Biomedical subjects

R C Eberhart

Publications and source records attributed to R C Eberhart.

At least 19 recordsLinked to original sources

PubMed2003

In vitro hemocompatibility studies of drug-loaded poly-(L-lactic acid) fibers.

Our objective was to evaluate the hemocompatibility of biodegradable stent fibers, employing a closed-loop circulation system filled with human blood. We also investigated the effects of the anti-inflammatory and anti-proliferative drugs curcumin and paclitaxel, incorporated into stent fibers. Fresh whole blood was circulated in four parallel closed-loop systems: the empty tube circuit (control) and tubes containing either a PLLA fiber coil (PLLA), a curcumin-loaded PLLA coil (C-PLLA) or a paclitaxel-loaded PLLA coil (P-PLLA). The influence of PLLA fiber, alone or loaded with drug incorporated during melt-extrusion, on leukocyte and platelet adhesion and activation was determined by flow cytometry. The effects of blood flow and fiber properties on cell deposition were assessed by scanning electron microscopy (SEM). The flow cytometry results clearly demonstrated that PLLA triggers blood cell activation at the site of deployment, as shown by increases in CD11b, CD62P and leukocyte-platelet aggregates, compared to controls. Curcumin and paclitaxel treatments both significantly reduced leukocyte and platelet activation and adhesion to PLLA fibers, as shown by flow cytometry and SEM. Activated leukocytes and platelets revealed significantly lower CD11b and CD62P receptor binding for C-PLLA compared with PLLA alone, and slightly lower for P-PLLA. Reductions in platelet-leukocyte aggregates were observed as well. In addition, there was less leukocyte and platelet adhesion to C-PLLA, compared with PLLA fiber controls, as shown by SEM. A continuous linear thrombus, composed of platelets, leukocytes, red blood cells and fibrin was occasionally detected along the line of tangency between the coil and the tube wall. Flow separation and eddying, proximal and distal to the line of tangency of coil and tube, is thought to contribute to this deposit. Curcumin was more effective than paclitaxel in reducing leukocyte and platelet activation and adhesion to PLLA stent fibers in this setting. However there was evidence of paclitaxel degeneration during melt extrusion that may have inhibited its effectiveness. Incorporation of the anti-inflammatory and anti-proliferative drug curcumin into bioresorbable stent fibers is proposed to prevent thrombosis and in-stent restenosis.

Anti-Inflammatory Agents↗

PubMed2002

In vitro study of drug-loaded bioresorbable films and support structures.

Bioresorbable films can serve simultaneously as anatomic support structures and as drug delivery platforms. In the present study, bioresorbable poly(L-lactic acid) (PLLA) films containing dexamethasone were prepared by solution processing methods. Their in vitro studies focused on the mechanical properties with respect to morphology and degradation and erosion processes. Novel expandable support devices (stents) developed from these films were studied. Such a stent would support conduits, such as the neonatal trachea to treat tracheal malacia, until the airway matures, and would then be totally resorbed, obviating the need for a removal operation. The PLLA films showed good initial mechanical properties. They can accommodate drug incorporation on the film surface and also in the bulk. Water incubation of the films results in a decrease in their tensile mechanical properties, due to chain scission and morphological changes. These changes can vary from degradation and small changes in morphological features to erosion, leading to a microporous structure, depending on the polymer. The cumulative release of dexamethasone from the films is linear. The rate of release is determined by the film's structure (drug location/dispersion). The stents demonstrated good mechanical properties. The initial radial compression strength of the stent is determined mainly by the polymer structure. Drug incorporation has a minor effect on the initial stent strength. Exposure to radial compression stress results in elastic reversible deformation or a sudden brittle fracture, depending on the polymer. A 20-week in vitro study of the stents showed that they are applicable for supporting body conduits, such as the trachea.

Absorbable Implants↗

PubMed2001

Structured drug-loaded bioresorbable films for support structures.

Bioresorbable films can serve simultaneously as anatomic support structures and as drug delivery platforms. In the present study, bioresorbable PLLA films containing dexamethasone were developed through solution processing. The effect of processing parameters on the film morphology and the resulting mechanical properties was studied. A model describing the structuring of these films is suggested. Generally, the solvent evaporation rate determines the kinetics of drug and polymer crystallization and thus, both the mode of drug dispersion in the polymer and the resulting mechanical properties. Two types of structured films were studied: (1) a polymer film with drug located on its surface, obtained due to drug skin formation accompanied by a later polymer core formation; and (2) a polymer film with small drug particles and crystals distributed within the bulk, obtained by parallel solidification of the two components. A prototypical application of these films is an expandable biodegradable support structure (stent). which we have developed. This stent demonstrated good initial mechanical properties. The film structure has only a minor effect on the stent radial compression strength, but more significantly affects the tensile mechanical properties.

Biocompatible Materials↗

PubMed2000

Laminin-coated poly(L-lactide) filaments induce robust neurite growth while providing directional orientation.

Cellular channels during development and after peripheral nerve injury are thought to provide guidance cues to growing axons. In tissue culture where these cues are absent, neurites from dorsal root ganglion neurons grow with a radial distribution. To induce directional axonal growth and to enhance the rate of axonal growth after injury, we have designed microfilaments of poly(L-lactide). We demonstrate that dorsal root ganglia grown on these filaments in vitro extend longitudinally oriented neurites in a manner similar to native peripheral nerves. The extent of neurite growth was significantly higher on laminin-coated filaments compared with uncoated and poly-L-lysine-coated filaments. As high as 5.8 +/- 0.2 mm growth was observed on laminin-coated filaments compared with 2.0 +/- 0.2 mm on uncoated and 2.2 +/- 0.3 mm on poly-L-lysine-coated filaments within 8 days. Schwann cells were found to grow on all types of filaments. They were, however, absent in the leading edges of growth on laminin-coated filaments. Photolysis of Schwann cells caused a significant reduction in the neurite length on all types of filaments. Laminin-coated filaments, however, induced significantly longer neurites compared with uncoated and/or poly-L-lysine-coated filaments even in the absence of Schwann cells. Our results suggest that laminin-coated poly(L-lactide) filaments are suitable for inducing directional and enhanced axonal growth. Implants designed by arranging these microfilaments into bundles should aid regenerating axons by providing guidance cues and channels to organize matrix deposition, cell migration, axon growth, and improve functional recovery.

Animals↗

PubMed2000

Enhancing hepatocyte adhesion by pulsed plasma deposition and polyethylene glycol coupling.

Decreased hepatocyte adhesion to polymeric constructs limits the function of tissue engineered hepatic assist devices. We grafted adhesion peptides (RGD and YIGSR) to polycaprolactone (PCL) and poly-L-lactic acid (PLLA) in order to mimic the in vivo extracellular matrix and thus enhance hepatocyte adhesion. Peptide grafting was done by a novel technique in which polyethylene glycol (PEG)-adhesion peptide was linked to allyl-amine coated on the surface of PCL and PLLA by pulsed plasma deposition (PPD). Peptide grafting density, quantified by radio-iodinated tyrosine in YIGSR, was 158 fmol/cm(2) on PLLA and 425 fmol/cm(2) on PCL surfaces. The adhesion of hepatocytes was determined by plating 250,000 hepatocytes/well (test substrates were coated on 12 well plates) and quantifying the percentage of adhered cells after 6 h by MTT assay. Adhesion on PCL surfaces was significantly enhanced (p < 0.05) by both YIGSR (percentage of adhered cells = 53 +/- 7%) and RGD (53 +/- 12%) when compared to control surfaces (31 +/- 8%). Hepatocyte adhesion on PLLA was significantly (p < 0.05) enhanced on PLLA-PEG-RGD surfaces (76 +/- 14%) compared to control surfaces (42 +/- 19%) and more (68 +/- 25%) but not statistically significant (p = 0.15) on PLLA-PEG-YIGSR surfaces compared to control surfaces. These results indicate that hepatocyte adhesion to PCL and PLLA based polymeric surfaces can be enhanced by a novel adhesion peptide grafting technique using pulsed plasma deposition and PEG cross-linking.

Animals↗

PubMed1999

Transient adhesion of platelets in pump-oxygenator systems: influence of SMA and nitric oxide treatments.

We employed gamma scintigraphy to quantify the transient accumulations of platelets in pump-oxygenator systems employed in cardiopulmonary bypass (CPB). A flat sheet microporous polypropylene membrane oxygenator (Cobe Duo) was employed, with and without siloxane/caprolactone oligomer coating (SMA) (n = 8 each). The effect of nitric oxide gas infusion on platelet deposition was also evaluated for the uncoated Cobe Duo system (n = 10 each). Scintigraphic images of radiolabelled cells were obtained and converted to numbers of all platelets, labeled and unlabeled, adhering to the pump and oxygenator surfaces. These numbers were compared, by study group, for a 90-min period of normothermic CPB in the adult pig, employing standard prime and anticoagulation regimens. Platelets adhered in large numbers to control oxygenators, reaching maxima (> 20% of the circulating platelet mass) 30 min following institution of CPB, and decreasing for the duration of CPB. SMA treatment significantly decreased platelet adhesion following a 5-10-min transient accumulation period. Nitric oxide infusion significantly reduced platelet adhesion throughout the CPB period. Platelet accumulations on the high fluid shear centrifugal pump surfaces increased monotonically to maxima at about the same time as for the oxygenators, but did not decrease thereafter. Higher platelet surface densities were observed on the centrifugal pump surfaces than on the oxygenator surfaces. CPB with the untreated circuit tended to reduce circulating platelet counts vs theoretical values based on hemodilution alone. In contrast, SMA significantly increased the circulating platelet count versus the untreated control group. These results indicate that platelet adherence to the foreign surfaces of CPB equipment are influenced in characteristic ways by time and fluid shear. SMA treatment and nitric oxide infusion both reduce platelet adhesion to oxygenator surfaces. SMA treatment spares these cells for the circulation.

Animals↗

PubMed1998

In vivo evaluation of a closed loop monitoring strategy for induced paralysis.

OBJECTIVE: Reliable closed loop infusion systems for regulating paralysis level can be a great convenience to the anesthesiologists in automating their task. This paper describes the in vivo performance evaluation of a self-tuning controller that is designed to accommodate large variations in patient drug sensitivity, drug action delays and environmental interfering noise. METHODS: The infusion system was evaluated in six adult mongrel dogs. Following the manual induction of paralysis by an anesthesiologist, the controller regulated the infusion of vecuronium to maintain a desired level of paralysis. The integrated EMG response of the hypothenar muscle to a train-of-four stimulation of the ulnar nerve quantified the depth of paralysis. The controller's robustness was tested by contaminating the sensed twitch signal with electrocautery noise and electrode disconnection. RESULTS: The controller reached the initial level of paralysis of 100% in about 4.0 minutes and arrived at the desired level of 90% with an overshoot of 6.38% (+/-6.82). It maintained the desired level of paralysis with a 2.04% (+/-1.20) mean offset at 90% and 0.4% (+/-0.5) mean offset at 80% steady state level, respectively. The mean infusion rate to sustain 90% and 80% paralysis were 2.70 (+/-2.05) and 2.15 (+/-2.57) ((mg/kg)/min), respectively. CONCLUSIONS: The system adapted to a large variation in the sample subject drug sensitivity. It remained stable despite large amplitude disturbances and maintained the paralysis at the desired level following the removal of the disturbances.

Animals↗

PubMed1997

Anti-platelet action of nitric oxide and selective phosphodiesterase inhibitors.

Nitric oxide gas is a potent inhibitor of platelet aggregation, with an IC50 of 3.6 microM for rabbit platelets. Since the NO effect is mediated via increased cGMP, this in vitro study was undertaken to test the hypothesis that selective phosphodiesterase (PDE) inhibitors might enhance aggregation inhibition at lower NO concentrations. Because the cAMP-selective PDE III and the cGMP-selective PDE V are prominent in platelets, milrinone, a PDE III inhibitor, and zaprinast, a PDE V inhibitor, were tested alone and in the presence of NO for their effect on aggregation. Aggregometry was performed on rabbit platelet-rich plasma following addition of ADP as agonist. Milrinone alone gave an IC50 of 12.4 microM. With each agent set to give suboptimal inhibition of aggregation, the combination of milrinone (3-16 microM) and NO (2-10 microM) produced a greater effect than either agent alone. Zaprinast exhibited no effect on aggregation in concentrations up to 160 microM. However, adding zaprinast to 2 microM NO, which alone reduced aggregation approximately 30%, produced a marked synergism in the inhibitory effect up to and including no observable aggregation. These results indicate that elevation of either cAMP or cGMP is sufficient to inhibit platelet function. The platelet cAMP concentration appears high enough to be inhibitory when degradation is suppressed by milrinone. However, basal cGMP levels must be increased by NO before the zaprinast effect is observed.

Animals↗

PubMed1996

Alkylation of cellulosic membranes results in reduced complement activation.

4-Vinyl pyridine was grafted to the surface of the cellulosic membrane Cuprophan, and subsequently alkylated with both C10 and C16 aliphatic chains. Complement activation of heparinized human blood, corrected for anaphylatoxin adhesion, was measured by radioimmunoassay. The surface treatments both yielded substantial reductions in C5a activity, with a lessor reduction in C3a and C4a activity. Alkylation with 10 and 16 carbon chains resulted both in enhancements of albumin adsorption and stability. These enhancements as well as the reductions in complement activation were statistically indistinguishable between the two treatments. The reduction in complement activation was influenced more by adsorption of endogenous albumin and possibly by the vinyl pyridine graft, than the removal of surface active hydroxyl groups from Cuprophan.

Adsorption↗

PubMed1995

Endothelial cells on Dacron vascular prostheses: adherence, growth, and susceptibility to neutrophils.

Human umbilical vein endothelial cells (HUVEC) on knitted and woven Dacron prostheses were compared with HUVEC on smooth surfaces (tissue culture polystyrene, PET film, and Natrix) with regard to adherence, growth, and susceptibility to injury by neutrophils (PMN). These are properties of importance for successful seeding or coating of prostheses. For prosthetic material of given macroscopic dimensions, more endothelial cells (EC) adhered than to smooth surfaces. However, the prostheses had a greater effective surface area as determined by the number of EC at confluency. When this parameter was taken into account, fewer EC were found adherent to prosthetic material per unit effective surface area than for the smooth surface substrates. Growth on prostheses was clearly inferior to that on smooth surfaces, and EC on prostheses were more susceptible to attack by activated PMN than on smooth surfaces. These differences may reflect the topographic differences in cells attached to fibers where they assume more distorted shapes by stretching to span fibers.

Antibodies, Monoclonal↗

PubMed1995

Neonatal extracorporeal membrane oxygenation complicated by sepsis. Extracorporeal Life Support Organization.

The onset of sepsis in neonates while on extracorporeal membrane oxygenation (ECMO) may portend adverse results. Nevertheless, ECMO has been used as a therapy in the management of septic conditions. This study assessed morbidity and mortality in neonates in whom septic complications developed while they were on ECMO. Of 5,123 neonates in the Extracorporeal Life Support Organization Registry undergoing ECMO for nonseptic indications, 217 patients had development of septic complications. A multivariate logistic regression analysis that considered 15 pre-ECMO criteria was performed to evaluate outcome. Mortality was higher in the septic group (35% versus 17%; p < 0.002) and ECMO duration averaged 85 hours longer (p < 0.001). Septic neonates had a greater frequency of complications including seizures, gastrointestinal bleeding, renal dysfunction, and metabolic problems (all p < 0.05). Transfusion requirements were doubled. Oxygenator thrombi and hemofilter malfunction occurred more often in septic patients (p < 0.03). New strategies to prevent sepsis and associated thrombotic and metabolic complications may be indicated. A critical reappraisal of continued aggressive support may be warranted when septic complications develop in neonates during ECMO.

Analysis of Variance↗

PubMed1995

Alkylated cellulosic membranes with enhanced albumin affinity: influence of competing proteins.

4-Vinyl pyridine was grafted to the surface of the cellulosic membrane Cuprophan, and subsequently alkylated with both non-fatty acid-like C10 (GVP-C10) and fatty acid-like C16 (GVP-C16) aliphatic chains. In vitro albumin adsorption studies from single and binary protein solutions, as well as from dilute plasma demonstrated a significant enhancement (1.4-3.89 times) of albumin binding to both the GVP-C10 and GVP-C16 surfaces, relative to unmodified Cuprophan. It is speculated that enhanced albumin adsorption to a surface may improve surface thromboresistance. Further, these results suggest that there is no difference between the enhanced albumin adsorption of the fatty acid and nonfatty like alkyl chains, C10 and C16.

Adsorption↗

PubMed1994

Comparison of tissue factor and prostacyclin production by human umbilical vein endothelial cells on Dacron vascular prostheses and Dacron smooth films.

The functional capacity of human umbilical vein endothelial cells (HUVEC) grown on Dacron (polyethylene terephthalate; PET) vascular prosthetic material was compared with the function of cells on smooth surfaced PET, tissue culture polystyrene (TCPS), and Natrix-coated TCPS. Prosthetic materials include two knitted fabrics (Bionit I and II) and two woven preparations (DeBakey Soft Woven and Extra Low Porosity). Two entities produced by HUVEC that influence blood coagulation were assessed: the procoagulant tissue factor (TF) and the anticoagulant prostacyclin (PGI2). Although TF activity was stimulated on all substrates by endotoxin (LPS), there was no difference among prostheses and no difference among smooth surface materials, but TF was reduced in cells on the prosthetic materials relative to those on smooth surface substrates. The reduced TF production by HUVEC on prosthetic material could be reversed by returning them to TCPS. In contrast, PGI2 production on prostheses was comparable to that on smooth surfaces for both stimulated and unstimulated cells. Stimulation with histamine (1 microM) gave a 2.4-fold increase in PGI2 whereas mellitin (10 micrograms/ml) increased production 12.5-fold. The differential response of HUVEC with regard to these two coagulation factors, one of which is secreted and the other membrane bound, may reflect the distorted shape of cells on fibers of the prosthesis.

Biocompatible Materials↗

PubMed1994

Anatomic basis for mitral valve modelling.

The increasing popularity of mitral valve repair and current interest in replacement with a mitral homograft or heterograft warrant a new look at the normal functional anatomy of the system. We conducted a detailed review of the anatomic structure of both the intact and excised mitral apparatus of porcine and human species. The following intact structural dimensions were measured: total annular length, anterior and posterior annular length. Excised measurements included: total annular length, anterior and posterior annular lengths, leaflet edge lengths, leaflet heights, and anterolateral and posteromedial commissural heights. Leaflet area was calculated from planimetric measurements. Chordal lengths were measured and distribution recorded. The majority of leaflet measurements were not statistically different between groups. For both groups, the measured annular length increased significantly upon valve excision. In both groups, the posterior leaflet area was significantly larger than the anterior leaflet area, and the area of each leaflet alone was significantly greater than the calculated orifice area. Chordal length was not significantly different between groups, however, distribution varied slightly with the ratio of origins to insertions being 8:1 (porcine) and 5:1 (human). The results are consistent with previous studies of the human mitral valve. This study showed little difference between human and porcine data, and the porcine valve was identified as an appropriate model for further investigation of the mitral valve system.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Molecular surface tailoring of biomaterials via pulsed RF plasma discharges.

A pulsed RF plasma glow discharge is employed to demonstrate molecular level controllability of surface film deposits. Molecular composition of plasma deposited films is shown to vary in a significant manner with the RF duty cycle. Three fluorocarbon monomers are used to illustrate the process. All three exhibit a trend towards increased surface CF2 content with decreasing pulsed RF duty cycle, including exclusion of oxygen. Significant variations in carbon-fluorine surface functionalities are obtained over a controllable range of film thickness. Film growth rate measurements reveal the occurrence of surface reactions during significant portions of the off portion of the duty cycle. Albumin adsorption on fluorocarbon-treated PET films is unchanged from PET controls for a 100-fold range of bulk concentrations and 60-fold range of adsorption times. However, increased retention of albumin is observed following incubation with protein-denaturing sodium dodecyl sulfate solution, the retention decreasing with increasing bulk concentration of albumin. The increased retention of albumin suggests the treated surfaces may have promise as biocompatible materials.

Adsorption↗

PubMed1993

Differential collagen distribution in the mitral valve and its influence on biomechanical behaviour.

Surgical repair of the mitral valve primarily involves endogenous valve tissue, however, the intrinsic mechanical behaviour of the tissue is not well described. To address this issue, porcine mitral valve leaflets were examined histologically and engineering concepts were applied to understand the mechanical behaviour of the layered tissue. Rectangular portions were excised from the anterior and posterior leaflets, either parallel or perpendicular to the annulus, and sections were stained for collagen (Masson's trichrome). The cross sectional layers of the valve (atrialis/spongiosa, fibrosa, and ventricularis) were identified by differences in cellularity and collagen density. The fibrosa is composed of dense collagen, while the atrialis/spongiosa and ventricularis are composed of loose collagen. Layer thicknesses were recorded digitally across the section. These values were averaged within tissue groups to determine changes in layer thickness over the length of the sample and average thickness of each layer. In all tissue groups, the fibrosa was the thickest layer, and the atrialis/spongiosa layer was thicker than the ventricularis layer. The total and fibrosa layer thicknesses of the anterior leaflet were significantly thicker than in the posterior leaflet. Mechanical engineering analysis of the layered structures under tension indicated that the anterior leaflet would be able to support greater tensile loads than the posterior leaflet. The layered arrangement was then examined as a beam in bending, and was shown to decrease the resistance of leaflets to bending, and decrease the overall bending stresses on the leaflet. This type of analysis may be extrapolated to gain insight into changes in function in diseased valves as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Continuous thermodilution cardiac output measurement in sheep.

A technique has been developed to continuously measure cardiac output by means of the principles of thermodilution. Pulmonary artery catheters were modified by placing a 10 cm filament near the usual injectate port. Small amounts of heat were infused according to a randomly repeating binary on-off sequence. The distal blood temperature was recorded and cross-correlated with the heat waveform to produce a dilution curve and calculate cardiac output. The technique was compared with bolus thermodilution in seven sheep. Cardiac output ranged from 1.5 to 13.2 L/min, and heart rate varied from 59 to 180 beats/min. The linear regression between the data obtained by the two methods is represented by the equation y = 1.00x + 0.13; the correlation coefficient, R, is 0.97, and the p value is less than 0.0001.

Animals↗

PubMed1992

T lymphocyte modification with the UTA microporous polyurethane vascular prosthesis: in vivo studies in rats.

Sequential quantification of blood T cell subsets by immunocytofluorometry was used to investigate the immune response of microporous polyurethane vascular prostheses after intraperitoneal implantation in rats. The experimental prosthesis, as developed by the University of Texas-Arlington group (UTA), and the Mitrathane prosthesis, as developed by Matrix Med., were implanted for 1, 2 and 6 weeks and compared with ePTFE and wounded rats without prostheses (control group). The implants were examined for histopathology by light microscopy. The percentages of CD4-(helper) and CD8-(suppressor) bearing cells of the PTFE group were significantly lower (p less than 0.05) than the control group 1 week post-implantation. The UTA and the Mitrathane grafts exhibited a significant decrease in both T cell subsets at 1 week, and CD4-bearing cells at 2 weeks. At 6 weeks, T cell subsets were similar among all groups. The ratio of CD4/CD8- cells was similar among all groups except for the PTFE group, which was lower than the control group after 1 week. Histological examination of Mitrathane and UTA grafts showed an acute phase of inflammation which lasted at least 2 weeks. Some foreign body giant cells (FBGC) were present 2 weeks post-implantation, and encapsulation was greater than that observed with PTFE grafts. On the other hand, PTFE grafts exhibited a different pattern of inflammation compared to polyurethane grafts. PTFE implants exhibited a moderate chronic inflammatory response for the first week, as shown by the formation of FBGC. At 2 and 6 weeks, the grafts were encapsulated by a thin layer of collagenous tissue and FBGC were still present around the implants, mostly located in contact with the reinforcing mesh.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗