Development of an automated liver perfusion system: The benefit of a hemofilter.

INTRODUCTION:: Liver perfusion machines are close to becoming a reality in the transplantation field. However, depending on the techniques used and the goals pursued, their application is limited in the research field. Here, we present the entire development of a perfusion system with self-made engineering, completely autonomous controls, and a high degree of versatility that allows the design of different studies on liver functionality. METHODS:: A user-friendly interface permits real-time monitoring and remote control by the devices within the circuit. Centrifugal pumps allow the perfusate enter the organ with controlled pressures and flows at both hepatic artery and portal vein. The implementation of a hemofilter as a novel tool permits to control and maintain homeostasis. Peristaltic pumps adjust pH, extraction rate, and total volume by means of sensors. RESULTS:: Real-time monitoring facilitates liver functionality assessment. The controlled system shows rapid stabilization and quick responses to changes during 6 h of perfusion experiments. Furthermore, the integration of a hemofilter helps the system to eliminate toxic waste and maintain homeostasis. DISCUSSION:: The machine provides the basis of a perfusion system with autonomous controls and the implementation of a hemofilter that enables a more efficient control of hemostasis. Moreover, the developed hardware and software are subjected to further tuning for additional purposes such as pathophysiologic studies, suboptimal grafts recovery, or recellularization of decellularized scaffolds among others.

3D bioprinting of functional human skin: production and in vivo analysis.

Significant progress has been made over the past 25 years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin, or for the establishment of in vitro human skin models. In this sense, laboratory-grown skin substitutes containing dermal and epidermal components offer a promising approach to skin engineering. In particular, a human plasma-based bilayered skin generated by our group, has been applied successfully to treat burns as well as traumatic and surgical wounds in a large number of patients in Spain. There are some aspects requiring improvements in the production process of this skin; for example, the relatively long time (three weeks) needed to produce the surface required to cover an extensive burn or a large wound, and the necessity to automatize and standardize a process currently performed manually. 3D bioprinting has emerged as a flexible tool in regenerative medicine and it provides a platform to address these challenges. In the present study, we have used this technique to print a human bilayered skin using bioinks containing human plasma as well as primary human fibroblasts and keratinocytes that were obtained from skin biopsies. We were able to generate 100 cm2, a standard P100 tissue culture plate, of printed skin in less than 35 min (including the 30 min required for fibrin gelation). We have analysed the structure and function of the printed skin using histological and immunohistochemical methods, both in 3D in vitro cultures and after long-term transplantation to immunodeficient mice. In both cases, the generated skin was very similar to human skin and, furthermore, it was indistinguishable from bilayered dermo-epidermal equivalents, handmade in our laboratories. These results demonstrate that 3D bioprinting is a suitable technology to generate bioengineered skin for therapeutical and industrial applications in an automatized manner.

Synchrony relationships between the left ventricle and a left ventricular assist device: an experimental study in pigs.

BACKGROUND: Synchronization between the left ventricle and a left ventricular assist device (LVAD) may be important for ventricular unloading and coronary perfusion. We assessed the synchrony between cardiac and LVAD cycles by increasing delays in steps of 100 msec throughout the cycle, under conditions of total and partial left ventricular support. METHODS: We studied 7 healthy minipigs weighing 30-40 kg. A 60-cc Berlin Heart Excor LVAD was implanted and connected to a BCM 1200 console, making it possible to synchronize the LVAD systole and the EKG signal with a prefixed delay. We recorded hemodynamic parameters (including aortic, pulmonary, and left ventricular pressure) and LVAD flow for each delay. RESULTS: Intraventricular pressure during LVAD systole was minimized with delays of around 40-80% of one cycle. In addition, total flow was higher under these conditions. CONCLUSIONS: This study shows that the synchronous mode of LVAD operation is feasible. Moreover, a delay in device contraction until the second half of the cardiac cycle optimizes ventricular unloading and may eventually improve myocardial recovery.

Heart support systems: from idea to clinical practice.

This paper describes the development of a pneumatic ventricular assist device by our group from the first steps to the clinical assay. The device, called BCM, has an input compliant cannula that improves the filling of the device. Results of the clinical assay showed that the BCM device was suitable for clinical use. New developments of our group are also mentioned.

Continuous renal replacement therapy with a pulsatile tubular pump: parameters must be adjusted in each case.

A three-valve, pulsatile tubular pump was used in 24 pigs weighing 10.2 +/- 3.2 kg; the pump was connected to a neonatal hemofiltration circuit. Ninety-two periods of 30 min were studied to analyze the efficacy of the system with variations in the percentage time in diastole, the diastolic speed, the systolic speed, and the percentage time in systole during which the postfilter valve was closed. System efficacy was determined by the blood flow through the filter, the ultrafiltrate volume, the vascular overload measured by the inlet aspiration pressure, and the filter overload measured by the cross-filter pressure drop and the transmembrane pressure. The variations in the pump parameters did not lead to significant differences in the efficacy of the system or in the vascular or filter overload. The parameters must be adjusted in each case to obtain the best yield with the lowest vascular and filter overload.

Continuous venovenous renal replacement therapy with a pulsatile tubular blood pump: analysis of efficacy parameters.

A three-valve pulsatile tubular pump was used in 10 pigs weighing 9.9+/-0.3 kg, connected to a neonatal hemofiltration (HF) circuit to analyze the parameters to determine the ultrafiltration effectiveness for venovenous continuous renal replacement therapy. Forty 30-min periods were studied to analyze the influence of the catheter diameter, purification technique (HF or hemodiafiltration), pump pulsation frequency, percentage time in diastole, percentage time in diastole in which the post pump valve was closed, and percentage time in systole in which the post filter valve was closed, on ultrafiltrate volume and blood flow through the filter. A higher ultrafiltrate flow was achieved with a frequency of 60 bpm than with 30 bpm, a diastolic time of 65% of the total cycle versus 50%, and a blood flow of greater than 20 mL/min versus less than 20 mL/min. The ultrafiltrate flow increases in relation to the blood flow, the frequency of the pump, and the diastolic time.

The European artificial organ scene: present status.

This article summarizes the current evolutions regarding artificial organs in Europe. The review emanates from the activities by four of the work groups of the European Society for Artificial Organs (ESAO) and is essentially based on the reports by these work groups at the latest ESAO meeting in Warsaw, Poland (2004). The topics are: apheresis, heart support, liver support, uremic toxins.