The purpose of this work was to understand effect of various process variables on the entrapment efficiency, particle size of the microspheres. Microspheres were prepared by emulsion cross linking method using different drug polymer ratios (formulation F1 to F6), stirring speed and concentration of emulsifying agent. Glutaraldehyde in toluene was used for cross linking agent. The mean particle size of the microspheres significantly increased with increasing gelatin ratio and was in the range 1.69±2.14 μm to 15.11±2.15 μm. The drug entrapment of the microspheres increased initially from 56.94±3.21 % to 80.87±2.93% with the increase in the drug polymer ratio from 1:1 to 1:4, the highest entrapment efficiency was found in F4 formulation. Then it decrease 76.00±1.71 and 68.91±2.14 for 1:5 and 1:6 respectively. Stirring rate increased from 500 rpm-1500 rpm, the mean particle size of the microspheres was decreased from 12.86±1.60 μm to 3.19±1.96 μm significantly and the entrapment efficiency was decreased from 80.94±3.21 % to 72.19±1.36 %. The stirring speed has negative effect on drug entrapment efficiency. As the concentration of the emulsifying agent (Span 80) was increased from 1% to 3% w/v, the particle size of the microspheres was decreased from 9.26±1.30 μm to 4.77±1.51 μm. Increase in concentration of emulsifying agent (Span 80) decrease the encapsulation efficiency from 80.94±1.02 to 78.19±1.68 of microspheres. The higher drug to polymer ratio inversely proportional to particle size, drug entrapment efficiency and directly proportional to release rate. Whereas stirring rate of emulsion system are inversely proportional to particle size and drug entrapment efficiency and high concentration of emulsifier decrease the particle size and increase the drug entrapment efficiency of microspheres.
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