Biomedical subjects

B C Thanoo

Publications and source records attributed to B C Thanoo.

27 records · Page 2Linked to original sources

PubMed1991

Hydrolysed microspheres from cross-linked polymethyl methacrylate (Hydrogel). A new embolic material for interventional neuroradiology.

Highly hydrophilic, perfectly smooth and spherical microspheres have been synthetized. These non-biodegradable microspheres absorb water in varying degrees and can be injected easily through microcatheters due to their slippery and compressible characteristics. The material was successfully used for embolization of 4 vascular intracranial tumours and 2 spinal vascular lesions in the cervical region, by superselective delivery. Histopathology confirmed absolute inertness of the microspheres.

Adult↗

PubMed1990

Suspension polymerization of 2-hydroxyethyl methacrylate in the presence of polymeric diluents: a novel route to spherical highly porous beads for biomedical applications.

Spherical, highly porous beads of poly(2-hydroxyethyl methacrylate) (PHEMA) cross-linked with ethylene glycol dimethacrylate (EGDM) were prepared by suspension polymerization of HEMA in concentrated NaCl solutions in presence of toluene, poly(methyl methacrylate) (PMMA) in toluene, and poly(tetramethylene glycol) (PTMG). Magnesium hydroxide prepared in situ in the dispersion medium gave the best stabilization effect for the monomer droplets. In the presence of PTMG, beads having nearly 1.0 mm in diameter could be prepared, while toluene alone as the diluent produced beads of very small size. Removal of PMMA or PTMG from the beads after polymerization using suitable solvents gave rise to highly porous PHEMA microspsheres. Polymerization in the presence of PTMG produced microspsheres with better spherical geometry as compared to those generated in the presence of PMMA. The effect of various factors such as NaCl concentration, concentration of Mg(OH)2, and the concentration of PMMA or PTMG in the monomer phase on the stability of the suspension and the particle size distribution was investigated.

Cross-Linking Reagents↗

PubMed1990

Preparation and evaluation of radiopaque hydrogel microspheres based on PHEMA/iothalamic acid and PHEMA/iopanoic acid as particulate emboli.

Highly porous poly(2-hydroxyethyl methacrylate) (PHEMA) microspheres prepared by suspension polymerization of 2-hydroxyethyl methacrylate (HEMA) in presence of polymeric diluents such as poly(methyl methacrylate) (PMMA) in toluene and poly(tetramethylene glycol) (PTMG) were made radiopaque by esterification of the reactive hydroxyl groups with iothalamic acid and iopanoic acid, two radiopaque substances clinically used. Of the various solvents and catalysts examined, tetrahydrofuran (THF) and N,N'-dimethyl paratoluidine (DMPT) were found to be best for obtaining a high degree of conversion. More than 30 wt% iodine could be bound to the microspheres which made them sufficiently radiopaque to be imaged radiographically. Microspheres retained their porosity, swelling ability, hydrophilicity, and surface morphology to a significant extent after iodination. Preliminary implantation studies of such microspheres subcutaneously in rats have shown no adverse tissue reactions over a 6-month period. It is suggested that these microspheres would prove to be useful as particulate emboli in endovascular embolization.

Animals↗

PubMed1990

Barium sulphate-loaded p(HEMA) microspheres as artificial emboli: preparation and properties.

Poly(2-hydroxyethyl methacrylate) p(HEMA) microspheres of good spherical geometry (diameter 90-1500 microns) encapsulated with 40-50% barium sulphate to impart radiopaque properties were prepared by a solvent evaporation process. These microspheres were cross-linked by reacting with hexamethylene diisocyanate (HMDI) or by gamma-irradiation in the presence of ethylene glycol dimethacrylate (EGDM) in n-heptane. Microspheres with a porous structure and a rough surface were also made by the incorporation of NaCl along with BaSO4. The effects of concentration of the polymer solution, concentration of the stabilizing agent, concentration of BaSO4, viscosity of the dispersion medium and ratio of the dispersed phase to the dispersion medium on the formation, stability and particle size distribution of the microspheres were investigated.

Barium Sulfate↗

PubMed1989

Synthetic hydrogel microspheres as substrata for cell adhesion and growth.

Cross-linked poly(methyl methacrylate) (PMMA) microspheres were subjected to alkaline hydrolysis to obtain hydrophilic microspheres having carboxyl residues distributed throughout the matrix. These microspheres were found to support the growth of human skin fibroblasts and human heart and lung cells. Further, fibroblasts grown on them were found to be comparable with those grown on the commercial tissue culture plate with respect to [14C]amino acid uptake and incorporation into proteins. The hydrolyzed PMMA microspheres may find application as a microcarrier for cell culture.

Cell Adhesion↗

PubMedDate not supplied

Radiopaque hydrogel microspheres.

Spherical, hydrophilic microspheres prepared from crosslinked poly(methyl methacrylate) (PMMA) by alkaline hydrolysis have been made radiopaque by impregnating with barium sulphate by the precipitation technique. Microspheres having carboxyl functions as their alkali metal salt were swollen in sodium sulphate solution and barium sulphate entrapment was effected by treating with barium chloride solution. The swelling characteristics of the microspheres could be controlled by acidification and further by anhydride formation thereby trapping the barium sulphate firmly inside the microspheres. Barium sulphate loading of up to 70 wt-per cent could be achieved by this technique. These microspheres have been found to possess excellent X-ray contrast properties and may find application as particulate emboli in endovascular embolization.

Barium Sulfate↗

PubMedDate not supplied

Tantalum loaded silicone microspheres as particulate emboli.

Chloroform solutions of medical grade silicone resin were cured in an aqueous dispersion medium containing poly(vinyl alcohol) (PVA) as the drop stabilizer at 40-60 degrees C to generate smooth, spherical, elastic microspheres. The microspheres were encapsulated with tantalum powder to render them radiopaque. Tantalum loaded microspheres having diameter more than 1.00 mm could be prepared by this technique. Incorporation of radiopaques such as barium sulphate and methyl iothalamate resulted in the instability of the suspension giving rise to an agglomerated product. Microspheres were grafted with hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and N-vinyl pyrrolidone (NVP) using ionizing radiation from a 60Co source in an effort to make their surfaces hydrophilic. While the graft yield was very little when HEMA alone was used for grafting, a combination of HEMA/NVP in a 1:1 ratio produced better graft yields resulting in improved surface hydrophilicity. The tantalum loaded microspheres were found to be very resistant to surface modification. Microspheres could be dispersed in water with the aid of small quantities of surfactants such as Tween 20. These microspheres may find use in particulate embolization.

Chemical Phenomena↗

PubMedDate not supplied

Effect of processing parameters on the properties of peptide-containing PLGA microspheres.

The physico-chemical properties of biodegradable polylactide-co-glycolide (PLGA) microspheres containing the peptide salmon calcitonin (sCT) were affected by the processing parameters. The microsphere size increased with an increase in the viscosity of the polymer solution. Concentration of methanol and peptide in the dispersed phase had the most discernible effects with the combination causing external and internal porosity. Increasing sCT in the presence of methanol increased the surface area and porosity. The surface area also increased as the molecular weight of the polymer was decreased. At higher ratios of the dispersed phase volume to the continuous phase volume, the surface area and surface porosity were higher and the particle size was lower. Thus, the physico-chemical properties of the microspheres can be easily altered by varying the processing parameters allowing formation of microspheres with a range of properties. The microspheres may be used to evaluate the relationship between the properties and ultimate in-vivo performance.

Calcitonin↗

PubMedDate not supplied

Effect of gamma-irradiation on peptide-containing hydrophilic poly (d,l-lactide-co-glycolide) microspheres.

The effect of gamma-irradiation on the physicochemical properties of peptide-containing hydrophilic poly (d,l-lactide-co-glycolide) (PLGA) microspheres was evaluated. PLGA (50/50, Mw: 8,600) with free carboxylic end groups was used to make drug-loaded and placebo microspheres by a solvent extraction evaporation method. Both formulated and non-formulated microspheres were gamma-irradiated at 0, 1, 1.5, and 2.5 Mrad doses. HPLC analysis based on extraction of peptide from the microspheres showed that peptide content of the microspheres was lowered upon irradiation and the reduction was more pronounced in formulated microspheres. The in-vitro release in 0.033M phosphate buffer, pH 7.0 at 37 degrees C (based on extraction of residual peptide) showed that the initial and subsequent release of peptide was higher in gamma-irradiated microspheres during the first 20 days. The difference became insignificant during the erosional controlled release of the peptide. There was no difference in release between the formulated and non-formulated microspheres of the nonirradiated or irradiated forms. Molecular weights (Mw and Mn), determined by size exclusion chromatography, were reduced by gamma-irradiation for both formulated and non-formulated placebo microspheres. Differential scanning calorimetry showed a gradual reduction in Tg of placebo microspheres but no reduction in peptide-loaded microspheres. In-vivo evaluation of the nonirradiated and the 1.5 Mrad irradiated microspheres showed no marked differences through 28 days. Since irradiation caused a lowering of Mw and Mn with the appearance of a low amount of unidentified substances, seemingly catalyzed by the polymer and the formulation excipients, gamma-irradiation sterilization of these parenteral delivery systems requires careful investigation on an individual product basis.

Gamma Rays↗