Preparation and characterization of biodegradable electrospun polyanhydride nano/microfibers

The biodegradable polyanhydride copolymers P(CPP-SA) composed of p-carboxyhenoxy propane (CPP) and sebacic acid (SA) at weight ratios of 20:80, 35:65 and 50:50 were polymerized by a melt polycondensation process without catalyst. The copolymers were characterized by fourier transform infrared spectroscopy (FT-IR), 1H-nuclear magnetic resonance (1H-NMR), Ubbelohde viscometer, differential scanning calorimetry (DSC) and wide angle X-ray powder-diffraction (XRD). P(CPP-SA) nano/microfibers were the first time to be fabricated by electrospinning. The copolymers hold an excellent fibre-forming performance and the diameter range of 80-3,200 nm can be obtained. The in vitro degradation of the polyanhydride copolymers was evaluated in form of the nano/microfibers by investigating the change of fibrous morphology, weight loss and pH change of degradation medium. The experimental results showed that degradation rate was fast in the fist day and slow in the following period, furthermore the degradation rate decreased with the increase of the content of CPP in copolymers. Therefore, the electrospun polyanhydride nano/microfibers exhibited strong potential as drug delivery vehicle and tissue engineering scaffold.     

Sustained-release butorphanol microparticles

Various butorphanol-loaded microparticles have been prepared with a biodegradable copolymer P(FAD-SA) of erucic acid dimer (FAD) and sebacic acid (SA) and a copolymer P(CPP-SA) of carboxyphenoxypropane (CPP) and SA using a melt compounding and milling method. Drug release was measured in vitro following incubation of drug-loaded microparticles in water for injection at 37°C. It was found that butorphanol was released in a sustained manner, yielding a cumulative drug release of about 100% over a period of 48 hr. Also, drug release was affected by drug loading and the size of the microparticles; however, it was not significantly influenced by the copolymer composition. Scanning electron microscopic (SEM) results showed that most of the particles were irregular in shape with uneven surfaces. The molecular weights of the copolymers were not changed after this fabrication process. In addition, 20% butorphanol-encapsulated microspheres were prepared with copolymer P(FAD-SA) by spray-drying. The SEM micrograph shows that the particle sizes of the microspheres ranged from 2 to 10 μm, and the external surfaces appear smooth. Moreover, rapid drug release was observed for these microspheres, with more than 92% of the encapsulated drug released within the first 2 hr.     

Sustained-Release Butorphanol Microparticles

Various butorphanol-loaded microparticles have been prepared with a biodegradable copolymer P(FAD-SA) of erucic acid dimer (FAD) and sebacic acid (SA) and a copolymer P(CPP-SA) of carboxyphenoxypropane (CPP) and SA using a melt compounding and milling method. Drug release was measured in vitro following incubation of drug-loaded microparticles in water for injection at 37°C. It was found that butorphanol was released in a sustained manner, yielding a cumulative drug release of about 100% over a period of 48 hr. Also, drug release was affected by drug loading and the size of the microparticles; however, it was not significantly influenced by the copolymer composition. Scanning electron microscopic (SEM) results showed that most of the particles were irregular in shape with uneven surfaces. The molecular weights of the copolymers were not changed after this fabrication process. In addition, 20% butorphanol-encapsulated microspheres were prepared with copolymer P(FAD-SA) by spray-drying. The SEM micrograph shows that the particle sizes of the microspheres ranged from 2 to 10 μm, and the external surfaces appear smooth. Moreover, rapid drug release was observed for these microspheres, with more than 92% of the encapsulated drug released within the first 2 hr.     

Evaluation of hydrophilic matrix tablets based on Carbopol® 971P and low-viscosity sodium alginate for pH-independent controlled drug release

Background: The aim of this study was to evaluate matrix tablets containing different ratios of Carbopol^® 971P (CP) to low-viscosity sodium alginate (SA) and assess their suitability for pH-independent controlled drug release. Methods: Two processing methods (physical mixing, PM and spray-drying, SD) were applied before compaction and the release from corresponding matrices was compared. The release from CP-SA PM matrices was also investigated using three model drugs (paracetamol, salicylic acid, and verapamil HCl) and two dissolution media (0.1 N HCl or phosphate buffer, pH?=?6.8), and the release rate, mechanism, and pH-dependence were characterized by fitting of Higuchi and Peppas models, and evaluation of similarity factor. Furthermore, swelling behavior of CP-SA matrix tablets was studied for evaluating its impact on drug release. Results: The processing method (SD or PM) markedly affected the drug release from CP-SA matrices. ANOVA tests showed significant effects of the CP:SA ratio and drug type on the release rate (expressed by the constant, K_H, from Higuchi model) and of the dissolution medium on the release mechanism (expressed by the exponent, n, from Peppas model). Similarity factor (f₂) indicated that the CP:SA ratios ≥?25:75 and ≥?50:50 were suitable for pH-independent release of paracetamol and salicylic acid, respectively, although for verapamil HCl, the matrix with low CP:SA ratio (0:100) showed remarkably reduced pH-dependence of release. Swelling parameters (water uptake and mass loss) were significantly changed with experimental variables (CP:SA ratio, medium, and time) and were in good correlation with drug release. Conclusion: Matrix tablets based on CP and SA form a potentially useful versatile system for pH-independent controlled drug release.     

预交联法制备海藻酸钠复合微球及其缓释性能

采用预交联法制备海藻酸钠(SA)/凹土(ATP)复合微球(PCM)以克服常规制备方法导致微球交联不均匀的缺陷,从而改善微球的缓释性能。将ATP先与Ca~(2+)进行部分离子交换制备Ca~(2+)-ATP,然后在与SA复合过程中同时进行预交联形成交联密度有所提高的微球内核,再采用滴注法制备该复合微球。利用红外光谱、扫描电镜和电子照片对微球结构和形貌进行表征,考察了Ca~(2+)浓度对PCM力学强度、溶胀率、载药和缓释性能的影响。结果表明,PCM在1h的累计释放率由预交联前的68%降为50%,显著改善了微球的"突释"。释放动力学研究表明,微球的释药可用Ritger-Peppas方程很好地拟合,释药速率受骨架溶蚀和药物扩散双重控制。     

Effect of Microsphere Size and Formulation Factors on Drug Release from Controlled-Release Furosemide Microspheres

Controlled-release furosemide microspheres were prepared with various combinations of Eudragit L: Eudragit RS and Eudragit S: Eudragit RS and release of drug from microspheres containing these polymers in different ratios was studied. A wide range of release rates of drug can obtained by a simple change in the ratio of polymers. An increase in Eudragit RS content of polymer microsphere matrix brought about a decrease in the release rate.

On the other hand, the effect of particle size on the drug release rate from furosemide microspheres was also investigated. The effect of microsphere sizes on release rate depends on the type of Eudragit. The decrease in release rates of small microspheres may be due to agglomerate formation. Dissolution data indicated that the release followed Higuchi's matrix model kinetics.     

Effect of Steareth-20 on the Release of Nitrofurantoin from Propylene Glycol Monostearate Microspheres

In vitro release of nitrofurantoin (NFT) from microspheres of propylene glycol monostearate (PGM) was investigated at NFT:PGM ratios of 1:1, 1:1.5, 1:3, 1:4, 1:5, and 1:9 in distilled water at 37°C. The rate and extent of drug release declined with decreasing NFT:PGM ratio. A maximum drug release of 52.4% over 24 hr was recorded for the microspheres of formulation I (highest load). The effect of Steareth-20 (ESA) over the concentration range of 0.01% to 0.1% w/w of PGM on the size of the microspheres and on the release profile of nitrofurantoin from the microsphere formulations was examined at NFT.PGM ratios of 1:1 and 1:4. The cumulative % of NFT released over a 24-hr period was found to be maximum at ESA concentration of 0.03% and 0.05% w/w of PGM. The plots of T₅₀ versus %w/w of ESA exhibited two minima, the first at 0.03% ESA and a second, weaker than the first, at 0.05% ESA, paralleling the earlier observations. Scanning electron micrographs of the exhausted microspheres revealed a very porous matrix of PGM at the ESA concentration of 0.03%. The formulations containing 0.03% and 0.05% ESA had the smallest mean particle diameter and the minimum contact angles (water over PGM-ESA films) corresponding to the two critical micelle concentrations (CMC), at 0.025% and 0.05% w/w.     

Encapsulation and characterization of controlled release flurbiprofen loaded microspheres using beeswax as an encapsulating agent

The aim of the present study was to extend the use of flurbiprofen in clinical settings by avoiding its harmful gastric effects. For this purpose, we designed the controlled release solid lipid flurbiprofen microspheres (SLFM) by emulsion congealing technique. Drug was entrapped into gastro resistant biodegradable beeswax microspheres which were prepared at different drug/beeswax ratios 1:1, 1:2 and 1:3 using gelatin and tween 20 as emulsifying agents. The effect of emulsifiers and the effect drug/beeswax ratios were studied on hydration rate, encapsulating efficiency, micromeritic properties, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (X-RD) analysis and in vitro drug release at pH 1.2 for 2 h and at pH 6.8 for 10 h. SEM revealed that microspheres made with tween 20 were smooth while microspheres made with gelatin showed porous morphology, however, they were all spherical in nature. The practical yield (recovery) showed a dependence on drug-beeswax ratio and it was variable from 53 to 84%. High loading encapsulating efficiency of flurbiprofen from 8 to 94% was achieved. FTIR and DSC analysis confirmed the absence of any drug polymer interaction indicating drug stability during microencapsulation. X-RD of pure flurbiprofen shows sharp peaks, which decreases on encapsulation, indicating decrease in the crystallinity of drug in microspheres. The micromeritic studies confirmed the presence of excellent and good flow properties of microspheres. Entrapment efficiency, morphology, practical yield, hydration rate, flow properties demonstrated their dependence on the HLB value of emulsifiers and emulsifiers with higher HLB were found more appropriate for effective microencapsulation of flurbiprofen. The release kinetics followed zero order mechanism of drug release at pH 6.8. Release pattern depends on the morphology of flurbiprofen microspheres and amount of beeswax used in the microspheres preparation. The microspheres prepared with high HLB values i.e., tween 20 showed effective control of drug release from microspheres. The absence of drug release at pH 1.2 proved the suitability of beeswax for its use as a gastro resistant material.     

氧化海藻酸钠交联壳聚糖载药复合体系的制备及其药物缓释初步研究

为获得一种新型的药物释放复合体系,本实验首先通过乳化交联法制备壳聚糖(CS)包载四环素(TC)微球,然后利用氧化海藻酸钠交联聚磷酸钙/壳聚糖(CPP/CS)复合材料,用冷冻干燥法制备了载药微球复合体系.并用傅立叶红外光谱仪(IR)、扫描电镜(SEM)及药物的体外释放等方法对该载药微球复合体系进行分析和表征.结果显示,经...     

Sustained release optimized formulation of anastrozole-loaded chitosan microspheres: in vitro and in vivo evaluation

The purpose of this study was to develop sustained release formulation of anastrozole-loaded chitosan microspheres for treatment of breast cancer. Chitosan microspheres cross-linked with two different cross-linking agents viz, tripolyphosphate (TPP) and glutaraldehyde (GA) were prepared using single emulsion (w/o) method. A reverse phase HPLC method was developed and used for quantification of drug in microspheres and rat plasma. Influence of cross-linking agents on the properties of chitosan microspheres was extensively investigated. Formulations were characterized for encapsulation efficiency (EE), compatibility of drug with excipients, particle size, surface morphology, swelling capacity, erosion and drug release profile in phosphate buffer pH 7.4. EE varied from 30.4 ± 1.2 to 69.2 ± 3.2% and mean particle size distribution ranged from 72.5 ± 0.5 to 157.9 ± 1.5 μm. SEM analysis revealed smooth and spherical nature of microspheres. TPP microspheres exhibited higher swelling capacity, percentage erosion and drug release compared to GA microspheres. Release of anastrozole (ANS) was rapid up to 4 h followed by slow release status. FTIR analysis revealed no chemical interaction between drug and polymer. DSC analysis indicated ANS trapped in the microspheres existed in amorphous form in polymer matrix. The highest correlation coefficients (R ²) were obtained for Higuchi model, suggesting a diffusion controlled mechanism. There was significant difference in the pharmacokinetic parameters (AUC_0−∞, Kel and t_1/2) when ANS was formulated in the form of microspheres compared to pure drug. This may be attributed to slow release rate of ANS from chitosan microspheres and was detectable in rat plasma up to 48 h which correlates well with the in vitro release data.     

Preparation and characterization of ibuprofen-loaded microspheres consisting of poly(3-hydroxybutyrate) and methoxy poly (ethylene glycol)-b-poly (D,L-lactide) blends or poly(3-hydroxybutyrate) and gelatin composites for controlled drug release

Poly-(3-hydroxybutyrate) (P(3HB)) is a biodegradable and biocompatible polymer that has been used to obtain polymer-based drug carriers. However, due to the high crystallinity degree of this polymer, drug release from P(3HB) microspheres frequently occurs at excessive rates. In this study, two strategies for prolonging ibuprofen release from P(3HB)-based microspheres were tested: blending with poly(D,L-lactide)-b-polyethylene glycol (mPEG-PLA); and obtaining composite particles with gelatin (GEL). SEM micrographs showed particles that were spherical and had a rough surface. A slight decrease of the crystallinity degree of P(3HB) was observed only in the DSC thermogram obtained from unloaded-microspheres prepared from 1:1 P(3HB):mPEG-PLA blend. For IBF-loaded microspheres, a reduction of around 10 °C in the melting temperature of P(3HB) was observed, indicating that the crystalline structure of the polymer was affected in the presence of the drug. DSC studies also yielded evidence of the presence of a molecular dispersion coexisting with a crystalline dispersion in the drug in the matrix. Similar results were obtained from X-ray diffractograms. In spite of 1:1 mPEG-PLA:P(3HB) blends having contributed to the reduction of the burst effect, a more controlled drug release was provided by the use of the 3:1 P(3HB):mPEGPLA blend. This result indicated that particle hydration played an important role in the drug release. On the other hand, the preparation of P(3HB):GEL composite microspheres did not allow control of the IBF release.     

Chitosan-Drug Conjugate Microspheres: Preparation and Drug Release Properties of Microspheres Composed of the Conjugate of 2'- or 3'-(4-Carboxy-butyryl)-5- Fluorouridine with Chitosan

The conjugate microspheres (Chi-glu-FUR-m) were prepared by the dry-in-oil method using chitosan-5-fuorouridine conjugate. Chi-glu-FUR-m were characterized by drug content, particle shape and size, swelling property, and drug release. Their characteristics were compared with those of the simple microspheres (Chi/ FUR-m), which were prepared under similar conditions using a mixture of chitosan and 5-fluorouridine. Both microspheres prepared showed a high retention of the drug after preparation and similar particle size and shape. Swelling ratios after incubation in aqueous buflers of pH 7.4 for 6 hr were similar for both microspheres. Chi-glu-FUR-m swelled quickly in aqueous buffers of pH 7.4 and the disintegration was observed to occur gradually from 24 hr afrer the incubation. Chi-glu-FUR-m showed a gradual drug release (50% release time = 61 hr), while Chi/FUR-m released the drug very rapidly, Such characteristics of Chi-glu-FURm as swelling, slow disintegration, and gradual drug release propose its usefulness for localization or chemoembolization therapy.     

掺钕介孔硼硅酸盐生物活性玻璃陶瓷骨水泥的制备与性能表征

骨肉瘤是一种常见的恶性骨肿瘤, 常通过手术切除进行治疗。但术后造成的骨缺损难以自愈, 残余肿瘤细胞还会增加复发可能性。本研究开发了一种用于修复骨缺损和协同治疗骨肉瘤的掺钕介孔硼硅酸盐生物活性玻璃陶瓷骨水泥。首先通过溶胶-凝胶法结合固态反应制备了可作为光热剂和药物载体的掺钕介孔硼硅酸盐生物活性玻璃陶瓷微球(MBGC-xNd), 然后将微球与海藻酸钠(SA)溶液混合制备了可同时进行光热治疗和化学治疗的可注射骨水泥(MBGC-xNd/SA)。结果表明掺Nd³⁺赋予微球可控的光热性能, 负载阿霉素(DOX)的微球显示出持续的药物释放行为。此外, 载药骨水泥的药物释放量随着温度的升高而显著增加, 说明光热疗法产生的热量可促进DOX释放。体外细胞实验结果表明, MBGC-xNd/SA具有良好的促成骨活性, 并且光热-化学联合疗法对MG-63骨肉瘤细胞起到了更显著的杀伤作用, 表现出协同效应。因此,MBGC-xNd/SA作为一种新颖的多功能骨修复材料, 在骨肉瘤的术后治疗方面具有良好的应用前景。     

The effect of chitosan molecular weight on the characteristics of spray-dried methotrexate-loaded chitosan microspheres for nasal administration

In this article, the effect of the chitosan molecular weight (MW) on the characteristics of methotrexate (MTX)-encapsulated non-cross-linked chitosan microspheres was studied. Microspheres composed of low-molecular-weight (LMW, 40,000 Da), medium-molecular-weight (MMW, 480,000 Da) and high-molecular-weight (HMW, 850,000 Da) chitosan with the same degree of deacetylation (96%) were obtained by a simple spray-drying method. The MW of chitosan had a noticeable influence on the size distribution, encapsulation efficiency, micromeritic properties (angle of repose and bulk density), controlled release behavior, and mucoadhesive properties. The entrapment efficiencies were in the range of 90-99%. Spray-dried microspheres had a D(50) value of 3.3-4.9 microm, which was suitable for nasal insufflations. The microspheres with LMW chitosan have the best flowability and highest bulk density but were found to be poor in terms of adhesion and in controlling the release behavior of MTX. The MMW chitosan microspheres exhibited the strongest adhesion to the mucosal surface, and the angle of repose values were between 34 and 47 degrees. They could control the release rate by modifying the drug/polymer ratios. Microspheres with HMW chitosan exhibited a lower adhesion than MMW chitosan and a lower release rate of MTX. The physical state of MTX in the chitosan matrix was studied by differential scanning calorimetry, which indicated the presence of a solid dispersion of the amorphous drug in the chitosan matrix. Nasal ciliotoxity showed only minor cilia irritation due to the microspheres, and consequently, they are suitable for nasal drug delivery.     

The Effect of Chitosan Molecular Weight on the Characteristics of Spray-Dried Methotrexate-Loaded Chitosan Microspheres for Nasal Administration

In this article, the effect of the chitosan molecular weight (MW) on the characteristics of methotrexate (MTX)-encapsulated non-cross-linked chitosan microspheres was studied. Microspheres composed of low-molecular-weight (LMW, 40,000 Da), medium-molecular-weight (MMW, 480,000 Da) and high-molecular-weight (HMW, 850,000 Da) chitosan with the same degree of deacetylation (96%) were obtained by a simple spray-drying method. The MW of chitosan had a noticeable influence on the size distribution, encapsulation efficiency, micromeritic properties (angle of repose and bulk density), controlled release behavior, and mucoadhesive properties. The entrapment efficiencies were in the range of 90–99%. Spray-dried microspheres had a D₅₀ value of 3.3–4.9 μm, which was suitable for nasal insufflations. The microspheres with LMW chitosan have the best flowability and highest bulk density but were found to be poor in terms of adhesion and in controlling the release behavior of MTX. The MMW chitosan microspheres exhibited the strongest adhesion to the mucosal surface, and the angle of repose values were between 34 and 47 degrees. They could control the release rate by modifying the drug/polymer ratios. Microspheres with HMW chitosan exhibited a lower adhesion than MMW chitosan and a lower release rate of MTX. The physical state of MTX in the chitosan matrix was studied by differential scanning calorimetry, which indicated the presence of a solid dispersion of the amorphous drug in the chitosan matrix. Nasal ciliotoxity showed only minor cilia irritation due to the microspheres, and consequently, they are suitable for nasal drug delivery.     

A pH-sensitive nanocomposite microsphere based on chitosan and montmorillonite with in vitro reduction of the burst release effect

Objective: The aim of this study was to prepare pH-sensitive ofloxacin (OFL)/montmorillonite (MMT)/chitosan (CTS) nanocomposite microspheres that improve the burst release effect of the drug by the solution intercalation technique and emulsification cross-linking techniques. Methods: First, OFL/MMT hybrids were prepared through the solution intercalation technique. Then, OFL/MMT-intercalated OFL/MMT/CTS nanocomposite microspheres were obtained through emulsification cross-linking technology. The intercalated nanocomposite was confirmed by Fourier-transform infrared spectroscopy and X-ray diffraction. Finally, in vitro release of OFL from the microspheres was performed in simulated gastric fluids and simulated intestinal fluids. The effect of MMT content on drug encapsulation efficiency and the drug release of the nanocomposite microspheres were investigated. Results: The results showed that the release rate of OFL from the nanocomposite microspheres at pH 7.4 was higher than that at pH 1.2. Compared with pure CTS microspheres, the incorporation of certain amount of MMT in the nanocomposite microspheres can enhance the drug encapsulation efficiency and reduce the burst release. Conclusion: A sustained release particulate system can be obtained by incorporating MMT into the nanocomposite microspheres and can improve the burst release effect of the drug.     

pH-sensitive sodium alginate/calcined hydrotalcite hybrid beads for controlled release of diclofenac sodium

Objective: The aim of this study was to prepare pH-sensitive sodium alginate/calcined hydrotalcite (SA/CHT) hybrid bead with improved the burst release effect of the drug.

Materials and methods: A series of pH-sensitive SA/CHT hybrid beads were prepared by using Ca²⁺ cross-linking in the presence of diclofenac sodium (DS) and SA. The structure and drug loading of the beads were characterized by Fourier transform infrared spectroscopy and X-ray diffraction. The swelling and the drug release of the fabricated beads were investigated by the pH of test medium and CHT content.

Result: The formed positively charged hydrotalcite layers were adsorbed on the negatively charged SA polymer chains through electrostatic interaction and act as inorganic cross-linkers in the three-dimensional network. Compared to pure SA beads, the incorporation of CHT enhanced the drug encapsulation efficiency, improved the swelling behaviors and slowed the drug release from the hybrid beads.

Discussion and conclusions: The electrostatic interaction between hydrotalcite and SA has restricted the movability of the SA polymer chains, and then slowed down swelling and dissolution rates in aqueous solutions. The results provided a simple method to moderate drug release and matrix degradation of the SA beads.     

The development of injectable gelatin/silk fibroin microspheres for the dual delivery of curcumin and piperine

The objective of this study was to develop the microspheres from gelatin (G) and silk fibroin (SF) aimed to be applied for the controlled release of curcumin and piperine. The glutaraldehyde-crosslinked G/SF microspheres at various weight blending ratios (100/0, 70/30, 50/50, and 30/70) were successfully fabricated by water in oil emulsion technique. The microspheres prepared from all compositions were in a round shape with homogeneous size distribution both in the dried (194–217 μm) and swollen states (297–367 μm). When subjected in collagenase solution at physiological condition, the G microspheres gradually degraded within 14 days while the blended G/SF microspheres, particularly at 50/50 and 30/70, were not degraded. For the release application, the microspheres were loaded with curcumin and/or piperine. It was found that the microspheres composed of SF tended to entrap curcumin and piperine with the high entrapment and loading efficiencies, possibly due to their hydrophobic interactions. The G/SF microspheres, particularly at the ratios of 50/50 and 30/70, released curcumin and piperine in a sustained manner both for the single and dual release systems. The controlled dual release of curcumin and piperine from the G/SF microspheres would prolong their half-life, provide the optimal concentrations for therapeutic effects at a target site, and improve the bioavailability of curcumin. These novel injectable microspheres dually releasing curcumin and piperine would be introduced for the treatment of diseases without the need of operation.     

Mathematical modelling of the evolution of protein distribution within single PLGA microspheres: prediction of local concentration profiles and release kinetics

Protein release from poly(D,L-lactide-co-glycolide) (PLGA) microspheres in an aqueous environment is governed by the diffusion of the protein through an autocatalytically degrading polymeric matrix. Many attempts have been made to model the release rate of proteins from biodegrading matrices, but the transport parameters involved in the process are not fully established at the microscale level. The aim of this work was to develop a new mathematical model taking into account the temporal evolution of the radial protein distribution during release, and to provide physical insight into the relation between local transport features and microsphere degradation. The model was validated by comparing its predictions with the experimentally determined protein concentration profiles in PLGA microspheres loaded with tetramethylrhodamine-labelled bovine serum albumin (BSA-Rhod) as a model protein. Morphological studies were carried out by scanning electron microscopy (SEM), while release kinetics and time-dependent BSA-Rhod concentration profiles within the microspheres were studied by a confocal laser scanning microscopy (CLSM)-assisted technique. The model, based on a modification of Fick's second law of diffusion, could closely fit the experimental protein radial distribution profiles in the microspheres as a function of time. It is also a useful tool to ab initio design protein release devices using degrading matrices.     

Characterization and in vitro degradation of poly(octadecanoic anhydride)

Poly(octadecanoic anhydride) (POA) has been prepared by melt polycondensation of octadecanoic diacid. POA was characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The results of in vitro degradation and SEM micrographs show that the erosion process of POA is neither bulk nor perfect surface erosion but rather has elements of both in phosphate buffer at 37 °C. The moving erosion front is characteristic of surface erosion whereas the remaining porous shell stems from bulk erosion. While a significant special degradation property of POA is that POA presents a very slow degradation rate in acidic condition (pH 5.98), only 1.64% weight loss for 20 days, and it completely degrades after 18 days in basic buffer (pH 7.4). Comparing with poly(sebacic anhydride) (PSA), POA has the higher crystallization degree, and the slower hydrolytic rate.