Effective clearance of uremic toxins using functionalised silicon Nanoporous membranes

In-house fabricated silicon nanoporous membranes (SNMs), functionalized for efficient clearance of uremic toxins, can lead to compact and portable dialysis systems. Efficacy of 15 nm thick SNMs, with average pore diameter of 8 nm, was tested for dialysis of two uremic toxins - urea and creatinine using custom made teflon apparatus of 2, 10 and 30 ml. The apparatus consisted of two reservoirs, with the cis containing the uremic fluid, and the trans containing the dialysate. Peristalsis was found to enhance the clearance rate by a factor of four as compared to unstirred condition. Functionalisation of the SNMs reduced protein binding, and surface binding of urea from 23% to negligible values. A lateral array of nine SNMs and a new design for the dialysis apparatus, increased the clearance rate by a factor of twelve from that of the single SNM. The arrays cleared about 42% of urea and 48% of creatinine from 30 ml of diluted serum samples, in 15 min. Periodic replacement of the trans fluid cleared about 81% of high concentration uremic toxins from the cis reservoir in 45 mins. The SNM arrays are stable, reproducible, and with the superior clearance rates for urea and creatinine, they have the potential to be used as membranes for portable hemodialysers.

In Vitro models for thrombogenicity testing of blood-recirculating medical devices

INTRODUCTION

Blood-recirculating medical devices, such as mechanical circulatory support (MCS), extracorporeal membrane oxygenators (ECMO), and hemodialyzers, are commonly used to treat or improve quality of life in patients with cardiac, pulmonary, and renal failure, respectively. As part of their regulatory approval, guidelines for thrombosis evaluation in pre-clinical development have been established. In vitro testing evaluates a device's potential to produce thrombosis markers in static and dynamic flow loops.

AREAS COVERED

This review focuses on in vitro static and dynamic models to assess thrombosis in blood-recirculating medical devices. A summary of key devices is followed by a review of molecular markers of contact activation. Current thrombosis testing guidance documents, ISO 10993-4, ASTM F-2888, and F-2382 will be discussed, followed by analysis of their application to in vitro testing models.

EXPERT OPINION

In general, researchers have favored in vivo models to thoroughly evaluate thrombosis, limiting in vitro evaluation to hemolysis. In vitro studies are not standardized and it is often difficult to compare studies on similar devices. As blood-recirculating devices have advanced to include wearable and implantable artificial organs, expanded guidelines standardizing in vitro testing are needed to identify the thrombotic potential without excessive use of in vivo resources during pre-clinical development.

Protein Separation and Hemocompatibility of Nitride Membranes in Microfluidic Filtration Systems

Improving the health outcomes for end-stage renal Disease (ESRD) patients on hemodialysis (HD) requires new technologies for wearable HD such as a highly efficient membrane that can achieve standard toxic clearance rates in small device footprints. Our group has developed nanoporous silicon nitride (NPN) membranes which are 100 to 1000 times thinner than conventional membranes and are orders-ofmagnitude more efficient for dialysis. Counter flow dialysis separation experiments were performed to measure urea clearance while microdialysis experiments were performed in a stirred beaker to measure the separation of cytochrome-c and albumin. Hemodialysis experiments testing for platelet activation as well as protein adhesion were performed. Devices for the counter flow experiments were constructed with polydimethylsiloxane (PDMS) and a NPN membrane chip. The counter flow devices reduced the urea by as much as 20%. The microdialysis experiments showed a diffusion of ~ 60% for the cytochrome-c while clearing ~ 20% of the Albumin. Initial hemocompatibility studies show that the NPN membrane surface is less prone to both protein adhesion and platelet activation when compared to positive control (glass).

Preliminary Diffusive Clearance of Silicon Nanopore Membranes in a Parallel Plate Configuration for Renal Replacement Therapy

Silicon nanopore membranes (SNMs) with compact geometry and uniform pore size distribution have demonstrated a remarkable capacity for hemofiltration. These advantages could potentially be used for hemodialysis. Here, we present an initial evaluation of the SNM's mechanical robustness, diffusive clearance, and hemocompatibility in a parallel plate configuration. Mechanical robustness of the SNM was demonstrated by exposing membranes to high flows (200 ml/min) and pressures (1,448 mm Hg). Diffusive clearance was performed in an albumin solution and whole blood with blood and dialysate flow rates of 25 ml/min. Hemocompatibility was evaluated using scanning electron microscopy and immunohistochemistry after 4 hours in an extracorporeal porcine model. The pressure drop across the flow cell was 4.6 mm Hg at 200 ml/min. Mechanical testing showed that SNM could withstand up to 775.7 mm Hg without fracture. Urea clearance did not show an appreciable decline in blood versus albumin solution. Extracorporeal studies showed blood was successfully driven via the arterial-venous pressure differential without thrombus formation. Bare silicon showed increased cell adhesion with a 4.1-fold increase and 1.8-fold increase over polyethylene glycol (PEG)-coated surfaces for tissue plasminogen factor (t-PA) and platelet adhesion (CD41), respectively. These initial results warrant further design and development of a fully scaled SNM-based parallel plate dialyzer for renal replacement therapy.

Extract of fetal membrane would inhibit thrombosis and hemolysis

The innermost layer of fetal membranes is amnion which has anti-adhesive, anti-inflammation and viscoelastic properties, as well as low immunogenicity. Amniotic membrane has been employed in variety of clinical fields as a natural biomaterial. Amniotic epithelial cells possess stem cell characteristics and capability to differentiate into endothelial cells. The basement membrane of amnion is an extracellular matrix enriched scaffold to support adhesion of endothelial cells. The matrix of amniotic membrane contains two kinds of glycosaminoglycans including perlecan (a heparan sulfate proteoglycan) and hyaluronic acid which both inhibit blood coagulation. Moreover, the other ingredients of amniotic membrane such as pigment-epithelium derived factor (PEDF), IL-10, MMP-9 inhibit platelet aggregation. Based on some biochemical and biomechanical evidences, we hypothesized in this paper that amniotic membrane could prevent thrombosis and hemolysis; therefore, has the capability to be applied in blood contacting devices and implants.