RESUMEN
Compression of a growth plate is known to correlate with changes to growth plate structure. The purpose of this study was to determine if the height of the physeal hypertrophic zones and chondrocyte size were directly related to the distance from a spine implant. The implant was designed with the goal of slowing spine growth asymmetrically. For stapled vertebrae, hypertrophic zone height, cell height and cell width were decreased across the coronal plane of the growth plate, with the lowest values under the staple, 8 weeks postoperatively.
Asunto(s)
Placa de Crecimiento , Prótesis e Implantes , Fusión Vertebral , Columna Vertebral/crecimiento & desarrollo , Fenómenos Biomecánicos , Condrocitos/citología , Humanos , Fusión Vertebral/métodos , Columna Vertebral/cirugía , Estados UnidosRESUMEN
The purpose of this pilot study was to determine if compressive stresses in the annulus of the intervertebral disc vary with activity in a quadruped and are affected by treatment with an implant. Pilot in vivo tests were conducted on skeletally immature domestic pigs (approved by IACUC). One pair of sensors was implanted within the annulus of T10-11, and the second pair at T8-9. A staple was them implanted across the right side of T8-9. Wires were routed subcutaneously and exited at the dorsal cervical region. Sensor signals were acquired before and after staple implantation, post-operatively during normal activities, and biweekly under anesthesia. After 8 weeks, spines were harvested and imaged. Early results from 2 sensors during walking and sitting, post-op day 5, clearly showed cyclic stresses during gait. Stresses were attenuated at the stapled vertebra compared to the unstapled vertebra.
Asunto(s)
Compresión de la Médula Espinal , Columna Vertebral/fisiología , Estrés Mecánico , Animales , Fenómenos Biomecánicos , Prótesis e Implantes , Sus scrofa , Estados UnidosRESUMEN
Direct power delivery to intracorporeal circulatory support devices risks infection. Electrical transformers spanning the integument (skin or mucosa) have long been attractive means of circumventing this risk. Yet all existing skin surface transformers leak substantial magnetic flux, with an intrinsic risk of battery draining cross-coupling by any nearby conductor, requiring strict control of surroundings. In a progression of designs, we have used the walls of a small pouch, surgically formed from ileum, rather than skin, as a barrier. Previously, we reported a torroidal design with complete magnetic circuits, having zero flux leakage and unmatched heat dissipation in a 2 week canine trial. This work was in three parts: (1) Devices were placed in eight dogs for 9-12 weeks to document performance of the existing design. (2) Based on these results, the device was further miniaturized. Iterative computational modeling was applied to material selection and design. Simultaneously, practical techniques for surgically constructing tiny accommodating ileal pouches were explored in cadavers, by using polymer "mock-ups" of potential designs. (3) The final design was tested by acute implantation in a live 52 kg goat and by in vitro testing of electrical transfer function. IN VIVO TRIALS: The earlier design demonstrated 97.2% AC/AC and 84.2% DC/DC efficiency with contiguous tissue warming of 0.1 degrees C. DESIGN AND PERFORMANCE: A transformer with a Square Permalloy torroidal core (6 cm3, 23 grams, both coils eight turns) was designed, by using human cadaver trials to optimize geometry. Input and output were 6 V, 12W at 9.2 kHz with AC-AC efficiency 96%. OPERATIVE PLACEMENT TRIAL: The primary coil easily fit into an isolated, vascularized, but otherwise disconnected "blind" ileal pouch < 2 cm long with a slender extension to a miniature stoma. With secondary turns, the pouch and transformer fit easily into the abdominal wall. This tiny system seems compatible with near "forgettable" power delivery allowing unprecedented freedom of environment and activity in circulatory support dependent people.
Asunto(s)
Corazón Auxiliar , Animales , Perros , HumanosRESUMEN
A durable bond between the end of skeletal muscles and prosthetic structures could, with appropriate linkage, allow circulatory support power by synchronous and/or sequential contraction of several in situ conditioned muscles. Potential advantages relative to a myoplasty wrap involve 1) less traumatic dissection, 2) efficient linear force development, 3) selectable contraction rate, 4) greater stroke work, 5) independent control of muscle pre-load and end diastolic pressure, and 6) independent control of duration of muscle tension and ejection time. However, no existing means of tissue-prosthetic bonding appears adequate. Practicality would demand that full tension bearing capacity by the bond take no longer than muscle conditioning. A prosthesis was developed to achieve those goals. As scaled for this study, it is made of 7,200-7,800 unspun, unplaited, 22 to 26 microns diameter polyester fibers swaged into four taper needles for weaving through distal muscle. The other end is formed into a polyurethane sheathed kernmantel cord for distal fixation. Devices were implanted in six 3 to 4 kg rabbits (unilateral posterior tibial tendon replacement, random side selection with contralateral dissection/closure controls), and their tensile strength was tested at 30 days. All healed well; leg movements were normal after 1 week. Limbs were frozen at -70 degrees C between death and testing. Control failure occurred at 243 +/- 94 N and experimental at 163 +/- 44 N (p = 0.065, t-test); highest estimated requirement was 17.2 N. Interface strength was adequate by 30 days. Continued investigations, addressing other questions, are warranted.
Asunto(s)
Corazón Auxiliar , Ventrículo de Músculo Esquelético , Tendón Calcáneo , Animales , Materiales Biocompatibles , Fenómenos Biomecánicos , Ingeniería Biomédica , Estudios de Evaluación como Asunto , Técnicas In Vitro , Ensayo de Materiales , Contracción Muscular , Poliésteres , Diseño de Prótesis , ConejosRESUMEN
A defunctionalized ileal pouch is thin-walled (1-2 mm), well perfused (blood flow, 0.3-1.0 ml/g/min), and tactile-insensitive. If fixed within the abdominal wall and provided with a miniature stoma for primary wire entry, the heat dissipating capacity and achievable geometries could facilitate small efficient intra- to extracorporeal power transformers with virtually complete magnetic flux containment. Two transformers (A, weighing 102 gm with dual ferrite cores, intraluminal primary and extraluminal secondary each with 10 turns on its own crescentic ferrite core, 90 kHz, coupling coefficient k = 0.90-0.96; and B, 68 gm, a single flexible torroidal magnetic metallic tape core with attached 11 turn primary and free 14 turn serosal secondary, 14.7 kHz, k = 0.99) met the electrical and anatomic requirements. Each was implanted (minilaparotomy, coil-pouch fixation within abdominal musculature) in 4 dogs for 14-21 days to test the operative feasibility, electrical function, warming, and flux containment. For canine testing, wires were tunneled to a chewing-inaccessible site. Neither tissue necrosis, infection, provokable interference from contiguous metal, nor coil displacement were observed; secretions were retained in Group A pouches only. The mean power transmissions for the transformers were A: 24.90 +/- 1.50 W and B: 24.92 +/- 0.89 W, after operation for 7 days or more. The mean efficiencies were A: 75.6 +/- 0.1% total DC/DC, 96.2% coils and B: 80.4 +/- 0.1% total DC/DC, 96.2% coils. The peak skin surface magnetic fluxes for transformers A and B, both trivial at 1.7 and 1.2 G, respectively, were similar. Warming was 0.62 +/- 0.30 degrees C in Group A and 0.73 +/- 0.19 degrees C in Group B. The probability values were p < 0.5 (NS) for DC/DC efficiency and p > 0.10 (NS), for A versus B in all other areas of comparison. Observations for both were encouraging. Transformer B, with less mass, lower frequency, higher efficiency, and intrinsic invulnerability to displacement, was selected for longer term evaluation.
Asunto(s)
Corazón Auxiliar/normas , Íleon/fisiología , Músculos Abdominales/fisiología , Animales , Fenómenos Biomecánicos , Perros , Conductividad Eléctrica , Estimulación Eléctrica , Diseño de Equipo/normas , Diseño de Equipo/tendencias , Corazón Auxiliar/efectos adversos , Técnicas In Vitro , Masculino , Monitoreo Fisiológico , Medición de RiesgoRESUMEN
Circulatory support devices require 10-20 W. Currently, several devices are under development for the transmission of this power via transcutaneous transformers, with the secondary implanted subcutaneously and the primary worn externally. Because these devices are air cored, they have relatively large, bulky external appliances, poor coil to coil coupling, and result in significant stray fields passing through adjacent tissues. This article reports on the engineering design of a novel, high permeability cored transformer implanted in a transenteric configuration using an isolated intestinal pouch. Such an approach offers greater energy transmission efficiency, less heat dissipation, less stray electromagnetic energy, and greatly reduced device size. Two competing designs using this concept have been developed and tested. Each consists of the transformer, together with power interface electronics, forming a direct current (DC)/DC resonant converter. Operating frequencies are 90.2 and 14.7 kHz, respectively, with primary/secondary turns ratios of 10/10 and 11/14, respectively. In addition, data interface electronics allows communication across the transformer of up to four signals at a per channel sample rate of 10 Hz. Both designs are able to continuously transmit 25 W at an output level of 12 Vdc into a 5.8 omega load. Calorimetry tests indicate DC to DC efficiencies greater than 75% and coil to coil efficiencies greater than 96%. Total package size for the implantable portion of each device (including sensor internal interface electronics) is less than 40 ml, with a weight weight of less than 100 g. The results of short-term implantation studies have been favorable. Long-term implantation studies currently are under way.
Asunto(s)
Electrónica Médica/instrumentación , Corazón Auxiliar , Animales , Ingeniería Biomédica , Perros , Diseño de Equipo , Estudios de Evaluación como Asunto , Humanos , Íleon/cirugía , Técnicas In Vitro , Masculino , PermeabilidadRESUMEN
Mechanical repowering of a failing heart with devices or skeletal muscle could circumvent blood-pump lining problems. Requirements are complex: indefinite support with preservation of valve competence and coronary flow, avoidance of wall coaptation, and allowance of both rapid low impedance refilling and independent left and right pressures. An accurate in vitro physical failing-heart analog could facilitate the choice and screening of surgical and engineering approaches in mock circulation experiments. Prosthetic models, transplant recipient hearts, normal animal hearts, existing in vivo animal failure models, and failing cadaver hearts all have serious limitations. One hundred and four excised porcine hearts were dilated and fixed by three iterative protocols. Geometric and passive mechanical parameters were assessed and compared with targets expected for an end-stage failing heart. For Protocol 3, Subgroup 2 (reinforcing valve support, dilatation by compliant ventricular balloon, and ethyl alcohol fixation), the left ventricular shape and capacity (ellipsoid, 201-377 ml/500 g of heart weight), passive valve function, wall flexural rigidity (Et3 range 0.101-0.331 Nm), and refilling mechanics (99 +/- 17.46 ml during 200-400 ms at < or = 10 mm Hg transmural gradient) were all within goal criteria.
Asunto(s)
Insuficiencia Cardíaca/fisiopatología , Disfunción Ventricular Izquierda/fisiopatología , Función Ventricular Izquierda/fisiología , Animales , Fenómenos Biomecánicos , Soluciones Cardiopléjicas , Cateterismo , Circulación Coronaria/fisiología , Corazón/anatomía & histología , Corazón/fisiología , Corazón Artificial/normas , Técnicas In Vitro , Válvula Mitral/fisiología , PorcinosRESUMEN
A new implantable transducer has been developed for in situ evaluation of ligament and tendon forces. Unlike previous devices, this sensor is placed within the specimen, minimizing measurement errors due to impingement on surrounding soft tissues and bone. In this study, we present the sensor design details as well as test results from initial in vitro trials in the goat patellar tendon model. Device performance and influence of the device on the specimen were evaluated under several loading conditions. In all cases, device output had a strong correlation with induced tissue load. Significant variations in device performance were only noted at high tissue deformation rates. More extensive investigations will be conducted to assess how changes in transducer design might alter performance characteristics.
Asunto(s)
Articulación de la Rodilla/fisiología , Modelos Biológicos , Prótesis e Implantes , Tendones/fisiología , Transductores , Animales , Diseño de Equipo , Estudios de Evaluación como Asunto , Cabras , Técnicas In Vitro , Rótula , Valores de Referencia , Estrés Fisiológico/fisiopatología , Resistencia a la TracciónRESUMEN
A mathematical model was developed for an implantable force transducer to be inserted within the midsubstance of a ligament or tendon. The model was generated by performing both equilibrium and strain-displacement analyses on a metallic, curved beam structure placed within a parallel-fibered tissue. The analysis permitted the transverse pressure acting between the device and fibers to be calculated along with peak device strain and sensitivity (ratio of strain output to axial tissue force). Transducer pressure and transducer strain were expressed in terms of nondimensionalized design factors. A parametric analysis of the key design factors was then performed. The transverse pressure was shown to vary little for large changes in these factors whereas device strain changed markedly. The analysis was verified by a bench test on an example device. Such a model permits a proposed design to be evaluated without having to conduct costly experiments.