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Biomedical subjects

R Viswanathan

Publications and source records attributed to R Viswanathan.

At least 37 records · Page 2Linked to original sources
PubMed1995

The structure and stability of phospholipid bilayers by atomic force microscopy.

Atomic force microscopy (AFM) was used to investigate the structure, stability, and defects of the hydrophilic surfaces of Langmuir-Blodgett bilayer films of distearoylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylethanolamine (DPPE) in the solid phase, and dilinoleoylphosphatidylethanolamine (DLPE) in the fluid phase. Their relative resilience to external mechanical stress by the scanning tip and by fluid exchange were also investigated. DPPE monolayers showed parallel ridges at the surface with a period of 0.49 nm, corresponding to the rows of aligned headgroups consistent with the known crystallographic structure. DSPC and DLPE monolayers did not show any periodic order. The solid DSPC and DPPE monolayers were stable to continued rastering by the AFM tip; however, the stability of DLPE monolayers depended on the pH of the aqueous environment. Structural defects in the form of monolayer gaps and holes were observed after fluid exchange, but the defects in DLPE monolayer at pH 11 were stable during consecutive scanning. At pH 9 and below, the defects induced by fluid exchange over DLPE monolayers were more extensive and were deformed easily by consecutive scanning of the AFM tip at a force of 10 nN. The pH dependence of resilience was explained by the increasing bending energy or frustration due to the high spontaneous curvature of DLPE monolayers at low pH. The tangential stress exerted by the AFM tip on the deformable monolayers eventually produced a ripple pattern, which could be described as a periodic buckling known as Shallamach waves.

Biophysical Phenomena↗
PubMed1994

Langmuir-Blodgett films.

The controlled transfer of organized monolayers of amphiphilic molecules from the airwater interface to a solid substrate was the first molecular-scale technology for the creation of new materials. However, the potential benefits of the technology envisioned by Langmuir and Blodgett in the 1930s have yet to be fully realized. Problems of reproducibility and defects and the lack of basic understanding of the packing of complex molecules in thin films have continued to thwart practical applications of Langmuir-Blodgett films and devices made from such films. However, modern high-resolution x-ray diffraction and scanning probe microscopy have proven to be ideal tools to resolve many of the basic questions involving thin organic films. Here, studies are presented of molecular order and organization in thin films of fatty acid salts, the prototypical system of Katharine Blodgett. Even these relatively simple systems present liquid, hexatic, and crystalline order; van der Waals and strained layer epitaxy on various substrates; wide variations in crystal symmetry and interfacial area with counterions; modulated superstructures; and coexisting lattice structures. The wide variety of possible structures presents both a challenge and an opportunity for future molecular design of organic thin-film devices.

Chemical Phenomena↗
PubMed1994

Nail gun injury to the brain: an unusual case of suicide.

An unusual case of fatal suicidal craniocerebral penetrating injury due to a nail gun is described. The victim, a 52 year old joiner experienced in the use of nail drivers, shot himself just above the forehead in the midline, driving the nail through his hypothalamus and midbrain. Death was delayed by nearly 24 hours.

Brain Injuries↗
PubMed1994

Stereotaxic brain biopsy in AIDS patients: does it contribute to patient management?

The authors analysed all cases of brain biopsy done in AIDS or HIV+patients at the Department of Clinical Neurosciences, Western General Hospital, Edinburgh, during the period 1989-92 to determine the clinical utility of the procedure. Thirteen lesions were biopsied revealing toxoplasmosis in five, lymphoma in four, progressive multifocal leucoencephalopathy in three, HIV encephalitis in two and encephalitis of unknown aetiology in one. One biopsy specimen contained abnormal tissue but was non-diagnostic. The median survival after biopsy was only 7 weeks, but preoperative immunological (median CD4 count 45) and clinical status of the patients were poor. Although the impact of tissue diagnosis on patient survival was minimal it did enable modification of drug therapy. The authors preliminary experience with biopsy in AIDS patients suggests that the diagnostic information obtained is of limited value in prolonging the lives of patients in poor immunological status, but may be useful in refining medical therapies for toxoplasmosis and progressive multifocal leucoencephalopathy. Whether biopsy should be performed earlier in the course of cerebral disease in an effort to prolong survival time remains unclear.

AIDS Dementia Complex↗
PubMed1993

Strained-layer van der Waals epitaxy in a Langmuir-Blodgett film.

Atomic force microscope images of Langmuir-Blodgett films of lead and manganese fatty acid salts show that these monolayers have long-range order and are oriented with respect to the mica substrate, although the lattice symmetries of the monolayers and substrate are dramatically different. The surface lattice of sequentially thicker films evolves toward the bulk structure while retaining the substrate alignment. This behavior is in distinct contrast to films of cadmium fatty acid salts on mica, or all films on amorphous silicon oxide, in which the monolayer structure is disordered and a three-layer-thick film displays the bulk structure.

Adsorption↗
PubMed1986

Alzheimer's disease in a patient on long-term hemodialysis: a case report.

This case report describes a progressive dementia in a 49-year-old black male on long-term hemodialysis. The initial presentation simulated depression. The dementia persisted after an unsuccessful cadaver homograft transplant. The character of the dementia was nonspecific but typical features of dialysis dementia were lacking. Autopsy revealed a ruptured cerebral aneurysm, polycystic kidneys, moderately severe atherosclerosis, miliary tuberculosis, and neurofibrillary degeneration of the hippocampus. The significance of a possible relationship between end-stage renal disease (ESRD), hemodialysis, and Alzheimer's disease in this case is discussed.

Alzheimer Disease↗
PubMed1986

Development of agoraphobia after surviving cancer.

We present a case conference on a 32-year-old accountant who developed embryonal carcinoma of the testis, two months after the birth of a son with a missing leg. His cancer was successfully treated with surgery and chemotherapy. After 5 years, when he was told that he need not be closely followed by his physicians anymore because he had been cured of cancer, he developed agoraphobia with panic attacks. This interfered with his occupational and social adjustment. His phobia was treated successfully with pharmacotherapy, behavior therapy, and psychotherapy. We explore the psychologic impact of cancer, the activation of separation anxiety and aggressive impulses after its successful treatment, the crippling nature of his agoraphobia, and the ingredients of his successful response to treatment.

Adult↗