Synthesis of a Semi-Interpenetrating Polymer Network as a Bioactive Curcumin Film

This study focused on the synthesis and characterization of a natural polymeric system employing the interpenetrating polymer network (IPN) comprising curcumin as a bioactive. Biopolymers and actives such as chitosan, hypromellose, citric acid, genipin, and curcumin were used to develop an effective, biodegradable, and biocompatible film employed therapeutically as a wound healing platform. The semi-IPN films were investigated for their physicochemical, physicomechanical, and biological properties by quantification by FTIR, DSC, and Young’s modulus. Following characterization, an optimum candidate formulation was produced whereby further in vitro and ex vivo studies were performed. Results revealed a burst release occurring at the first hour with 1.1 mg bioactive released when in contact with the dissolution medium and 2.23 mg due to bioactive permeation through the skin, thus suggesting that the lipophilic nature of skin greatly impacted the bioactive release rate. Furthermore, chemical and mechanical characterization and tensile strength analysis revealed that the degree of crosslinking and concentration of polymeric material used significantly influenced the properties of the film.KEY WORDS: biomaterials, crosslinker, curcumin, films, semi-interpenetrating polymer network, wound healing     

Sustained Release of a Water-Soluble Drug from Alginate Matrix Tablets Prepared by Wet Granulation Method

Alginate matrix tablet of diltiazem hydrochloride (DTZ), a water-soluble drug, was prepared using sodium alginate (SAL) and calcium gluconate (CG) by the conventional wet granulation method for sustained release of the drug. The effect of formulation variables like SAL/CG ratio, drug load, microenvironmental pH modulator, and processing variable like compression force on the extent of drug release was examined. The tablets prepared with 1:2 w/w ratio of SAL/CG produced the most sustained release of the drug extending up to 13.5 h. Above and below this ratio, the drug release was faster. The drug load and the hardness of the tablets produced minimal variation in drug release. The addition of alkaline or acidic microenvironmental modulators did not extend the release; instead, these excipients produced somewhat faster release of diltiazem. This study revealed that proper selection of SAL/CG ratio is important to produce alginate matrix tablet by wet granulation method for sustained release of DTZ.     

<Emphasis Type="Italic">In Vivo</Emphasis> Evaluation of a PEO-Gellan Gum Semi-Interpenetrating Polymer Network for the Oral Delivery of Sulpiride

In this study, an optimized epichlorohydrin-crosslinked semi-interpenetrating polymer network xerogel matrix system (XePoMas) for the controlled delivery of sulpiride was prepared. The ability of XePoMas to sustain drug release was determined by in vitro and in vivo drug release experiments. Swelling of the xerogel over the 24-h experimental period ranged from 346 to 648%; swelling was observed to increase exponentially over the initial 8 h. In vitro drug release depicted a linear zero order drug release profile with an R ² value of 0.9956. The ability of the fabricated XePoMas to sustain drug release and enhance bioavailability of sulpiride in vivo was investigated by evaluating the plasma drug concentration over 24 h in the large pig model. The optimized XePoMas formulation was shown to increase intestinal absorption of sulpiride to a greater extent than the marketed product in vivo, with a C _max of 830.58 ng/mL after 15 h.     

Novel Polyurethane Matrix Systems Reveal a Particular Sustained Release Behavior Studied by Imaging and Computational Modeling

The aim of the present work was to better understand the drug-release mechanism from sustained release matrices prepared with two new polyurethanes, using a novel in silico formulation tool based on 3-dimensional cellular automata. For this purpose, two polymers and theophylline as model drug were used to prepare binary matrix tablets. Each formulation was simulated in silico, and its release behavior was compared to the experimental drug release profiles. Furthermore, the polymer distributions in the tablets were imaged by scanning electron microscopy (SEM) and the changes produced by the tortuosity were quantified and verified using experimental data. The obtained results showed that the polymers exhibited a surprisingly high ability for controlling drug release at low excipient concentrations (only 10% w/w of excipient controlled the release of drug during almost 8 h). The mesoscopic in silico model helped to reveal how the novel biopolymers were controlling drug release. The mechanism was found to be a special geometrical arrangement of the excipient particles, creating an almost continuous barrier surrounding the drug in a very effective way, comparable to lipid or waxy excipients but with the advantages of a much higher compactability, stability, and absence of excipient polymorphism.     

Cogrinding as a Tool to Produce Sustained Release Behavior for Theophylline Particles Containing Magnesium Stearate

The aim of the present study was to explore the cogrinding technique as a tool to slow down the drug release from capsule formulations. To this end, the physical mixtures of theophylline–magnesium stearate were prepared and subjected to different milling times (1, 15, 30, 120 min). In order to investigate the effect of magnesium stearate concentration on drug release, various concentrations of magnesium stearate (1%, 3%, 5%, and 10%, w/w) were used. The dissolution rate of the drug from coground samples and physical mixtures were determined at pH 6.5 according to USP. The results showed that all coground formulations showed slower release rates than their physical mixture counterparts. The effect of cogrinding time on the drug release was complex. Cogrinding time had no significant effect on drug release when the amount of magnesium stearate was 1% (w/w). When the amount of magnesium stearate was increased from 1% to 3% and cogrinding time increased from 1 to 5 min, there was a significant reduction in drug release. Beyond 5-min cogrinding, the drug release increased again. For coground samples containing 5% or 10% (w/w) magnesium stearate, generally, the highest drug release was obtained at higher cogrinding time. This was due to a significant increase in surface area of particles available for dissolution as proven by scanning electron microscopy results. Fourier transform infrared and differential scanning calorimetry results ruled out any significant interaction between theophylline and magnesium stearate in solid state.     

Design and Evaluation of Hydrophilic Matrix System for pH-Independent Sustained Release of Weakly Acidic Poorly Soluble Drug

The aim of this research was to design and evaluate a hydrophilic matrix system for sustained release of glipizide, a weakly acidic poor soluble drug. A combination of inclusion complexation and microenvironmental pH modification techniques was utilized to improve the dissolution and pH-independent release of glipizide. Hydroxypropyl-β-cyclodextrin (HP-β-CD) was used as the complexation agent while sodium citrate and magnesium oxide (MgO) were used as model pH modifiers. The hydrophilic matrix tablets were prepared by powder direct compression and evaluated by in vitro dissolution study respectively in pH 6.8 and pH 1.2 dissolution media. The formulations containing MgO exhibited increased cumulative drug release from less than 40% in the reference formulation to 90% within 24 h in acidic media (pH 1.2). The release profile in acidic media was similar to the alkaline media (pH 6.8) with a similarity factor (f₂) of 55.0, suggesting the weakening of the effect of pH on the dissolution efficiency of glipizide. The release profile fitted well into the Higuchi model and the dominant mechanism of drug release was Fickian diffusion while case II transport/polymer relaxation occurred. In conclusion, combining inclusion complexation agents and pH modifiers had improved the dissolution of glipizide as well as achieved the pH-independent release profile.     

Investigation of PEGylated Derivatives of Rosin as Sustained Release Film Formers

The purpose of the present study was to investigate the potential use of two PEGylated derivatives of rosin (PD) as sustained release film forming materials. The derivatives differed chemically by their acid numbers—PD-1 with 120.93 and PD-2 with 88.19. The derivative films were characterized for surface morphology, water uptake-weight loss, angle of contact, water vapor transmission rate, mechanical properties and permeability study. Dissolution of diclofenac sodium (DS) and propranolol hydrochloride (PHL) as model drugs was studied from coated pellets. The films of derivatives with and without plasticizers were smooth and continuous. PD-2 films developed greater numbers of pores when in contact with phosphate buffer pH 6.8. The low weight loss, low angles of contact and high water vapor transmission rate of PD-2 films were related to presence of higher concentration of PEG esters. Higher tensile strength and percent elongation of PD-2 films was due to greater degree of internal plasticization of the derivative. The permeability of films to model drugs propranolol hydrochloride and diclofenac sodium was inversely proportional to the film thickness and dibutyl phthalate concentration in them; the permeability being greatest in PD-2 films containing 10% PEG 200. Dissolution rate of propranolol hydrochloride was higher from the coated pellets. The dissolution data followed zero order, Baker–Lonsdale equation and Hixon–Crowell equation of release kinetics with high correlation coefficients. The mechanism of drug release from these coated systems however followed class II transport (n > 1.0). The derivatives investigated could successfully retard release of the model drugs and offers an alternative to the conventionally used polymers.     

Sugar End-Capped Poly-d,l-lactides as Excipients in Oral Sustained Release Tablets

Sugar end-capped poly-d,l-lactide (SPDLA) polymers were investigated as a potential release controlling excipient in oral sustained release matrix tablets. The SPDLA polymers were obtained by a catalytic ring-opening polymerization technique using methyl α-d-gluco-pyranoside as a multifunctional initiator in the polymerization. Polymers of different molecular weights were synthesized by varying molar ratios of monomer/catalyst. The matrix tablets were prepared by direct compression technique from the binary mixtures of SPDLA and microcrystalline cellulose, and theophylline was used as a model drug. The tablet matrices showed in vitro reproducible drug release profiles with a zero-order or diffusion-based kinetic depending on the SPDLA polymer grade used. Further release from the tablet matrices was dependent on the molecular weight of the SPDLA polymer applied. The drug release was the fastest with the lowest molecular weight SPDLA grade, and the drug release followed zero-order rate. With the higher molecular weight SPDLAs, more prolonged dissolution profiles for the matrix tablets (up to 8–10 h) were obtained. Furthermore, the prolonged drug release was independent of the pH of the dissolution media. In conclusion, SPDLAs are a novel type of drug carrier polymers applicable in oral controlled drug delivery systems.     

Coaxial Electrospray of Ranibizumab-Loaded Microparticles for Sustained Release of Anti-VEGF Therapies

Age-related macular degeneration (AMD) is the leading cause of vision loss and blindness in people over age 65 in industrialized nations. Intravitreous injection of anti-VEGF (vascular endothelial growth factor) therapies, such as ranibizumab (trade name: Lucentis), provides an effective treatment option for neovascular AMD. We have developed an improved coaxial electrospray (CES) process to encapsulate ranibizumab in poly(lactic-co-glycolic) acid (PLGA) microparticles (MPs) for intravitreous injection and sustained drug release. This microencapsulation process is advantageous for maintaining the stability of the coaxial cone-jet configurations and producing drug-loaded MPs with as high as 70% encapsulation rate and minimal loss of bioactivitiy. The utility of this emerging process in intravitreous drug delivery has been demonstrated in both benchtop and in vivo experiments. The benchtop test simulates ocular drug release using PLGA MPs encapsulating a model drug. The in vivo experiment evaluates the inflammation and retinal cell death after intravitreal injection of the MPs in a chick model. The experimental results show that the drug-load MPs are able to facilitate sustained drug release for longer than one month. No significant long term microglia reaction or cell death is observed after intravitreal injection of 200 μg MPs. The present study demonstrates the technical feasibility of using the improved CES process to encapsulate water-soluble drugs at a high concentration for sustained release of anti-VEGF therapy.     

Hot Melt Extrusion for Sustained Protein Release: Matrix Erosion and <Emphasis Type="Italic">In Vitro</Emphasis> Release of PLGA-Based Implants

The design of biodegradable implants for sustained release of proteins is a complex challenge optimizing protein polymer interaction in combination with a mini-scale process which is predictive for production. The process of hot melt extrusion (HME) was therefore conducted on 5- and 9-mm mini-scale twin screw extruders. Poly(lactic-co-glycolic acid) (PLGA) implants were characterized for their erosion properties and the in vitro release of the embedded protein (bovine serum albumin, BSA). The release of acidic monomers as well as other parameters (pH value, mass loss) during 16 weeks indicated a delayed onset of matrix erosion in week 3. BSA-loaded implants released 17.0% glycolic and 5.9% lactic acid after a 2-week lag time. Following a low burst release (3.7% BSA), sustained protein release started in week 4. Storage under stress conditions (30°C, 75% rH) revealed a shift of erosion onset of 1 week (BSA-loaded implants: 26.9% glycolic and 9.3% lactic acid). Coherent with the changed erosion profiles, an influence on the protein release was observed. Confocal laser scanning and Raman microscopy showed a homogenous protein distribution throughout the matrix after extrusion and during release studies. Raman spectra indicated a conformational change of the protein structure which could be one reason for incomplete protein release. The study underlined the suitability of the HME process to obtain a solid dispersion of protein inside a polymeric matrix providing sustained protein release. However, the incomplete protein release and the impact by storage conditions require thorough characterization and understanding of erosion and release mechanisms.     

Evaluation of Sustained BMP-2 Release Profiles Using a Novel Fluorescence-Based Retention Assay

The purpose of this study was to develop and characterize a novel fluorescence-based retention assay for the evaluation of the release profile of bone morphogenetic protein-2 (BMP-2) released from bone graft carrier. In this study, we evaluated the binding, release kinetics, and delivery efficacies of BMP-2 incorporated into hydroxyapatite (HA) bone grafts. The evaluation of the release profile of BMP-2 from HA bone grafts using a fluorescence-based retention assay revealed initial burst releases from the HA bone grafts followed by long sustained releases up to 14 weeks. The sustained biological activity of the released BMP-2 from HA bone grafts over the full 14-week period supports a long sustained mechanism via fluorescence-based retention assay. Thus, the results from this study show that BMP-2 could be incorporated into HA bone grafts for sustained release over a prolonged period of time with retention of bioactivity and our fluorescence-based retention assay, which is principally detecting the retention profile of BMP-2 in HA bone grafts, is more accurate than conventionally collecting the released BMP-2 for evaluation of BMP-2 release profiles.     

Bimatoprost-Loaded Ocular Inserts as Sustained Release Drug Delivery Systems for Glaucoma Treatment: In Vitro and In Vivo Evaluation

The purpose of the present study was to develop and assess a novel sustained-release drug delivery system of Bimatoprost (BIM). Chitosan polymeric inserts were prepared using the solvent casting method and characterized by swelling studies, infrared spectroscopy, differential scanning calorimetry, drug content, scanning electron microscopy and in vitro drug release. Biodistribution of ^99mTc-BIM eye drops and ^99mTc-BIM-loaded inserts, after ocular administration in Wistar rats, was accessed by ex vivo radiation counting. The inserts were evaluated for their therapeutic efficacy in glaucomatous Wistar rats. Glaucoma was induced by weekly intracameral injection of hyaluronic acid. BIM-loaded inserts (equivalent to 9.0 µg BIM) were administered once into conjunctival sac, after ocular hypertension confirmation. BIM eye drop was topically instilled in a second group of glaucomatous rats for 15 days days, while placebo inserts were administered once in a third group. An untreated glaucomatous group was used as control. Intraocular pressure (IOP) was monitored for four consecutive weeks after treatment began. At the end of the experiment, retinal ganglion cells and optic nerve head cupping were evaluated in the histological eye sections. Characterization results revealed that the drug physically interacted, but did not chemically react with the polymeric matrix. Inserts sustainedly released BIM in vitro during 8 hours. Biodistribution studies showed that the amount of ^99mTc-BIM that remained in the eye was significantly lower after eye drop instillation than after chitosan insert implantation. BIM-loaded inserts lowered IOP for 4 weeks, after one application, while IOP values remained significantly high for the placebo and untreated groups. Eye drops were only effective during the daily treatment period. IOP results were reflected in RGC counting and optic nerve head cupping damage. BIM-loaded inserts provided sustained release of BIM and seem to be a promising system for glaucoma management.     

Applying the Taguchi Design for Optimized Formulation of Sustained Release Gliclazide Chitosan Beads: An In Vitro/In Vivo Study

Gliclazide is a second generation of hypoglycemic sulfonylurea and acts selectively on pancreatic β cell to control diabetes mellitus. The objective of this study was to produce a controlled release system of gliclazide using chitosan beads. Chitosan beads were produced by dispersion technique using tripolyphosphate (TPP) as gelating agent. The effects of process variables including chitosan molecular weight, concentration of chitosan and TPP, pH of TPP, and cross-linking time after addition of chitosan were evaluated by Taguchi design on the rate of drug release, mean release time (MRT), release efficiency (RE₈%), and particle size of the beads. The blood glucose lowering effect of the beads was studied in normal and streptozotocin-diabetic rats. The optimized formulation CL₂T₅P₂t₁₀ with about 31% drug loading, 2.4 h MRT, and 69.16% RE₈% decreased blood glucose level in normal rats for 24 h compared to pure powder of gliclazide that lasted for just 10 h.     

Sustained Release of BMP-2 in Bioprinted Alginate for Osteogenicity in Mice and Rats

The design of bioactive three-dimensional (3D) scaffolds is a major focus in bone tissue engineering. Incorporation of growth factors into bioprinted scaffolds offers many new possibilities regarding both biological and architectural properties of the scaffolds. This study investigates whether the sustained release of bone morphogenetic protein 2 (BMP-2) influences osteogenicity of tissue engineered bioprinted constructs. BMP-2 loaded on gelatin microparticles (GMPs) was used as a sustained release system, which was dispersed in hydrogel-based constructs and compared to direct inclusion of BMP-2 in alginate or control GMPs. The constructs were supplemented with goat multipotent stromal cells (gMSCs) and biphasic calcium phosphate to study osteogenic differentiation and bone formation respectively. BMP-2 release kinetics and bioactivity showed continuous release for three weeks coinciding with osteogenicity. Osteogenic differentiation and bone formation of bioprinted GMP containing constructs were investigated after subcutaneous implantation in mice or rats. BMP-2 significantly increased bone formation, which was not influenced by the release timing. We showed that 3D printing of controlled release particles is feasible and that the released BMP-2 directs osteogenic differentiation in vitro and in vivo.     

Matrix mineralization as a trigger for osteocyte maturation.

The morphology of the osteocyte changes during the cell's lifetime. Shortly after becoming buried in the matrix, an osteocyte is plump with a rich rough endoplasmic reticulum and a well-developed Golgi complex. This "immature" osteocyte reduces its number of organelles to become a "mature" osteocyte when it comes to reside deeper in the bone matrix. We hypothesized that mineralization of the surrounding matrix is the trigger for osteocyte maturation. To verify this, we prevented mineralization of newly formed matrix by administration of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) and then examined the morphological changes in the osteocytes in rats. In the HEBP group, matrix mineralization was disturbed, but matrix formation was not affected. The osteocytes found in the unmineralized matrix were immature. Mature osteocytes were seen in the corresponding mineralized matrix in the control group. The immature osteocytes in the unmineralized matrix failed to show immunoreactivity with anti-sclerostin antibody, whereas mature osteocytes in the mineralized matrix showed immunoreactivity in both control and HEBP groups. These findings suggest that mineralization of the matrix surrounding the osteocyte is the trigger for cytodifferentiation from a plump immature form to a mature osteocyte. The osteocyte appears to start secreting sclerostin only after it matures in the mineralized bone matrix.     

Arabidopsis LON2 Is Necessary for Peroxisomal Function and Sustained Matrix Protein Import

Relatively little is known about the small subset of peroxisomal proteins with predicted protease activity. Here, we report that the peroxisomal LON2 (At5g47040) protease facilitates matrix protein import into Arabidopsis (Arabidopsis thaliana) peroxisomes. We identified T-DNA insertion alleles disrupted in five of the nine confirmed or predicted peroxisomal proteases and found only two—lon2 and deg15, a mutant defective in the previously described PTS2-processing protease (DEG15/At1g28320)—with phenotypes suggestive of peroxisome metabolism defects. Both lon2 and deg15 mutants were mildly resistant to the inhibitory effects of indole-3-butyric acid (IBA) on root elongation, but only lon2 mutants were resistant to the stimulatory effects of IBA on lateral root production or displayed Suc dependence during seedling growth. lon2 mutants displayed defects in removing the type 2 peroxisome targeting signal (PTS2) from peroxisomal malate dehydrogenase and reduced accumulation of 3-ketoacyl-CoA thiolase, another PTS2-containing protein; both defects were not apparent upon germination but appeared in 5- to 8-d-old seedlings. In lon2 cotyledon cells, matrix proteins were localized to peroxisomes in 4-d-old seedlings but mislocalized to the cytosol in 8-d-old seedlings. Moreover, a PTS2-GFP reporter sorted to peroxisomes in lon2 root tip cells but was largely cytosolic in more mature root cells. Our results indicate that LON2 is needed for sustained matrix protein import into peroxisomes. The delayed onset of matrix protein sorting defects may account for the relatively weak Suc dependence following germination, moderate IBA-resistant primary root elongation, and severe defects in IBA-induced lateral root formation observed in lon2 mutants.Peroxisomes are single-membrane-bound organelles found in most eukaryotes. Peroxin (PEX) proteins are necessary for various aspects of peroxisome biogenesis, including matrix protein import (for review, see Distel et al., 1996; Schrader and Fahimi, 2008). Most matrix proteins are imported into peroxisomes from the cytosol using one of two targeting signals, a C-terminal type 1 peroxisome-targeting signal (PTS1) or a cleavable N-terminal type 2 peroxisome-targeting signal (PTS2) (Reumann, 2004). PTS1- and PTS2-containing proteins are bound in the cytosol by soluble matrix protein receptors, escorted to the peroxisome membrane docking complex, and translocated into the peroxisome matrix (for review, see Platta and Erdmann, 2007). Once in the peroxisome, many matrix proteins participate in metabolic pathways, such as β-oxidation, hydrogen peroxide decomposition, and photorespiration (for review, see Gabaldon et al., 2006; Poirier et al., 2006).In addition to metabolic enzymes, several proteases are found in the peroxisome matrix. Only one protease, DEG15/Tysnd1, has a well-defined role in peroxisome biology. The rat Tysnd1 protease removes the targeting signal after PTS2-containing proteins enter the peroxisome and also processes certain PTS1-containing β-oxidation enzymes (Kurochkin et al., 2007). Similarly, the Arabidopsis (Arabidopsis thaliana) Tysnd1 homolog DEG15 (At1g28320) is a peroxisomal Ser protease that removes PTS2 targeting signals (Helm et al., 2007; Schuhmann et al., 2008).In contrast with DEG15, little is known about the other eight Arabidopsis proteins that are annotated as proteases in the AraPerox database of putative peroxisomal proteins (Reumann et al., 2004; Carter et al., 2004; Shimaoka et al., 2004), which, in combination with the minor PTS found in both of these predicted proteases (Reumann, 2004), suggests that these enzymes may not be peroxisomal. Along with DEG15, only two of the predicted peroxisomal proteases, an M16 metalloprotease (At2g41790), which we have named PXM16 for peroxisomal M16 protease, and a Lon-related protease (At5g47040/LON2; Ostersetzer et al., 2007), are found in the proteome of peroxisomes purified from Arabidopsis suspension cells (Eubel et al., 2008). DEG15 and LON2 also have been validated as peroxisomally targeted using GFP fusions (Ostersetzer et al., 2007; Schuhmann et al., 2008).

Table I.

Putative Arabidopsis proteases predicted or demonstrated to be peroxisomal

5-FU壳聚糖-阿拉伯胶缓释微囊的制备工艺研究

研究以壳聚糖和阿拉伯胶为基质材料,制备5-FU缓释微囊.以微囊的药物包封率为制备工艺优化指标,利用复凝聚法,通过L_9(3~4)正交实验得出微囊的最佳制备工艺条件.以最佳制备工艺条件制备的5-FU缓释微囊,所制微囊形态及稳定性较好.体外释放研究表明,微囊有良好的缓释效果.     

Biodegradable Injectable In Situ Implants and Microparticles for Sustained Release of Montelukast: In Vitro Release,Pharmacokinetics, and Stability

The objective of this study was to investigate the sustained release of a hydrophilic drug, montelukast (MK), from two biodegradable polymeric drug delivery systems, in situ implant (ISI) and in situ microparticles (ISM). N-Methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), triacetin, and ethyl acetate were selected as solvents. The release of 10% (w/v) MK from both systems containing poly-lactic-co-glycolic acid (PLGA) as the biodegradable polymer was compared. Upon contact with the aqueous medium, the PLGA in ISI and ISM systems solidified resulting in implants and microparticles, respectively. The in vitro drug release from the ISI system showed marked difference from miscible solvents (NMP and DMSO) than the partially miscible ones (triacetin and ethyl acetate), and the drug release decreased with increased PLGA concentration. In the ISM system, the initial in vitro drug release decreased with decreased ratio of polymer phase to external oil phase. In vivo studies in rats showed that ISM had slower drug release than the drug release from ISI. Also, the ISM system when compared to ISI system had significantly reduced initial burst effect. In vitro as well as the in vivo studies for both ISI and ISM systems showed sustained release of MK. The ISM system is suitable for sustained release of MK over 4-week period with a lower initial burst compared to the ISI system. Stability studies of the ISI and ISM formulations showed that MK is stable in the formulations stored at 4°C for more than 2 years.