Insulin Nano-and Micro-particles And Its Composites Prepared By SAS-A

Supercritical fluid(SCF) technology has been widely applied to various areas,and very important progress has been achieved.Among the applications,particle formation or encapsulation with assistance of SCF by using its high solvency power and expansion ability to lots of solvents is a hot research topic in recent decades.It is possible to control the morphology,particle size(PS),and particle size distribution(PSD) for the produced products due to the sensitivity of SCF to the operating temperature and pressure. Furthermore,it is also available for the formulation of those materials such as active substances,thermosensitive substances,which usually cannot be processed by conventional methods.In this thesis,supercritical anti-solvent atomization(SAS-A),which is a combination of SEDS(solution enhanced dispersion by supercritical fluids) and PGSS (particle formation from gas-saturated solution),was employed to study the precipitation of polyethylene glycol 6000(PEG) and insulin microparticles,as well as PEG/insulin and tripalmitin/insulin composite mieroparticles.Prior to the particle formation study,the volume expansion of the liquid phases for the CO₂/acetone and CO₂/ethanol binary systems and the CO₂/ethanol/water ternary system was investigated using the t-mPR equations of state(t-mPR EoS) and the PR equations of state(PR-EoS).The correlations for the published vapor-liquid equilibrium(VLE) data of the above systems show that both the EoS can provide fairly good VLE calculations for the binary systems,but t-mPR EoS gives slightly better results.The volume expansion prediction for the above systems and the comparison with the published data show that, compared to PR-EoS,t-mPR EoS gives better results for the binary systems but worse results for the ternary system,but provides more reasonable results around 7.8MPa. Moreover,the calculations indicate that the volume expansion of the CO₂/acetone system is always larger than that of the CO₂/ethanol system.The volume expansion of the ternary system shows a maximum point corresponding to about the CO₂/ethanol mixture's critical pressure(about 7.8MPa);increase in the content of ethanol can improve the maximun volume expansion and therefore help to enhance the removal of water.The SAS-A process was applied to the generation of PEG microparticles from different solvents(acetone,ethanol,and ethanol/water).The effect of the processing conditions,including operating pressure,PEG concentration,and solution flow rate,on the morphology and size of the produced PEG particles was investigated,especially,the influence of using different solvents was evaluated.The PEG particles produced by using acetone and ethanol are generally spherical with sizes of 1-5μm and 2-15μm,respectively. A high pre-expansion pressure can produce spherical and discrete particles with relatively small size and narrow size distribution.Increasing the PEG concentration in acetone can evidently increase the PEG particle sizes and widen the PSD for the PEG/acetone system, while increasing the PEG concentration can slightly widen the PSD,but has little effect on the PEG particle sizes for the PEG/ethanol system in the studied concentration range. Decreasing the content of ethanol in the ethanol/water solution can generate irregular and agglomerated particles due to the difficulty of water removal.The SAS-A process was employed to produce insulin particles from its ethanol/water solutions at 45℃.The effect of the operating conditions on the morphology,size and bioactivity of the produced insulin particles was evaluated.The formed primary particles are spherical and discrete with sizes of 0.1-1.5μm.The loss of the activity of the insulin particles depends on the ethanol content in the solution;other operating conditions show little effect on the insulin particles' activity.It is possible to produce insulin microparticles with almost no loss of its bioactivity by the SAS-A process at low ethanol content(less than 40%in mass).The FTIR and DTA analyses compared to that of the unprocessed insulin confirm that the changes in the content ofα-helix andβ-sheet decrease the protein activity.Finally,the SAS-A process was employed to produce PEG/insulin composite microparticles,and a modified SAS-A process was employed to produce tripalmitin/insulin composite microparticles.The effects of different cartier materials,different ratios of carrier/insulin on the particle morphology and PSD and the insulin release from the produced composites were examined.Good combination of insulin to PEG in spherical composites is indicated on the basis of the insulin release from the PEG/insulin composite. Initial burst completely disappears for the insulin release from the tripalmitin/insulin composite particles(particles like flowers) produced at 50℃by the modified SAS-A process,while the intial burst is still high(36%in 1 min) for the tripalmitin/insulin composite particles(large particles attached with spheres) obtained at 45℃.