RESUMEN
Human adjuvant disease is the label given to a syndrome that resembles a connective tissue disease such as scleroderma and that has been hypothesized to follow augmentation mammoplasty with silicone gel implants or silicone with adulerants. To date, there is no proof that pure silicone is the cause of these symptoms. The cases presented in the literature suggest a comparison to the events seen in the rat adjuvant arthritis model. Male Lew/SsN rats (n = 65) were used. To evaluate both the adjuvant and antigenic properties of the gel implant, variations of the standard Freund's complete adjuvant inoculum were prepared. Tested were the abilities of low molecular weight silicone to act as an adjuvant and for fumed silica to act as an antigen by modifying a rat adjuvant arthritis model to include silicone and fumed silica. On day 0, 0.25 ml of each inoculum was injected intradermally into the plantar aspect of the hindfoot of each rat. The foot diameter was recorded at each time period, compared with the contralateral hindfoot, and normalized to controls at regular time periods over the course of 120 days. Silicone oil did not act as an adjuvant. Furthermore, fumed silica alone did not act as an antigen; however, it is capable of eliciting a reaction that is both delayed and uncharacteristic of the rat adjuvant arthritis model. These results indicate that "human adjuvant disease" may be inappropriate and misleading.
Asunto(s)
Adyuvantes Inmunológicos , Artritis Experimental/etiología , Dióxido de Silicio/efectos adversos , Aceites de Silicona/efectos adversos , Animales , Antígenos , Artritis Experimental/patología , Enfermedades Autoinmunes/etiología , Implantes de Mama , Enfermedades del Tejido Conjuntivo/etiología , Enfermedades del Tejido Conjuntivo/inmunología , Pie , Adyuvante de Freund/inmunología , Masculino , Mycobacterium/inmunología , Ratas , Ratas Endogámicas Lew , Dióxido de Silicio/inmunología , Aceites de Silicona/inmunologíaRESUMEN
Previous work with subcutaneous implants in a rat animal model has shown that pillarlike surface microstructure will reduce fibrosis and enhance blood vessel approximation to the implant surface when compared with nontextured controls. This study was designed to determine the effect of microtissue anatomy and implant site on the observed response, as well as the effect of implant fixation. The lateral posterior sites were found to contain a fat pad which produced a dramatically reduced fibrosis for the micro-structured implants compared with smooth controls. Although significant differences between pillar-micro-structured implants and controls were found for most sites, neither fascia nor muscle reduces the level of cellular response to the same degree as fat. Suture fixation of the implants did not produce a significantly different response in these tests. The occupation of the interpillar spaces by fat and moderation of interfacial shear forces is proposed as a mechanism to explain these results.
Asunto(s)
Prótesis e Implantes , Elastómeros de Silicona , Tejido Adiposo/anatomía & histología , Tejido Adiposo/fisiología , Animales , Vasos Sanguíneos/anatomía & histología , Vasos Sanguíneos/fisiología , Cartílago/anatomía & histología , Cartílago/fisiología , Fibrosis/patología , Masculino , Músculo Esquelético/anatomía & histología , Músculo Esquelético/fisiología , Ratas , Ratas Sprague-Dawley , Propiedades de Superficie , SuturasRESUMEN
The procedure of choice for enteral feeding access is now percutaneous endoscopic gastrostomy (PEG). Standard PEG tubes have the disadvantages of clogging, stomal enlargement, and external bulkiness. Button replacement tubes can covert the more cumbersome PEG tubes to low external profile devices. A procedure and an early experience is described for placement of a button as a single-step procedure. This procedure is an over-the-wire, "push" procedure. Sixty-nine buttons were placed, 47 (61%) for neurologic reasons and 22 (32%) for cancer and other reasons. In 49 of the 69 (71%), there was no difficulty at all with insertion, and in only two (3%) could the button not be placed. Complications were assessed at 48 h and at 3 wk. No complications were found in 61 (90%). In only two patients (3%) were there serious complications (gastro-colon-cutaneous fistula and "peritonitis"). The One-Step Button represents a rapid, safe procedure for the placement of a low-profile PEG with its attendant advantages.
Asunto(s)
Nutrición Enteral/métodos , Gastrostomía/métodos , Animales , Perros , Nutrición Enteral/instrumentación , Estudios de Factibilidad , Gastrostomía/efectos adversos , HumanosRESUMEN
A microtextured, pillared drug delivery system has been designed and tested in rabbits. This model has allowed for the calculation of the mass transport rate indicating after a 4 week time period a pillar device's mass transport rate K1 [min-1] is K1p 1.54 x 10(-2) in contrast to the smooth control which is K1C .043 x 10(-2) and K1im IM which is 0.136 x 10(-2). As a result of these experiments, it is apparent a micropillared drug delivery system is an order magnitude faster than an intramuscular injection and is 30 times faster than the smooth control device. The etiology for this difference is related to close blood vessel proximity and minimal to no fibrous capsule formation with the micropillared implant. Finally, even after a 6-month implantation time, the pillared device has greater reproducibility regarding curve profile and there is no loss in magnitude or rate of mass transport, in contrast the smooth control devices in many instances resulted in complete occlusion with total loss of mass transport capabilities.
Asunto(s)
Catéteres de Permanencia , Bombas de Infusión Implantables , Tasa de Depuración Metabólica/fisiología , Farmacocinética , Animales , Diseño de Equipo , Verde de Indocianina/farmacocinética , Masculino , Conejos , Propiedades de SuperficieRESUMEN
The implant-tissue response to the silicone gel mammary prosthesis requires a more thorough evaluation in light of recent concerns related to human connective-tissue diseases, contracture, infection, and neoplasia. The silicone prosthesis is not a homogeneous implant but is a milieu of various silicone chemistries. Silicone polymer precursors and prosthesis components (silicone shells, shells extracted of their low-molecular-weight components, silica-free silicone, silicone oil, fumed silica, and silicone extract) were implanted subcutaneously using a nonhemorrhagic technique into the backs of Lew/SsN rats (n = 90), two implants per rat, for periods of 7, 14, 28, 56, and 90 days for a total of 6 implants per material per time period. Histologic analysis was performed on specimens from the harvested soft tissue. The intensity of the cellular and capsular response was lowest for the silicone oil and increased as the material's molecular weight increased and material compliance decreased. Fumed silica elicited the most highly reactive cellular response. From this study it is apparent that the polymer's molecular weight influences its migration, encapsulation, and intensity of cellular response. Further, the silicone extract distillate elicited a highly intense cellular response with pronounced lymphocyte invasion. The human relevance of this work awaits further correlation with implant retrieval and in vivo performance.
Asunto(s)
Mama , Reacción a Cuerpo Extraño/patología , Prótesis e Implantes , Elastómeros de Silicona/toxicidad , Animales , Masculino , Ratas , Ratas Endogámicas Lew , Dióxido de Silicio/toxicidad , Aceites de Silicona/toxicidad , Siliconas/toxicidadRESUMEN
An animal model was developed using the male Sprague-Dawley rat to establish a protocol and design criteria for the growth of autologous tissue based on a microvascular pedicle. It became apparent that growth within the chamber depended heavily on membrane porosity and the presence of the microarteriovenous shunt. Different membrane porosities ranging from 0.0, 0.25, 1.2, to 8.0 microns were evaluated (n = 48). Optimal growth occurred with the 1.2-microns and the 8.0-microns micropore Millipore. Growth within the chamber consisted of a radial deposition of collagen and neovascularization originating from the arteriovenous (A-V) anastomosis. In contrast, control chambers (no A-V anastomosis), with the preceding range in membrane porosity, experienced little to no cell growth. In addition, the majority of A-V shunts did not remain patent in chambers having 0.0-microns porosity or 0.25-microns porosity. Thus it is apparent that a strong relationship exists between membrane porosity, patency, and in situ vascularization allowing for the proliferation of cells and collagen.
Asunto(s)
Derivación Arteriovenosa Quirúrgica/métodos , Técnicas de Cultivo/métodos , Colgajos Quirúrgicos , Animales , División Celular , Técnicas de Cultivo/instrumentación , Cámaras de Difusión de Cultivos , Arteria Femoral/cirugía , Vena Femoral/cirugía , Masculino , Membranas Artificiales , Microcirculación , Neovascularización Patológica , Porosidad , Ratas , Ratas Endogámicas , Grado de Desobstrucción VascularRESUMEN
An animal model was developed to determine the feasibility of vascularizing a porous biomaterial and transferring it as part of a free flap to a recipient site with enhanced resistance to infection due to the maintenance of a blood supply. To that end, the experiment was divided into three stages. Stage 1 compared the soft-tissue response of Interpore-200 to Interpore-500, both continuously porous hydroxyapatite materials implanted beneath the panniculus carnosus of the male Sprague-Dawley rat. Pore size was an important factor as it influenced vascular ingrowth, with Interpore-200 vascularizing earlier (complete at 1 week) and more intensely. Interpore-200 was therefore used for the remainder of the experiment. After 1 week of tissue ingrowth, the implants were moved from the abdomen to the skull on a vascular pedicle as a "biocomposite" free flap. Stage 2 was the histologic evaluation of 15 "biocomposite" free flaps over various time intervals up to 8 months. The free flaps formed a fibrous union to the skull, while a simple nonvascularized Interpore-200 onlay graft (stage 2 control) demonstrated a bony union in three of four implants placed up to 2 months. Stage 3 confirmed the free flap's resistance to bacterial infection. A highly significant difference (p less than 0.005) in infection rates was demonstrated between the "biocomposite" and nonvascularized stage 3 controls with no Pseudomonas growth from 9 of 10 cultures of the free flaps 5 days after exposure to 10(4) Pseudomonas aeruginosa, while stage 3 controls demonstrated Pseudomonas growth in all cultures (heavy growth in 8 of 10). The "biocomposite" free flap has excellent potential to provide form and structure to wounds requiring reconstruction where bacterial contamination is a significant risk factor.
Asunto(s)
Huesos/irrigación sanguínea , Hidroxiapatitas , Prótesis e Implantes , Colgajos Quirúrgicos/métodos , Abdomen/cirugía , Animales , Durapatita , Masculino , Microscopía Electrónica , Porosidad , Ratas , Ratas Endogámicas , Cráneo/cirugíaRESUMEN
A prerequisite for the development of an implantable artificial pancreas is the availability of a stable, long-life glucose sensor. Platinum (Pt) catalyzed electrodes have been demonstrated in vitro to show high sensitivity to glucose and long cycle life but are more sensitive to co-reactants compared with enzymatic methods. The authors developed a special data processing method (compensated net charge ratio, or CNCR) in which the measured electrode response is very sensitive to glucose, completely insensitive to urea, and only moderately sensitive to amino acids. Other endogenous and exogenous co-reactants show only minor interferences. The CNCR method involves the determination of the ratio of net oxidation charge to total charge during one complete cycle of a cyclic voltammogram. Prototype electrodes tested in vitro in spiked plasma have shown typical sensitivities of greater than 2 x 10(-4) CNCR units per 1 mg/dl change in glucose concentration, with linear response up to 400 mg/dl. For in vivo testing, a modified 5 F vascular catheter with membrane covered surface mounted electrodes was used at a vena cava site in swine. Several sensor designs were tested in vivo, with sensitivities of 1-5 x 10(-4) CNCR units (mg/dl).
Asunto(s)
Automonitorización de la Glucosa Sanguínea/instrumentación , Diabetes Mellitus/sangre , Animales , Catéteres de Permanencia , Bovinos , Diseño de Equipo , HumanosRESUMEN
The polyurethane foam-covered breast prosthesis is experiencing increased clinical use. The polyurethane is felt to be responsible for altering capsule formation and reducing the contracture rate. This study characterizes the soft-tissue response to the Natural-Y Même polyurethane foam versus smooth silicone in a rat model. Implants were fashioned from an unbacked polyurethane foam specimen used to cover the Natural-Y prosthesis, a silicone shell covered with the Natural-Y foam, and a smooth silicone control. Materials were placed subcutaneously into the backs of male Lew/SsN rats (n = 81) for 3, 7, 14, and 28 days and 3, 6, and 12 months. Implants were then harvested with their soft-tissue response and evaluated histologically. Analysis demonstrates that microstructuring of a surface, as opposed to a smooth material, will dramatically alter the early, intermediate, and late wound-healing events. The soft-tissue response was observed to be dependent on implant site, material chemistry, and morphology as characterized by exudate formation, macrophage invasion, multinucleated giant cell formation, collagen deposition, foam degradation, and angiogenesis.
Asunto(s)
Materiales Biocompatibles , Tejido Conectivo/ultraestructura , Reacción a Cuerpo Extraño/patología , Poliuretanos , Prótesis e Implantes , Siliconas , Cicatrización de Heridas , Animales , Masculino , Microscopía Electrónica , Ratas , Ratas Endogámicas Lew , Factores de TiempoRESUMEN
The utility for a prosthetic microvascular graft is well demonstrated, but previous studies have been inconclusive. Expanded polytetrafluoroethylene (Gore-Tex) has been most widely tested as a prosthetic graft. Polytetrafluoroethylene is composed of transverse nodules connected by long fibrils. This study evaluates the effect of fibril length on observed patency in a 1-mm inner-diameter system. Fibril lengths tested were 30, 60, 90, and 120 micron. One-hundred and sixty-three grafts were implanted in the abdominal aorta of Sprague-Dawley rats by a single surgeon using a standardized technique. No anticoagulants were used. Grafts were harvested at predetermined times and evaluated macroscopically, by scanning electron microscope, and by standard histology. The highest patency observed was 97.7 percent in the 90-micron fibril-length grafts. Fibril morphology also affected patency. Increased patency was associated with an amorphous fibril pattern. The graft functioned as a matrix for the formation of a pseudoartery, complete with monocell-thick intima and smooth-muscle media. A foreign-body reaction was observed in the 60-micron fibril-length graft only. Expanded polytetrafluoroethylene does show promise as a microvascular graft. Both fibril length and morphology affect observed patency.
Asunto(s)
Prótesis Vascular , Oclusión de Injerto Vascular/etiología , Politetrafluoroetileno , Animales , Aorta Abdominal/cirugía , Prótesis Vascular/efectos adversos , Estudios de Evaluación como Asunto , Oclusión de Injerto Vascular/patología , Microcirculación/cirugía , Microscopía Electrónica de Rastreo , Ratas , Ratas Endogámicas , Infección de la Herida Quirúrgica/etiologíaRESUMEN
In an effort to eliminate the common problems associated with gastrostomy tubes in children, we developed a silicone rubber gastrostomy "button" designed to replace the standard long latex tube. Easily inserted and self-retaining, the device remains practically flush with the skin. The intragastric portion is similar to a dePezzer catheter, and a one-way valve prevents reflux of gastric contents. Prototypes were evaluated in five children for a time period of 3 to 18 months. In two additional patients with esophageal stricture, the device was used as a temporary plug to maintain gastric stoma patency. Parents and nurses are pleased with the button's low profile, appearance, and ease to use. It is neither painful nor irritating, and there is no fear of dislodgement.
Asunto(s)
Nutrición Enteral , Gastrostomía , Elastómeros de Silicona , Preescolar , Humanos , LactanteRESUMEN
A series of polyurethanes based on the hard segment MDI and soft segment PTMG were synthesized. The molecular weight of the PTMG was 730, 1000, and 2000, and ethylene diamine was used as chain extender. The fabrication process was varied so as to achieve the maximum disorder (nonequilibrium state) and maximum order, fully annealed. It was demostrated that the "quenched" non-equilibrium state reduces the rate of activation of the intrinsic systems, factor XII pathway, when compared to the fully annealed state. Platelet attachment is primarily affected by phase separation.