Use of a composite Biomer-butyl rubber/Biomer material to prevent transdiaphragmatic water permeation during long-term, electrically-actuated left ventricular assist device (LVAD) pumping.

The pumping diaphragm of the Texas Heart Institute (THI) E-Type ALVAD must perform the dual functions of providing a flexible blood interface and isolating the electrical actuator from adjacent fluids. Thus, protection is required against fluid leakage and moisture diffusion to prevent corrosion and damage to electrical actuator components. Average diffusion rates up to 1 ml per day through currently used elastomeric diaphragm materials have been measured during static in-vitro and in-vivo tests. To circumvent this problem, an improved pumping diaphragm has been recently developed for use with the electrically-actuated THI E-Type ALVAD. This trilaminar diaphragm consists of a composite Biomer and butyl rubber design. A.010 inch layer of butyl rubber (characterized by an extremely low diffusion rate for water, approximately 0 ml per day) is positioned between two Biomer layers (.020 and.010 inches in thickness). Initial invitro and in-vivo studies, in calves, indicate that this composite diaphragm provides an excellent barrier to water permeation, without sacrificing biocompatibility or structural integrity under conditions of chronic flexure.

ULTRASTRUCTURAL ANALYSES OF BLOOD-INTERFACING LININGS FORMED WITHIN PARTIAL ARTIFICIAL HEARTS OR ABDOMINAL LEFT VENTRICULAR ASSIST DEVICES: A QUALITATIVE SCHEME FOR HUMAN PSEUDONEOINTIMAL ACCRETION KINETICS.

Following each of 21 clinical trials with the partial artificial heart or abdominal left ventricular assist device (ALVAD), we have examined the blood-interfacing human pseudoneointimal (PNI) linings formed on the fibril-flocked pumping surface by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The salient results of these ultrastructural analyses can be summarized: (1) early PNI accretion kinetics (< 24 hrs) involve plasma protein adsorption, entrapment of erythrocytes, platelets, lymphocytes, numerous neutrophils and macrophages, and the deposition of fibrin within fibril flock interstices (TEM); (2) the surface (< 24 hrs) consists of interconnected fibrin strands (SEM); (3) later PNI accretion kinetics (1-6 days) involve the formation of alternating cellular and fibrin layers (TEM); (4) the surface (1-6 days) consists of cellular aggregates (inter-membrane distances of 340 A) simulating an endothelial interface (SEM, TEM). Based on these analyses, a plausible sequence of events for human PNI accretion kinetics can be advanced, i.e., 0-24 hrs: (a) maximal foreign body response of blood in contact with Dacron fibrils, (b) cellular lysis and fibrin compaction; 1-6 days: (c) accretion and lysis of cellular aggregates (neutrophils, macrophages) 3-4micro thick, (d) accretion of linear fibrin aggregates, 8-10micro thick, and (e) cyclic replication (up to six) of phases c and d.

MACROSCOPIC, MICROSCOPIC, AND MECHANICAL ANALYSES OF PROTOTYPE DOUBLE VELOUR VASCULAR GRAFTS.

In-vivo and ex-vivo evaluations of two prototype double velour tube grafts have been conducted. The experimental grafts were fabricated from terry cloth derivatives of the Dacron polyester material that is used in the construction of presently available Microvel(R) Double Velour and Cooley Double Velour Guideline(R) grafts.(*) The use of terry cloth derivatives in the experimental grafts provides a velour pile that is more uniform in height and density than current clinical grafts. The hypothesis examined by these studies was whether the utilization of terry cloth derivatives provides a more perfect capsular and luminal surface for fibrous tissue attachment and ingrowth, thereby enhancing neointimal formation at the blood contacting surface. Using standard techniques, prototype grafts were implanted in the abdominal aortas of dogs for test periods of 1 to 6 months. All grafts remained patent throughout the healing period. At explantation, the macroscopic and microscopic properties of the grafts were examined and characterized. Neointimal analysis demonstrated that the lighter denier, higher porosity prototype consistently produced more homogeneous blood-contacting surfaces with smoother contours and more complete endothelialization than the heavier denier, lower porosity prototype. From these analyses, we can conclude that both prototype grafts possess the basic properties of useful arterial prostheses. They are not prone to early thrombosis, and exhibit rapid healing properties. This study indicates that the use of terry cloth derivatives provides a more uniform, less random velour pile and that arterial grafts constructed from such materials produce more uniform and biologically stable neointimas.

THEORETICAL DESIGN CONSIDERATIONS AND PHYSIOLOGIC PERFORMANCE CRITERIA FOR AN IMPROVED INTRACORPOREAL (ABDOMINAL) ELECTRICALLY ACTUATED LONG-TERM LEFT VENTRICULAR ASSIST DEVICE ("E-TYPE" ALVAD) OR PARTIAL ARTIFICIAL HEART.

Our laboratories are engaged in the design of a clinically-oriented electrically actuated long-term intracorporeal (abdominal) left ventricular assist device ("E-type" ALVAD) or partial artificial heart. This infradiaphragmatic blood pump is designed to be powered by implantable electrical to mechanical energy converter systems. THE FOLLOWING ANALYSES WERE UNDERTAKEN TO: [List: see text] The proposed "E-type" ALVAD should be capable of pumping 4-7 liters per minute at heart rates of 75-100 beats per minute during rest, and 10 liters per minute at rates of 120 beats per minute during moderate exercise. These performance levels should be exceeded with a maximum device stroke volume of 85-90 ml and a mean pump inflow (filling) impedance of