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Biomedical subjects

A S Chawla

Publications and source records attributed to A S Chawla.

At least 19 recordsLinked to original sources
PubMed2000

Effect of reuse on surface characteristics of balloon angioplasty catheters.

Surfaces of reused angioplasty catheter balloons were characterized by scanning electron microscopy (SEM), image analysis, Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The surfaces were found to have longitudinal ridges, cracks, wrinkled regions and particulates. Most of the particles were carbon-based, and contained traces of Cl and Si. The average number of particles ranged between 11 and 38 per mm2, while the average particle size ranged from 14 micron to 28 micron. About 70%-90% of the particles were larger then 10 micron which is approximately the diameter of the fine blood capillaries. The particles appeared to be firmly attached to the outer surface of the balloon. FT-IR and XPS analysis revealed the presence of Si, the absence of proteins, and suggested that the surface of the reused balloon catheters was oxidized. The study highlights the large number of particles created and released during angioplasty.

Angioplasty, Balloon↗
PubMed1993

Release of chemicals from polyurethane foam in the Même breast implant.

Samples of polyurethane (PU) foam from the Même breast implant were incubated at 37 degrees C in either 0.3-3.0 N sodium hydroxide (NaOH) solutions, normal saline, or methanol. The chemicals released were analyzed by gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS), and Fourier-transform infra-red (FT-IR) spectroscopy. The surfaces of the treated and untreated foam samples were studied by scanning electron microscopy (SEM). The NaOH solutions hydrolysed the foam, releasing toluene diamine (TDA). Incubating the foam in methanol washed out trace quantities of anti-oxidant, 2,4-dimethyl-6-t-butylphenol (DBP). When the foam was incubated in normal saline at 37 degrees C no TDA was detectable but another compound with a mass ion of 173 was detected. Further GC/MS studies confirmed that this compound was polyol, one of the reagents used to manufacture the PU foam. Repeatedly incubating or washing the foam in normal saline or methanol eliminated the release of polyol. SEM studies of the foam samples before and after incubation experiments, showed no evidence of polymer degradation. These findings indicated that polyol was present in the PU foam only as an impurity or residue and did not originate from the breakdown of the foam itself.

Breast↗
PubMed1993

Ascitic fluid cholesterol in differential diagnosis of ascites.

Cholesterol was estimated in ascitic fluid of 89 patients (29 malignant and 60 non-malignant ascites). Mean ascitic cholesterol level was significantly higher in malignant ascites (89.52 mg/dl) as compared to non-malignant ascites (29.93 mg/dl). At a cut off value of 48 mg/dl, the sensitivity, specificity, positive and negative predictive value and overall diagnostic accuracy for diagnosing malignant ascites is 96.5%, 96.6%, 93.3%, 98.3% and 96.6% respectively. Ascitic fluid cholesterol estimation is an easy and reliable test for differentiating malignant ascites from non-malignant ascites.

Ascites↗
PubMed1992

Chemical investigation and anti-inflammatory activity of Vitex negundo seeds.

The CHCl3 extract of the defatted seeds of Vitex negundo exhibited anti-inflammatory activity and yielded four triterpenoids: 3 beta-acetoxyolean-12-en-27-oic acid [1], 2 alpha, 3 alpha-dihydroxyoleana-5,12-dien-28-oic acid [2], 2 beta,3 alpha-diacetoxyoleana-5,12-dien-28-oic acid [3], and 2 alpha,3 beta-diacetoxy-18-hydroxyoleana-5,12-dien-28-oic acid [5]. This is the first report of the isolation of compounds 2, 3, and 5 from a natural source.

Animals↗
PubMed1991

In vitro degradation of a poly(ether urethane) by trypsin.

In vitro enzymatic degradation of non-porous films of segmented poly(ether urethane) (Pellethane 2363-80AE) was investigated by incubating the biomaterial in concentrated trypsin solutions for 5 months at room temperature. Chemical degradation of films was monitored by surface analysis techniques such as Fourier transform infrared spectroscopy-attenuated total reflectance and electron spectroscopy for chemical analysis. This latter technique proved to be much superior in detecting chemical changes. Extraction of films with methanol and characterization of the extracts by gel permeation chromatography revealed the presence of low-molecular-weight polymers. Results have shown that trypsin has the ability to induce degradation in PEU, the soft segment being most affected, particularly the CH2-O bond of the ether linkages.

Biocompatible Materials↗
PubMed1991

Leaching of plasticizers from and surface characterization of PVC blood platelet bags.

The leaching of phthalate plasticizers from four types of blood platelet bags was investigated. The anticoagulant solutions used in the blood collection bags had pH values of 5.64 +/- .04 and contained no detectable amounts of phthalates. Platelet bag materials from each bag were soaked in normal salines for up to 5 days. The salines were tested for the leached phthalates from the bags but none could be found. However, di-(2-ethylhexyl) phthalate (DEHP) leached out of the PL-146 and Terumo bags into bovine calf serum used for soaking the bag materials. There was an increase in the amount of DEHP leached from about 1.1 mg at the end of one day to about 3.3 mg per gm of bag material at the end of a five day extraction with the serum. In PL-732 sets, a platelet bag made of a specialty polyolefin, the amount of DEHP leached out was less than 0.02 mg per g of bag material. CLX bags, which contained tri-(2-ethylhexyl) trimelliate (TETM) as a plasticizer, showed a negligible amount of it leaching into the calf serum. Infra-red spectra showed that PL-146 bags had been coated with a layer of a fatty acid amide while the Terumo bags contained a layer of a silicone fluid on their inner surfaces. CLX bags showed a coating of stearates, which were probably soaps of calcium or zinc. Scanning electron microscopy (SEM) showed that the inner surfaces of each brand of the bag were distinctly different morphologically. The two PVC bags were very similar whereas the surfaces morphology of PL-732 was rougher. Terumo bag had a different surface morphology than those of the other bags whereas the CLX bags had a very regular surface pattern. The exact significance of the surface morphology is not certain but excessively rough surfaces may not be desirable for the bags.

Benzoates↗
PubMed1988

Immobilization of enzymes on polypropylene bead surfaces by anhydrous ammonia gaseous plasma technique.

Anhydrous ammonia gaseous plasma technique was used for the surface modification of polypropylene beads. Amino groups were added onto the surfaces of beads by exposing them to ammonia plasma. Through these amino groups covalent immobilization of glucose oxidase and peroxidase were carried out. The total amounts of immobilized glucose oxidase and immobilized peroxidase were found to be 52 and 43 micrograms/cm2, respectively. To assess the stability of enzyme-polypropylene linkage, beads with covalently immobilized glucose oxidase and peroxidase were washed with phosphate buffer. It was found that after the removal of the adsorbed enzymes, the concentration of covalently immobilized enzymes tended to reach a steady state. After additional washing with buffer for 5 to 6 h, 40-55% of the immobilized enzymes were found to be in the active form.

Ammonia↗
PubMed1988

Degradation of explanted polyurethane cardiac pacing leads and of polyurethane.

Polyurethane cardiac pacing leads explanted at autopsy and from reoperated patients were examined for degradation in the insulation. Scanning electron microscopy (SEM) analysis showed cracks on the polyurethane surface which were both parallel and perpendicular to the longitudinal axis of the lead. Surface analyses of leads were performed using Fourier-Transform Infra-red (FT-IR) spectrophotometry in the attenuated total reflectance mode. The FT-IR spectra of visibly deteriorated polyurethane from explanted lead sheaths were compared with that of unused polyurethane tubing used for such sheaths. Changes were most evident in the regions of 3000-2800, 1730 and 1368 cm-1. The observed alterations in the FT-IR spectra were consistent with a degradation mechanism involving oxidative chain cleavage in the polyurethane amorphous regions. New polyurethane tubing (Pellethane-Type 80A) was exposed to sodium hypochlorite to simulate a possible in-vivo process and generate reference material. Degradation with associated decreases in tensile strength and molecular weight was recorded. This study showed that polyurethane insulation used in pacing leads is susceptible to oxidative degradation.

Biocompatible Materials↗
PubMed1986

Enhanced albumin binding to polypropylene beads via anhydrous ammonia gaseous plasma.

Plasma surface modification technique was used to add amino groups onto the surfaces of polypropylene beads by exposing them to anhydrous ammonia plasma. Through these amino groups, albumin was attached to the polypropylene beads. Attached albumin was further stabilized by crosslinking with glutaraldehyde. The effect of washing albuminated polypropylene beads with saline and human plasma was investigated. It was found that after initial rapid removal of albumin, the concentration of attached albumin tended to reach a steady-state. After 52 h of washing, the amount of albumin retained on the beads varied between 125 and 171 micrograms/cm2.

Albumins↗
PubMed1986

Characterization of plasma polymerized polypropylene coatings.

Propylene was polymerized at low pressure in a radio frequency plasma reactor. The plasma polymerized propylene (PPP) films were insoluble in toluene. Thermal analysis of PPP showed no phase transition took place up to 255 degrees C. From these results, it was concluded that PPP is a highly crosslinked polymer. To further characterize the deposited PPP, Fourier Transform infrared (FTIR) spectroscopy in the attenuated total reflection (ATR) mode was used. The deposited material was shown to be polymerized propylene as a spectrum of the material showed absorption bands characteristic of polypropylene.

Biocompatible Materials↗
PubMed1985

Aggregation of insulin, containing surfactants, in contact with different materials.

The aggregation of insulin and of insulin protected with surfactants was studied by shaking at 37 degrees C in glass, in polypropylene and polystyrene vials, and in CPI and Auto-Syringe insulin syringes and infusion sets. Surfactants such as Pluronic 17R8 and 25R5 hastened the aggregation, whereas Pluronic F68 was effective in preventing it. Furthermore, there was no change in the immunoreactivity of insulin containing Pluronic F68 even after 8 days of shaking. Unprotected insulin aggregated in all the vials. There appears to be little problem with the commercial syringes tested, but the infusion sets could cause aggregation of insulin if used over an extended period of time. Although Pluronic F68 prevented insulin aggregation in situ, it extracted more impurities from the contacting plastics. Further development in materials and design of insulin sets and insulin containers appears necessary.

Chemical Phenomena↗
PubMed1983

Albuminated polymer surfaces for biomedical application.

Amino groups were added on to the surfaces of Celgard-2400 membranes by exposing them to an ammonia plasma. The presence of amino groups on the surfaces was detected by an attenuated total reflection Fourier Transform infrared spectrometer and by the Auger electron spectrometer. Through these amino groups, albumin was attached to the membranes. In some experiments, the attached albumin was further stabilized by cross-linking with glutaraldehyde. The effect of washing the albuminated membranes with saline and with plasma was investigated. It was observed that after the initial wash-out of albumin, the concentration of attached albumin tends to level off. The amount of albumin retained on the membranes varied between 275 to 357 micrograms/cm2.

Albumins↗