Biodegradation and biocompatibility of PLA and PLGA microspheres

Bupivacaine in microcapsules prolongs analgesia after subcutaneous infiltration in humans: a dose-finding study

In this study, we examined the onset and duration of local analgesic effects of bupivacaine incorporated into biodegradable microcapsules (extended-duration local anesthetic; EDLA) administered as subcutaneous infiltrations in different doses in humans. In 18 volunteers, the skin on the medial calf was infiltrated with 10 mL of EDLA, and the opposite calf was infiltrated with 10 mL of aqueous bupivacaine (5.0 mg/mL) in a double-blinded, randomized manner. Three different concentrations of EDLA were tested (6.25, 12.5, and 25 mg/mL), with 6 subjects in each group. Pain responses to mechanical and heat stimuli and sensory thresholds (touch, warm, and cold detection thresholds) were examined by von Frey hairs and contact thermodes. Assessments were made before and 2, 4, 6, 8, 24, 48, 72, 96, and 168 h after the injections. Safety evaluations were performed daily for the first week and at 2 wk, 6 wk, and 6 mo after the injections. The time to maximum effects was significantly shorter for aqueous bupivacaine (2-6 h) than for EDLA (4-24 h), but there were no significant differences between the maximum effects of EDLA and aqueous bupivacaine. From 24 to 96 h after the injections, EDLA was significantly more efficient than aqueous bupivacaine for all variables, and significant effects of EDLA were demonstrated for at least 96 h for all variables. In general, a dose-response gradient was seen in the EDLA group for 5 of 7 variables when the curves expressing effect over time for the different concentrations were evaluated. No serious side effects were observed for up to 6 mo after administration. In conclusion, bupivacaine incorporated in microcapsules provided analgesia for 96 h after subcutaneous infiltration.

In vitro and in vivo correlation of buserelin release from biodegradable implants using statistical moment analysis

Here we investigated the possibility to develop different levels of correlation between in vitro drug release profiles and in vivo pharmacokinetic parameters for three Buserelin implant formulations. The in vitro and in vivo data were analyzed using model-independent and model-dependent methods. Since diffusion, dissolution and erosion effects influence drug release in most cases a simple kinetic model is unlikely to explain the overall in vivo release behavior. Thus the in vitro drug release curves were analyzed according to the theoretical models of Higuchi and Korsmeyer-Peppas. For the formulation with predominant diffusion controlled release level A IVIVC could be established (R2=0.986). Independent on drug release mechanism, a level B correlation between the mean in vitro dissolution time (MDT) and mean in vivo residence time (MRT) was obtained with a correlation coefficient of 0.983. Finally, level C correlation were observed when single in vitro parameters, e.g. T50% (time required to release 50% of drug in vitro) where compared with single in vivo parameters like AUC. This study suggests that a level B correlation could be achieved even when drug release occurs by a combination of diffusion and erosion processes. More sophisticated in vitro models mimicking drug release under in vivo conditions are clearly desirable for parenteral depot formulations.

Factorial design, physicochemical characterisation and activity of ciprofloxacin-PLGA nanoparticles

Poly(lactide-co-glycolide) nanoparticles incorporating ciprofloxacin HCl were prepared by means of a W/O/W emulsification solvent evaporation method. The stabiliser selected was poly(vinylalcohol). A 2(4) full factorial design based on four independent variables was used to plan the experiments and the variable parameters were the number of homogenisation cycles, addition of boric acid to the inner water phase containing the drug, ciprofloxacin concentration in the inner water phase and oil:outer water phase ratio. The effects of these parameters on the particle size, zeta potential, drug loading efficiency and drug release were investigated. Also the effect of gamma irradiation on the particle size and drug release was evaluated and DSC and XRD analyses of the compounds and the nanoparticles were performed. The activity on two series of microorganisms, Pseudomonas aeruginosa and Staphylococcus aureus, was examined.

Biodegradable poly(ether-ester) multiblock copolymers for controlled release applications: Anin vivoevaluation

Multiblock poly(ether-ester)s based on poly(ethylene glycol), butylene terephthalate, and butylene succinate segments were evaluated for their in vivo degradation and biocompatibility in order to establish a correlation with previously reported in vitro results. Porous polymer sheets were implanted subcutaneously for 32 weeks in rats. The degradation was monitored visually (histology), by molecular weight (GPC), and by copolymer composition (NMR). Substitution of the aromatic terephthalate units by aliphatic succinate units was shown to accelerate the degradation rate of the copolymers. Direct correlation of the in vivo and in vitro degradation of the porous implants showed a slightly faster initial molecular weight decrease in vivo. Besides hydrolysis, oxidation occurs in vivo due to the presence of radicals produced by inflammatory cells. In addition, the higher molecular weight plateau of the residue found in vivo indicated a higher solubility of the oligomers in the extracellular fluid compared to a phosphate buffer. Minor changes in the poly(ether-ester) compositions were noted due to degradation. Microscopically, fragmentation of the porous implants was observed in time. At later stages of degradation, macrophages were observed phagocytozing small polymer particles. Both in vitro cytotoxicity studies and histology on in vivo samples proved the biocompatibility of the poly(ether-ester)s.

Comparative study on sustained release of human growth hormone from semi-crystalline poly(L-lactic acid) and amorphous poly(D,L-lactic-co-glycolic acid) microspheres: morphological effect on protein release

Recombinant human growth hormone (rhGH) was encapsulated by a double emulsion solvent evaporation method within two biodegradable microspheres having different polymer compositions. Semi-crystalline poly(L-lactic acid) (PLA) and amorphous poly(D,L-lactic-co-glycolic acid) (PLGA) were used for the encapsulation of hGH. Protein release profiles from the two microspheres were comparatively evaluated with respect to their morphological difference. Both of the microspheres similarly exhibited rugged surface and porous internal structures, but their inner pore wall morphologies were quite different. The slowly degrading PLA microspheres had many nano-scale reticulated pores on the wall, while the relatively fast degrading PLGA microspheres had a non-porous and smooth wall structure. From the PLA microspheres, hGH was released out in a sustained manner with an initial approximately 20% burst, followed by constant release, and almost 100% complete release after a 1-month period. In contrast, the PLGA microspheres showed a similar burst level of approximately 20%, followed by much slower release, but incomplete release of approximately 50% after the same period. The different hGH release profiles between PLA and PLGA microspheres were attributed to different morphological characters of the pore wall structure. The inter-connected nano-porous structure of PLA microspheres was likely to be formed due to the preferable crystallization of PLA during the solvent evaporation process.

Preparation and characterization of poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA) microspheres for controlled release of paclitaxel

Microspheres of a new kind of copolymer, poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid) (PLA-PEG-PLA), are proposed in the present work for clinical administration of an antineoplastic drug paclitaxel with hypothesis that incorporation of a hydrophilic PEG segment within the hydrophobic PLA might facilitate the paclitaxel release. Paclitaxel-loaded PLA-PEG-PLA microspheres of various compositions were prepared by the solvent extraction/evaporation method. Characterization of the microspheres was then followed to examine the particle size and size distribution, the drug encapsulation efficiency, the colloidal stability, the surface chemistry, the surface and internal morphology, the drug physical state and its in vitro release behavior. The effects of polymer types, solvents and drug loading were investigated. It was found that in the microspheres the PEG segment was homogeneously distributed and caused porosity. Significantly faster release from PLA-PEG-PLA microspheres resulted in comparison with the PLGA counterpart. Incorporation of water-soluble solvent acetone in the organic solvent phase further increased the porosity of the PLA-PEG-PLA microspheres and facilitated the drug release. A total of 49.6% sustained release of paclitaxel within 1 month was achieved. Potentially, the presence of PEG on the surface of PLA-PEG-PLA microspheres could improve their biocompatibility. PLA-PEG-PLA microspheres could thus be promising for the clinical administration of highly hydrophobic antineoplastic drugs such as paclitaxel.

Studies on biodegradation and release of gentamicin sulphate from interpenetrating network hydrogels based on poly(acrylic acid) and gelatin: in vitro and in vivo

Interpenetrating network hydrogels (IPNs) based on poly(acrylic acid) and gelatin (Ge) were evaluated for in vitro and in vivo biodegradation and in vivo release of gentamicin sulphate. In vitro and in vivo degradation studies demonstrated that with the increase of acrylic acid content in the polymer, the rate of degradation decreases, and a reverse phenomenon was observed with increasing Ge content in the hydrogel. The rate of in vivo degradation was much lower than in vitro degradation. Incorporation of gentamicin sulphate in hydrogel further reduces their degradation. In vitro and in vivo drug release profile showed a burst effect, followed by controlled release. Drug concentration was measured in the local skin tissue, blood serum, kidney, liver and spleen. The local skin tissue concentration of 50% and 100% gentamicin sulphate, loaded full IPNs (i.e., Ax-1 and Ax-2), was found to be higher (20+/-2mug/g) than the minimum bactericidal concentration for Staphylococcus aureus (1.2mug/g) and Pseudomonas aeruginosa (10mug/g), respectively, for a study time of 60 days.

Characterization and in vitro degradation of poly(2,3-(1,4-diethyl tartrate)-co-2,3-isopropyliden tartrate)

In the present study, a less known polyester based on tartaric acid was characterized with respect to its degradation mechanism. Poly(2,3-(1,4-diethyl tartrate)-co-2,3-isopropyliden tartrate) (PTA) differs from commonly used biodegradable polyesters, such as poly(lactides-co-glycolides) (PLGA) by the presence of additional cleavable bonds in the polymer side chains. This modification results in different polymer properties and influences polymer degradation. The hydrolytic degradation of PTA was studied in parallel to PLGA using disc-shape matrices, which were obtained by compression-molding. The discs were incubated in pH 7.4 phosphate buffer solution at 37 degrees C. The degraded samples were characterized for percentage mass loss, water absorption, decay of molecular weight and change in glass transition temperature. The results demonstrate that the degradation of PTA proceeds via bulk erosion similar to PLGA. However, the degradation of PTA implants is characterized by a rapid mass loss within a short period of time appearing after a definite lag phase without remarkable mass loss. This makes the polymer promising for pulsatile drug release systems.

Indocyanine green-loaded biodegradable nanoparticles: preparation, physicochemical characterization and in vitro release

PURPOSE

The objective of this study is to develop indocyanine green (ICG)-loaded biodegradable nanoparticles by using biodegradable polymer, poly(DL-lactic-co-glycolic acid) (PLGA).

METHOD

PLGA nanoparticles entrapping ICG were prepared by a modified spontaneous emulsification solvent diffusion method. To optimize the nanoparticle formulation, the influence of formulation parameters such as types of ICG, amount of ICG and the polymer were investigated. The ICG entrapment in nanoparticles, nanoparticle size and zeta potential were determined. The surface characterization was performed by atomic force microscopy (AFM) and the release of ICG from nanoparticles was determined.

RESULTS

All PLGA nanoparticle formulations were found to have the mean diameter within the range of 300-410 nm with polydispersity index (PI) within the range of 0.01-0.06. Indocyanine green showed more efficient entrapment as compared to indocyanine green sodium iodide salt. All indocyanine green-loaded nanoparticle formulations were found to have almost similar ICG content of nanoparticles and showed increase in ICG entrapment with increase in the amount of polymer. The ICG entrapment reached 74% when ICG: PLGA weight ratio in the formulation reached 1:800. AFM images indicated that the nanoparticles were almost spherical in shape and had numerous pores on their surfaces. The release pattern consisted of two phases, with initial exponential phase releasing about 78% of ICG (within 8 h) followed by a slow phase releasing about 2% of ICG (within next 16 h).

CONCLUSIONS

ICG-loaded PLGA nanoparticles were prepared and the formulation was optimized. The increase in amount of polymer in formulation leads to higher ICG entrapment. Nanoparticles formed were spherical and had porous surfaces and exhibited the characteristic release pattern of a monolithic matrix based system.

Specific role of polysorbate 80 coating on the targeting of nanoparticles to the brain

It was reported that nanoparticles with polysorbate 80 (Tween 80, T-80) coating represented tools used for delivering drugs to brain. Nevertheless, disputations were once aroused for some complications. Aimed to have a better understanding of the specific role of T-80 coating on nanoparticles and simplify the problem, the direct observation of brain targeting combined with in vivo experiments was carried out in this work using the model nanoparticles (MNPs). The presence of a complex composed by the model loading, T-80 and nanoparticles was found in the preparation of MNPs. The result was further supported by some surface properties of MNPs. Being bound to nanoparticles that were overcoated by T-80 later, was necessary for the loading to be delivered to brain. Partial coverage was enough for T-80 coating to play a specific role in brain targeting. It seemed that brain targeting of nanoparticles was concerned with the interaction between T-80 coating and brain micro-vessel endothelial cells. Therefore, the specific role of T-80 coating on nanoparticles in brain targeting was confirmed.

Controlled degradation of hydrogels using multi-functional cross-linking molecules

Hydrogels, chemically cross-linked or physically entangled, have found a number of applications as novel delivery vehicles of drugs and cells. However, the narrow ranges of degradation rates and mechanical strength currently available from many hydrogels limits their applications. We have hypothesized that utilization of multi-functional cross-linking molecules to form hydrogels could provide a wider range and tighter control over the degradation rates and mechanical stiffness of gels than bi-functional cross-linking molecules. To address the possibility, we isolated alpha-L-guluronate residues of sodium alginate, and oxidized them to prepare poly(aldehyde guluronate) (PAG). Hydrogels were formed with either poly(acrylamide-co-hydrazide) (PAH) as a multi-functional cross-linking molecule or adipic acid dihydrazide (AAD) as a bi-functional cross-linking molecule. The initial properties and degradation behavior of both PAG gel types were monitored. PAG/PAH hydrogels showed higher mechanical stiffness before degradation and degraded more slowly than PAG/AAD gels, at the same concentration of cross-linking functional groups. The enhanced mechanical stiffness and prolonged degradation behavior could be attributed to the multiple attachment points of PAH in the gel at the same concentration of functional groups. This approach to regulating gel properties with multifunctional cross-linking molecules could be broadly used in hydrogels.

Delivering DNA from photocrosslinked, surface eroding polyanhydrides

Sustained delivery of DNA has the potential to enhance long-term gene therapy; however, precise control of a wide range of DNA release profiles may be needed. In this work, multifunctional anhydride monomers were photocrosslinked to produce hydrophobic, highly crosslinked polymer networks that degrade by surface erosion. Surface-eroding polymers can deliver molecules of a wide range of sizes at sustained, steady rates, which is advantageous for DNA delivery, where the high molecular weight may complicate control of the release profiles. When plasmid DNA was released from photocrosslinked polyanhydride matrices, DNA recovery was low (approximately 25%). Electrophoresis indicated that the plasmid DNA was released primarily in the relaxed and supercoiled forms, yet the relative fraction of released DNA in the supercoiled form decreased over time. To improve DNA recovery and reduce the damaging effects of polymer degradation, DNA was pre-encapsulated in alginate microparticles, which served as a temporary coating that quickly dissolved upon microparticle release from the polyanhydride matrix. As photocrosslinked polyanhydrides have highly predictable drug release profiles that depend on the polymer erosion rate and implant geometry and not on the entrapped molecule size, they can serve dual purposes in many biomaterial applications where structural support and drug release would be beneficial.

Biodegradable PLGA microparticles for sustained release of a new GnRH antagonist: part II. In vivo performance

Poly (DL-lactide-co-glycolide) microparticles (MP) containing a highly potent peptidic gonadotropin releasing hormone antagonist (degarelix) of interest in the prostate cancer indication were screened for biological performance. Efficacy was tested in a castrated male rat model at 3 doses (0.4, 1.0 and 1.5 mg/kg) and assessed as inhibition of luteinizing hormone (LH) secretion. When increasing the dose, onset of inhibition was faster, inhibition was more intense, and duration of action was prolonged. The MP type was also highly influent. If spray-dried and microextrusion particles exhibited comparable potencies, double emulsion microspheres were significantly less potent, both for onset and duration of inhibition. Interestingly, for the latter type it was found that the degarelix fraction released upon reconstitution in the solution for injection was significantly lower (max 0.3%), in comparison to spray-dried MP (max 2%) or microextrusion (max 4%). With the three types of particles, increasing peptide content was detrimental for duration of action, but only little difference was noticed between particles based on different polymers. At 1.5 mg/kg, LH inhibition was achieved over 36 days with spray-dried MP based on 75/25 lactate/glycolate copolymer. This was superior by 1 week to the performance of unformulated degarelix given at the same dose.

A single vaccination with protein-microspheres elicits a strong CD8 T-cell-mediated immune response against Mycobacterium tuberculosis antigen Mtb8.4

Efficient protein-based vaccine delivery systems are needed to achieve a persistent memory immune response capable of detecting and eliminating intracellular pathogens such as Mycobacterium tuberculosis (TB). We have developed a novel protein-microsphere formulation using the recently discovered TB antigen Mtb8.4. Immunization of mice with a single dose of this Mtb8.4-microsphere formulation resulted in both humoral and cellular responses against Mtb8.4. The Mtb8.4-specific CD8 T-cell responses following a single administration of Mtb8.4-microspheres exceeded that elicited by protein plus adjuvant following multiple immunizations. These results demonstrate the efficacy of a single dose protein-microsphere vaccine for the induction of strong cell-mediated and humoral immune responses against M. tuberculosis antigens.

Self-porating polymersomes of PEG–PLA and PEG–PCL: hydrolysis-triggered controlled release vesicles

Controlled release polymer vesicles are prepared using hydrolysable diblock copolymers of polyethyleneglycol-poly-l-lactic acid (PEG-PLA) or polyethyleneglycol-polycaprolactone (PEG-PCL). Encapsulation studies with a common anti-cancer agent, doxorubicin, show loading comparable to liposomes. Rates of encapsulant release from the hydrolysable vesicles are accelerated with an increased proportion of PEG but are delayed with a more hydrophobic chain chemistry (i.e. PCL). Rates of release also rise linearly with the molar ratio of degradable copolymer blended into membranes of a non-degradable, PEG-based block copolymer (PEG-polybutadiene (PBD)). With all compositions, in both 100 nm and giant vesicles, the average release time (from hours to days) reflects a highly quantized process in which any given vesicle is either intact and retains its encapsulant, or is porated and slowly disintegrates. Poration occurs as the hydrophobic PLA or PCL block is hydrolytically scissioned, progressively generating an increasing number of pore-preferring copolymers in the membrane. Kinetics of this evolving detergent mechanism overlay the phase behavior of amphiphiles with transitions from membranes to micelles allowing controlled release.

Polymeric contrast agent with targeting potential

The Arg-Gly-Asp (RGD) peptide sequence was conjugated to poly (lactid acid), (PLA), microcapsules. These hollow, biodegradable PLGA microcapsules were developed in our laboratory for use as ultrasound contrast agents. By modifying the surface of the agent with a targeting ligand, it can be targeted to a specific address within the body. This application is ideal for both targeted imaging and/or targeted drug delivery. Integrins are membrane-spanning proteins in cells that play a vital role in cell attachment and many other processes. The RGD peptide sequence targets integrins expressed during angiogenesis, alphavbeta3 and alphavbeta5. The integrins specific to angiogenesis are more active during cancer and can be used as receptors for the RGD-conjugated contrast agents. Although the generic RGD sequence is not specific to only alphavbeta3 and alphavbeta5 integrins, it is an excellent candidate for proof of concepts studies such as described here. Preliminary in vitro results indicate that the modified capsules remain highly echogenic (maximum enhancement of 20 dB in vitro) and adhere specifically to a breast cancer cell line MDA-MB-231 in static experiments. However, no adherence is seen with either unmodified capsules (negative control), or when cells that have been pre-saturated with RGD ligand are contacted with modified capsules (positive control). Specific targeting of ultrasound contrast agents could lead the way to imaging as a method for discrimination of malignant from benign.

Molecularly engineered poly(ortho ester) microspheres for enhanced delivery of DNA vaccines

Genetic vaccination using plasmid DNA presents a unique opportunity for achieving potent immune responses without the potential limitations of many conventional vaccines. Here we report the design of synthetic biodegradable polymers specifically for enhancing DNA vaccine efficacy in vivo. We molecularly engineered poly(ortho ester) microspheres that are non-toxic to cells, protect DNA from degradation, enable uptake by antigen-presenting cells, and release DNA rapidly in response to phagosomal pH. One type of microsphere of poly(ortho esters) that releases DNA vaccines in synchrony with the natural development of adaptive immunity, elicited distinct primary and secondary humoral and cellular immune responses in mice, and suppressed the growth of tumour cells bearing a model antigen. This polymer microparticulate system could, with further study, have implications for advancing the clinical utility of DNA vaccines as well as other nucleic-acid-based therapeutics against viral infections and cancer.

Molecular release from a polymeric microreservoir device: Influence of chemistry, polymer swelling, and loading on device performance

A polymeric microreservoir device for controlled-release drug delivery relies on the degradation of thin poly(lactic-co-glycolic acid) membranes that seal each reservoir to achieve pulsatile drug delivery. In vitro release studies in which the swelling of the reservoir membranes was measured indicate a correlation between the release times of various radiolabeled molecules from the devices and the time at which the maximum membrane swelling was observed. Varying the chemistry (lipophilicity/hydrophilicity) or molecular weight of the molecules loaded into the devices did not appear to affect the degree of membrane swelling that was observed, or the time at which the molecules were released from the devices. The amount of drug that was loaded into the reservoirs also did not appear to affect the observed release time of the drug from the device, a significant departure from the behavior of many matrix-type polymeric drug delivery systems.

Vivitrex, an injectable, extended-release formulation of naltrexone, provides pharmacokinetic and pharmacodynamic evidence of efficacy for 1 month in rats

While oral naltrexone is effective in treating alcohol and opiate dependencies, poor patient adherence and widely fluctuating plasma levels limit its efficacy. To overcome these problems, an extended-release formulation of naltrexone (Vivitrex) was developed by encapsulating naltrexone into injectable, biodegradable polymer microspheres. Pharmacokinetic studies in rats demonstrated that this formulation produced stable, pharmacologically relevant plasma levels of naltrexone for approximately 1 month following either subcutaneous or intramuscular injections. While rats receiving placebo microspheres demonstrated a pronounced analgesic response to morphine in the hot-plate test, morphine analgesia was completely blocked in rats treated with extended-release naltrexone. This antagonism began on day 1 following administration and lasted for 28 days. Rats reinjected with extended-release naltrexone 34 days after the initial dose and tested for another 35 days showed consistent suppression of morphine analgesia for an additional 28 days. mu-Opioid receptor density, as measured by [(3)H]DAMGO autoradiography, increased up to two-fold following a single injection of extended-release naltrexone. Saturation binding assays using [(3)H]DAMGO showed changes in the midbrain and striatum at 1 week after extended-release naltrexone administration, and after 1 month in the neocortex. These receptor increases persisted for 2-4 weeks after dissipation of the morphine antagonist actions of naltrexone. These data suggest that therapeutically relevant plasma levels of naltrexone can be maintained using monthly injections of an extended-release microsphere formulation, and that changes in mu-opioid receptor density do not impact its efficacy in suppressing morphine-induced analgesia in the rat. Clinical trials of extended release naltrexone for treating alcohol and opiate dependency are currently ongoing.

Preparation and Characterization of Temperature-Sensitive Poly(N-isopropylacrylamide)-b-poly(d,l-lactide) Microspheres for Protein Delivery

Temperature-sensitive diblock copolymers, poly(N-isopropylacrylamide)-b-poly(D,L-lactide) (PNIPAAm-b-PLA) with different PNIPAAm contents were synthesized and utilized to fabricate microspheres containing bovine serum albumin (BSA, as a model protein) by a water-in-oil-in-water double emulsion solvent evaporation process. XPS analysis showed that PNIPAAm was a dominant component of the microspheres surface. BSA was well entrapped within the microspheres, and more than 90% encapsulation efficiency was achieved. The in vitro degradation behavior of microspheres was investigated using SEM, NMR, FTIR, and GPC. It was found that the microspheres were erodible, and polymer degradation occurred in the PLA block. Degradation of PLA was completed after 5 months incubation in PBS (pH 7.4) at 37 degrees C. A PVA concentration of 0.2% (w/v) in the internal aqueous phase yielded the microspheres with an interconnected porous structure, resulting in fast matrix erosion and sustained BSA release. However, 0.05% PVA produced the microspheres with a multivesicular internal structure wrapped with a dense skin layer, resulting in lower erosion rate and a biphasic release pattern of BSA that was characterized with an initial burst followed by a nonrelease phase. The microspheres made from PNIPAAm-b-PLA with a higher portion of PNIPAAm provided faster BSA release. In addition, BSA release from the microspheres responded to the external temperature changes. BSA release was slower at 37 degrees C (above the LCST) than at a temperature below the LCST. The microspheres fabricated with PNIPAAm-b-PLA having a 1:5 molar ratio of PNIPAAm to PLA and 0.2% (w/v) PVA in the internal aqueous phase provided a sustained release of BSA over 3 weeks in PBS (pH 7.4) at 37 degrees C.

Biodegradable microparticles for sustained release of a new GnRH antagonist – part I: screening commercial PLGA and formulation technologies

The formulation of a new GnRH antagonist (degarelix) in biodegradable poly(DL-lactide-co-glycolide) (PLGA) microparticles was investigated for the development of a 3-month sustained release formulation to treat prostate cancer. The aim was to screen formulation technologies and distinct copolymers to produce microparticles (MP) of different types with good entrapment efficiency (>85%) and peptide purity (>95%) after gamma sterilization. Basically, three types of degarelix-loaded MP (4, 8 and 16% w/w nominal content) were produced with solvent and non-solvent technologies, namely double-emulsion solvent evaporation, spray-drying and two extrusion methods. Besides composition, commercial copolymers differing in residual monomer content and functional group at the carboxylic terminus (acid or ester) were characterized and employed. Peptide loading capacity and purity, as well as shape, size characteristics, and porosity of the produced microparticles were discussed in relation to technology and copolymer choice. Spray-drying and micro-extrusion were the two preferred formulation technologies because of higher entrapment efficiency and better preservation of peptide purity during production and gamma-sterilization. The impact of formulation technologies on the MP characteristics overwhelmed the impact of copolymer selection. Nevertheless, one particular polymer was discarded since it was more susceptible towards radiolytic degradation. The resulting degarelix-MP will be tested in a biological assay for selection of the formulation based on performance.

Multi-pulse drug delivery from a resorbable polymeric microchip device

Controlled-release drug delivery systems have many applications, including treatments for hormone deficiencies and chronic pain. A biodegradable device that could provide multi-dose drug delivery would be advantageous for long-term treatment of conditions requiring pulsatile drug release. In this work, biodegradable polymeric microchips were fabricated that released four pulses of radiolabelled dextran, human growth hormone or heparin in vitro. Heparin that was released over 142 days retained on average 96 +/- 12% of its bioactivity. The microchips were 1.2 cm in diameter, 480-560 microm thick and had 36 reservoirs that could each be filled with a different chemical. The devices were fabricated from poly(L-lactic acid) and had poly(D,L-lactic-co-glycolic acid) membranes of different molecular masses covering the reservoirs. A drug delivery system can be designed with the potential to release pulses of different drugs at intervals after implantation in a patient by using different molecular masses or materials for the membrane.

Simulation of Drug Release from Biodegradable Polymeric Microspheres with Bulk and Surface Erosions

New models are developed to account for the kinetics of drug release from porous, biodegradable polymeric microspheres under the schemes of bulk erosion and surface erosion of the polymer matrix, respectively. Three mechanisms of drug release, namely, drug diffusion, drug dissolution, and polymer erosion jointly govern the overall release process. For bulk erosion, the model incorporates an erosion term into the dissolution and diffusion equation and is solved numerically for various boundary conditions. Dissolution and erosion are defined in the model by introducing three equations which take into account the drug concentration in the liquid phase, virtual solid phase, and effective solid phase. For surface erosion, drug concentrations in liquid and solid phases are defined and a substitution is introduced to convert the moving-boundary problem to a fixed-boundary problem. The resulting differential equations are solved simultaneously to obtain the concentration profile in the liquid and solid phases, respectively. Numerical solutions are provided to illustrate the effects of drug dissolution constant, drug diffusion coefficient, and erosion rate constant. In general, increasing erosion rate, diffusivity, dissolution, and decreasing particle radius enhance the drug release rate. Predictions from the models are also compared with experimental data to verify their validity and possible improvements are proposed.

Formulations containing poly(lactide-co-glycolide) and plasmid DNA expression vectors

DNA expression vectors have the potential to be useful therapeutics for a wide variety of applications. However, development has been hindered by the lack of systems that provide protection from nuclease-based attack, enable cell or tissue localisation, promote adequate gene expression or provide for controlled release. At least one synthetic polymer, poly(lactide-co-glycolide) (PLG), may provide benefit in this regard. This polymer has a history of safe use in humans, has been demonstrated effective as a delivery system, its use is not hindered by composition patents, and Good Manufacturing Practices grade material is readily available from commercial sources. Safety and applicability to clinical medicine have been proven by use of the polymer as a microparticle delivery vehicle for peptides (luteinizing hormone releasing hormone agonist peptides; Lupron Depot [TAP Pharmaceuticals]; Zoladex [AstraZeneca]) and proteins (human growth hormone recombinant protein, Nutropin Depot [Genentech]). This report focuses on the expanding field of PLG-based DNA delivery and provides a review on research and clinical experience with PLG-plasmid formulations.

Characterization of a homologous series of D,L-lactic acid oligomers; a mechanistic study on the degradation kinetics in vitro

A series of low molecular weight polymers of D,L-lactic acid has been synthesized. The oligomers were characterized with respect to molecular weight, glass transition temperature and solubility. The number average molecular weight of the oligomers ranged from 290 to 1320Da. Oligomers with an M(n)<800Da were soluble in buffer at pH 7.4 but insoluble in water and acidic medium. Kinetic studies were performed at pH 1.5, 4.5 and 7.4 using an accelerated in vitro monomer release test. The hydrolytic rate was dependent on molecular weight of oligomer, temperature and pH of the media, with the lowest rate found around pH 4.5. The activation energy was dependent on molecular weight and ranged from 47 to 67kJmol(-1). Random ester cleavage was identified as mechanism of hydrolysis in basic media whereas in acidic media chain-end cleavage ("unzipping") was the mode of action.

Polymer degradation and in vitro release of a model protein from poly(d,l-lactide-co-glycolide) nano- and microparticles

The objective of the study was to investigate the effect of particle size of nano- and microparticles formulated from poly(D,L-lactide-co-glycolide) (50:50 PLGA) on polymer degradation and protein release. Since the surface area to volume ratio is inversely proportional to the particle size, it is hypothesized that the particle size would influence the polymer degradation as well as the release of the encapsulated protein. PLGA nano- and microparticles of approximate mean diameters of 0.1, 1 and 10 microm, containing bovine serum albumin as a model protein, were formulated using a multiple water-in-oil-in-water emulsion solvent evaporation technique. These particles were incubated at 37 degrees C in phosphate-buffered saline (pH 7.4, 154 mM) and the particles were characterized at various time points for molecular weight of polymer, surface-associated polyvinyl alcohol content (PVA), and the particle surface topology using scanning electron microscopy. The supernatants from the above study were analyzed for the released protein and PVA content. Polymer degradation was found to be biphasic in both nano- and microparticles, with an initial rapid degradation for 20-30 days followed by a slower degradation phase. The 0.1 microm diameter nanoparticles demonstrated relatively higher polymer degradation rate (P<0.05) during the initial phase as compared to the larger size microparticles (first order degradation rate constants of 0.028 day(-1), 0.011 day(-1) and 0.018 day(-1) for 0.1, 1 and 10 microm particles, respectively), however the degradation rates were almost similar (0.008 to 0.009 day(-1)) for all size particles during the later phase. All size particles maintained their structural integrity during the initial degradation phase; however, this was followed by pore formation, deformation and fusion of particles during the slow degradation phase. Protein release from 0.1 and 1 microm particles was greater than that from 10 microm size particles. In conclusion, the polymer degradation rates in vitro were not substantially different for different size particles despite a 10- and 100-fold greater surface area to volume ratio for 0.1 microm size nanoparticles as compared to 1 and 10 microm size microparticles, respectively. Relatively higher amounts of the surface-associated PVA found in the smaller-size nanoparticles (0.1 microm) as compared to the larger-size microparticles could explain some of the observed degradation results with different size particles.

The preparation of monodisperse biodegradable polyester nanoparticles with a controlled size

In local drug delivery, nanoparticles based on biodegradable polymers can function as vehicles with controlled drug-release properties. To achieve a well-controlled drug-release profile, control over the particle size is of great importance. Therefore, biodegradable polyester nanoparticles were prepared by the salting-out method. Process variables were varied to study the effect on the particle size. The monodisperse particles obtained were between 100 and 400 nm in size and spherical in shape. It was found that the particle size could be adjusted by varying the preparation conditions upon which the polymer concentration had the most pronounced effect.

Biocompatibility of implantable synthetic polymeric drug carriers: focus on brain biocompatibility

Numerous polymeric biomaterials are implanted each year in human bodies. Among them, drug delivery devices are potent novel powerful therapeutics for diseases which lack efficient treatments. Controlled release systems are in direct and sustained contact with the tissues, and some of them degrade in situ. Thus, both the material itself and its degradation products must be devoid of toxicity. The knowledge and understanding of the criteria and mechanisms determining the biocompatibility of biomaterials are therefore of great importance. The classical tissue response to a foreign material leads to the encapsulation of the implant, which may impair the drug diffusion in the surrounding tissue and/or cause implant failure. This tissue response depends on different factors, especially on the implantation site. Indeed, several organs possess a particular immunological status, which may reduce the inflammatory and immune reactions. Among them, the central nervous system is of particular interest, since many pathologies still need curative treatments. This review describes the classical foreign body reaction and exposes the particularities of the central nervous system response. The recent in vivo biocompatibility studies of implanted synthetic polymeric drug carriers are summarized in order to illustrate the behavior of different classes of polymers and the methodologies used to evaluate their tolerance.

PLG microsphere size controls drug release rate through several competing factors

PURPOSE

Although the rate of drug release from poly(D,L-lactide-co-glycolide) (PLG) microspheres is often modulated by changing fabrication conditions or materials, the specific factors directly controlling the release profiles are often unclear. We have fabricated uniform rhodamine- and piroxicam-containing microspheres, 10 to 100 microm in diameter, to better understand how microsphere size controls drug release.

METHODS

Drug distribution within the microspheres was examined using confocal fluorescence microscopy. The rate of polymer degradation was determined as the change in molecular weight, measured by gel permeation chromatography, during in vitro degradation experiments. Further, changes in the surface and interior morphology of the particles during in vitro degradation were investigated by scanning electron microscopy.

RESULTS

Microsphere size greatly affected drug distribution. Small (approximately 10-microm) microspheres showed an essentially uniform drug distribution. Larger (approximately 100-microm) microspheres showed redistribution of drug to specific regions of the microspheres. Rhodamine partitioned to the surface and piroxicam partitioned to the interior of large PLG microspheres. Further, the rate of polymer degradation increased with microsphere size, possibly the result of a more acidic interior caused by increased accumulation of hydrolyzed polymer products in larger particles. Finally, larger microspheres developed a more porous interior structure during the drug release.

CONCLUSION

Microsphere size affects drug release not only through changes in diffusion rates but also through secondary effects including drug distribution in the particle, polymer degradation rate, and microsphere erosion rates.

A model to evaluate the pharmacokinetic and pharmacodynamic variables of extended-release products using in vivo tissue microdialysis in humans: bupivacaine-loaded microcapsules

Biodegradable microcapsules produce an ultra-long duration of local anesthesia. We hypothesized that this duration is caused by the sustained-release of bupivacaine from the microcapsules into the surrounding tissue. Previous studies investigated the pharmacokinetics (PKs) of bupivacaine after release from microcapsules and absorption into the systemic circulation. Microdialysis sampling can determine the PKs of any drug at its site of injection. This study was performed to characterize the PKs of bupivacaine and dexamethasone released from microcapsules at a subcutaneous injection site over a 96-h period in volunteers. Bupivacaine concentrations were compared with clinical variables of local anesthetic blockade. This study demonstrates that bupivacaine is released in a sustained manner from microcapsules, that bupivacaine concentrations increase for 24-34 h after microcapsule injection, and that analgesia parallels the tissue bupivacaine concentration obtained by microdialysis. Analgesia was equally rapid in onset with aqueous and microcapsule bupivacaine (P = 0.23). Analgesia was still present at 78% of microcapsule-injected sites after 96 h, significantly longer than for aqueous bupivacaine (P < 0.001). Mild pruritus was the most common side effect, occurring with 56% of the microcapsule injections. Dexamethasone-containing bupivacaine microcapsules are well tolerated and produce a prolonged duration of skin analgesia. Systemic absorption of bupivacaine produces higher peak plasma levels after aqueous injection than after microcapsule injection, despite the injection of a threefold larger load of bupivacaine in the latter.

IMPLICATIONS

Microcapsules loaded with bupivacaine and dexamethasone and administered by subcutaneous injection produce prolonged cutaneous anesthesia and analgesia. Determination of local tissue pharmacokinetic variables of bupivacaine by microdialysis confirms that the prolonged duration of anesthesia is caused by the extended release characteristics of the microcapsules.

Controlled release of anti-cocaine catalytic antibody from biodegradable polymer microspheres

Recent reports have shown that anti-cocaine catalytic monoclonal antibody 15A10 reduces the toxic effect of cocaine by increasing its breakdown to systemically inert products ecgonine methylester and benzoic acid. This study reports the microencapsulation of antibody 15A10 using biodegradable poly (lactic-glycolic) acid (PLGA) by double emulsion technique. Formulation parameters such as protein loading, polymer molecular weight and the presence of zinc carbonate were studied for their effects on in-vitro release of antibody from microspheres. The initial burst release was decreased by the reduction of the protein (as % of total ingredients) in the formulation. Although changing the polymer molecular weight did not cause a reduction in initial burst release, it was effective in improving the release rate. The inclusion of zinc carbonate in microsphere preparation resulted in increase in initial burst release. An in-vivo study in mice revealed the presence of antibody in blood up to ten days following subcutaneous injections. These data demonstrate a potential for a sustained-release formulation of monoclonal antibody 15A10 for treatment of cocaine addiction.

Tissue reaction and biodegradation of implanted cross-linked high amylose starch in rats

The biocompatibility and degradation characteristics of cross-linked high amylose starch (Contramid were investigated in rats over 4 months. Contramid pellets (3-mm diameter and thickness) obtained by direct compression, were implanted subcutaneously and intramuscularly. On sequential time points, macroscopic observations of implantation sites were performed and tissue samples were removed, fixed, and histologically evaluated. No macroscopic inflammatory reaction was observed with Contramid.. Upon histologic examination, inflammatory reaction produced by Contramid was moderate and restricted to implantation sites. The sequence of inflammatory events with Contramid was similar regardless of implantation site. Degradation of Contramid pellets was characterized by fragmentation with formation of fibrovascular septa and phagocytosis by macrophages. Finally Contramid was mostly absorbed by the end of the 4-month period and substituted by adipocytes. It has been demonstrated that Contramid is a biocompatible and absorbable material.

Fabrication of PLGA scaffolds using soft lithography and microsyringe deposition

Construction of biodegradable, three-dimensional scaffolds for tissue engineering has been previously described using a variety of molding and rapid prototyping techniques. In this study, we report and compare two methods for fabricating poly(DL-lactide-co-glycolide) (PLGA) scaffolds with feature sizes of approximately 10-30 microm. The first technique, the pressure assisted microsyringe, is based on the use of a microsyringe that utilizes a computer-controlled, three-axis micropositioner, which allows the control of motor speeds and position. A PLGA solution is deposited from the needle of a syringe by the application of a constant pressure of 20-300 mm Hg, resulting in a controlled polymer deposition. The second technique is based on 'soft lithographic' approaches that utilize a poly(dimethylsiloxane) mold. Three variations of the second technique are presented: polymer casting, microfluidic perfusion, and spin coating. Polymer concentration, solvent composition, and mold dimensions influenced the resulting scaffolds as evaluated by light and electron microscopy. As a proof-of-concept for scaffold utility in tissue engineering applications, multilayer structures were formed by thermal lamination, and scaffolds were rendered porous by particulate leaching. These simple methods for forming PLGA scaffolds with microscale features may serve as useful tools to explore structure/function relationships in tissue engineering.

Peripheral nerve regeneration with sustained release of poly(phosphoester) microencapsulated nerve growth factor within nerve guide conduits

Prolonged delivery of neurotrophic proteins to the target tissue is valuable in the treatment of various disorders of the nervous system. We have tested in this study whether sustained release of nerve growth factor (NGF) within nerve guide conduits (NGCs), a device used to repair injured nerves, would augment peripheral nerve regeneration. NGF-containing polymeric microspheres fabricated from a biodegradable poly(phosphoester) (PPE) polymer were loaded into silicone or PPE conduits to provide for prolonged, site-specific delivery of NGF. The conduits were used to bridge a 10 mm gap in a rat sciatic nerve model. Three months after implantation, morphological analysis revealed higher values of fiber diameter, fiber population and fiber density and lower G-ratio at the distal end of regenerated nerve cables collected from NGF microsphere-loaded silicone conduits, as compared with those from control conduits loaded with either saline alone, BSA microspheres, or NGF protein without microencapsulation. Beneficial effects on fiber diameter, G-ratio and fiber density were also observed in the permeable PPE NGCs. Thus, the results confirm a long-term promoting effect of exogenous NGF on morphological regeneration of peripheral nerves. The tissue-engineering approach reported in this study of incorporation of a microsphere protein release system into NGCs holds potential for improved functional recovery in patients whose injured nerves are reconstructed by entubulation.

Reduced adhesion of blood cells to biodegradable polymers by introducing phosphorylcholine moieties

Aliphatic polyesters are believed to be good biocompatible polymers for tissue engineering because of their biodegradability and nontoxicity of the degradated products. However, it is necessary to reduce the nonspecific protein adsorption for the application of biodegradable polymers to drug delivery systems or antiadhesive membranes. We hypothesized that novel biodegradable polymers could be synthesized by introducing phosphorylcholine moieties into aliphatic polyesters. The L-lactide was polymerized in the presence of L-alpha-glycelophosphorylcholine (LGPC) using stannous octate as the catalyst. The molecular weight and crystallinity of poly(L-lactide) (PLLA)-based phospholipid polymers (PLLA-PC) decreased with an increase in the composition of the LGPC unit in the PLLA-PC. The hydrolysis of the PLLA-PC was evaluated by soaking the polymer membranes in a phosphate buffer solution. The rate of weight loss was increased with increasing the LGPC units in PLLA-PC. The surface analysis of the membranes using an X-ray photoelectron microscope showed the composition of phosphorylcoline groups on the surface. The amount of adsorbed protein and adherent blood cell on the polymer surface was decreased with introducing LGPC unit. PLLA-PC is a promising biodegradable polymer having blood compatibility and antiadhesive property.

Synthesis and properties of star-shaped polylactide attached to poly(amidoamine) dendrimer

Star-shaped polylactide was synthesized by bulk polymerization of lactide with poly(amidoamine) (PAMAM) dendrimer as initiator, which was marked as PAMAM-g-PLA for simplicity. The nonlinear architecture of PAMAM-g-PLA was confirmed by gel permeation chromatograph, nuclear magnetic resonance, and differential scanning calorimetry analysis. Unlike the linear polylactide (PLA) with similar molecular weight, PAMAM-g-PLA had a higher hydrophilicity and a faster degradation rate because of shortened polymer chains and increased polar terminal endgroups due to its branch structure. The highly branched structure significantly accelerated the release of water-soluble bovine serum albumin from PAMAM-g-PLA microspheres, whereas the linear PLA with similar molecular weight exhibited an initial time lag release. This star polymer may have potential applications for hydrophilic drug delivery in tissue engineering, including growth factor and antibodies to induce tissue regeneration, by adjusting the chain lengths of PLA branches.

Polyphosphoesters in drug and gene delivery

Polymers with repeating phosphoester bonds in the backbone are structurally versatile, and biodegradable through hydrolysis, and possibly enzymatic digestion at the phosphoester linkages under physiological conditions. These biodegradable polyphosphoesters are appealing for biological and pharmaceutical applications because of their potential biocompatibility and similarity to bio-macromolecules such as nucleic acids. In the first part of this review, we will focus on one particular structure synthesized by extending oligomeric lactide prepolymers with ethylphosphate groups. This amorphous to semi-crystalline polymer is promising in delivering anti-cancer therapeutics in the form of microspheres. In the second half, we will discuss the conjugation of charged groups to the side chain of the phosphate, constituting one of the few biodegradable cationic polymers in the field for non-viral gene delivery. Capable of delivering exogenous genes to a cell nucleus or providing an extracellular sustained release of DNA, these cationic polyphosphoesters also serve as a valuable model to understand the important characteristics that render a polymer an effective gene carrier.

Synthesis of pegylated immunonanoparticles

PURPOSE

This work describes the synthesis of pegylated immunonanoparticles by conjugation of an anti-transferrin receptor monoclonal antibody (MAb) to maleimide-grafted pegylated nanoparticles prepared from poly(lactic acid) (PLA) and a bi-functional polyethyleneglycol (PEG).

METHODS

Maleimide-PEG3500-PLA40000 and methoxyPEG2600-PLA40000 copolymers were synthesized by ring opening polymerization of L-lactide using stannous octoate as catalyst. Pegylated nanoparticles were prepared from these copolymers by a multiple emulsion/solvent evaporation method and thiolated OX26 MAb was conjugated through the maleimide function located at the distal end of the PEG spacer. The pegylated immunonanoparticles were characterized by quasi-elastic light scattering, gel permeation chromatography, turbidimetry assays, and transmission electron microscopy.

RESULT

NMR spectroscopy confirmed the synthesis of both copolymers and the preservation of the maleimide function. The pegylated immunonanoparticles had an average diameter of 121 +/- 5 nm and appeared spherical by transmission electron microscopy. The number of OX26 MAb molecules conjugated per individual pegylated nanoparticle was 67 +/- 4. The MAb conjugated to the surface of the pegylated immunonanoparticle was visualized directly by electron microscopy using a conjugate of 10 nm gold and an anti-mouse immunoglobulin secondary antibody.

CONCLUSION

Pegylated immunonanoparticles can be synthesized with bifunctional PEG derivatives that bridge the nanoparticle and the targeting MAb. This novel formulation may enable the targeted delivery of small molecules, protein drugs, and gene medicines.

Immunization with low doses of HIV-1 tat DNA delivered by novel cationic block copolymers induces CTL responses against Tat

Cytotoxic T cell responses are key to the control of intracellular pathogens including HIV-1. In particular, HIV-1 vaccines based on regulatory proteins, such as Tat, are aimed at controlling HIV-1 replication and at blocking disease development by inducing cytotoxic T cell responses. Naked DNA is capable of inducing such responses but it requires several inoculations of high amounts of DNA, and/or prime-boost regimens. Here, we show that a novel class of cationic block copolymers protect the DNA from DNAse I digestion, and improve DNA delivery to antigen-presenting cells (APCs) after intramuscular (i.m.) vaccination. In particular, three cationic block copolymers (K1, K2 and K5) were used to deliver the HIV-1 pCV-tat DNA vaccine in BALB/c mice. The results indicate that vaccination with a very low dose (1 microg) of pCV-tat delivered by the cationic block copolymer K2 is safe and, as compared to naked DNA (up to 30 microg), greatly increases the CTL response against Tat, which was detected in all animals in the absence or in the presence of re-stimulation.

Layer-by-layer engineering of biocompatible, decomposable core-shell structures

The objective of the present investigation was to fabricate composite colloidal particles consisting of a sacrificial, decomposable template of biodegradable nature covered with biocompatible polyelectrolyte multilayers using the layer-by-layer sequential adsorption technique. Poly-dl-lactic acid and poly(dl-lactic-co-glycolic acid) were chosen to design the microparticulate template, and a preliminary feasibility study was carried out with poly(styrene sulfonate sodium)-poly(allylamine hydrochloride) as shell components. The properties of both core-shell and hollow structures obtained by core dissolution were characterized by confocal laser scanning microscopy, microelectrophoresis, scanning force microscopy, and scanning electron microscopy. The concept was then extended to biocompatible polyelectrolytes as shell wall building blocks to deduce stable hollow capsules with tailored properties. Uniform, complete coating with oppositely charged polyelectrolyte pairs was achieved for all the combinations investigated. The results demonstrate that polyester microparticles could serve as viable alternative components to conventionally employed templates to derive hollow capsules with defined size, shape, and shell thickness. With all the components used for fabrication being biocompatible, these polyelectrolyte capsules may find interesting applications in the fields of biology, biochemistry, biotechnology, and drug delivery.