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Biomedical subjects

R S Krishnan

Publications and source records attributed to R S Krishnan.

At least 19 recordsLinked to original sources
PubMed2006

General strategies for nanoparticle dispersion.

Traditionally the dispersion of particles in polymeric materials has proven difficult and frequently results in phase separation and agglomeration. We show that thermodynamically stable dispersion of nanoparticles into a polymeric liquid is enhanced for systems where the radius of gyration of the linear polymer is greater than the radius of the nanoparticle. Dispersed nanoparticles swell the linear polymer chains, resulting in a polymer radius of gyration that grows with the nanoparticle volume fraction. It is proposed that this entropically unfavorable process is offset by an enthalpy gain due to an increase in molecular contacts at dispersed nanoparticle surfaces as compared with the surfaces of phase-separated nanoparticles. Even when the dispersed state is thermodynamically stable, it may be inaccessible unless the correct processing strategy is adopted, which is particularly important for the case of fullerene dispersion into linear polymers.

Journal Article↗
PubMed2005

Influence of molecular architecture on the dewetting of thin polystyrene films.

The control of dewetting for thin polymer films is a technical challenge and of significant academic interest. We have used polystyrene nanoparticles to inhibit dewetting of high molecular weight, linear polystyrene, demonstrating that molecular architecture has a unique effect on surface properties. Neutron reflectivity measurements were used to demonstrate that the nanoparticles were uniformly distributed in the thin (ca. 40 nm) film prior to high temperature annealing, yet after annealing, they were found to separate to the solid substrate, a silanized silicon wafer. Dewetting was eliminated when the nanoparticles separated to form a monolayer or above while below this surface coverage the dewetting dynamics was severely retarded. Blending linear polystyrene of similar molecular weight to the polystyrene nanoparticle with the high molecular weight polystyrene did not eliminate dewetting.

Journal Article↗
PubMed2003

Ascorbic acid dynamics in the seriously ill and injured.

BACKGROUND: In addition to the known beneficial effects of ascorbic acid on wound healing and the immune response, it is also a potent extracellular antioxidant. Recent work in septic rats suggests that high-dose ascorbic acid total parenteral nutrition (TPN) supplementation may protect cells from free radical injury and improve survival. In this study, we determined ascorbic acid levels in the immediate post-injury/illness period and evaluated the ability of early short-term high levels of ascorbic acid in TPN to normalize plasma levels. MATERIALS AND METHODS: Ascorbic acid levels were determined in 12 critically injured patients and 2 patients with severe surgical infections. Each patient received TPN supplemented with increasing doses of ascorbic acid over a 6-day period. Therapeutic responses were determined by plasma and urine measurements using high-pressure liquid chromatography. RESULTS: The initial mean +/- SEM baseline plasma ascorbic acid concentration was depressed (0.11 +/- 0.03 mg/dl) and unresponsive following 2 days on 300 mg/day supplementation (0.14 +/- 0.03; P = 1.0) and only approached low normal plasma levels following 2 days on 1000 mg/day (0.32 +/- 0.08; P = 0.36). A significant increase was noted following 2 days on 3000 mg/day (1.2 +/- 0.03; P = 0.005). CONCLUSION: We confirmed extremely low plasma levels of ascorbic acid following trauma and infection. Maximal early repletion of this vitamin requires rapid pool filling early in the post-injury period using supraphysiologic doses for 3 or more days.

Adult↗
PubMed2001

Acantholytic dermatosis of the vulvocrural area.

Acantholytic dermatosis of the vulvocrural area is a rare skin disorder characterized by solitary or multiple skin-colored to white, smooth papules or plaques. Histopathological features of both Hailey-Hailey disease and Darler's disease are present. There is acantholysis, which may involve the full thickness of the epidermis, and dyskeratosis with corps ronds and grains. There may be marked hyperkeratosis and focal parakeratosis. We report a case of this rare disease and discuss its differential diagnosis and treatment.

Acantholysis↗
PubMed2001

Erythema elevatum diutinum mimicking extensive keloids; quiz 386.

GOAL: To describe a case of erythema elevatum diutinum (EED) that clinically mimicked extensive keloids. OBJECTIVES: Upon completion of this activity, dermatologists and general practitioners should be able to: 1. Describe the clinical presentation and lesion appearance in EED. 2. Discuss the electron microscopic and laboratory findings of EED. 3. Outline treatment options for EED. CME: This article has been peer reviewed and approved by Michael Fisher, MD, Professor of Medicine, Albert Einstein College of Medicine. REVIEW DATE: April 2001. This activity has been planned and implemented in accordance with the Essentials and Standards of the Accreditation Council for Continuing Medical Education through the joint sponsorship of Albert Einstein College of Medicine and Quadrant HealthCom, Inc. The Albert Einstein College of Medicine is accredited by the ACCME to provide continuing medical education for physicians. Albert Einstein College of Medicine designates this educational activity for a maximum of 1.0 hour in category 1 credit toward the AMA Physician's Recognition Award. Each physician should claim only those hours of credit that he/she actually spent in the educational activity. This activity has been planned and produced in accordance with ACCME Essentials.

Dapsone↗
PubMed1998

In vitro and in vivo degradation of poly(propylene fumarate-co-ethylene glycol) hydrogels.

The degradation of poly(propylene fumarate-co-ethylene glycol) hydrogels was examined in vitro in phosphate-buffered saline at pH 7.4 and in vivo in a subcutaneous rat model. These hydrogels have potential application as biodegradable, injectable cardiovascular stents, and, as such, their mass loss, dimensional changes, mechanical properties, morphology, and biocompatibility over a 12-week time course were evaluated. Three formulations were fabricated: one base formulation consisting of 25% (w/w) PEG, molecular weight 4,600; one high weight percent PEG formulation with 50% (w/w) PEG; and one high molecular weight PEG formulation, molecular weight 10,500. All three formulations showed significant weight loss (between 40 and 60%) on the first day due to leaching of the uncrosslinked fraction. Further weight loss was observed only for the low weight percent PEG copolymers in the in vivo case, and a slight increase in volume was observed due to degradative swelling. The mechanical properties of the P(PF-co-EG) hydrogels decreased significantly in the first 3 weeks, showing the biphasic pattern typical of bulk degradation. In vitro, the hydrogels showed at least a 20% retention of their initial ultimate tensile stress after 3 weeks. The dynamic mechanical properties showed similar retention, with the in vivo mechanical properties differing from the in vitro properties only after 6 weeks of degradation. Differences in PEG molecular weight appeared to have little effect, but increasing the weight percent PEG decreased the rate of degradation both in vitro and in vivo. The morphology of the copolymer films, based on scanning electron microscopy observation, was not significantly different either among the three formulations or over the time course of the study, suggesting there were no macroscopic structural changes during this time period. The P(PF-co-EG) hydrogels demonstrated good initial biocompatibility, showing responses characteristic of biomaterial implants.

Animals↗
PubMed1998

Preparation and characterization of poly(propylene fumarate-co-ethylene glycol) hydrogels.

We describe the preparation and bulk characterization of a cross-linked poly(propylene fumarate-co-ethylene glycol), p(PF-co-EG), hydrogel. Eight block copolymer formulations were made varying four different design parameters including: poly(ethylene glycol) (PEG) molecular weight, poly(propylene fumarate) (PPF) molecular weight, copolymer molecular weight, and ratio of PEG to PPF. Two different cross-linking formulations were also tested, one with a cross-linking monomer and one without. The extent of the cross-linking reaction and the degree of swelling in aqueous solution were determined on copolymer formulations made without a cross-linking monomer. The values of molecular weight between cross-links, Mc ranged from 300 +/- 120 to 1190 +/- 320 as determined from swelling data (n = 3). The equilibrium volume swelling ratios, Q, varied from 1.5 +/- 0.1 to 3.0 +/- 0.1. This ratio was found to increase with increasing PEG content in the copolymer and decrease with increasing PPF molecular weight. The values for complex dynamic elastic moduli magnitudes of E*, ranged from 0.9 +/- 0.2 to 13.1 +/- 1.1 MPa for the formulations with the cross-linking monomer, N-vinyl pyrrolidinone (VP) (n = 3). The ultimate tensile stresses on the formulations made with VP ranged from 0.15 +/- 0.03 to 1.44 +/- 1.06 MPa, and tensile moduli ranged from 1.11 +/- 0.20 to 20.66 +/- 2.42 MPa (n = 5). All of the mechanical properties increased with increasing PPF molecular weight and decreased with increasing PEG content in the copolymer. These data show that the physical properties of p(PF-co-EG) hydrogels can be tailored for specific applications by altering the material composition.

Biocompatible Materials↗
PubMed1998

Enterovaginal fistula as a complication of intraoperative small bowel endoscopy.

Intraoperative endoscopy has been accepted as a method of small bowel evaluation for occult gastrointestinal bleeding. Although methodology of the procedure has been evolving, reported complications have been few, consisting of prolonged ileus, adhesions, submucosal hemorrhage, and serosal injuries. This case report describes an enterovaginal fistula as a complication of intraoperative small bowel endoscopy performed during a total colectomy procedure in a patient with chronic gastrointestinal bleeding, possibly caused by ischemia resulting from pleating of small bowel over the endoscope. This complication may be prevented by use of longer commercially available enteroscopes or by use of an enterotomy to insert the endoscope.

Colonoscopy↗