Controlled release of recombinant insulin-like growth factor from a novel formulation of polylactide-co-glycolide microparticles

An overview of translational research in bone graft biomaterials

Natural bone healing is often inadequate to treat fractures with critical size bone defects and massive bone loss. Immediate surgical interventions through bone grafts have been found to be essential on such occasions. Naturally harvested bone grafts, although are the preferred choice of the surgeons; they suffer from serious clinical limitations, including disease transmission, donor site morbidity, limited supply of graft etc. Synthetic bone grafts, on the other hand, offer a more clinically appealing approach to decode the pathways of bone repair through use of tissue engineered biomaterials. This article critically retrospects the translational research on various engineered biomaterials towards bringing transformative changes in orthopaedic healthcare. The first section of the article discusses about composition and ultrastructure of bone along with the global perspectives on statistical escalation of bone fracture surgeries requiring use of bone grafts. The next section reviews the types, benefits and challenges of various natural and synthetic bone grafts. An overview of clinically relevant biomaterials from traditionally used metallic, bioceramic, and biopolymeric biomaterials to new generation composites have been summarised. Finally, this narrative review concludes with the discussion on the emerging trends and future perspectives of the promising bone grafts.

VEGF-PLGA controlled-release microspheres enhanced angiogenesis in encephalomyosynangiosis-based chronic cerebral hypoperfusion

Treatments enhancing angiogenesis for chronic cerebral hypoperfusion (CCH) are still in the research stage. Although encephalomyosynangiosis (EMS) is a common indirect anastomosis for the treatment of CCH, the effectiveness to promote angiogenesis is not satisfactory. Vascular endothelial growth factors (VEGF) is a cytokine found to specifically act directly on vascular endothelial cells, promote neovascularization, and enhance capillary permeability. However, the short half life and unstable property of VEGF underlies the need to explore available delivery system. In this study, poly (lactide-co-glycolide) (PLGA) was used to prepare VEGF controlled-release microspheres. In vitro and in vivo analysis of release kinetics showed that the microspheres could release VEGF continuously within 30 days. Then, modified chronic cerebral hypoperfusion rat model was established by ligation of bilateral internal carotid artery and one vertebral artery. At 14 days after ischemia, the EMS and the VEGF microspheres injection were performed. At 30 days after the injection, the result of Morris water maze displayed that combinating VEGF microspheres and EMS significantly ameliorated cognitive deficit after ischemia. We observed that combinating VEGF microspheres and EMS could further significantly increase cerebral blood flow. We speculated that this enhancement of cerebral blood flow was attributed to more angiogenesis induced by combination of VEGF microspheres and EMS, which verified by more collateral circulation with cerebral angiography and higher expression of CD31 or α-SMA. Our study demonstrated that combinating VEGF-PLGA controlled-release microspheres could significantly promote angiogenesis in EMS-based CCH rats model, providing new ideas for clinical treatment of CCH.

Recent progress in preparation and agricultural application of microcapsules

Recent advances in life science technology have prompted the need to develop microcapsule delivery systems that can encapsulate many different functional or active materials such as drugs, peptides, and live cells, etc. The encapsulation technology is now commonly used in medicine, agriculture, food, and other many fields. The application of biodegradable microcapsule systems can not only effectively prevent the degradation of core materials in the body or the biological environment, but also improve the bioavailability, control the release and prolong the halftime or storage of core active materials. Various wall materials, preparation methods, encapsulation processes, and release mechanisms are covered in this review, as well as several main factors including pH values, temperatures, particle sizes, and additives, which can strongly influence the encapsulation efficiency, the strength, and release of microcapsules. The improvement of coating materials, preparation techniques, and challenges are also highlighted, as well as application prospects.

One-pot preparation of polymer microspheres with different porous structures to sequentially release bio-molecules for cutaneous regeneration

Herein, we reveal a double emulsion method combining the sol–gel method to prepare poly(lactic-co-glycolic acid) microspheres with different porous structures for sequential release of two types of biomolecules.

Sustained release of PTH(1-34) from PLGA microspheres suppresses osteoarthritis progression in rats

We previously reported that PTH(1-34) inhibits the terminal differentiation of articular chondrocytes and, in turn, suppresses the progression of osteoarthritis (OA). However, this treatment requires an injection of PTH(1-34) once every 3 days over the treatment period. In this study, we studied the effect of sustained administration of PTH(1-34) in a papain-induced OA rat model. We developed an effective controlled-release system for prolonging the treatment duration of an intra-articular injection for OA treatment in rats. The effects of released PTH(1-34) from PLGA(65:35)-encapsulated PTH(1-34) microspheres (PTH/PLGA) on papain-induced OA in rat knees were studied. Microsphere morphology was observed in vitro by scanning electron microscopy, and microsphere size was determined with a particle size analyzer. The PTH(1-34) encapsulation efficiency and release profile, as well as the toxicity of PTH/PLGA, were examined. The bioactivity of released PTH(1-34) was tested by examining cAMP levels in MC3T3E1 cells. In vivo, we evaluated the changes of localized GAG, Col II, and Col X in the articular cartilage of rat knees. Our results demonstrated that the surface of the PLGA microspheres was smooth, and the size of the microspheres was in the range of 51-127 μm. PTH/PLGA microspheres sustainably released PTH(1-34) for 19 days with a concentration range of 0.01-100 nM that covered the expected concentration of 10nM at 37°C. The cAMP levels of MC3T3E1 cells were elevated in the response to released PTH(1-34) from PTH/PLGA microspheres, indicating that the released PTH(1-34) is bioactive. Most importantly, intra-articular treatment with either PTH(1-34) (0.1-100 nM) 3 days/injection or PTH/PLGA microspheres (15 days/injection) for 5 weeks revealed the similar effect on suppressing papain-induced OA changes (decreasing GAG and Col II and increasing Col X) in rat knee cartilage. The effect of PTH/PLGA microspheres on suppressing OA progression was similar to that of a once-every-three-day injection of PTH(1-34), indicating that both the sustained and intermittent action of PTH(1-34) effectively suppress OA progression. The developed PLGA microspheres with sustained release and long-term effect may be potent carriers for PTH(1-34) used to treat early OA.

Slow release and delivery of antisense oligonucleotide drug by self-assembled peptide amphiphile nanofibers

Antisense oligonucleotides provide a promising therapeutic approach for several disorders including cancer. Chemical stability, controlled release, and intracellular delivery are crucial factors determining their efficacy. Gels composed of nanofibrous peptide network have been previously suggested as carriers for controlled delivery of drugs to improve stability and to provide controlled release, but have not been used for oligonucleotide delivery. In this work, a self-assembled peptide nanofibrous system is formed by mixing a cationic peptide amphiphile (PA) with Bcl-2 antisense oligodeoxynucleotide (ODN), G3139, through electrostatic interactions. The self-assembly of PA-ODN gel was characterized by circular dichroism, rheology, atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM and SEM images revealed establishment of the nanofibrous PA-ODN network. Due to the electrostatic interactions between PA and ODN, ODN release can be controlled by changing PA and ODN concentrations in the PA-ODN gel. Cellular delivery of the ODN by PA-ODN nanofiber complex was observed by using fluorescently labeled ODN molecule. Cells incubated with PA-ODN complex had enhanced cellular uptake compared to cells incubated with naked ODN. Furthermore, Bcl-2 mRNA amounts were lower in MCF-7 human breast cancer cells in the presence of PA-ODN complex compared to naked ODN and mismatch ODN evidenced by quantitative RT-PCR studies. These results suggest that PA molecules can control ODN release, enhance cellular uptake and present a novel efficient approach for gene therapy studies and oligonucleotide based drug delivery.

Preparation and in vitro characterization of vascular endothelial growth factor (VEGF)-loaded poly(D,L-lactic-co-glycolic acid) microspheres using a double emulsion/solvent evaporation technique

Biodegradable Poly(lactic-co-glycolic acid; PLGA), microspheres encapsulating the angiogenic protein recombinant human vascular endothelial growth factor (rhVEGF) were formed to achieve VEGF release in a sustained manner. These microspheres are a promising delivery system which can be used for therapeutic angiogenesis. The PLGA microspheres incorporating two different initial loading amounts of rhVEGF have been prepared by a modified water-in-oil-in-water (w/o/w) double emulsion/solvent evaporation technique. The microspheres have been characterized by particle size distribution, environmental scanning electron microscopy (ESEM), light microscopy, encapsulation efficiency and their degradation was studied in vitro. The rhVEGF released from microspheres was quantified by the competitive enzyme-linked immunosorbent assay (ELISA) and human umbilical vein endothelial cell (HUVEC) proliferation assay was used to assess biological activity of the released VEGF. The microspheres were spherical with diameters of 10-60 µm and the encapsulation efficiency was between 46% and 60%. The release kinetics of rhVEGF was studied for two different amounts: 5 µg VEGF (V5) and 50 µg VEGF (V50) per 500 mg starting polymer. The total protein (VEGF:BSA) release increased up to 4 weeks for two rhVEGF concentrations. The ELISA results showed that the burst release for V5 and V50 microspheres were 4 and 27 ng/mL, respectively. For V5, the microspheres showed an initial burst release, followed by a higher steady-state release until 14 days. VEGF release increased up to 2 weeks for V50 microsphere. HUVEC proliferation assay showed that endothelial cells responded to bioactive VEGF by proliferating and migrating.

Controlled release of IGF-1 and HGF from a biodegradable polyurethane scaffold

PURPOSE

Biodegradable elastomers, which can possess favorable mechanical properties and degradation rates for soft tissue engineering applications, are more recently being explored as depots for biomolecule delivery. The objective of this study was to synthesize and process biodegradable, elastomeric poly(ester urethane)urea (PEUU) scaffolds and to characterize their ability to incorporate and release bioactive insulin-like growth factor-1 (IGF-1) and hepatocyte growth factor (HGF).

METHODS

Porous PEUU scaffolds made from either 5 or 8 wt% PEUU were prepared with direct growth-factor incorporation. Long-term in vitro IGF-1 release kinetics were investigated in saline or saline with 100 units/ml lipase to simulate in vivo degradation. Cellular assays were used to confirm released IGF-1 and HGF bioactivity.

RESULTS

IGF-1 release into saline occurred in a complex multi-phasic manner for up to 440 days. Scaffolds generated from 5 wt% PEUU delivered protein faster than 8 wt% scaffolds. Lipase-accelerated scaffold degradation led to delivery of >90% protein over 9 weeks for both polymer concentrations. IGF-1 and HGF bioactivity in the first 3 weeks was confirmed.

CONCLUSIONS

The capacity of a biodegradable elastomeric scaffold to provide long-term growth-factor delivery was demonstrated. Such a system might provide functional benefit in cardiovascular and other soft tissue engineering applications.

Intra-discal vancomycin-loaded PLGA microsphere injection for MRSA discitis: an experimental study

OBJECTIVE

To prepare the vancomycin hydrochloride (VA)-loaded poly lactic acid-glycolic acid (PLGA) copolymer microsphere by the multiple emulsion method and evaluate its therapeutic effects on infective discitis.

METHODS

Firstly, the particle diameter distribution, shape, encapsulation efficiency, drug-loaded dosage and release curve of VA-PLGA microspheres were evaluated in vitro. Rabbits with methicillin-resistant Staphylococcus aureus infective discitis were treated with VA-PLGA intra-discal injection. Meanwhile, VA intravenous injection, blank PLGA microspheres intra-discal injection served as controls. Thirty days later, therapeutic effects were evaluated through X-ray radiophotography, histopathological and bacteriological examination.

RESULTS

Mean particle diameter was between 61.57 ± 4.37 and 67.45 ± 8.13 μm, and mean encapsulation efficiency was between 60.20 ± 1.61 and 75.27 ± 1.60 %m/m. In vitro release experiment showed that the release time was over 30 days. The result of in vivo experiment showed that inflammatory reaction in the VA-PLGA intra-discal injection group was milder than the intravenous injection group (P < 0.05), also with less inflammation. The bacterial count was also significantly lower (1.02 × 10(3) ± 1.22 × 10(3) CFU/g) than the intravenous injection group (7.51 × 10(4) ± 7.16 × 10(4) CFU/g) (P < 0.05). Besides these data, the amount used in VA-PLGA intra-discal injection group is about 20 mg, and that used in the intravenous injection group is about 2.4 g. So, we just use 1/120 of VA i.v. to obtain the better results with our microparticles.

CONCLUSION

Intra-discal injection with VA-PLGA sustained-release microspheres can use much less dosage, and effectively control and reduce infective discitis, and the therapeutic effect is superior to that of intravenous injection. A need for the clinical trials will be carried out in the near future.

Delivery systems for bone growth factors — the new players in skeletal regeneration

Given the challenge of an increasing elderly population, the ability to repair and regenerate traumatised or lost tissue is a major clinical and socio-economic need. Pivotal in this process will be the ability to deliver appropriate growth factors in the repair cascade in a temporal and tightly regulated sequence using appropriately designed matrices and release technologies within a tissue engineering strategy. This review outlines the current concepts and challenges in growth factor delivery for skeletal regeneration and the potential of novel delivery matrices and biotechnologies to influence the healthcare of an increasing ageing population.

Hoffmeister Series Ions Protect Diphtheria Toxoid from Structural Damages at Solvent/Water Interface

During the W₁/O phase (in the W₁/O/W₂ process) of protein microencapsulation within poly-lactide-co-glycolide (PLGA), hydrophobic interfaces are expanded where interfacial adsorption occurs followed by protein unfolding and aggregation. Spectroscopic and immunological techniques were used to ascertain the effects of the Hoffmeister series ions on Diphtheria toxoid (Dtxd) stability during the W₁/O phase. A correlation was established between salts used in aqueous solutions and the changes in Dtxd solubility and conformation. The Dtxd α-helical content was quite stable thus leading to the conclusion that encapsulation was followed by protein aggregation, with minor exposition of hydrophobic residues and a small change at the S-S dihedral angle. Dtxd aggregation is 95% avoided by the chaotropic SCN^-. This was used to prepare a stable Dtxd and immunologically recognized/PLGA formulation in the presence of 30 mM SNC^-. The recovery increased by 10.42% or 23.2% when microencapsulation was within the -COOMe or -COOH (12kDa) PLGA, respectively. In conclusion, the aim of this work was achieved, which was to obtain the maximum of Dtxd stability after contact with CH₂Cl₂ to begin its PLGA microencapsulation within ideal conditions. This was a technological breakthrough because a simple solution like salt addition avoided heterologous proteins usage.

Microencapsulation by solvent evaporation: state of the art for process engineering approaches

Microencapsulation by solvent evaporation technique is widely used in pharmaceutical industries. It facilitates a controlled release of a drug, which has many clinical benefits. Water insoluble polymers are used as encapsulation matrix using this technique. Biodegradable polymer PLGA (poly(lactic-co-glycolic acid)) is frequently used as encapsulation material. Different kinds of drugs have been successfully encapsulation: for example hydrophobic drugs such as cisplatin, lidocaine, naltrexone and progesterone; and hydrophilic drugs such as insulin, proteins, peptide and vaccine. The choice of encapsulation materials and the testing of the release of drug have been intensively investigated. However process-engineering aspects of this technique remain poorly reported. To succeed in the controlled manufacturing of microspheres, it is important to investigate the latter. This article reviews the current state of the art concerning this technique by focusing on the influence of the physical properties of materials and operating conditions on the microspheres obtained. Based on the existing results and authors' reflection, it gives rise to reasoning and suggested choices of materials and process conditions. A part of this paper is also dedicated to numerical models on the solvent evaporation and the solidification of microspheres. This review reveals also the surprising lack of knowledge on certain aspects, such as the mechanism of formation of pores in the microspheres and the experimental study on the solidification of microspheres.

Interaction of cells and nanofiber scaffolds in tissue engineering

Nanofibers and nanomaterials are potentially recent additions to materials in relation to tissue engineering (TE). TE is the regeneration of biological tissues through the use of cells, with the aid of supporting structures and biomolecules. Mimicking architecture of extracellular matrix is one of the challenges for TE. Biodegradable biopolymer nanofibers with controlled surface and internal molecular structures can be electrospun into mats with specific fiber arrangement and structural integrity for drug delivery and TE applications. The polymeric materials are widely accepted because of their ease of processability and amenability to provide a large variety of cost-effective materials, which help to enhance the comfort and quality of life in modern biomedical and industrial society. Today, nanotechnology and nanoscience approaches to scaffold design and functionalization are beginning to expand the market for drug delivery and TE is forming the basis for highly profitable niche within the industry. This review describes recent advances for fabrication of nanofiber scaffolds and interaction of cells in TE.

Biodegradable polymeric microspheres with “open/closed” pores for sustained release of human growth hormone

A new approach for attaining sustained release of protein is introduced, involving a pore-closing process of preformed porous PLGA microspheres. Highly porous biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres were fabricated by a single water-in-oil emulsion solvent evaporation technique using Pluronic F127 as an extractable porogen. Recombinant human growth hormone (rhGH) was incorporated into porous microspheres by a simple solution dipping method. For their controlled release, porous microspheres containing hGH were treated with water-miscible solvents in aqueous phase for production of pore-closed microspheres. These microspheres showed sustained release patterns over an extended period; however, the drug loading efficiency was extremely low. To overcome the drug loading problem, the pore-closing process was performed in an ethanol vapor phase using a fluidized bed reactor. The resultant pore-closed microspheres exhibited high protein loading amount as well as sustained rhGH release profiles. Also, the released rhGH exhibited structural integrity after the treatment.

Release of albumin from oligoester plastic matrices: effect of magnesium oxide and bivalent stearates

Biodegradable implantable matrices containing bovine serum albumin were prepared from oligoesters by melting, and subsequently tested on in vitro albumin release. The linear poly (DL-lactic acid) and the branched terpolymer of DL-lactic acid, glycolic acid, and mannitol were synthesized. Products were of similar molecular weight and possessed different thermal and swelling characteristics. Oligoesters were loaded with 4% albumin and plasticized by 30% triacetin. Other additives added into the matrices as albumin stabilizers were divalent stearates and magnesium oxide. The influences of oligomer molecules constitution, divalent ion stearates or magnesium oxide addition, and triacetin concentration on the albumin release were quantified. SDS-PAGE revealed protein hydrolysis during the dissolution tests.

Novel Biodegradable Aliphatic Poly(butylene Succinate-co-cyclic carbonate)s Bearing Functionalizable Carbonate Building Blocks: II. Enzymatic Biodegradation and in Vitro Biocompatibility Assay

In a previous study, we have reported chemical synthesis of novel aliphatic poly(butylene succinate-co-cyclic carbonate) P(BS-co-CC)s bearing various functionalizable carbonate building blocks, and this work will continue to present our new studies on their enzymatic degradation and in vitro cell biocompatibility assay. First, enzymatic degradation of the novel P(BS-co-CC) film samples was investigated with two enzymes of lipase B Candida Antartic (Novozyme 435) and lipase Porcine Pancreas PPL, and it was revealed that copolymerizing linear poly(butylene succinate) PBS with a functionalizable carbonate building block could remarkably accelerate the enzymatic degradation of a synthesized product P(BS-co-CC), and its biodegradation behavior was found to strongly depend on the overall impacts of several important factors as the cyclic carbonate (CC) comonomer structure and molar content, molar mass, thermal characteristics, morphology, the enzyme-substrate specificity, and so forth. Further, the biodegraded residual film samples and water-soluble enzymatic degradation products were allowed to be analyzed by means of proton nuclear magnetic resonance (1H NMR), gel permeation chromatograph (GPC), differential scanning calorimeter (DSC), attenuated total reflection FTIR (ATR-FTIR), scanning electron microscope (SEM), and liquid chromatograph-mass spectrometry (LC-MS). On the experimental evidences, an exo-type mechanism of enzymatic chain hydrolysis preferentially occurring in the noncrystalline domains was suggested for the synthesized new P(BS-co-CC) film samples. With regard to their cell biocompatibilities, an assay with NIH 3T3 mouse fibroblast cell was conducted using the novel synthesized P(BS-co-CC) films as substrates with respect to the cell adhesion and proliferation, and these new biodegradable P(BS-co-CC) samples were found to exhibit as low cell toxicity as the PLLA control, particularly the two samples of poly(butylene succinate-co-18.7 mol % dimethyl trimethylene carbonate) P(BS-co-18.7 mol % DMTMC) and poly(butylene succinate-co-21.9 mol % 5-benzyloxy trimethylene carbonate) P(BS-co-21.9 mol % BTMC) were interestingly found to show much better cell biocompatibilities than the PLLA reference.

In vitro release of vascular endothelial growth factor from gadolinium-doped biodegradable microspheres

A drug delivery vehicle was constructed that could be visualized noninvasively with MRI. The biodegradable polymer poly(DL-lactic-co-glycolic acid) (PLGA) was used to fabricate microspheres containing vascular endothelial growth factor (VEGF) and the MRI contrast agent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The microspheres were characterized in terms of size, drug and contrast agent encapsulation, and degradation rate. The PLGA microspheres had a mean diameter of 48 +/- 18 microm. The gadolinium loading was 17 +/- 3 microg/mg polymer and the VEGF loading was 163 +/- 22 ng/mg polymer. Electron microscopy revealed that the Gd was dispersed throughout the microspheres and it was confirmed that the Gd loading was sufficient to visualize the microspheres under MRI. VEGF and Gd-DTPA were released from the microspheres in vitro over a period of approximately 6 weeks in three phases: a burst, followed by a slow steady-state, then a rapid steady-state. Biodegradable Gd-doped microspheres can be effectively used to deliver drugs in a sustained manner, while being monitored noninvasively with MRI.

Microspheres containing insulin-like growth factor I for treatment of chronic neurodegeneration

The therapeutic potential of peptide growth factors as insulin-like growth factor I (IGF-I) is currently under intense scrutiny in a wide variety of diseases, including neurodegenerative illnesses. A new poly(lactic-co-glycolide)-based microsphere IGF-I controlled release formulation for subcutaneous (SC) delivery has been developed by a triple emulsion method. The resulting microspheres displayed a mean diameter of 1.5microm, with an encapsulation efficiency of 74.3%. The protein retained integrity after the microencapsulation process as evaluated by circular dichroism and SDS-PAGE. The administration of IGF-I in microspheres caused at least a 30-fold increase in IGF-I mean residence time in rats and mice when compared with the conventional SC solution. Therefore, dosing can be changed from the conventional twice a day to once every 2 weeks. Therapeutic efficacy of this new formulation has been studied in mutant mice with inherited Purkinje cell degeneration (PCD). These mice show a chronic limb discoordination that is resolved after continuous systemic delivery of IGF-I. Normal motor coordination was maintained as long as IGF-I microsphere therapy is continued. Moreover, severely affected PCD mice, with marked ataxia, muscle wasting and shortened life-span showed a significant improvement after continuous IGF-I microsphere therapy as determined by enhanced motor coordination, marked weight gain and extended survival. This new formulation can be considered of great therapeutic promise for some chronic brain diseases.

The release profiles and bioactivity of parathyroid hormone from poly(lactic-co-glycolic acid) microspheres

Poly(lactic-co-glycolic acid) (PLGA) microspheres containing bovine serum albumin (BSA) or human parathyroid hormone (PTH)(1-34) were prepared using a double emulsion method with high encapsulation efficiency and controlled particle sizes. The microspheres were characterized with regard to their surface morphology, size, protein loading, degradation and release kinetics, and in vitro and in vivo assessments of biological activity of released PTH. PLGA5050 microspheres degraded rapidly after a 3-week lag time and were degraded completely within 4 months. In vitro BSA release kinetics from PLGA5050 microspheres were characterized by a burst effect followed by a slow release phase within 1-7 weeks and a second burst release at 8 weeks, which was consistent with the degradation study. The PTH incorporated PLGA5050 microspheres released detectable PTH in the initial 24h, and the released PTH was biologically active as evidenced by the stimulated release of cAMP from ROS 17/2.8 osteosarcoma cells as well as increased serum calcium levels when injected subcutaneously into mice. Both in vitro and in vivo assays demonstrated that the bioactivity of PTH was maintained largely during the fabrication of PLGA microspheres and upon release. These studies illustrate the feasibility of achieving local delivery of PTH to induce a biologically active response in bone by a microsphere encapsulation technique.

Incorporation and controlled release of a hydrophilic antibiotic using poly(lactide-co-glycolide)-based electrospun nanofibrous scaffolds

The successful incorporation and sustained release of a hydrophilic antibiotic drug (Mefoxin, cefoxitin sodium) from electrospun poly(lactide-co-glycolide) (PLGA)-based nanofibrous scaffolds without the loss of structure and bioactivity was demonstrated. The morphology and density of the electrospun scaffold was found to be dependent on the drug concentration, which could be attributed to the effect of ionic salt on the electrospinning process. The drug release behavior from the electrospun scaffolds and its antimicrobial effects on Staphylococcus aureus cultures were also investigated. In all tested scaffolds, the maximum dosage of drug was released after 1 h of incubation in water at 37 degrees C. The usage of the amphiphilic block copolymer (PEG-b-PLA) reduced the cumulative amount of the released drug at earlier time points and prolonged the drug release rate at longer times (up to a 1-week period). The antibiotic drug released from these electrospun scaffolds was effective in their ability to inhibit Staphylococcus aureus growth (>90%). The combination of mechanical barriers based on non-woven nanofibrous biodegradable scaffolds and their capability for local delivery of antibiotics increases their desired utility in biomedical applications, particularly in the prevention of post-surgical adhesions and infections.

Effect of gamma-sterilization process on PLGA microspheres loaded with insulin-like growth factor-I (IGF-I)

The influence of gamma-sterilization on the physicochemical properties of a controlled release formulation for the insulin-like growth factor-I (IGF-I) was investigated in this study. Recombinant human insulin-like growth factor-I (rhIGF-I) was efficiently entrapped in poly (D,L-lactide-co-glycolide) (PLGA) microspheres by water-in-oil-in-water (W/O/W) solvent evaporation technique. Microspheres were irradiated at a dose of 25kGy and evaluated by means of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The stability of the released protein was investigated by circular dichroism (CD) and sodium dodecyl sulfate polyacrilamide gel electrophoresis (SDS-PAGE). No difference was noticed in microsphere size and morphology before and after irradiation. Drug loading remains essentially the same after the sterilization process. However, rhIGF-I aggregation was detected by electrophoresis. In addition, subtle changes in DSC pattern were noticed for irradiated microspheres. In vitro drug release from irradiated microspheres was also affected, showing an increased burst effect. From this results it can be concluded that gamma-sterilization process causes changes in the properties of rhIGF-I loaded microspheres.

Potential applications of polymeric microsphere suspension as subcutaneous depot for insulin

The objective of this investigation was to develop an injectable, depot-forming drug delivery system for insulin based on microparticle technology to maintain constant plasma drug concentrations over prolonged period of time for the effective control blood sugar levels. Formulations were optimized with two well-characterized biodegradable polymers namely, poly(DL-lactide-co-glycolide) and poly-epsilon-caprolactone and evaluated in vitro for physicochemical characteristics, drug release in phosphate buffered saline (pH 7.4), and evaluated in vivo in streptozotocin-induced hypoglycemic rats. With a large volume of internal aqueous phase during w/o/w double emulsion solvent evaporation process and high molecular weight of the polymers used, we could not achieve high drug capture and precise control over subsequent release within the study period of 60 days. However, this investigation revealed that upon subcutaneous injection, the biodegradable depot-forming polymeric microspheres controlled the drug release and plasma sugar levels more efficiently than plain insulin injection. Preliminary pharmacokinetic evaluation exhibited steady plasma insulin concentration during the study period. These formulations, with their reduced frequency of administration and better control over drug disposition, may provide an economic benefit to the user compared with products currently available for diabetes control.

Polyhydroxyalkanonate derivatives in current clinical applications and trials

Polyhydroxyalkanonate is a typical biodegradable material, which is permitted for use in the medical and pharmaceutical fields. For its biodegradability, biocompatibility, and toxicological safety, the majority of products practically used are composed of homo-polymers of poly(lactic acid), poly(glycolic acid), and poly(epsilon-caprolactone) and their co-polymers. On the market, suture strings are still the main usage. The needs of biodegradable materials have been being gradually increased by the development of drug delivery systems, tissue engineering, and regenerative medicine. Some types of formulation, that is, mono-fibers, twisted fibers, films, fabrics, sponges, and injectable particles are developed to match each purpose. This article reviews the current clinical applications and trials of polyhydroxyalcanonate products.

Structure and morphology changes during in vitro degradation of electrospun poly(glycolide-co-lactide) nanofiber membrane

Electrospun poly(glycolide-co-lactide) (PLA10GA90, LA/GA ratio 10/90) biodegradable nanofiber membranes possessed very high surface area to volume ratios and were completely noncrystalline with a relatively lowered glass transition temperature. These characteristics led to very different structure, morphology, and property changes during in vitro degradation, which were examined systematically. A shrinkage study showed that the electrospun crystallizable but amorphous PLA10GA90 membranes exhibited a very small shrinkage percentage when compared with the electrospun membranes of noncrystallizable poly(lactide-co-glycolide) (PLA75GA25, LA/GA 75/25) and poly(d,l-lactide). Although the weight loss of electrospun PLA10GA90 membranes exhibited a similar degradation behavior as cast thin films, detailed studies showed that the structure and morphology changes in electrospun membranes followed different pathways during the hydrolytic degradation. After 1 day of degradation in buffer solution at 37 degrees C, electrospun PLA10GA90 membranes exhibited a sudden increase in crystallinity and glass transition temperature, due to the fast thermally induced crystallization process. The continuous increase in crystallinity and apparent crystal size, as well as the decrease in long period and lamellae thickness, indicated that the thermally induced crystallization was followed by a chain cleavage induced crystallization process. The mass loss rate was accelerated after 6 days of degradation. The increase in glass transition temperature during this period further confirmed that the degradation of PLA10GA90 nanofibers was initiated from the amorphous region within the lamellar superstructures. A mechanism of structure and morphology changes during in vitro degradation of electrospun PLA10GA90 nanofibers is proposed.

Potential applications of PLGA film-implants in modulating in vitro drugs release

In this work we evaluate poly(lactic/glycolic) acid (PLGA) film-implants as potential biodegradable devices for controlled release of two different drugs: 5-Fluorouridine (5-FUR), a conventional low molecular weight water-soluble compound and SPf66 malaria vaccine, a therapeutic synthetic polypeptide. Three types of devices were prepared by solvent-casting techniques alone or combined with compression method: simple monolithic discs (SMD), multilayer discs with a central monolithic layer (MLDM), and multilayer discs with a central drug-reservoir (MLDR). For the highly water-soluble drug, 5-FUR, in vitro release from SMD showed an initial burst (24% in 2 h) followed by prolonged release over 20 days. In contrast, from a MLDM (two drug-free PLGA discs were added to the SMD) showed an initial lag-time of 12 days followed by a very fast second release phase. Finally, when the load of this system was increased from 3 to 9%, an extended release over 20 days with a low burst effect was obtained. For SPf66, the central reservoir containing the synthetic polypeptide MLDR reduces the possibility of degradation due to peptide contact with polymer solution. When four layers were added, 10 days sustained-release was obtained without any burst effect. With six layers a moderate pulse was obtained, 18-22 days from the beginning of the release. The results show the suitability of the proposed devices to control release and avoid the burst effect with highly water-soluble drugs; as well as modulate in vitro peptide release.

Recent trends in stabilizing protein structure upon encapsulation and release from bioerodible polymers

Sustained release of pharmaceutical proteins from biocompatible polymers offers new opportunities in the treatment and prevention of disease. The manufacturing of such sustained-release dosage forms, and also the release from them, can impose substantial stresses on the chemical integrity and native, three-dimensional structure of proteins. Recently, novel strategies have been developed towards elucidation and amelioration of these stresses. Non-invasive technologies have been implemented to investigate the complex destabilization pathways that can occur. Such insights allow for rational approaches to protect proteins upon encapsulation and release from bioerodible systems. Stabilization of proteins when utilizing the most commonly employed procedure, the water-in-oil-in-water (w/o/w) double emulsion technique, requires approaches that are based mainly on either increasing the thermodynamic stability of the protein or preventing contact of the protein with the destabilizing agent (e.g. the water/oil interface) by use of various additives. However, protein stability is still often problematic when using the w/o/w technique, and thus alternative methods have become increasingly popular. These methods, such as the solid-in-oil-in-oil (s/o/o) and solid-in-oil-in-water (s/o/w) techniques, are based on the suspension of dry protein powders in an anhydrous organic solvent. It has become apparent that protein structure in the organic phase is stabilized because the protein is "rigidified" and therefore unfolding and large protein structural perturbations are kinetically prohibited. This review focuses on strategies leading to the stabilization of protein structure when employing these different encapsulation procedures.