Improved performance of a chitosan-based adsorbent for the sequestration of some transition metals.

Polyethyleneimine (PEI) was chemically introduced onto chitosan by its reaction with epoxide groups of grafted poly(glycidyl methacrylate) (poly(GMA)) chains for enhanced metal chelating properties and improved physical stability in acidic conditions. Graft polymerization of poly(GMA) onto chitosan was initiated by Ce(IV) ammonium nitrate (CAN). Infrared spectroscopy revealed the presence of significant epoxide groups to confirm the success of both grafting and amination stages. Batch adsorption experiments showed the higher affinity of the modified chitosan resin for Cu2+, Zn2+ and Pb2+. The capacity enhancement was even more pronounced in the case of Zn2+ and Pb2+, which exhibits more complicated three dimensional coordination requirements. Optimum metal adsorption occurs at above pH4. Regeneration of the resin with sulphuric acid-ammonium sulphate was also found to be feasible.

Role of anions on heavy metal sorption of a cellulose modified with poly(glycidyl methacrylate) and polyethyleneimine.

The influence of anions on the equilibrium and kinetic uptake of heavy metals from an aqueous solution by a novel nitrogen-type chelating adsorbent was evaluated. Equilibrium experiments revealed that stoichiometric amounts of metals and anions are adsorbed by the resin. Kinetic studies showed that during the initial stage of adsorption, the anions are adsorbed by the adsorbent prior to the metal ions. This occurred almost simultaneously with an increase in solution pH. At equilibrium, the pH returned towards its initial value. The concentration of anion also fluctuated during the entire equilibration process. Following these observations, mechanisms governing the role of anions on enhancing capacity and rate of metal uptake of this type of chelating adsorbent type were established.

Long-term in vivo study of gas diffusion in bilaminar compliance chambers.

The problem of gas diffusion from compliance chambers in long-term pulsatile blood pump implantation continues. To evaluate and predict gas diffusion at the intrathoracic tissue interface, eight air-filled static bilaminar compliance chambers were implanted in four calves for a mean duration of 191 days. Mean volume loss was 40.3 +/- 6.2 ml (0.2 ml/day) compared with previous results of 1.2 ml/day for pure Hexsyn diaphragms. The residual gas in the chamber was analyzed as nitrogen = 89.6 +/- 0.6%; oxygen = 1.5 +/- 1.1%; and carbon dioxide = 8.8 +/- 0.6%. The resulting gas composition is assumed equivalent to that of the tissue interface and was used in developing a diffusion model. For a complete left ventricular assist system (LVAS), gas diffusion at the arterial blood and tissue interface was simulated. The predicted time to reach a minimum volume of 90 ml (compliance volume equal to full pump stroke volume) was in excess of 1 year.

Methods for volume assessment of an air filled compliance chamber.

The air-filled (120 ml) compliance chamber employs a Dacron covered Hexsyn-butyl bilaminar diaphragm to minimize gas diffusion. Finite permeability dictates the need for a means to detect the remaining air volume and a refill port for gas addition. X-ray studies were used to detect radiopaque chamber markers in cadavers. Tangential X-ray cinematography enabled detection of chamber volumes less than 100 ml and diaphragm center deflection predicted volume to within +/- 6 ml of the actual volume. An electrically driven left ventricular assist pump (90 cc) was used to evaluate motor current (MC) and intracompliance pressure (IP) as indicators of low compliance volume. Peak MC was a function of both hemodynamic output power and compliance volume. Thus, if the peak current for a given hemodynamic output is known, variances may be indicative of low compliance volumes. The cyclic minimum IP vs. volume was +1, -3, and -13 mmHg for compliance volumes of 120, 90, and 80 cc, respectively. Ejection velocity did not significantly affect IP. In conclusion, X-ray studies and MC are useful as noninvasive means of assessing the need for compliance refill. IP, though measured invasively, is the most sensitive volume-dependent parameter.

Heat dissipation through the blood contacting surface of a thermally driven LVAS.

A heat exchanger for a totally implantable heat driven LVAD is an essential element in overall system thermal management. The heat exchange is accomplished by supplying cooling water from a pusher-plate driven water pump to the engine and then to the heat exchanger on the pump housing. The temperature of the interface between the blood and pump surface is of critical importance for clinically acceptable operation of the system. Temperatures were measured by instrumenting a pump housing with thermocouples and an electric heater on a mock circulatory loop. Flows were varied from 1 to 8 l/min and heat input was 20 watts. At 1.0 l/min pump flow the maximum inner surface temperature rise is 4.5 degrees C. In vitro tests were conducted to examine the effect of elevated temperature on platelete function. Both platelet aggregation and adhesion were reduced at elevated temperatures of 42 and 47 degrees C indicating a potential benefit of reduced thrombogenesis on the heated housing surface.

Systemic and local effects of heat dissipation in the thermally powered LVAS.

A thermally powered left ventricular assist system (LVAS) requires 20 W of heat dissipation either to the blood or to the surrounding tissues, such as the lung subcutaneous tissues. Postoperative systemic and local effects of heat dissipation were studied in 5 thermally powered LVASs and 2 heated blood pumps implanted in calves, and compared with 10 pneumatically powered left ventricular assist devices (LVADs). Postoperative mean temperatures of the heat dissipation group were as follows: 1. rectal (RT), 39.1 x 0.4 degrees C (NS versus control); 2. Lung interface, 41.6 +/- 0.6 degrees C (P less than 0.01 versus RT); 3. tissue interface, 40.2 +/- 1.2 degrees C (P less than 0.01 versus RT); and 4. blood, 39.2 +/- 0.8 degrees C (NS versus RT). There was no significant postoperative change in heart rate, respiratory rate, or rectal temperature between the two groups. No difference was shown between the two groups in hematologic parameters, plasma free hemoglobin, liver and renal function, fibrinogen levels, or coagulation processes at the same postoperative time. Heat dissipation to the pump-blood interface promoted a thinner neointima when compared with the nonheated surface. Angioneogenesis was observed in the tissue capsule adjacent to the heat dissipating surface. These results indicated that the thermal LVAS induced no deleterious local or systemic effects on recipient animals.

In vivo evaluation of a permanently implantable thermal ventricular assist system.

The System 7 pump/actuator/engine combination has demonstrated biologic compatibility and physiologic effectiveness and responsiveness in five TVAS in vivo studies. The recent 75-day implant supports the feasibility of extended reliability of the system components. Postoperative system maintenance was necessary only because of the nonhermetic design of System 7. However, the ability to pump 11 l/min at 120 beats/min, synchronize at beat rates of 144 beats/min, and pump against mean arterial pressures of more than 150 mmHg while maintaining hematologic and biochemical values within physiologic range sets a very optimistic stage for System 8 hardware. A System 8 concept is shown in Figure 14. The System 8 hardware will include a thermal salt package capable of providing completely untethered circulatory support for a nominal 8-h period. Recharge will be accomplished with a transcutaneous transformer in 1 h. Thermal management problems become minimal, with an average energy input of 15.8 W (peak of 24.9 W). The human preclinical testing of System 8 will start in 1988.