Endothelial and vascular smooth muscle cell function on poly(lactic-co-glycolic acid) with nano-structured surface features

Biomaterials that successfully integrate into surrounding tissue should match not only the tissue's mechanical properties, but also its topography. The cellular response to a biomaterial may be enhanced in synthetic polymer formulations by mimicking the surface roughness created by the associated nano-structured extra-cellular matrix components of natural tissue. As a first step towards this endeavor, the goal of the present in vitro study was to use these design parameters to develop a synthetic, nano-structured, polymeric biomaterial that promotes cell adhesion and growth for vascular applications. In a novel manner, poly(lactic-co-glycolic acid) (PLGA) (50/50wt% mix) was synthesized to possess a range (from micron to nanometer) of surface features. Reduction of surface features was accomplished by treating conventional PLGA with various concentrations of NaOH for select periods of time. Results from cell experiments indicated that, compared to conventional PLGA, NaOH treated PLGA enhanced vascular smooth muscle cell adhesion and proliferation. However, PLGA prepared by soaking in NaOH decreased endothelial cell adhesion and proliferation compared to conventional PLGA. After further investigation, this finding was determined to be a result of chemical (and not topographical) changes during polymer synthesis. Surface chemistry effects were removed while retaining nano-structured topography by using polymer/elastomer casting methods. Results demonstrated that endothelial and smooth muscle cell densities increased on nano-structured cast PLGA. For these reasons, the present in vitro study provided the first evidence that nano-structured surface features can significantly improve vascular cell densities; such design criteria can be used in the synthesis of the next-generation of more successful tissue-engineered vascular grafts.     

Nano-structured polymers enhance bladder smooth muscle cell function

It is the hypothesis of the present study that a biocompatible material which mimics the nanometer topography of native bladder tissue will enhance cellular responses and lead to better tissue integration in vivo. Previous in vitro studies have verified the ability to successfully reduce the surface feature dimensions of poly(lactic-co-glycolic acid) (PLGA) and poly(ether urethane) (PU) films into the nanometer regime via chemical etching procedures. Results from these studies also provided the first evidence that bladder smooth muscle cell adhesion was enhanced on chemically treated nano-structured polymeric surfaces compared to their conventional counterparts. Although cell adhesion is necessary for a biomaterial's success, subsequent cell functions (such as long-term cell growth and proliferation) are also critical for tissue ingrowth and long-term implant survival. The present in vitro study, therefore, investigated the function of bladder smooth muscle cells on these novel, nano-structured polymers over the expanded periods of 1, 3 and 5 days. Results indicated that cell number was influenced by both surface roughness and surface chemistry changes; the important contributor, however, was increased nanometer surface roughness. This claim is supported by the fact that cell number was enhanced on nano-structured compared to conventional PLGA and PU once chemistry changes were eliminated using casting techniques.     

Bileaflet Aortic Valve Prosthesis Pivot Geometry Influences Platelet Secretion and Anionic Phospholipid Exposure

The clinical histories of the Medtronic Parallel (MP) and St. Jude Medical (SJM) Standard valves suggest pivot geometry influences the thrombogenic characteristics of bileaflet prostheses. This work studied the effects of various pivot geometries on markers of platelet damage in a controlled, in vitro apparatus. The Medtronic Parallel valve, two St. Jude Medical valves, and two demonstration prostheses were used to study the effects of bileaflet pivot design, gap width, and size on platelet secretion and anionic phospholipid expression during leakage flow. A centrifugal pump was used to drive blood through a circuit containing a bileaflet prosthesis. Samples were taken at set time intervals after the start of the pump. These samples were analyzed by cell counting, flow cytometry, and enzyme-linked immunosorbant assay. No significant differences were observed in platelet secretion or anionic phospholipid expression between experiments with the SJM 27 Standard regular leaker, the SJM 20 regular leaker, and the MP 27 valves. Significant differences in platelet secretion and anionic phospholipid expression were observed between a SJM 27 Standard regular leaker and a SJM 27 high leaker valve. These studies suggest that leakage gap width within bileaflet valve pivots has a significant effect on platelet damage initiated by leakage flow. © 2001 Biomedical Engineering Society. PAC01: 8719Uv, 8719Tt, 8380Lz, 8768+z