing the cribriform fascia. Colour duplex scanning was performed after 2 and 12 months. RESULTS: In the no implant group neovascularisation was observed in 35 (17%) after 12 months, but only in 13 (6%) limbs treated with a silicone implant (p<0.05). CONCLUSIONS: Interposition of a partition of silicone implant seems to lower the incidence of neovascularisation one year after saphenofemoral ligation. This technique may constitute an efficient method to prevent recurrence at the correctly ligated saphenous stump. (+info)
Sustained release of low-dose ganciclovir from a silicone formulation prolonged the survival of rats with gliosarcomas under herpes simplex virus thymidine kinase suicide gene therapy.
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A silicone formulation of ganciclovir (GCV-pellet) was developed to enhance the cytotoxic effects of herpes simplex virus thymidine kinase suicide gene therapy. The effectiveness of this drug delivery system was assessed in a rat 9L gliosarcoma model. The GCV-pellets (1 mm in length and in diameter) used in this experiment contained a total amount of 0.15 mg of GCV. In vitro experiments demonstrated that GCV was gradually released over a period of 7 days. Five days after stereotactic tumor inoculation into the right caudate nucleus, a herpes simplex virus type 1 (HSV-1) vector expressing herpes simplex virus thymidine kinase (HSV-tk) (T1, 2x10(6) pfu) was administered at the same location. The survival rate of the group treated with the GCV-pellet was compared with that of the T1 group injected intraperitoneally (IP) with GCV (30 mg/kg/day for 7 days). The GCV-pellet-treated group had a significantly prolonged survival (a median of more than 80 days) compared with the GCV IP group (a median of 65 days) and with control groups (P<0.05). The control groups (untreated or receiving only the virus vector) had a survival of 35-38 days. The survival rate of the GCV-pellet group over 80 days was 75%, and all the rats that survived more than 80 days and did not show tumors upon histological examination of the brain were deemed cured. No toxic effects or immunological reactions were observed histologically around the pellet in brain sections from the rats treated with the GCV-pellet. After GCV-pellet inoculation into the tumor, drug concentrations were kept at 1-10 microg/g tissue for 3-4 days. When the same dose of GCV (0.15 mg) in aqueous solution was injected into the tumor, GCV concentrations reached a peak of 0.5 mg/g tissue after 30 min and decreased below measurable level within 12 h. After IP injections of 3 mg GCV, GCV concentrations in the tumor reached a peak of 5.7 microg/g tissue after 30 min and also decreased below measurable level within 12 h. This sustained release of a low and effective GCV dose with the silicone formulation significantly prolonged survival in combinations with HSV-tk expression if compared to IP administration of GCV. Histological examination suggests that the treatment appears to be safe. (+info)
Development of a new hollow fiber silicone membrane oxygenator for ECMO: the recent progress.
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Throughout the last 50 years, many improvements have been made for a more effective oxygenator. A large plate type membrane oxygenator, used by Clowes, and a coil type, used by Kolff, has evolved into the small hollow fiber oxygenator. The complex bubble oxygenator, or rotating disk oxygenator, has become a small disposable bubble oxygenator. The currently available oxygenators are extremely small, efficient, and can be used for extended periods of time. However, there are some problems with extracorporeal membrane oxygenation (ECMO). Currently in the United States, there are no clinically applicable hollow fiber ECMO oxygenators available, in spite of the extended ECMO application. Therefore, the development of a small, yet efficient, silicone hollow fiber membrane oxygenator for long-term ECMO usage was attempted. Based on the results of many experimental models, preclinical oxygenator models for long-term ECMO were developed in our laboratory using an ultra-thin silicone rubber hollow fiber membrane. (+info)
Novel method to control release of lipophilic drugs with high potency from silicone.
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Silicone has been utilized as a carrier material for sustained release system of lipophilic drugs. Extensive studies revealed that drug release rate is influenced by factors such as physicochemical properties of the drug and additives.(1-5)) When a lipophilic drug is highly potent at low concentrations, the drug release rate should be strictly controlled so as to avoid side effects. In this study, using vitamin D(3) (VD(3)) as an example of such drugs, we investigated novel method to suppress initial burst and to modify drug release rate from silicone matrix. As a result, it was found that (a). addition of human serum albumin (HSA) suppressed initial burst and enhanced release rate in the later stage, resulting constant release of VD(3), (b). covering a matrix formulation with a membrane of low diffusivity (core-rod formulation) suppressed initial burst and released drug in a constant rate, and (3) using materials for which the drug has high affinity as dissolution solvent (reservoir formulation), the drug release rate was reduced. (+info)