Sustained release of bee venom peptide from biodegradable thermosensitive PLGA-PEG-PLGA triblock copolymer-based hydrogels in vitro

Biodegradable thermosensitive poly (DL-lactide-co-glycolide-b-ethylene glycol-b-DL-lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers with DL-lactide/glycolide molar ratio ranging from 6/1 to 15/1 were synthesized from monomers of DL-lactide, glycolide and polyethylene glycol and were evaluated for sustained release of bee venom peptide in vitro. The resulting copolymers are soluble in water to form free flowing fluid at room temperature but become hydrogels at body temperature. The gelation temperature of the copolymer solutions can be influenced by the concentration and DL-lactide/glycolide molar ratio of the copolymers. The release of bee venom peptide from the copolymer-based hydrogel and hydrogel degradation in the phosphate buffer (pH 7.4) was studied at 37 degrees C under agitation. Bee venom peptide was released from the copolymer-based hydrogels over 40 days in vitro and the variation of DL-lactide/glycolide molar ratio in the PLGA block of the copolymer did not significantly affect the release rate of bee venom peptide (P > 0.05). The hydrogels undergo slower degradation and then faster degradation rate during the whole release stage. Accordingly, the mechanism of bee venom peptide was Fickian diffusion during initial stage and then may be a combination of diffusion and degradation. The synthesized copolymers have the advantage of gelation temperature over the ReGel system. These results indicate that the PLGA-PEG-PLGA copolymer-based hydrogel could be a promising platform for sustained delivery of bee venom peptide.     

Injectable thermosensitive PLGA-PEG-PLGA triblock copolymers-based hydrogels as carriers for interleukin-2

Thermosensitive PLGA-PEG-PLGA triblock copolymers with the DL-lactide/glycolide molar ratio ranging from 6/1 to 15/1 were synthesized by bulk copolymerization of DL-lactide, glycolide and PEG1500. The resulting copolymers are soluble in water to form a freely flowing fluid at room temperature but become hydrogels at body temperature. The release of IL-2 from the copolymer-based hydrogel in the phosphate buffer (pH 7.2) was studied at 37 degrees C under agitation. IL-2 was released from the copolymer-based hydrogels over 20 days in vitro and the release rate decreased with increasing copolymer concentration. The change of DL-lactide/glycolide molar ratio in the PLGA block of the copolymer had little effect on the IL-2 release. The released IL-2 remained 57-90% of its original activity during the release period. To evaluate the anti-tumor effect of the IL-2 loaded copolymer, solutions were injected subcutaneously to H22 tumor-bearing mice. IL-2 loaded copolymer hydrogel for in vivo use showed good anti-tumor effect. These results indicate that the thermosensitive PLGA-PEG-PLGA triblock copolymers could be a promising platform for sustained delivery of IL-2.     

Injectable block copolymer hydrogels for sustained release of a PEGylated drug

The paper employs the spontaneous physical gelling property of a biodegradable polymer in water to prepare an injectable sustained release carrier for a PEGylated drug. A series of thermogelling PLGA-PEG-PLGA triblock copolymers were synthesized. The PEGylated camptothecin (CPT) was also prepared and employed as the model of a PEGylated drug, and the solubility of this hydrophobic drug was significantly enhanced to over 150mg/mL. The model drug was completely entrapped into the polymeric hydrogel, and the sustained release lasted for 1 month. The mechanism of the sustained release was diffusion-controlled at the first stage and then was the combination of diffusion and degradation at the late stage. In vivo anti-tumor tests in mice further confirmed the efficacy of the model PEGylated drug released from the hydrogel. This work also revealed the specificity of the PEGylated drug in such a kind of carrier systems by decreasing the critical gelling temperature and increasing the viscosity of the sol. Due to the very convenient drug formulation and highly tunable release rate, an injectable carrier platform for PEGylated drugs is thus set up.     

壳聚糖-羧甲基壳聚糖凝胶的温敏性及体外药物缓释试验

目的研究壳聚糖/羧甲基壳聚糖/甘油磷酸钠（CS/CMCS/GPS）体系水凝胶的温敏性,载药凝胶以及共混β-环糊精（β-CD）包合物对药物的缓释性能。方法试管倒置法研究不同配比,不同pH值对CS/CMCS/GPS体系温敏凝胶化性能的影响;饱和水溶液法制备吲哚美辛/β-CD包合物,红外光谱表征包合物;紫外分光光度法测定包合物载药量和药物的累积释放度。结果 2%CS-2%CMCS-56%GPS体积比从10∶1∶2变为10∶10∶2（体系pH6.8）,37℃下凝胶化时间由370s升至490s,后又降至90s;三者体积比从10∶3∶1变为10∶3∶6（体系pH6.8）,37℃下凝胶化时间从407s降至66s。pH值在6.8~7.2范围适合于体系凝胶化。调节体积比及合适的pH值,在37℃下可实现CS/CMCS/GPS体系快速凝胶化。以吲哚美辛和吲哚美辛/β-CD包合物为模型药物,载有吲哚美辛温敏凝胶12h的累积释放度为65.2%,载有吲哚美辛/β-CD包合物温敏凝胶累积释放度为52.8%,而吲哚美辛原药12h的累积释放度为87.6%,吲哚美辛/β-CD包合物的累积释放度为82.1%。结论一定体积配比CS/CMCS/GPS体系在37℃具有快速凝胶特性,β-CD包合物与温敏性凝胶共混,对药物具有更加明显的缓释作用。     

Poly(lactide-co-glycolide) microparticles as systems for controlled release of proteins -- preparation and characterization

Poly(DL-lactide-co-glycolide) (PDLLGA) and poly(L-lactide-co-glycolide) (PLLGA) copolymers were prepared by bulk ring opening polymerization of lactide and glycolide and characterized by GPC, FTIR, 1H NMR and DSC. Copolymers with different molar masses at a constant lactide/glycolide ratio were used for preparation of bovine serum albumin (BSA)-loaded microparticles by the double emulsion w/o/w method. The influence of the copolymer molar mass and composition on the microparticle morphology, size, yield, degradation rate, BSA-loading efficiency and BSA release profile were studied. For microparticles prepared from PDLLGA copolymers, a biphasic profile for BSA release was found and for those made from PLLGA copolymers the release profile was typically triphasic; both of them were characterized by high initial burst release. Possible reasons for such behavior are discussed.     

嵌段共聚物OSM1-PCLA-PEG-PCLA-OSM1的pH和温度敏感性质及体外释药特性考察

目的 为嵌段共聚物磺胺甲嘧啶低聚物-聚-ε-己内酯-丙交酯-聚乙二醇-聚-ε-己内酯-丙交酯-磺胺甲嘧啶低聚物（sulfamerazine oligomers-poly(ε-caprolactone-co-DL-lactide-b-ethyleneglycol-b-ε-caprolactone-co-DL-lactide)-sulfamerazine oligomers,OSM₁-PCLA-PEG-PCLA-OSM1)作为缓控释给药系统的载体提供依据。方法 采用激光粒度仪对不同pH和温度下嵌段共聚物OSM₁-PCLA-PEG-PCLA-OSM₁胶束粒径大小、分布进行考察;通过表面张力和相转变温度测定对其临界胶束浓度和溶液-凝胶相转变行为进行考察;以5-氟尿嘧啶为模型药,通过透射电镜观察载药和空白共聚物胶束形态;采用物理混合法制备5-氟尿嘧啶载药水凝胶;采用HPLC法测定载药水凝胶中药物释放速率。结果 嵌段共聚物OSM₁-PCLA-PEG-PCLA-OSM₁胶束溶液具有pH和温度双重敏感的性质,在一定pH和温度条件下可发生溶液-凝胶相转变;5-氟尿嘧啶载药水凝胶体外释放可持续9 d,具有较好的缓释作用。结论 pH和温度双重敏感型嵌段共聚物OSM₁-PCLA-PEG-PCLA-OSM₁作为注射缓释给药系统载体材料具有良好的应用前景。     

Injectable and biodegradable poly(organophosphazene) gel containing silibinin: its physicochemical properties and anticancer activity

The biodegradable poly(organophosphazene) hydrogels were developed as a locally injectable drug carrier for a hydrophobic silibinin to overcome its limited bioavailability. The aqueous solution of poly(organophosphazene) enhanced the solubility of silibinin up to 2000 times compared with that of phosphate buffered saline (0.0415 vs. 84.55 mg/mL). Both aqueous polymer solutions with and without silibinin showed a sol-gel transition as a function of temperature. A faster in vitro degradation rate of the gel and drug release rate from the gel at pH 6.8 than those at pH 7.4 were observed when the degradation and release study on hydrogels were conducted at 37 °C. Silibinin was sustainedly released from the hydrogel mainly by a diffusion-controlled mechanism. The silibinin released from the hydrogel was shown to be effective considering the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In the HT-29 xenografted mice model, the intratumorally injected hydrogel containing silibinin exhibited a good antitumor effect in comparison with the control groups. The Western blotting indicated that one of the reasons for the enhanced antitumor effect of the hydrogel system was the sustained antiangiogenic effect of silibinin. The poly(organophosphazene) gels are expected to be an effective candidate of the locally injectable drug carrier for silibinin.     

Effect of bee venom peptide-copolymer interactions on thermosensitive hydrogel delivery systems

The objectives of this study were to investigate the potential interactions between the model protein drug (bee venom peptide, BVP) and thermosensitive poly(dl-lactide-co-glycolide-b-ethyleneglycol-b-dl-lactide-co-glycolide) (PLGA-PEG-PLGA) copolymers and to examine the drug-copolymer interactions on the in vitro drug release and hydrogel degradation. The PLGA-PEG-PLGA copolymers were synthesized by ring-opening copolymerization of dl-lactide and glycolide with PEG as an initiator. Drug-copolymer co-precipitate blends were prepared and analyzed by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) to characterize the specific interactions between drug and copolymer. For the better understanding the drug-copolymer interactions on drug release, insulin was selected for comparison. The release of the two protein drugs from the copolymer-based hydrogels and hydrogel degradation was studied at 37 degrees C under agitation. The results of FTIR and XRD indicated that the hydrogen bonding interactions existed between the NH group of BVP and CO group of the copolymers. The insulin and BVP released from the copolymer hydrogel over 15 and 40 days, respectively. The BVP-copolymer interactions retarded the BVP release rate and degradation of hydrogel, but did not significantly affect the biological activity of BVP. These results indicate that the drug-copolymer interactions need to be considered when attempting to use PLGA-PEG-PLGA hydrogels as sustained delivery carriers of protein or peptide drugs.     

Solubilization of hydrophobic drugs by methoxy poly(ethylene glycol)-block-polycaprolactone diblock copolymer micelles: theoretical and experimental data and correlations

The solubilization of five model hydrophobic drugs by a series of micelle-forming, water-soluble methoxy poly(ethylene glycol)-block-polycaprolactone diblock copolymers (MePEG-b-PCL) with varying methoxy poly(ethylene glycol) (MePEG) and polycaprolactone (PCL) block lengths was investigated. Variation of the feed weight ratio of MePEG to caprolactone resulted in the synthesis of copolymers with predictable block lengths. The micelle diameter and pyrene partition coefficient (Kv) were directly related to the PCL block length whereas the critical micelle concentrations (CMC) were inversely related to the PCL block length. The aqueous solubilities of the model hydrophobic drugs, indomethacin, curcumin, plumbagin, paclitaxel, and etoposide were increased by encapsulation within the micelles. Drug solubilization was directly related to the compatibility between the solubilizate and PCL as determined by the Flory-Huggins interaction parameter (chisp). Furthermore, the concentration of solubilized drug was also directly related to the PCL block length.     

Controlled delivery of testosterone from smart polymer solution based systems: in vitro evaluation

The objective of this research is to develop injectable polymers solution based controlled release delivery systems for testosterone (TSN), using phase sensitive and thermosensitive polymers. A combination of poly(lactide) (PLA) and solvents mixture of benzyl benzoate (BB) and benzyl alcohol (BA) was used in the phase sensitive polymer delivery system. The effects of solvents system and drug loading on the in vitro TSN release were evaluated. In the case of thermosensitive polymer delivery systems, a series of low-molecular-weight poly(lactide-co-glycolide)-poly(ethylene glycol)-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers with varying ratio of lactide/glycolide (LA/GA, 2.0-3.5) were studied to control the release of TSN. The effects of varying block length of copolymers 1-4 on the in vitro TSN release were evaluated. Phosphate buffer saline (pH 7.4) containing 0.5% (w/v) Tween-80 was used as in vitro release medium. The amount of the released TSN was determined by an HPLC method. A controlled (zero-order) in vitro release of TSN was observed from both the phase sensitive and thermosensitive polymer delivery systems. Addition of BA (15%, v/v) in solvents system significantly (p<0.05) increased the release rate of TSN (0.33+/-0.01 mg/ml) from phase sensitive delivery system in comparison to solvent without BA (0.27+/-0.00 mg/day). Increasing drug loading also increased release rate. In the case of thermosensitive polymer delivery system, increasing the hydrophobic PLGA block length of copolymers significantly (p<0.05) decreased the release rate of TSN. It is evident from this study that the phase sensitive and thermosensitive polymers are suitable for developing prolong-release injectable implant delivery systems for TSN.     

Synthesis and characterization of PEG-PCL-PEG thermosensitive hydrogel

In this work, a series of biodegradable triblock poly(ethylene glycol)-poly(epsilon-caprolactone)-poly(ethylene glycol) (PEG-PCL-PEG, PECE) copolymers were successfully synthesized by ring-opening copolymerization, and were characterized by (1)H NMR, FT-IR, GPC, and DSC. Aqueous solutions of PECE copolymers underwent thermosensitive sol-gel-sol transition as temperature increases when the concentration was above corresponding critical gel concentration (CGC). Sol-gel-sol phase transition diagrams were recorded using test tube inverting method, which depended on hydrophilic/hydrophobic balance in macromolecular structure, as well as some other factors, including topology of triblock copolymers and solution composition of the hydrogel. As a result, the sol-gel-sol transition temperature range could be varied, which might be very useful for its application as injectable drug delivery systems. The in vivo gel formation and degradation behavior was conducted by injecting aqueous PECE solution into KunMing mice subcutaneously. In vitro degradation behavior, in vitro drug release behavior, and cytotoxicity were also investigated in this paper. Therefore, owing to great thermosensitivity and biodegradability of these copolymers, PECE hydrogel is believed to be promising for in situ gel-forming controlled drug delivery system.     

A novel thermo-responsive drug delivery system with positive controlled release

The model drug, 5-fluorouracil (5-FU) was loaded into the poly(N-isopropylacrylamide) (PNIPA) hydrogel at 25 degrees C, then the drug-loaded, swollen hydrogel sample was carefully enveloped in the dialysis bag to form a novel thermo-responsive drug delivery system (DDS). The concentration of released 5-FU was monitored at 266 nm on the UV spectrophotometer. We found that this novel DDS provides a positive drug release pattern and the drug, 5-FU, was released faster at the increased temperature (37 degrees C, >25 degrees C) than the one at the decreased temperature (10 degrees C, <25 degrees C). This was attributed to the double control of the thermo-sensitivity of the hydrogel matrix and the dialysis membrane. By employing the fast response PNIPA hydrogel instead of the conventional hydrogel in this novel DDS, we can further control the drug release rate and/or drug release amount etc., without changing the positive, thermo-responsive drug release pattern.     

Sustained release of bovine serum albumin using implantable wafers prepared by MPEG-PLGA diblock copolymers

MPEG-PLGA diblock copolymers, consisting of methoxy polyethylene glycol (MPEG) and poly(L-lactic-co-glycolic acid) (PLGA), were synthesized by ring-opening polymerization of L-lactide and glycolide in the presence of MPEG as an initiator. Implantable wafers, using diblock copolymers as a drug carrier, were fabricated by direct compression method after freeze milling of the diblock copolymers and bovine serum albumin-fluorescein isothiocyanate (BSA-FITC) as a model protein drug. The wafers prepared with MPEG-PLGA diblock copolymers exhibited initial burst in the release of BSA. The BSA release profiles from the wafers depended on MPEG-PLGA diblock copolymer compositions. The in vitro release of the BSA also correlated with the degradation rate of the PLGA part in the diblock polymers. The wafers prepared from diblock copolymers with an increased MPEG segment showed the more structural metamorphosis of crack form due to higher water absorption of MPEG inside the wafer, and induced faster BSA release. The wafers prepared by using MPEG-PLGA diblock copolymers in the presence of small intestinal submucosa (SIS) as a drug carrier additive exhibited controlled BSA release profiles, although the wafers exhibited release patterns with a lag time at the initial stage as the MPEG segment in diblock copolymer compositions increased. Thus, we confirmed that the MPEG-PLGA diblock copolymers could be used as a protein delivery carrier in implantable wafer form.     

Characterization of Drug Release and Diffusion Mechanism Through Hydroxyethylmethacrylate/Methacrylic Acid pH-Sensitive Hydrogel

Hydroxyethylmethacrylate/methacrylic acid copolymer cross-linked with ethylenglycol dimethacrylate was prepared by a bulk free radical polymerization method. The permeability studies of this pH-sensitive hydrogel to drugs with different water solubilities showed a water-content dependent diffusion or pore mechanism for ephedrine HCl (water-soluble model drug), whereas, a partition or solute-diffusion mechanism for indomethacin (a water-insoluble drug) was seen. Data analysis of release tests, according to the swelling interface number and Peppas equation for ephedrine HCl in pH 7.4, showed a biexponential model kinetic, whereas in pH 1.2 a swelling-controlled mechanism was seen. Indomethacin was released by an anomalous or non-Fickian release kinetics.     

Characterization of drug release and diffusion mechanism through hydroxyethylmethacrylate/methacrylic acid pH-sensitive hydrogel

Hydroxyethylmethacrylate/methacrylic acid copolymer cross-linked with ethylenglycol dimethacrylate was prepared by a bulk free radical polymerization method. The permeability studies of this pH-sensitive hydrogel to drugs with different water solubilities showed a water-content dependent diffusion or pore mechanism for ephedrine HCl (water-soluble model drug), whereas, a partition or solute-diffusion mechanism for indomethacin (a water-insoluble drug) was seen. Data analysis of release tests, according to the swelling interface number and Peppas equation for ephedrine HCl in pH 7.4, showed a biexponential model kinetic, whereas in pH 1.2 a swelling-controlled mechanism was seen. Indomethacin was released by an anomalous or non-Fickian release kinetics.     

Stability and Release Performance of a Series of Pegylated Copolymeric Micelles

Purpose. The aim of this work is to evaluate the capability of a series of biocompatible amphiphilic copolymers as a nano-sized drug carrier. Methods. The influences of the type of lactone monomer, the feed molar ratios of lactone/PEG, and the molecular weight of PEG on the performance and release behavior of micelles are investigated. Results. These pegylated amphiphilic copolymers efficiently form micelles with a low CMC value in the range of 10^–6-10^–7 M. The average particle size of micelles is 100 nm. The phenomenon of increasing particle size as increasing the chain length of poly(lactone) block is observed. The different hydrophobicity, based on chemical structure of poly(lactone), accounts for different interaction strength between indomethacin and hydrophobic inner core, which further influences the drug loading in copolymeric micelles and their release character. In addition, the PCL/PEG/PCL micellar solutions maintain their sizes at 4°C for 8 weeks without occurring significant aggregation or dissociation. Conclusions. A series of biocompatible pegylated amphiphilic copolymers have been elucidated possessing micellization potential to form nano-sized micelles in an aqueous environment, which enable incorporate hydrophobic drug and regulate drug release.     

Indomethacin-Dipalmitoylphosphatidylcholine Interaction. A Calorimetric Study of Drug Release from Poly(Lactide-co-glycolide) Microspheres into Multilamellar Vesicles

A comparative study of indomethacin controlled release from poly(lactide-co-glycolide) (50:50, molecular weight 3000) (PLGA) microspheres loaded with two different amounts of drug (10.9 ± 1%, and 34.1 ± 1% w/w) and pure free indomethacin, considering the effects exerted by the drug on the thermotropic behavior of dipalmitoylphosphatidylcholine multilamellar vesicles, was carried out by differential scanning calorimetry (DSC). The release was monitored by comparing the effect exerted by the free indomethacin on lipid thermotropic behavior with that of the drug released by the microspheres and relating these effects to a lipid aqueous dispersion containing the molar ratio of drug able to cause it. By DSC measurements, the pure free indomethacin was found to be able to have a fluidifying effect on the model membrane, causing a shift toward lower values of the transitional temperature (T_m), characteristic of phospholipid liposomes, without variations in the enthalpic changes (ΔH). This shift was found to be modulated by the drug molar fraction with respect to the lipid concentration in the aqueous dispersion. Successively, calorimetric measurements were performed on suspensions of blank liposomes added to weighed amounts of unloaded and indometha-cin-loaded microspheres as well as free powdered indomethacin, and the T_m shifts of the lipid bilayer caused by the drug released from the polymeric system, as well as by the free drug, were compared with that caused by free drug increasing molar fractions dispersed directly on the membrane, employed as a calibration curve to obtain the fraction of drug released. This drug release model could be employed to determine the different kinetics involved in the drug transfer from the microspheres to a membrane. This in vitro study suggests that the kinetic process involved in drug release is influenced by the amount of drug loaded in the microspheres. This calorimetric study shows that the PLGA microspheres are a good delivery system able to sustain drug release. Moreover, the DSC technique applied to the drug interaction with biomembranes constitutes a good tool for determining the drug release representing an innovative alternative in vitro model.     

Thermosensitive sol-gel reversible hydrogels.

Aqueous polymer solutions that are transformed into gels by changes in environmental conditions, such as temperature and pH, thus resulting in in situ hydrogel formation, have recently attracted the attention of many investigators for scientific interest and for practical biomedical or pharmaceutical applications. When the hydrogel is formed under physiological conditions and maintains its integrity for a desired period of time, the process may provide various advantages over conventional hydrogels. Because of the simplicity of pharmaceutical formulation by solution mixing, biocompatibility with biological systems, and convenient administration, the pharmaceutical and biomedical uses of the water-based sol-gel transition include solubilization of low-molecular-weight hydrophobic drugs, controlled release, labile biomacromolecule delivery, such as proteins and genes, cell immobilization, and tissue engineering. When the formed gel is proven to be biocompatible and biodegradable, producing non-toxic degradation products, it will provide further benefits for in vivo applications where degradation is desired. It is timely to summarize the polymeric systems that undergo sol-gel transitions, particularly due to temperature, with emphasis on the underlying transition mechanisms and potential delivery aspects. This review stresses the polymeric systems of natural or modified natural polymers, N-isopropylacrylamide copolymers, poly(ethylene oxide)/poly(propylene oxide) block copolymers, and poly(ethylene glycol)/poly(D,L-lactide-co-glycolide) block copolymers.     

温敏型姜黄素鼻用原位凝胶增强脑靶向性

目的：制备温度敏感型的姜黄素鼻用凝胶制剂,以提高姜黄素的脑部生物利用度。方法：通过粘度实验进行原位凝胶制剂的处方筛选,以胶凝时间、胶凝温度等为指标,优化处方;采用透析袋法考察原位凝胶的体外释放：以大鼠为模型,考察姜黄素原位凝胶的脑靶向性及脑内分布．并与其静脉注射剂相比较。结果：姜黄素原位凝胶剂优化处方具有最短的胶凝时间,可以长时间粘附在鼻腔粘膜上：释放行为属于Fickian扩散机制;姜黄素脑内分布试验表明,原位凝胶在大脑、小脑、海马、嗅球中的药物靶向效率（DTE）分别为静脉给药的1.82、2．05、2．07、1．51倍,说明原位凝胶给药显著增强了姜黄素的脑靶向性。结论：制备的姜黄素原位凝胶剂具有温度敏感的特点．并显著提高了姜黄素的脑靶向性。     

In situ gelling hydrogels incorporating microparticles as drug delivery carriers for regenerative medicine

Aqueous solutions of blends of biodegradable triblock copolymers, composed of poly(D,L-lactide-co-glycolide) (PLGA) and poly(ethylene glycol) (PEG) with varied D,L-lactide to glycolide ratios, displayed thermosensitivity and formed a gel at body temperature. The gel window of the blend solutions could be tuned by varying the blending ratio between the two components. Furthermore, the storage modulus of the resultant hydrogel from the copolymer blends at body temperature was higher than that of each individual component. Incorporation of poly(D,L-lactide) (PDLLA) microparticles (0.5-40% w/v) within the in situ gelling hydrogel did not change the sol-gel transition temperatures of the polymer solutions, while the mechanical strength of the resultant hydrogels was enhanced when the content of the microparticles was increased up to 30% and 40%. Incorporation of proteins into both the gel and microparticle components resulted in composites that controlled the kinetics of protein release. Protein within the gel phase was released over a 10-day period whilst protein in the microparticles was released over a period of months. This system can be used to deliver two drugs with differing release kinetics and could be used to orchestrate tissue regeneration responses over differing timescales.