Influence of microstructure of lactone‐based triblock copolymers on drug release behavior of their microspheres

The current work focuses on the influence of microstructure of different lactone‐based triblock copolymers on drug delivery, where the middle segment was δ‐valerolactone or ?‐caprolactone and the terminal segment was d ,l ‐lactide or cis ‐lactide. Microspheres were fabricated from the triblocks using salicylic acid as the model drug. The microsphere formation and drug release were investigated by scanning electron microscopy, ultraviolet–visible spectroscopy, X‐ray diffraction, and thermogravimetry. The size of the microspheres ranged from 2 to 20 µm in diameter. The diffusion coefficient values showed that replacement of the middle segment, δ‐valerolactone with ?‐caprolactone, retarded the diffusion of the drug molecules. The diffusion coefficient was lowered when d ,l ‐lactide content was decreased in the triblock. Mathematical models were used to predict the drug release from the microspheres of different triblocks. The modeling study on drug release profiles revealed that the biodegradable nature of the triblock played a crucial role in determining the drug release kinetics. The diffusion and degradation reaction justified the drug release from microsphere. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45284.     

APPLICATION OF A DISSOLUTION-DIFFUSION MODEL TO THE RELEASE OF 5-FLUOROURACIL FROM POLYMER MICROSPHERES

A theoretical discussion of drug release from microspheres is provided and a model-based predictive algorithm developed. The model verification step includes literature data describing the release profile of 5-fluorouracil (5-FU) from poly(lactic acid) polymer. Material balance equations were written to describe drug transport from a porous sphere. The model included combined effects of dissolution, diffusion, and void fraction on the release of 5-FU and was validated against in vitro experimental data. Analyses, conducted on published 5-FU release test data, revealed that the process was governed by a dissolution-diffusion mechanism. Approximately 1.5 million microspheres were formed; the drug density, diffusivity, and dissolution rate constant were estimated at 1.110 g/cm³, 2.324 × 10^?15 m²/s, and 17.60 g/m³h, respectively. The dissolution rate was faster than the rate of diffusion by a ratio of 12.79 to 1. Manipulation of the microsphere porosity was an effective way to influence the diffusion-controlled process. The procedure, outlined in the study, for estimating process properties will help fabricate microspheres that meet specific requirements.     

Biodegradable polymeric injectable implants for long‐term delivery of contraceptive drugs

Development of injectable, long‐lasting, contraceptive drug delivery formulations, and implants are highly desired to avoid unplanned pregnancies while improving patient compliance and reducing adverse side effects and treatment costs. The present study reports on the fabrication and characterization of two levonorgestrel (LNG) microsphere injectable formulations. Poly(?‐caprolactone) (PCL) with 12.5% and 24% (w/w) LNG were fabricated into microspheres, measuring 300 ± 125 µm, via the oil‐in‐water (o/w) emulsion solvent evaporation technique. Formulations showed sustained drug release up to 120 days. FTIR, XRD, DSC, and TGA confirmed the absence of LNG chemical interaction with PCL as well as its molecular level distribution. The in vitro release of LNG was calculated to be Fickian diffusion controlled and properly characterized. The inclusion of multiple elevated release temperatures allowed for the application of the Arrhenius model to calculate drug release constants and representative sampling intervals, demonstrating the use of elevated temperatures for accelerated‐time drug release studies. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46068.     

PCL/poloxamer 188 blend microsphere for paclitaxel delivery: Influence of poloxamer 188 on morphology and drug release

A novel controlled release system, paclitaxel‐loaded poly (ε‐caprolactone) (PCL)/poloxamer 188 (Pluronic F68, F68) blend microspheres is proposed in the present work. F68 was incorporated into PCL matrices as both a pore‐forming agent and a drug releasing enhancer. Paclitaxel‐loaded PCL/F68 blend microspheres with different amounts of F68 were prepared by the oil‐in water (O/W) emulsion/solvent evaporation method. Characterization of the microspheres followed to examine the particle size, the drug encapsulation efficiency, the surface morphology, and in vitro release behavior. The influences of F68 on microsphere morphology and paclitaxel release are discussed. The porosity of the surface of PCL/F68 blend microspheres and the release rate of paclitaxel from the PCL/F68 blend microspheres increased as the initial amount of blended F68 increased. Faster and controlled release was achieved in comparison with the PCL microspheres. Through this study, the developed microporous PCL/F68 blend microspheres could be used as a drug delivery system to enhance and control drug release in the future. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci 104: 1895–1899, 2007     

Mass transfer kinetics and diffusion coefficient estimation of bioinsecticide terpene ketones in LDPE films obtained by supercritical CO2‐assisted impregnation

Release kinetics of thymoquinone and R ‐(+)‐pulegone impregnated in low‐density polyethylene (LDPE) films into air and the effect of supercritical CO₂‐assisted impregnation process on the diffusional properties of these films were investigated. The incorporation of both ketones into LDPE films was performed under different conditions (pressure, depressurization rate, time, and initial ketone mole fraction). Release experiments were performed under controlled laboratory conditions (24 °C, 60% relative humidity), and the total release profile was determined gravimetrically, while the individual release of each ketone was quantified by Fourier transformed infrared. The experimental data were used to fit a mass transfer model based on the second Fick's law for unsteady‐state diffusion, and the diffusion coefficients of both ketones in LDPE were estimated, ranging from 2.35 × 10^?13 to 5.53 × 10^?13 m² s^?1 (thymoquinone) and from 1.24 × 10^?13 to 4.52 × 10^?13 m² s^?1 (pulegone). Finally, analysis of variance testing indicated that impregnation pressure and depressurization rate (and their combination) have significant effects on the diffusion coefficient values. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45558.     

Fabrication and characterization of colon specific eudragit coated graphene oxide microsphere for sustained delivery of tramadol hydrochloride

ABSTRACT

Present investigation reports a straight forward method for synthesis of graphene oxide (GO) followed by fabrication of graphene oxide microsphere (GMS) using water in oil (w/o) emulsification technique. For colon specific drug delivery, enteric coating is desirable, which was done using Eudragit S100 and characterized by Fourier transform Infrared Spectroscopy (FTIR). The surface morphology of fabricated microsphere was confirmed using scanning electron microscopy (SEM). Drug loaded microspheres demonstrated a high payload capacity for model drug tramadol hydrochloride (TmH). The comparative In-vitro drug release showed around 72.37% release from uncoated microspheres, whereas eudragit coated microspheres retarded the drug release upto 10 h.     

聚己内酯/纳米羟基磷灰石复合微球中的药物分布及体外释放

采用单乳化溶剂挥发法制备了聚己内酯[poly(ε-caprolactone),PCL]/纳米羟基磷灰石(nano-hydroxyapatite,n-HA)复合微球.使用两种具有不同水溶性的模型药物对硝摹苯胺(p-nitroaniline)和罗丹明B(RhodamineB,RhB),研究n-HA在复合微球中的作用.用扫描电子显微镜观察微球的表面形貌.通过紫外-可见光分光光度法计算药物载量和包封率.用共聚焦激光显微镜分析药物在微球中的分布.分别研究了PCL微球和PCL/HA复合微球的体外释放性质.复合微球可以持续释放药物4周以上,在前3 d的突释后,其释放曲线符合Higuchi扩散方程.n-HA的加入使较亲水药物RhB在复合微球中分布更均匀,对较疏水药物对硝基苯胺则影响不明显.n-HA减少了载亲水药物的复合微球在前 3d 的突释,并减缓了其后的释放速率.结果表明:PCL/n-HA复合结构的材料有希望作为一种新的长效药物释放载体应用.     

Dynamic adsorption behaviors between Cu2+ ion and water‐insoluble amphoteric starch in aqueous solutions

Dynamic adsorption behavior between Cu²⁺ ion and water‐insoluble amphoteric starch was investigated. The sorption process occurs in two stages: external mass transport occurs in the early stage and intraparticle diffusion occurs in the long‐term stage. The diffusion rate of Cu²⁺ ion in both stages is concentration dependent. In the external mass‐transport process, the diffusion coefficient (D₁) increases with increasing initial concentration in the low‐ (1 × 10^?3‐4 × 10^?3M) and high‐concentration regions (6 × 10^?3‐10 × 10^?3M). The values of adsorption activation energy (k_d1) in the low‐ and high‐concentration regions are 15.46–24.67 and ?1.80 to ?11.57 kJ/mol, respectively. In the intraparticle diffusion process, the diffusion coefficient (D₂) increases with increasing initial concentration in the low‐concentration region (1 × 10^?3‐2 × 10^?3M) and decreases with increasing initial concentration in the high‐concentration region (4 × 10^?3‐10 × 10^?3M). The k_d2 values in the low‐ and high‐concentration regions are 9.96–15.30 and ?15.53 to ?10.71 kJ/mol, respectively. These results indicate that the diffusion process is endothermic in the low‐concentration region and is exothermic in the high‐concentration region for both stages. The external mass‐transport process is more concentration dependent than the intraparticle diffusion process in the high‐concentration region, and the dependence of concentration for both processes is about equal in the low‐concentration region. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2849–2855, 2001     

Preparation and evaluation of alginate/chitosan microspheres containing pheromones for pest control of Megaplatypus mutatus Chapuis (Platypodinae: Platypodidae)

This work describes the optimization of an alginate/chitosan microsphere preparation for the encapsulation of a sexual pheromone, 6‐methyl‐5‐hepten‐2‐ol (sulcatol), to realize a slow‐release device for the biological control of the Megaplatypus mutatus pest. To evaluate and select the best encapsulation/release conditions three parameters were studied: alginate concentration, pH of gelling solution and Ca²⁺/COO^? ratio. The preparation was optimized using biopolymers with improved mechanical properties and swelling behavior. The obtained microspheres were characterized using Fourier transform infrared spectroscopy, scanning electron and optical microscopies, swelling degree, mechanical properties and in vitro release of encapsulated pheromone. The microspheres performed best when they were synthesized using an alginate concentration of 4% w/v, at pH = 9 and with a Ca²⁺/COO^? ratio of 3.5. The attractiveness of the alginate/chitosan microspheres towards M. mutatus was demonstrated by behavioral bioassay with the completed pheromonal blend of the species (sulcatol, sulcatone and 3‐pentanol). The formulation can be considered as an efficient slow‐release biological control system, with no negative environmental impact. © 2015 Society of Chemical Industry     

Preparation of injectable paclitaxel sustained release microspheres by spray drying for inhibition of glioma in vitro

The major aim of this work was to prepare injectable paclitaxel‐loaded poly(D ,L ‐lactide) microspheres for the inhibition of brain glioma. Paclitaxel‐loaded PLA microspheres were prepared by spray drying method employing ethyl acetate as solvent. And the microspheres were characterized by scanning electron microscopy (SEM) for the morphology and differential scanning calorimetry for thermal analysis. The encapsulation efficiency (EE) and in vitro release profiles of paclitaxel‐loaded microspheres were determined by using ultraviolet spectrophotometer. The results showed that the microspheres possess a narrow size distribution with the average diameter of 4.6 μm. The surface of the microspheres was smooth, and the paclitaxel dispersed in microspheres in amorphous state. The solvent residue was 0.03%, and the EE reaches ～ 90%. The microspheres exhibited a sustained release behavior, and the release period last for at least three months, depending on the EE of the microspheres. The γ irradiation sterilization had little effect on the EE and drug release in vitro. Compared with the commercial formulation, the sustained release microsphere showed a stronger inhibition on the tumor cells, suggesting the potential application of long‐term delivery of paclitaxel‐loaded PLA microspheres in clinic tumor therapy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on Micellar Behavior of PEO‐PBO or PEO‐PBO‐PEO Copolymers,or Surface Active Amphiphilic Ionic Liquids in Aqueous Media and Exploration of the Micellar Solutions for Solubilization of Dexamethasone and its Delayed Release

The aggregation behavior of a di‐ and tri‐block copolymers of type PEO‐PBO, PEO‐PBO‐PEO, surface‐active ionic liquid (SAIL) of type 4‐dodecyl‐4‐methylmorpholinium chloride [C₁₂mmor][Cl], and 1‐dodecyl‐1‐methylpyrrolidinium chloride [C₁₂mpyrr][Cl]) in water as well as in 10 mM of a poorly water soluble dexamethasone (dex) aqueous solution was studied by determining the critical micelle concentrations using drug solubilization, surface tension, and isothermal titration calorimetry (ITC) methods. ITC measurements were also made on solutions prepared by mixing the micellar aqueous solutions of copolymers and simple aqueous solutions of SAIL across the mole fractions at three different temperatures (298.15, 308.15, and 318.15 K). The thermodynamic parameters, namely Gibbs free energy (ΔG_m), enthalpy (ΔH_m), and entropy (ΔS_m), of micellization were calculated, and it was observed that the negative ΔG_m and positive ΔS_m for the mixture solutions increase with the increase in mole fraction of SAIL. Otherwise, the micellization is reported to be a spontaneous and highly entropy‐driven process. The dex‐solubilized micellar solutions were mixed with agar to obtain standing gels. The gel samples were dry‐cast into thin films, and the release of dex from films by simple dilution was monitored by UV measurements. The drug release data was fitted to several mechanistic models, and it was inferred that the release mechanism for dex from thin films is non‐Fickian for mixtures and Fickian in copolymer or SAIL micellar aqueous solutions. The transport of dex is diffusion‐controlled with diffusivities of 5.8–12 × 10^?11 m² s^?1 for copolymer micelles, 5–11 × 10^?11 m² s^?1 for micelles of SAIL, and 3–14 × 10^?11 m² s^?1 for the mixed micelles of copolymer and SAIL in aqueous media.     

Effects of drug and polymer molecular weight on drug release from PLGA‐mPEG microspheres

This study investigated the effects of drug and polymer molecular weight on release kinetics from poly (g ‐co‐glycolic acid)‐methoxypoly(ethyleneglycol) (PLGA‐mPEG) microspheres. Bovine serum albumin (BSA, 66 kDa), lysozyme (LZ, 13.4 kDa), and vancomycin (VM, 1.45 kDa) were employed as the model drugs, and encapsulated in PLGA‐mPEG microspheres of different molecular weight. Release of macromolecular BSA was mainly dependent on diffusion of drug at/ near the surface of the matrix initially and dependent on degradation of matrix at later stages, while, the small drug of vancomycin seemed to depend totally on diffusion for the duration of the release study. The release behavior of lysozyme was similar to bovine serum albumin, except a shorter lag period. PLGA‐mPEG molecular weight also affected the release behavior of bovine serum albumin and lysozyme, but not obviously. PLGA‐mPEG microspheres in smaller molecular weight seemed to degrade more quickly to obtain a mass lose and matrix erosion, and thus, an accelerated release rate of bovine serum albumin and lysozyme. Vancomycin released much faster than bovine serum albumin and lysozyme, and exhibited no lag period, as it is thought to be diffusion‐controlled. Besides, vancomycin showed no difference in release behavior as PLGA‐mPEG molecular weight change. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41431.     

Diffusion of drugs from hydrogels and liposomes as drug carriers

BACKGROUND: The mass transfer of model drugs Lidocaine hydrochloride and Dihydroquercetin from hydrogels (the usual carriers for topical drugs), and hydrogels containing liposomes, as novel drug vehicles, was studied. Diffusion experiments were performed using a Franz diffusion cell. Experimental data were used to calculate drug diffusion coefficients across membranes, and their effective diffusion coefficients from hydrogels and liposome containing hydrogels. For the first time the diffusion resistance of all drug carriers was determined from corresponding diffusion coefficients. The main aim of this work was the study of drug diffusion coefficients from liposomes and their comparison with related diffusion coefficients from hydrogels to find how liposomes contribute to prolonged and controlled drug release. RESULTS: Drug diffusion coefficients were: 1.38 · 10^?8m² s^?1 for Lidocaine hydrochloride and 5.96 · 10^?9m² s^?1 for Dihydroquercetin, while corresponding effective diffusion coefficients from hydrogels were: 7.82 · 10^?10m² s^?1 and 7.98 · 10^?10m² s^?1, respectively. Effective diffusion coefficients from liposome‐containing hydrogels were:4.82 · 10^?10m² s^?1 (Lidocaine hydrochloride) and 4.305 · 10^?10m² s^?1 (Dihydroquercetin). Diffusion resistances for the two hydrogels were almost the same. Very similar values of diffusion resistances for all liposome dispersions were obtained. CONCLUSION: Calculated diffusion coefficients and resistances demonstrate that liposomes, as drug carriers, significantly affect diffusion rates. The results obtained could be used whenever diffusion‐controlled drug release is required. Copyright © 2010 Society of Chemical Industry     

Preparation of novel amphiphilic copolymer microspheres and their drug‐release and glucose‐sensitive properties

A novel amphiphilic copolymer was prepared by the copolymerization of N‐acryloyl‐3‐aminophenylboronic acid with β‐cyclodextrin containing maleic anhydride. The copolymer was fully characterized with ¹³C‐NMR, ¹H‐NMR, IR, and scanning electron microscopy. The self‐assembling mechanism of the copolymer in H₂O–CH₃OH cosolvents was studied. Gliclazide as a model drug was loaded inside the copolymer microspheres, and the drug‐release behavior of the microspheres was studied. The results of in vitro oscillating release tests indicated that the microspheres responded to glucose rapidly in 30 min, and the microspheres exhibited self‐regulated on–off release behavior four to six times in 6 h between the solution with 3 g/L glucose and the medium without glucose; this met the clinical requirements of multidrug delivery. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Poly(Caprolactone)‐Poly(N‐Isopropyl Acrylamide)‐Fe3O4 Magnetic Nanofibrous Structure with Stimuli Responsive Drug Release

Poly(caprolactone; PCL)—poly(N‐isopropylacrylamie; PNIPAAm)—Fe₃O₄ fiber, that can be magnetically actuated, is reported. Here, a structure is engineered that can be utilized as a smart carrier for the release of chemotherapeutic drug via magneto‐thermal activation, with the aid of magnetic nanoparticles (MNPs). The magnetic measurement of the fibers revealed saturation magnetization values within the range of 1.2–2.2 emu g^?1. The magnetic PCL‐PNIPAAm‐Fe₃O₄ scaffold shows a specific loss power value of 4.19 W g^?1 at 20 wt% MNPs. A temperature increase of 40 °C led to a 600% swelling after only 3 h. Doxorubicin (DOX) as a model drug, demonstrates a controllable drug release profile. 39% ± 0.92 of the total drug loaded is released after 96 h at 37 °C, while 25% drug release in 3 h at 40 °C is detected. Cytotoxicity results show no significant difference in cell attachment efficiency between the MNP‐loaded fibers and control while the DOX‐loaded fibers effectively inhibited cell proliferation at 24 h matching the drug release profile. The noncytotoxic effect, coupled with the magneto‐thermal property and controlled drug release, renders excellent potential for these fibers to be used as a smart drug‐release agent for localized cancer therapy.     

Adsorption of diclofenac sodium from aqueous solution using polyaniline as a potential sorbent. I. Kinetic studies

This study describes dynamic uptake of antibiotic drug diclofenac sodium from aqueous solution using polyaniline as sorbent. The sorbent polyaniline was prepared by oxidative polymerization of aniline and characterized by FTIR spectrum analysis and TGA. The optimum sorbent/sorbate mg/mL ratio and pH range for maximum drug uptake have been found to be 2.0 and 5.5 to 10.5, respectively. Out of various kinetic models applied, the pseudo second‐order kinetic equation has been found to fit well on the kinetic uptake data. The pseudo second‐order rate constants for adsorption have been found to be 0.982 × 10^?2, 7.24 × 10^?2, and 18.09 × 10^?2 min^?1 mg^?1 g for drug solutions with initial concentrations of 10, 20, and 30 mg L^?1, respectively. The overall sorption process has been found to be governed by intraparticle diffusion.The sorptive removal of drug from aqueous solution has also resulted in enhancement in bacterial growth of Escherichia coli. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cytarabine trapping in poly(2-hydroxyethyl methacrylate-co-acrylamide) hydrogels: drug delivery studies

Copolymeric hydrogels of poly(2-hydroxyethyl methacrylate-co-acrylamide) [p(HEMA-co-A)] crosslinked with ethylene glycol dimethacrylate, with a high equilibrium degree of swelling (37–65 wt%) in saline solution (NaCl 0.9 wt%) were synthesized as devices for controlled release of cytarabine (ara-C). Two compositions of the copolymer, each with a different degree of crosslinking have been studied, HEMA80/A20 and HEMA60/A40. The antineoplasic drug was included in the feed mixture of polymerization, and discs 3.7 ± 0.4 mm thick and 11.8 ± 0.2 mm in diameter with 5–40 mg (1.0–8.3 wt%) of ara-C were obtained. The diffusion studies followed Fick's second law. The diffusion coefficients for swelling of the gels were between 3.60 × 10⁻¹¹ and 15.8 × 10⁻¹¹ m² s⁻¹; those for release of ara-C were between 0.31 × 10⁻¹¹ and 7.18 × 10⁻¹¹ m² s⁻¹. The activation energies for swelling were in the range 23.4–31.9 kJ mol⁻¹ and those for ara-C release were 42.2–61.6 kJ mol⁻¹; their values indicate that the drug release process depends on drug–matrix and drug–water interactions that are influenced by the aqueous solution content and the network size of the gels. Total release of the drug takes place between 17 h from H60/A40/E2 at 310 K and 6 days from H80/A20/E10 at 288 K. Ara-C degradation was not observed either during loading of the gels or during drug release. © 1999 Society of Chemical Industry     

Poly‐3‐hydroxyalkanoates‐co‐polyethylene glycol methacrylate copolymers for pH responsive and shape memory hydrogel

Multifunctional hydrogels combining the capabilities of cellular pH responsiveness and shape memory, are highly promising for the realization of smart membrane filters, controlled drug released devices, and functional tissue‐engineering scaffolds. In this study, lipase was used to catalyze the synthesis of medium‐chain‐length poly‐3‐hydroxyalkanoates‐co‐polyethylene glycol methacrylate (PHA‐PEGMA) macromer, which was used to prepare pH‐responsive and shape memory hydrogel via free radical polymerization. Increasing the PEGMA fraction from 10 to 50% (mass) resulted in increased thermal degradation temperature (T_d) from 430 to 470°C. Highest lower critical solution temperature of 37°C was obtained in hydrogel with 50% PEGMA fraction. The change in PEGMA fraction was also found to highly influence the hydrogel's hydration rate (r) from 2.8 × 10^?5 to 7.6 × 10^?5 mL·s^?1. The hydrogel's equilibrium weight swelling ratio (q_e), protein release and its diffusion coefficient (D_m) were all found to be pH dependent. Increasing the phosphate buffer pH from 2.4 to 13 resulted in increased q_e from 2 to 16 corresponding to the enlarging of network pore size (ξ) from 150 to 586 nm. Different types of crosslinker for the hydrogel influenced its flexibility and ductility. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41149.     

Preparation and release study of ibuprofen‐loaded porous matrices of a biodegradable poly(ester amide) derived from L‐alanine units

Scaffolds of a biodegradable poly(ester amide) constituted of L ‐alanine, sebacic acid, and 1,12‐dodecanediol units (abbreviated as PADAS) were prepared by the compression‐molding/particulate‐leaching method. The influence of the type, size, and percentage of salt on the scaffold porosity and morphology was evaluated. The thermal behavior and crystallinity were also studied for samples obtained under different processing conditions. PADAS scaffolds were not cytotoxic because they showed good cell viability and supported cell growth at a similar ratio to that observed for the biocompatible materials used as a reference. The use of PADAS scaffolds as a drug‐delivery system was also evaluated by the employment of ibuprofen, a drug with well known anti‐inflammatory effects. Different drug‐loading methods were considered, and their influence on the release in a Sörensen's medium was evaluated as well as the influence of the scaffold morphology. A sustained release of ibuprofen could be attained without the production of a negative effect on the cell viability. The release kinetics of samples loaded before melt processing was well described by the combined Higuchi/first‐order model. This allowed the estimation of the diffusion coefficients, which ranged between 3 × 10^?14 and 5 × 10^?13 m²/s. Samples loaded by immersion in ibuprofen solutions showed a rapid release that could be delayed by the addition of polycaprolactone to the immersion medium (i.e., the release rate decreased from 0.027 to 0.015 h^?1). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Chitosan microspheres: modification of polymeric chem‐physical properties of spray‐dried microspheres to control the release of antibiotic drug

Antibiotic drug releasing from chitosan and acylchitosan microspheres was studied. The acylchitosan microspheres were prepared by modifying the microencapsulation process from spray‐drying to spray in‐liquid coagulating process for the improvement of chem‐physical properties of polymer in controlling the release of antibiotic drug. A higher yield of microspheres was recovered by this improved process. Crystallinity, swelling ability, and the morphology of various microspheres were investigated by X‐ray, water adsorption, and scanning electron microscopy studies. Results show that by modifying the microencapsulation process from spray‐drying to spray in‐liquid coagulating process, the chemical properties of the microsphere were varied from a hydrophilic chitosan microsphere to a hydrophobic acylchitosan microsphere, while the physical structure of the microsphere was varied from a porous chitosan microsphere to a dense acylchitosan microsphere. For the reasons, drug release rate of acylchitosan microspheres prepared by the novel spray microencapsulation method were apparently depressed, and the long‐acting release of antibiotic drug was possible to be achieved. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 747–759, 1999