Preparation and in vitro release behaviour of 5-fluorouracil-loaded microspheres based on poly (L-lactide) and its carbonate copolymers

A modified oil-in-oil (o/o) emulsion solvent evaporation technique was adopted to prepare 5-fluorouracil (5-Fu)-loaded poly (L-lactide) (PLLA) or its carbonate copolymer microspheres. The disperse phase was a drug:polymer solution using a solvent mixture of N,N-dimethylformamide (DMF) and acetonitrile and the continuous phase was liquid paraffin containing 1-10% (w/v) Span 80(R). The effects of preparative parameters, such as the composition of the inner oil phase, drug:polymer ratio, polymer concentration and agitation rate, on 5-Fu entrapment efficiency and microsphere characteristics were investigated. By introducing 25% (v/v) DMF into the inner oil phase, microspheres with high drug entrapment efficiency and an ameliorated burst effect were achieved. Using this modified method, microspheres with various particle sizes could be produced with a high 5-Fu entrapment efficiency (about 80%). In vitro drug release tests showed a burst release of 5-Fu from PLLA microspheres, followed by a sustained release over 50 days. In the case of poly (L-lactide-co-1,3-trimethylene carbonate) (PLTMC) and poly (L-lactide-co-2,2-dimethyl-1,3-trimethylene carbonate) (PLDTMC), the drug release could be continued for over 60 days.     

Particle Size Studies for Subcutaneous Delivery of Poly(lactide-co-glycolide) Microspheres Containing Ovalbumin as Vaccine Formulation

The primary objectives of the present study were to produce poly(lactide-co-glycolide) (PLGA) microspheres with different diameters, to characterize these microspheres which were loaded with a model antigen, ovalbumin and to evaluate the effect of microsphere particle size on the serum antibody levels following administration to mice. Four kinds of ovalbumin-loaded PLGA microspheres with different diameters (1·2, 3·5, 7·0 and 14·3 μm as mean volume diameter) were manufactured by a w/o/w emulsion/solvent evaporation method. Low loading percent (0·08%-0·25%w/w) and efficiencies (8–25% w/w) were observed. Examination using scanning electron photomicrographs showed smooth spherical particles. The in-vitro release of ovalbumin from microspheres showed an expected burst release with all batches and the extent of the burst release increased with decreasing diameters of spheres; PLGA microspheres with the smallest diameter (1·2/μm) showed an 80% burst release within one day. Approximately 10–60% of ovalbumin remained unreleased 30 days later. The single subcutaneous administrations of ovalbumin-loaded PLGA microspheres with different diameters to mice induced good antibody responses above ovalbumin saline negative controls at 3, 6, 9, and 12 weeks after inoculation. Especially, 0·16% ovalbumin-loaded PLGA microspheres having mean volume diameter of 3·5 /μm exhibited the best immune responses with values greater than those obtained after inoculation with adjuvants such as complete Freund's adjuvant or alum as positive control. The strong adjuvant activity of PLGA microspheres as vaccine formulation was suggested.     

Preparation of ONO-1301-loaded poly(lactide-co-glycolide) microspheres and their effect on nerve conduction velocity

Objectives The aim of this study was to prepare poly(lactide‐co‐glycolide) (PLGA) microspheres containing ONO‐1301, a novel long‐acting prostacyclin agonist with thromboxane synthase inhibitory activity, with 10% of drug released in the initial burst and a sustained‐release period of about 3 weeks after administration. The effect of PLGA type (molecular weight and the lactide/glycolide (L/G) ratio in PLGA), the preparative conditions and the particle size on the in‐vitro release profile were examined. The effect of optimized ONO‐1301‐loaded PLGA microspheres on delayed nerve condition velocity (NCV) was investigated in streptozotocin (STZ) induced diabetic rats. Methods ONO‐1301 PLGA microspheres were produced by the oil‐in‐water emulsion/solvent evaporation method. Drug release from the prepared microspheres was monitored in phosphate buffer solution at 37°C for 4 weeks by high‐performance liquid chromatography. The in‐vivo study was performed in STZ‐induced diabetic rats treated with optimized ONO‐1301 PLGA microspheres (10 mg/kg by intramuscular or subcutaneous injection every 3 weeks). NCV was measured in the thigh 4, 8 and 12 weeks after induction. Key findings The molecular weights of PLGA, the L/G ratio in PLGA and the particle diameter all affected the length of the sustained release period. Drug release from microspheres containing PLGA 5050 (MW 50 000, L/G 50/50), with an average diameter of about 30 µm, could be sustained for 3 weeks in vitro. In the in‐vivo study, delayed NCV was significantly increased by treatment with these ONO‐1301 PLGA microspheres once every 3 weeks, in comparison with vehicle only. Conclusion Local intramuscular injection of sustained‐release ONO‐1301 PLGA microspheres improved delayed NCV in STZ‐induced diabetic rats.     

Preparation of bovine serum albumin loaded poly (D, L-lactic-co-glycolic acid) microspheres by a modified phase separation technique

BSA-loaded mcirospheres were prepared by a modified phase separation method, in which petroleum ether (PE) containing a certain amount of Span 80 rather than poly (dimethylsiloxane) (PDMS) was adopted as coacervating agent. Process parameters such as Span 80 concentration, the volume and addition rate of coacervating agent, polymer concentration, agitation rate during the phase separation process and PE type were evaluated to optimize the protein encapsulation. It was found microspheres with high yield (>80.0%) and entrapment efficiency (>90%) could be obtained using PE containing 5.0% Span 80 as the coacervating agent. Microspheres with small particle size (<10 microm) could be produced successfully with appropriate process parameters. In vitro release study suggested that burst release was significantly influenced by Span 80 concentration, polymer concentration and PE type and the burst release could be reduced to <20% with optimized formulation. A biphasic release behavior in vitro test was observed for the microspheres prepared by this method. GC analysis demonstrated that residual solvent of DCM and petroleum ether was decreased dramatically in comparison with PDMS used as a conventional coacervating agent.     

Effects of solvent selection and fabrication method on the characteristics of biodegradable poly(lactide-co-glycolide) microspheres containing ovalbumin

To demonstrate the effect of formulation conditions on the controlled release of protein from poly(lactide-co-glycolide) (PLGA) microspheres for use as a parenteral drug carrier, ovalbumin (OVA) microspheres were prepared using the W/O/W multiple emulsion solvent evaporation and extraction method. Methylene chloride or ethyl acetate was applied as an organic phase and poly(vinyl alcohol) as a secondary emulsion stabilizer. Low loading efficiencies of less than 20% were observed and the in vitro release of OVA showed a burst effect in all batches of different microspheres, followed by a gradual release over the next 6 weeks. Formulation processes affected the size and morphology, drug content, and the controlled release of OVA from PLGA microspheres.     

Preparation and characterization of poly(D,L-lactic-co-glycolic Acid) microspheres containing flurbiprofen sodium

This study aimed to prepare biodegradable microspheres containing flurbiprofen sodium, a nonsteroidal anti-inflammatory drug (NSAID), as the drug delivery system to the periodontal pocket. Microspheres were prepared from biodegradable copolymers of poly (D,L-lactic-co-glycolic acid) (PLGA) using solvent evaporation method. The effects of the different copolymers and amounts of polyvinyl alcohol (PVA) as a dispersing agent on characteristics of the microspheres were evaluated. Although there was no correlation between microsphere size and amount of PVA, an optimum PVA concentration was essential to achieve narrower size distributions of microspheres. As the concentration of PVA increased, the drug loading of the microspheres increased. The effect of PVA on drug loading was found to be statistically significant for those microspheres prepared from PLGA 50:50 (p < 0.05). Regarding copolymer composition, PLGA 85:15 provided higher drug loading into the microspheres than PLGA 50:50 (p < 0.05). The recoveries of microspheres (60-80%) were affected neither by different PVA concentrations nor by copolymer compositions (p > 0.05). According to the first-order release rate constants of the microspheres, the microspheres of PLGA 50:50 released the drug at the highest rate consistently, with the highest hydrophilicity of this copolymer.     

Preparation of bovine serum albumin loaded poly (D,L-lactic-co-glycolic acid) microspheres by a modified phase separation technique

BSA-loaded mcirospheres were prepared by a modified phase separation method, in which petroleum ether (PE) containing a certain amount of Span 80 rather than poly (dimethylsiloxane) (PDMS) was adopted as coacervating agent. Process parameters such as Span 80 concentration, the volume and addition rate of coacervating agent, polymer concentration, agitation rate during the phase separation process and PE type were evaluated to optimize the protein encapsulation. It was found microspheres with high yield (>80.0%) and entrapment efficiency (>90%) could be obtained using PE containing 5.0% Span 80 as the coacervating agent. Microspheres with small particle size (<10?µm) could be produced successfully with appropriate process parameters. In vitro release study suggested that burst release was significantly influenced by Span 80 concentration, polymer concentration and PE type and the burst release could be reduced to <20% with optimized formulation. A biphasic release behavior in vitro test was observed for the microspheres prepared by this method. GC analysis demonstrated that residual solvent of DCM and petroleum ether was decreased dramatically in comparison with PDMS used as a conventional coacervating agent.     

Dose and Load Studies for Subcutaneous and Oral Delivery of Poly(lactide-co-glycolide) Microspheres Containing Ovalbumin

Poly(lactide-co-glycolide) microspheres containing different loads of OVA (0.05, 0.1, 0.5 and 1.0% w/w) were manufactured by a w/o/w emulsion/solvent evaporation method. Low load efficiencies of less than 20% were observed. Normal size distributions with mean volume diameters ranging from 3.7 to 4.7 µm were obtained for different batches. The in vitro release of OVA from different loaded microspheres showed an expected burst release with all batches. The in vivo dose study (1, 10, 25, 50 µg of OVA) was performed by subcutaneous and oral inoculation in mice by single (0 week) or double (0 and 3 weeks) administration of PLGA 50/50 microspheres containing 0.1% OVA. Subcutaneous administration showed an immune response (serum Ig levels by ELISA) statistically (Fishers paired t-test; P < 0.05) above OVA saline negative controls at 3, 6 and 12 weeks after administration. Oral administration of microspheres produced statistically higher systemic immune responses at the higher doses. Single and double inoculation orally and subcutaneously produced similar serum antibody levels. The in vivo load study was performed by subcutaneous and oral administration to mice of 25 µg OVA contained in various loaded (0.05, 0.1, 0.5 and 1.0% w/w) microspheres. Serum immune responses at 3, 6, and 12 weeks after inoculation were statistically above OVA saline controls and were inversely proportional to the OVA load using either route. This observation suggested a relationship between the number of microspheres delivered and the in vivo serum response. Single subcutaneous administration of 0.05 or 0.1% OVA loaded PLGA 50/50 microspheres induced larger immune responses compared with complete Freunds adjuvant.     

Preparation and characterization of hCG-loaded polylactide or poly(lactide-co-glycolide) microspheres using a modified water-in-oil-in-water (w/o/w) emulsion solvent evaporation technique

A modified w/o/w emulsion solvent evaporation technique was adopted to prepare human Chorionic Gonadotropin (hCG)-loaded polylactide (PLA) or poly(lactide-co-glycolide) (PLGA) microspheres. The effects of preparative parameters, such as stirring rate, polymer MW and concentration, and the composition of both the inner aqueous phase and oil phase etc., on hCG entrapment efficiency and microsphere characteristics were investigated. It was found that by adding 20% glycerol into the inner aqueous phase and 40% acetone into the oil phase, smooth microspheres 1mum in diameter could be produced with high hCG entrapment efficiency (&gt;90%). In vitro release test showed a burst release of hCG from PLGA (75:25) microspheres, followed by sustained release of 55% hCG over 2 months. The initial hCG burst from PLGA microspheres increased with the glycerol concentration in the inner aqueous phase, but decreased to a low value (ca. 20%) with the addition of acetone into the oil phase, which could beattributed to the associated changes in surface morphology of the microspheres. In vivo experiments demonstrated that a single shot of hCG-loaded PLGA microspheres could produce a comparable antibody response with the inoculation of free hCG four times.     

Carboplatin-loaded PLGA microspheres for intracerebral injection: formulation and characterization.

The purpose of this study is to prepare and characterize injectable carboplatin-loaded poly(D,L,-lactic-co-glycolic) acid copolymer (PLGA) microspheres for the intracerebral treatment of malignant glioma. The microspheres were prepared by an acetone/mineral oil emulsion and solvent evaporation method. Preparation variables were optimized and the following processing conditions resulted in the highest drug loading and best yields of the microspheres compared with those prepared with the other variables: the PLGA concentration was 8% (w/w) in the internal phase; the emulsifier (Span 80) concentration was 8% (w/w) in the external phase; the ratio of the internal phase: the external phase was 1:8; the stirring speed was 1500 rpm; the emulsion time was 15 min; the solvent evaporation time was 3.75 hr. Microspheres so prepared were analysed for size distribution, drug loading, in vitro release and morphological characteristics. The drug release in phosphate buffer solution started with a 10-day slow release period, followed by a fast near zero order release period from 12 to 22 days. The carboplatin release in brain homogenate was slower than in phosphate buffer solution. The morphological changes of the microspheres during the in vitro degradation correlated with the drug relase profile. In conclusion, the carboplatin-loaded PLGA microspheres were specifically prepared to meet the specification as an injectable and biodegradable brain implant.     

海藻酸-壳聚糖-聚乳酸羟乙醇酸复合微球的制备及其对蛋白释放的调节

目的制备蛋白的海藻酸-壳聚糖-聚乳酸羟乙醇酸(PLGA)复合微球，以增加蛋白药物的包封率、减少突释和不完全释放。方法以牛血清白蛋白为模型药物采用修饰的乳化、醇洗法制备小粒径海藻酸微囊，再以壳聚糖孵育制得海藻酸-壳聚糖双层微囊，并进一步用PLGA包裹制得复合微球。采用微量BCA试剂盒测定蛋白浓度，考察其包封率及释放行为，改变各种制备因素调节微球的释放特性。结果复合微球粒径约30 μm，形态圆整。与单纯PLGA微球相比，包封率由60%-70%上升至80%以上。复合微球在磷酸盐缓冲液的1 h突释量由40%-50%下降至25%以下，在生理盐水中则进一步下降至5%以下。结论海藻酸-壳聚糖-PLGA复合微球提高了蛋白药物的包封率，减少了药物的突释，并可通过调节PLGA比例调节药物的释放。     

Preparation and characterization of hCG-loaded polylactide or poly(lactide-co-glycolide) microspheres using a modified water-in-oil-in-water (w/o/w) emulsion solvent evaporation technique

A modified w/o/w emulsion solvent evaporation technique was adopted to prepare human Chorionic Gonadotropin (hCG)-loaded polylactide (PLA) or poly(lactide-co-glycolide) (PLGA) microspheres. The effects of preparative parameters, such as stirring rate, polymer MW and concentration, and the composition of both the inner aqueous phase and oil phase etc., on hCG entrapment efficiency and microsphere characteristics were investigated. It was found that by adding 20% glycerol into the inner aqueous phase and 40% acetone into the oil phase, smooth microspheres approximately 1 microm in diameter could be produced with high hCG entrapment efficiency (>90%). In vitro release test showed a burst release of hCG from PLGA (75:25) microspheres, followed by sustained release of 55% hCG over 2 months. The initial hCG burst from PLGA microspheres increased with the glycerol concentration in the inner aqueous phase, but decreased to a low value (ca. 20%) with the addition of acetone into the oil phase, which could be attributed to the associated changes in surface morphology of the microspheres. In vivo experiments demonstrated that a single shot of hCG-loaded PLGA microspheres could produce a comparable antibody response with the inoculation of free hCG four times.     

Effect of different dispersing agents on the characteristics of Eudragit microspheres prepared by a solvent evaporation method

Eudragit RS microspheres containing verapamil HCl for oral use were prepared using three different dispersing agents: aluminium tristearate, magnesium stearate and sucrose stearate, by a solvent evaporation method. The effects of the type and concentration of the dispersing agents and the inner phase polymer concentration on the size and T63.2%, (the time at which 63.2% of the drug is released) of microspheres were determined by multiple linear regression analysis. The morphology of microspheres was characterized by scanning electron microscopy. The surface of microspheres prepared with sucrose stearate was smoother and non-porous and the drug release from these microspheres was the fastest. When aluminium tristearate or magnesium stearate were used as dispersing agents, the particle size of microspheres became smaller. Increasing amounts of these two dispersing agents led to the accumulation of their free particles onto the surfaces of the microspheres. The drug release from the microspheres was slower than that of the microspheres from sucrose stearate depending on their hydrophobic structures. According to the results of the multiple linear regression analysis among the dispersing agents used, aluminium tristearate showed the best correlation between the examined input (dispersing agent and polymer concentrations) and output (T63.2%. and particle size) variables.     

Reduction in burst release after coating poly(D,L-lactide-co-glycolide) (PLGA) microparticles with a drug-free PLGA layer

The high initial burst release of a highly water-soluble drug from poly (D,L-lactide-co-glycolide) (PLGA) microparticles prepared by the multiple emulsion (w/o/w) solvent extraction/evaporation method was reduced by coating with an additional polymeric PLGA layer. Coating with high encapsulation efficiency was performed by dispersing the core microparticles in peanut oil and subsequently in an organic polymer solution, followed by emulsification in the aqueous solution. Hardening of an additional polymeric layer occurred by oil/solvent extraction. Peanut oil was used to cover the surface of core microparticles and, therefore, reduced or prevented the rapid erosion of core microparticles surface. A low initial burst was obtained, accompanied by high encapsulation efficiency and continuous sustained release over several weeks. Reduction in burst release after coating was independent of the amount of oil. Either freshly prepared (wet) or dried (dry) core microparticles were used. A significant initial burst was reduced when ethyl acetate was used as a solvent instead of methylene chloride for polymer coating. Multiparticle encapsulation within the polymeric layer increased as the size of the core microparticles decreased (< 50 µm), resulting in lowest the initial burst. The initial burst could be controlled well by the coating level, which could be varied by varying the amount of polymer solution, used for coating.     

Carboplatin-loaded PLGA microspheres for intracerebral injection: formulation and characterization

The purpose of this study is to prepare and characterize injectable carboplatinloaded poly(D,L-lactic-co-glycolic) acid copolymer (PLGA) microspheres for the intracerebral treatment of malignant glioma. The microspheres were prepared by an acetone/mineral oil emulsion and solvent evaporation method. Preparation variables were optimized and the following processing conditions resulted in the highest drug loading and best yields of the microspheres compared with those prepared with the other variables: the PLGA concentration was 8%(w/w) in the internal phase; the emulsifier (Span 80) concentration was 8%(w/w) in the external phase; the ratio of the internal phase: the external phase was 1:8; the stirring speed was 1500 rpm; the emulsion time was 15 min; the solvent evaporation time was 3.75 hr. Microspheres so prepared were analysed for size distribution, drug loading, in vitro release and morphological characteristics. The drug release in phosphate buffer solution started with a 10- day slow release period, followed by a fast near zero order release period from 12 to 22 days. The carboplatin release in brain homogenate was slower than in phosphate buffer solution. The morphological changes of the microspheres during the in vitro degradation correlated with the drug relase profile. In conclusion, the carboplatin-loaded PLGA microspheres were specifically prepared to meet the specification as an injectable and biodegradable brain implant.     

Microspheres made by w/o/o emulsion method with reduced initial burst for long-term delivery of endostar, a novel recombinant human endostatin

The purpose of this work is to design biodegradable Poly(lactide-co-glycolide) (PLGA) microspheres with low initial burst for sustained delivery of Endostar (a novel recombinant human endostatin) and investigate effects of PLGA molecular weight and composition on the release behavior of Endostar microspheres. Endostar microspheres were prepared by using novel w/o/o multiple emulsification-evaporation technique. Effects of polymer molecular weight and copolymer composition on particle properties and release behavior (in vitro and in vivo) have been reported. Drug release in vitro decreased with increase in molecular weight and lactide content of PLGA. Zero order release and low initial burst were obtained with all microsphere formulations. The in vivo performance of Endostar microspheres were also found to be dependent on the polymer molecular weight and copolymer composition. Together, these results suggest that the initial burst release can be reduced by w/o/o emulsion method and the release of Endostar can be changed significantly by varying the polymer molecular weight and copolymer composition.     

Comparative study of some biodegradable polymers on the entrapment efficiency and release behavior of etoposide from microspheres

Etoposide-loaded biodegradable microspheres of poly lactic-co-glycolide (PLGA) 50:50, PLGA 75:25, and polycaprolactone (PCL) were prepared by simple o/w emulsification solvent evaparation method and characterized by size analysis and microscopy. The influence of drug to polymer ratio on the entrapment of etoposide was studied. Of all the three types of microspheres, polycaprolactone microspheres (PCL MS) showed the highest entrapment efficiency (94.64%), followed by PLGA 75:25 microspheres (PLGA 75:25 MS) (88.64%) and PLGA 50:50 microspheres (PLGA 50:50 MS) (79.19%). The drug to polymer ratio of 1:20 gave the highest entrapment efficiency for all the three types of microspheres. The in vitro release of etoposide from the three microsphere formulations were studied in phosphate buffer pH 7.4 (pH 7.4 PB) containing 0.1% Tween 80. The microspheres showed an initial burst release, which was highest from the PLGA 50:50 MS and least from the PCL MS. PCL MS microspheres showed the lower and slow drug release than the remaining formulations. The release of etoposide from all the three microsphere formulations followed Higuchi's diffusion pattern. The microspheres in the dissolution medium for 28 days appeared irregular in shape and slightly fragmented.     

Hyaluronan-based microspheres as tools for drug delivery: a comparative study

The present paper describes the production of biodegradable microparticles using different hyaluronan polymers, such as native hyaluronan, the esterified derivative of hyaluronan Hyaff 11p50 (where 50% of the carboxy groups of hyaluronic acid are esterified with benzyl alcohol) and the autocross-linked polymer (ACP) internally esterified derivative of hyaluronan, by solvent evaporation and spray-drying methods. As model drugs cromolyn sodium salt, metronidazole and prednisolone hemisuccinate sodium salt were employed. The influence of polymer and preparation procedure has been evaluated on microparticle characteristics (i.e. morphology and encapsulation yield) and on the drug release profiles. The use of solvent evaporation method, a polymeric matrix constituted of Hyaff 11p50 3% (w/v), a dispersing phase constituted of 80 g of mineral oil (w/o ratio: 0.1), Span 85 0.1% (w/w) as stabilizer, and a stirring speed of 700 rpm resulted in the production of microspheres characterized by spherical shape, absence of aggregates, a mean diameter of 6.4 microm and a recovery of 90% (w/w). The production of drug containing microspheres led to an increase of mean diameter of microspheres and to high encapsulation yields. Moreover in vitro models have demonstrated that in all cases drugs were released from Hyaff 11p50 microspheres in a controlled fashion. Finally mathematical analysis of the drug release modalities has evidenced that drug release from Hyaff 11p50 microspheres is more consistent with kinetics of the diffusion rather than of the dissolution type.     

Preparation,characterization and in vitro release study of BSA-loaded double-walled glucose-poly(lactide-co-glycolide) microspheres

The aim of this study was to prepare a model protein, bovine serum albumin (BSA) loaded double-walled microspheres using a fast degrading glucose core, hydroxyl-terminated poly(lactide-co-glycolide) (Glu-PLGA) and a moderate-degrading carboxyl-terminated PLGA polymers to reduce the initial burst release and to eliminate the lag phase from the release profile of PLGA microspheres. The double-walled microspheres were prepared using a modified water-in-oil-in-oil-in-water (w/o/o/w) method and single-polymer microspheres were prepared using a conventional water-in-oil-in-water (w/o/w) emulsion solvent evaporation method. The particle size, morphology, encapsulation efficiency, thermal properties, in vitro drug release and structural integrity of BSA were evaluated in this study. Double-walled microspheres prepared with Glu-PLGA and PLGA polymers with a mass ratio of 1:1 were non-porous, smooth-surfaced, and spherical in shape. A significant reduction of initial burst release was achieved for the double-walled microspheres compared to single-polymer microspheres. In addition, microspheres prepared using Glu-PLGA and PLGA polymers in a mass ratio of 1:1 exhibited continuous BSA release after the small initial burst without any lag phase. It can be concluded that the double-walled microspheres made of Glu-PLGA and PLGA polymers in a mass ratio of 1:1 can be a potential delivery system for pharmaceutical proteins.     

In vitro study of lysozyme in poly(lactide-co-glycolide) microspheres with sucrose acetate isobutyrate

This study investigated the suitability of microsphere formulations for extended protein delivery and complete protein release. These microspheres were prepared by a multi-emulsion method and prepared using a mixture of poly(lactide-co-glycolide) (PLGA), RG 502H (lactide:glycolide=50:50, M(W) 9300) and sucrose acetate isobutyrate (SAIB). SAIB embedded into the microspheres and mixed with PLGA, improved the efficiency of enzyme encapsulation. The in vitro release rate of lysozyme (Lys) from the microspheres was reduced due to the high viscosity of the added SAIB and less degradation of PLGA by SAIB. These properties enabled prolonged release of Lys for up to 2 months, characterized by a minimal initial burst of Lys and nearly zero-order protein release kinetics result from co-administration of sorbitan monooleate 80. When it is considered that degradation products of SAIB are inactive for labile proteins, SAIB may be regarded as a promising candidate for long-acting protein delivery.