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Biomedical subjects

L S Wan

Publications and source records attributed to L S Wan.

63 records · Page 4Linked to original sources
PubMedDate not supplied

Compact cell blocks. Use for body fluids, fine needle aspirations and endometrial brush biopsies.

OBJECTIVE: To obtain an ideal cell block wherein the maximal number of cells are displayed within the smallest area on the block surface. STUDY DESIGN: Cyto-Rich Red (AutoCyte, Inc., Elon College, North Carolina, U.S.A.) is added to fresh cellular sediment in a centrifuge tube at a ratio of 1:1. After two minutes, three to four drops of plasma and topical thrombin (5,000 U/10 mL) is added. The tube is then gently agitated for two minutes, until a gelatinous clot is obtained. The clot is then slid onto a lens tissue on top of paper towels. The lens tissue is folded once over the clot. By gently squeezing the excess fluid from it through the lens tissue into the paper towels, the clot is transformed into a flat, compact, densely cellular aggregate, which is painted with mercurochrome prior to fixation in formaldehyde. RESULTS: From each of the 495 cases, including 250 body cavity fluids, 170 fine needle aspirates and 75 endometrial brush biopsies, processed with the above protocol, there was a compact cell block containing packed cells or tissue fragments in a clean background devoid of red blood cells. CONCLUSION: The compact cell block is about 10-20% the size of a conventional cell block, yet more cells are on display, thus reducing the need for deeper cuts and screening time while increasing the efficiency of cytodiagnosis. The compact cell block technique is particularly helpful for endometrial brush biopsies.

Biopsy↗
PubMedDate not supplied

Plasticizers and their effects on microencapsulation process by spray-drying in an aqueous system.

Microencapsulated theophylline particles were prepared by an aqueous spray-drying process using hydroxypropylmethylcellulose. The effect of different plasticizers, triethylcitrate, polyethylene glycol, propylene glycol, glycerin and citric acid, was investigated. Triethylcitrate, a water-insoluble plasticizer, produced a porous honeycomb-like microcapsule wall resulting in rapid drug release. The presence of the plasticizers also influenced crystallization of the drug. The formation of a solid drug dispersion was observed with the addition of citric acid or glycerin. Changes in the pH of liquid feed caused by the plasticizer had an effect on the product dissolution profile, but this was not a major factor. Formation of pores due to leaching of plasticizers during dissolution enhanced drug release. Flow property measurements indicated that the plasticizers also affect the cohesiveness of the spray-dried products. Compared to the microcapsules formed without any plasticizers, propylene glycol, glycerin and citric acid appeared to be beneficial to the microcapsule wall formation, with microcapsules containing citric acid having the slowest drug release.

Crystallization↗
PubMedDate not supplied

Drug encapsulation in alginate microspheres by emulsification.

A method based on an emulsification process was developed for the production of calcium alginate microspheres. Isopropyl alcohol and acetone, which are strong dehydrating agents, were used to aid in the hardening and drying of the microspheres. However, the amount of drug encapsulated was very low. This was due to the drug being soluble in the dehydrating solvents. In the absence of the solvents a high percentage of drug was encapsulated, and this was further increased by forming the microspheres by phase inversion. It was also found that a suspension of the drug particles was required for effective microencapsulation. The efficiency of drug encapsulation generally increased with the ratio of drug to encapsulating material. The microspheres produced were free-flowing and most of them were smaller than 150 microns.

1-Propanol↗
PubMedDate not supplied

Citric acid as a plasticizer for spray-dried microcapsules.

An aqueous spray-drying process was used to coat theophylline particles with a cellulose polymer, sodium carboxymethylcellulose (NaCMC) or hydroxypropylmethylcellulose (HPMC). Effect of a plasticizer, citric acid, was studied. Strength of cast films have a direct relationship to the dissolution T50% values of the respective spray-dried products. With varying plasticizer concentrations, changes in interaction between plasticizer and polymer, and in size of crystallized drug crystals, were observed with HPMC films. The plasticizer content also affected the films of NaCMC by bringing about a change in the form and arrangement of the drug. X-ray diffraction analyses of the different spray-dried products revealed a possibility of the predominance of different crystal forms. Spherical spray-dried microcapsules of NaCMC were formed with a 20-30% w/w plasticizer content. With HPMC, as plasticizer concentration was increased there was a corresponding increase in mean size of the spray-dried products. In terms of drug release and formation of spherical particles, a plasticizer concentration of 30% w/w was found to be suitable for both HPMC and NaCMC.

Capsules↗
PubMedDate not supplied

Deviation of the ratio of drugs in a two-component mixture encapsulated in cellulose phthalate microspheres.

Microspheres were formed when a solution of cellulose phthalate was extruded into 30% glacial acetic acid solution. Sulphonamides entrapped in such microspheres leached into the hardening solution because they dissolved freely in the acetic acid solution. This resulted in poor loading efficiency of the sulphonamides in the microspheres. When mixtures of sulphaguanidine and sulphathiazole in various drug ratios were microencapsulated by this method, the observed drug ratios were found to be markedly changed. This was attributed to the difference in solubility of the two sulphonamides in acid such that their extent of diffusion into the hardening solution was not similar. NSAIDS such as ibuprofen and mefenamic acid which are acidic and more hydrophobic in nature are less soluble in acetic acid. These drugs were retained better in the microspheres during the hardening process and the loading efficiency was consequently improved. In cases where mixture of the NSAIDS were encapsulated, the drug ratios showed little deviation from the theoretical values. This study shows that loading of the CAP microspheres is dependent on the solubility of the drugs in acetic acid. When more than one drug is required to be microencapsulated, the drug ratio may change if the drugs have different solubility in acetic acid.

Cellulose↗
PubMedDate not supplied

Effect of cellulose derivatives on alginate microspheres prepared by emulsification.

Generally discrete and spherical calcium alginate microspheres with a high drug encapsulation efficiency were readily prepared by an emulsification process. They were found to release drug rapidly. In the present study, co-polymer in the form of cellulose derivatives was added to sodium alginate in an attempt to modify the drug release profiles of the microspheres. The effects of cellulose derivatives on the morphology and drug encapsulation efficiency of the microspheres were also evaluated. The cellulose derivatives increased the degree of agglomeration of the microspheres. Small and spherical microspheres were produced from cellulose derivatives of low viscosity while larger microspheres which tended to be elongated were produced from cellulose derivatives of high viscosity. The drug encapsulation efficiency and the drug release profiles were influenced by the chemical nature of the cellulose derivative as well as its viscosity. The efficiency of drug encapsulation generally increased while the rate of drug release decreased with increasing viscosity of the cellulose derivatives. Less hydrophilic cellulose derivatives such as methyl cellulose and hydroxypropylmethyl cellulose were found to increase the efficiency of encapsulating sulphaguanidine, while more hydrophilic cellulose derivatives such as hydroxypropyl cellulose and carboxymethyl cellulose had the opposite effect. Among the cellulose derivatives used, only hydroxypropyl cellulose retarded the drug release of the microspheres.

Alginates↗
PubMedDate not supplied

Prolonged retention of cross-linked trypsin in calcium alginate microspheres.

Trypsin microencapsulated in a calcium alginate matrix was lost quickly through diffusion when the microspheres were placed in an aqueous medium. This problem was overcome by first reacting trypsin with glutaraldehyde to form cross-linkages and then incorporating the enzyme in the alginate microspheres. The performance of the cross-linked trypsin remained optimal at pH 8 while it was found to be more heat-stable and remained highly active even at 80 degrees C. Esters and amides of L-arginine were preferentially hydrolysed by the enzyme indicating that cross-linking did not adversely affect the conformation of the active site. There was a suppression in enzymatic activity when the microspheres were placed in reaction media with an increasing concentration of organic solvent such as ethanol, acetonitrile or isopropanol. However, when returned to a totally aqueous environment, the enzyme resumed its initial tryptic capability. Such a microencapsulated form of cross-linked enzyme may find application in enzyme replacement therapy, optical resolution of racemic compounds as well as organic synthesis in an aqueous-organic environment.

Alginates↗
PubMedDate not supplied

Effect of magnesium stearate on chitosan microspheres prepared by an emulsification-coacervation technique.

Chitosan microspheres were prepared using an emulsification-coacervation technique. The w/o emulsion comprised a mixture of light and heavy liquid paraffins containing sodium dioctyl sulphosuccinate as the oil phase and chitosan solution as the aqueous phase. Pentasodium tripolyphosphate was included as a counterion. The chitosan microspheres obtained showed a high degree of aggregation. This was markedly reduced, by the incorporation of magnesium stearate in the disperse phase. The resultant microspheres were then discrete, spherical with smooth surfaces. Additionally, with an increasing magnesium stearate content, larger-sized microspheres were produced. The DSC analysis data suggested that the magnesium stearate was converted to stearic acid during the preparation process. Chitosan microspheres containing propranolol hydrochloride were similarly prepared, but their surface was convoluted and their shape not well defined. Unlike the microspheres without drug, the size of the drug-loaded microspheres decreased with increasing magnesium stearate content. The release of propranolol hydrochloride from the microspheres was fast, irrespective of the content of magnesium stearate. Drug encapsulation efficiency was enhanced when a greater amount of magnesium stearate was used.

Animals↗