A permanent prosthesis for converting in situ muscle contractions into hydraulic power for cardiac assist

Abstract

The key to utilizing muscle power for circulatory support lies with the development of a practical scheme by which contractile energy may be collected and efficiently delivered to the bloodstream. This work describes initial in vitro testing of a prototype muscle energy converter (MEC) designed to transform the power of in situ muscle contractions into hydraulic form. The MEC resembles a simple piston pump and is designed for implant beneath the humeral insertion of the latissimus dorsi muscle. Bench tests were conducted to measure component function and to characterize device performance under various hydraulic loads. Under simulated muscle-pull conditions, MEC energy transfer capacity was found to be 170 mJ/stroke while operating at peak efficiencies (i.e., > 98% of input power converted into hydraulic energy and preload work). Transfer efficiencies dropped from 96 to 38% as mean generated pressures increased from 23 to 36 N/cm2 due to metal bellows flexion. These results demonstrate that a significant amount of contractile energy can be efficiently transformed to hydraulic power via this mechanism.

Improved Mechanism for Capturing Muscle Power for Circulatory Support

“…Each was designed to operate as a linear piston‐in‐cylinder type pump with an eye toward keeping device complexity to a minimum. Despite numerous design improvements, however, stroke length demands raised concerns over long‐term bellows performance, and the piston‐in‐cylinder design proved difficult to reconcile with certain anatomic constraints (15–17). Based on these findings, a radical design change was implemented in an effort to reduce bellows flexion stresses, lower the housing profile, and minimize the risk of tissue encumbrance to actuator motion (18).…”

“…At Allegheny, lessons learned through four previous design iterations (15–19) have now been incorporated into a fifth‐generation device (MEC5) with significantly enhanced energy transfer capacity and tissue interface characteristics. This report details current improvements in the MEC design and summarizes results from in vitro mechanical tests.…”

Method for measuring long-term function of muscle-powered implants via radiotelemetry

“…The most salient aspects of MEC design and function have not changed appreciably since they were first described in 1997 (13). In brief, this device assumes the form of a cylindrical pump, 12-14 cm in length, with a reciprocating piston stationed at one end.…”

Models of Metabolic Utilization Predict Limiting Conditions for Sustained Power from Conditioned Skeletal Muscle

“…To harness the mechanical work of conditioned muscle, implantable energy converters are being developed to convert the work of linearly contracting muscle into hydraulic energy. 18,19,23,24 The available power from electrically conditioned muscle is inherently limited; therefore, the sustained power output must be maximized for cardiac assist applications.…”