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At least 1,279 records · Page 71Linked to original sources
PubMed1987

Controlled-release drug delivery of diphosphonates to inhibit bioprosthetic heart valve calcification: release rate modulation with silicone matrices via drug solubility and membrane coating.

Calcification (CALC) is the most frequent cause of the clinical failure of bioprosthetic heart valves (BHV) fabricated from glutaraldehyde pretreated porcine aortic valves or bovine pericardium. The present investigation describes the formulation, characterization, and the in vivo efficacy of prolonged controlled-release silicone matrices containing the anticalcification agent disodium 1,1-hydroxyethylidene diphosphonate (Na2EHDP). Controlled release of EHDP was regulated by codispersions of Na2EHDP and the less soluble salt Ca2EHDP. Prolonged and constant release rates (zero-order) were obtained by coating silicone matrices with permeable silicone membranes, which were prepared by leaching with acetone pre-embedded polyethyleneglycol. All EHDP-containing matrices (co-implanted subdermally with BHV cusps in rats) significantly inhibited BHV CALC without detectable adverse effects on bone mineral and calcium metabolism. Matrices containing Na2EHDP:Ca2EHDP ratios of 10:90 or greater with respect to Na2EHDP completely inhibited CALC. Significant inhibition of BHV CALC was also observed with prereleased matrices (5 months in vitro), thus demonstrating prolonged efficacy. It is concluded that sustained release of effective anticalcification therapy without side effects was achieved by using codispersions of calcium and sodium EHDP salts, and that a delayed and/or constant release rate of EHDP was obtained by coating reservoir-type matrices with silicone membranes that were pre-embedded with polyethyleneglycol.

Animals↗
PubMed1986

Adenocarcinoma of the breast associated with silicone injections.

A 42-year-old woman developed inflammatory breast cancer in a breast with "silicone mastitis" 12 years after bilateral breast augmentation with liquid silicone injections. Despite aggressive local and systemic therapy, the patient died of her disease. Breast cancer arising in silicone-injected breasts is reported infrequently, and physicians caring for patients with silicone breast injection augmentation should be aware of this potentially fatal association with breast cancer.

Adult↗
PubMed1993

In vivo 1H chemical shift imaging of silicone implants.

In order to study the aging process (i.e., silicone migration, fat infiltration) of silicone (polydimethylsiloxane, PDMS) based biomaterials in living subjects by NMR imaging, a hybrid 1H selective excitation and saturation chemical shift imaging technique (IR/CHESS-CSSE) has been developed. This sequence allows selective mapping of the distribution of silicone protons in vivo, while suppressing the contributions of fat and water. Our results indicate that a combined inversion recovery and CHESS pulse, followed by a spoiler gradient, must be applied to suppress all contributions of fat protons to the NMR signal. The sensitivity of our experiments allows the detection of a chemically unchanged silicone concentration of 5% in a voxel of 0.9 mm3 at a signal/noise ratio of 2.

Adipose Tissue↗
PubMed2005

Perineal noise recording as a non-invasive diagnostic method of urinary bladder outlet obstruction: a study in polyvinyl alcohol and silicone model urethras.

AIMS: At present, an invasive pressure flow study is recommended to diagnose urinary bladder outlet obstruction. This method induces the risk of urinary tract infection and urethral trauma. We studied perineal noise recording as an alternative, non-invasive diagnostic method in three flexible/extensible model urethras and two silicone tubes. METHODS: The flexible/extensible model urethras were made of a 10% aqueous solution of polyvinyl alcohol (PVA) and differed in wall- stiffness, the silicone tubes differed in diameter and wall-thickness. Three degrees of obstruction were applied by inflating a cuff placed around the PVA-urethras and by compressing the silicone tubes with an adjustable clamp. Noise, produced during flow, was recorded at three positions distal to the obstruction using a piëzoceramic contact microphone. RESULTS: The average amplitude of the noise and the essential frequency of the power spectrum of each noise recording depended significantly on the degree of obstruction, the position of the microphone and the wall-stiffness in PVA-urethras and the diameter in silicone tubes. CONCLUSIONS: Based on the results of this study perineal noise recording shows good potential as an alternative method for diagnosing bladder outlet obstruction.

Data Interpretation, Statistical↗
PubMed1997

Influence of distal nerve segment volume on nerve regeneration in silicone tubes.

The influence of a volume of a distal nerve segment upon nerve regeneration in an 8-mm gap created within a silicone tube was examined. The rats were randomly divided into four groups. Each group had 5 mm, 1 mm, or a half volume of 1-mm nerve segment (a nerve piece of 1 mm transected longitudinally) inserted into the distal end of a silicone tube of 11 mm. The empty group without a nerve segment was used as control. Diameters of regenerated cylindrical structure between the nerve ends in the silicone tube were measured under an operation microscope and myelinated axon diameter, myelinated axon density, myelin sheath width, and ratio of myelinated axon area to total cross sectional area were measured using the transverse sections at the midpoint of the silicone tube at 6 weeks after surgery. Although there was a significant difference in all of those parameters between the control group and any of the remaining three groups, no significant difference was found between any pair of these three groups. The results of this study indicated that the degree of nerve regeneration does not correlate with the volume of a distal nerve segment and even a very small piece can play an important role in supporting regenerating nerve beyond a definitive gap.

Animals↗
PubMed1995

Induction of plasmacytomas in genetically susceptible mice with silicone gels.

Silicone gels injected intraperitoneally into strains of mice related to BALB/c develop plasmacytomas in approximately the same numbers and with similar phenotypes as previously obtained with pristane. Silicone gels produce few side effects and are well tolerated for long periods. Silicone gels contain several components that are potentially biologically active: residual vinyl groups and platinum. Microscopic and histological evidence suggests the silicone gel is degraded over a long period of time. Preliminary studies with long chain liquid dimethylpolysiloxanes with viscosities of 1000 cSt and 12,500 cSt have not produced plasmacytomas as yet. The plasmacytomagenic action of the gel appears to be due to the release of liquids from the gel matrix.

Animals↗
PubMed1996

Silicone-induced modulation of natural killer cell activity.

Current controversy regarding the effects of silicone gel mammary implants on the immune system has led to increased focus on the potential biological activity of silicone materials. Studies were undertaken in the B6C3F1 mouse to evaluate the immunotoxicological effects of the following components of a mammary gel prosthesis: polydimethylsiloxane fluid, silicone gel, elastomer shell and a polyurethane implant cover. Material was implanted subcutaneously (s.c.) for either 10 or 180 days. The only toxicological or immunological parameter which differed from control values was the natural killer (NK) cell activity in gel implanted mice. In these animals, basal NK activity was decreased. NK activity was comparably inhibited in female Fischer 344 rats implanted with silicone gel following short term (14 or 30 days) as well as chronic (1 year) exposure. The response was variable in both the rat and mouse. Host resistance to B16F10 melanoma in the mouse is known to be related to NK activity. Despite suppression of NK activity following gel implantation, host resistance was unaltered. Inhibition of NK activity by the administration of anti-asialo GM1 indicated that resistance was not adversely affected until NK activity was decreased by 40 to 50%. As with basal NK activity, augmented NK activity was inhibited in gel implanted rats when compared to controls. Administration of polyinosinic:polycytidylic acid to gel implanted rats resulted in an increase of approximately 65% in NK activity compared to gel implanted controls. This level of augmented NK activity was significantly less than the level of augmented NK activity in vehicle implanted animals where 100% enhancement in NK activity was noted. The results of these studies indicate that (1) NK cytolytic activity is altered in two animal models, the mouse and rat, although the results were variable, that (2) the level of suppression noted in the mouse is ineffective when compared to the level of suppression required to alter host resistance to B16F10 melanoma and that (3) the gel implanted animals exhibit a suppressed response to NK augmentation.

Animals↗
PubMed1996

Development of scleroderma-like syndrome in Tsk/+ mice is not enhanced by silicone administration.

The possible role of silicone in the pathogenesis of a scleroderma-like syndrome is still unresolved. It has been proposed that silicone escaping from breast implants potentiates the progression of the disease. To clarify whether silicone enhances development of fibrotic skin lesions and autoantibodies, we tested its effect on tight skin (TSK/+) mice. TSK/+ mice spontaneously develop skin fibrosis and characteristic autoantibodies which resemble human scleroderma. The results of the present study indicate that silicone administration does not enhance development of skin fibrosis nor synthesis of autoantibodies to RNA polymerase and topoisomerase in TSK/+ mice.

Animals↗
PubMed1988

Regular silicone and fluorosilicone oil in the prevention of retinal detachment caused by experimental proliferative vitreoretinopathy.

The effect of both regular silicone and fluorosilicone in preventing retinal detachment caused by experimental proliferative vitreoretinopathy was studied in rabbit eyes which received 250,000 fibroblasts after vitrectomy and lensectomy. In the control group, 14 out of 20 eyes which received fibroblasts had retinal detachments with disorganization of internal structures. In eyes receiving fibroblast and regular silicone, 4 out of 20 eyes had shallow retinal detachment. In the eyes receiving fibroblasts and fluorosilicone, 5 of 28 eyes had shallow retinal detachment. Our findings indicate that both regular silicone and fluorosilicone were effective in preventing retinal detachments caused by experimental proliferative vitreoretinopathy. There was no statistical difference between the two silicone oils.

Animals↗
PubMed1986

The influence of intravitreously injected silicone oil on electrophysiological potentials of the eye.

In a prospective study the effect of silicone oil injected in the vitreous cavity was monitored electrophysiologically in six patients who were treated for retinal detachment. Electroretinograms (ERG) and electrooculograms (EOG) were recorded before, shortly after, and up to four months following the removal of the oil. An evident increase of the standing potential could be observed in all eyes after removal of the silicone oil. In some patients the ERG amplitudes increased also. No fast oscillations and virtually no slow oscillations could be recorded in the EOG. Follow-up studies did not show a significant recovery of the bioelectric activity. Intravitreal silicone oil appears to cause an insulation effect which interferes with the propagation of electrical potentials. The result of the present study do not provide information concerning possible retinotoxic effects of silicone oil.

Electrooculography↗
PubMed1991

Cell-ingrowth in a silicone plombe. Interactions between biomaterial and scleral tissue after 8 years in situ: a SEM and TEM investigation.

A male patients (42 years) who had been treated for retinal detachment by the implantation of a silicone plombe into the sclera, returned to the clinic 8 years after implantation because of inflammation of the tissue and partial protrusion from the sclera. After removal of the plombe this was processed for TEM and SEM and examination of the plombe material after 8 years in situ could be carried out in order to get information about the cell-biomaterial interface. A large proportion of the silicone pores was filled with cellular material, including macrophages, giant cells and erythrocytes thus indicating a foreign body granuloma. The external surface of the pores showed a granular osmiophilic dense amorphous layer including extracellular debris. Engulfing of silicone particles by macrophages and the evidence of long-term tissue response suggest partial biodegradation of the silicone and certainly not complete inertness as was formerly claimed.

Adult↗
PubMedDate not supplied

Glaucoma after vitreo-retinal surgery with silicone oil injection: epidemiologic aspects.

PURPOSE: To evaluate the prevalence of glaucoma after pars plana vitrectomy with silicone oil injection and to determine the different clinical forms. METHODS: Authors have carried out a retrospective longitudinal study on patients who underwent pars plana vitrectomy with silicone oil injection from 1981 to 1995. The examined population consists of 301 patients (301 eyes), with an age ranging from 8 to 85 years, affected by retinal detachment and proliferative vitreoretinopathy. RESULTS: The prevalence of the secondary glaucoma has been 18.5%. In all cases glaucoma was caused by trabecular meshwork obstruction due to silicone oil emulsification. The glaucoma has been more frequent after surgery for recurrent rhegmatogenous retinal detachment with fibrous PVR (52.86%) and for particular forms of rhegmatogenous retinal detachment (giant tears, multiple breaks, pseudophakia) with incipient PVR (30%). CONCLUSION: Glaucoma after intravitreal silicone oil injection for complicated retinal detachments is a relatively frequent complication mostly when surgery needs endophotocoagulation, endodiatermy and lensectomy.

Adolescent↗
PubMedDate not supplied

Transmission electron microscopic analysis of trabecular meshwork in secondary glaucoma after intravitreal silicone oil injection.

PURPOSE: We analyzed morphological changes in trabecular meshwork in glaucoma developing after intravitreal silicone oil injection with transmission electron microscopy (TEM). METHODS: Specimens obtained from 2 patients after surgical trabeculectomy were fixed in McDowell fixative in one patient and in buffered formaldehyde in the other, dehydrated and embedded in Epon. Ultrathin sections were made and stained with lead citrate and uranyl acetate for TEM. RESULTS: In specimens mainly connective tissue sheets with disorganized and narrowed intertrabecular spaces were observed. At higher magnification the collagen sheets were composed of interstitial collagen and some of them were covered by amorphous basal membrane structures resembling material. Cellular remnants were present along the intertrabecular spaces. No other cells or clearly evident silicone oil were noted. CONCLUSION: Changes such as decrease in cell content, fibrosis and build-up of basement membrane-like material have been described by other authors. They are not specific and can be seen in many secondary glaucomas. No macrophages and foreign-body granulomas in response to silicone oil were present. The pathological changes in angle structures are probably caused by other mechanisms and are not induced by silicone oil itself.

Collagen↗
PubMed1993

Local reaction and migration of injected silicone gel: experimental study.

A study of the local and migratory effects of free silicone gel taken from a mammary prosthesis is reported. Thirty eight Wistar rats were injected in their subcutaneous space with 1 cm3 of silicone gel. The animals were sacrificed on day: 3, 7, 15, 30, 60, 180, 240, 360, 420, 450. The visceral organs (heart, kidneys, lungs, stomach, gonads, liver, pancreas, spleen, intestine), as well as the tissue adjacent to the region of injection, were histologically analyzed. There was no detectable silicone and no damage to the visceral organs based on routine histopathological analysis. The greatest fibrosis was observed at the extremities of the disk formed by the silicone in the subcutaneous space.

Animals↗
PubMed1992

Twenty years of experience with particulate silicone in plastic surgery.

The use of particulate silicone in plastic surgery involves the introduction of solid silicone into the body. The silicone is in small pieces in order for it to adapt to the shape of the defect. This way large quantities can be introduced through small incisions. It is also possible to distribute the silicone particles from outside the skin to make the corrections more regular. This method has been very useful for correcting post-traumatic depressions in the face and all areas where the depression has a rigid back support. We consider it the treatment of choice for correcting the funnel chest deformity.

Face↗
PubMed1990

Temporary silicone oil tamponade in the treatment of complicated diabetic retinal detachments.

A retrospective study is reported on 132 eyes with retinal detachment, resulting from advanced proliferative diabetic retinopathy, treated using vitrectomy techniques and silicone oil tamponade. Epiretinal surgery was performed using a bimanual technique. Silicone oil was removed in 64 eyes (49%) which regained an improved final vision of 5/200 or better. In 17 eyes (13%), vision was improved but silicone oil could not be removed. It is expected that the function of several of these eyes will eventually deteriorate because of progressive silicone-induced glaucoma. The remaining 51 eyes (38%) were surgical and functional failures.

Diabetic Retinopathy↗
PubMed1993

Cataract after silicone oil implantation.

During the period January 1987 till December 1990 192 patients (204 eyes) underwent pars plana vitrectomy (PPV) with silicone oil internal tamponade. 141 eyes were phakic and 63 eyes aphakic. 65 of the phakic eyes were diabetic, and 76 eyes nondiabetic. The silicone oil was removed on average at 8.3 months postoperatively. Cataract developed faster in the nondiabetic group and in the eyes with partially detached retinas. In all cases there was a direct contact between the posterior capsule and silicone bubble. Extracapsular cataract extraction (ECCE) was done in 75 eyes. In 59 eyes intracapsular cataract extraction (ICCE) was performed and in 7 eyes pars plana lensectomy (PPL). Histologically proliferation and metaplasia of the lens epithelium was observed. Clinical and histological findings suggested that the silicone cataract formation was malnutritional due to inhibition of lens metabolism (anaerobic glycolysis).

Cataract↗
PubMed1982

[Silicone anti-reflux prosthesis--an artificial fundoplication?].

Of all anti-reflux operations fundoplication has proved the most effective method in experimental and clinical examinations [3, 5, 9, 12, 13]. In 1979 Angelchik reported a silicon prosthesis as an anti-reflux barrier which proved effective in examinations on patients. An explanation for these results is still missing [1]. Our examinations in dogs show that: 1. anti-reflux prosthesis is an effective anti-reflux barrier in dogs after circular myectomy; 2. silicon prosthesis proved to be equally as effective as fundoplication with regard to reflux prevention; 3. the mechanism of action is a mechanical one. The difference between silicon prosthesis and fundoplication is, that the fundoplication represents a 'ring' around the LES, which is elastic and is subject to the same regulations as the LES, and that it can relax in a swallowing reflex manner. In the silicon prosthesis the 'ring-formation' is only mechanical.

Animals↗