Parenteral protein delivery systems using biodegradable polyesters of ABA block structure, containing hydrophobic poly(lactide-co-glycolide) A blocks and hydrophilic poly(ethylene oxide) B blocks

Effect of polymer source on in vitro drug release from PLGA microspheres

Determination of the qualitative (Q1) sameness of poly (lactic-co-glycolic acid) (PLGA) polymers can be very challenging due to PLGA being a random copolymer with inherent heterogeneity. Performance variation of PLGA microsphere drug product as a result of altered PLGA characteristics has been recognized as a critical limiting factor in product development. It has been reported that PLGA characteristics and degradation profiles are sensitive to minor differences in the manufacturing and control processes. Accordingly, the objectives of the present research were: 1) to determine minor differences in the physicochemical properties (such as inherent viscosity/molecular weight (Mw), blockiness, and glass transition temperature (Tg)) and the hydrolytic degradation profiles of PLGA polymers from different sources; and 2) to investigate the impact of any differences determined in (1) on the physicochemical properties (Q3) and in vitro release of leuprolide acetate microspheres. PLGA polymers were purchased from three different sources with similar inherent viscosity/Mw, monomer (Lactide/Glycolide) ratio, and end group as per the manufacturers' certificate of analysis (COA). These PLGA polymers were evaluated using the same in-house methods and showed differences in their properties such as Mw and blockiness. Three compositionally equivalent leuprolide acetate microspheres were prepared via a solvent evaporation method using the three PLGA polymers from different sources. The prepared microspheres showed differences in their physicochemical properties (such as particle size, porosity and average pore diameter) as well as in their in vitro drug release characteristics (burst effect and release rate). These results indicate that polymer source related variations have the potential to significantly impact the Q3 sameness and therapeutic performance of long-acting PLGA microspheres. The fundamental understanding gained on polymer properties will make a critical contribution to the development of quality control strategies as well as to future regulatory guidance on the evaluation of such complex drug products.

Translating the fabrication of protein-loaded poly(lactic-co-glycolic acid) nanoparticles from bench to scale-independent production using microfluidics

In the formulation of nanoparticles, poly(lactic-co-glycolic acid) (PLGA) is commonly employed due to its Food and Drug Administration and European Medicines Agency approval for human use, its ability to encapsulate a variety of moieties, its biocompatibility and biodegradability and its ability to offer a range of controlled release profiles. Common methods for the production of PLGA particles often adopt harsh solvents, surfactants/stabilisers and in general are multi-step and time-consuming processes. This limits the translation of these drug delivery systems from bench to bedside. To address this, we have applied microfluidic processes to develop a scale-independent platform for the manufacture, purification and monitoring of nanoparticles. Thereby, the influence of various microfluidic parameters on the physicochemical characteristics of the empty and the protein-loaded PLGA particles was evaluated in combination with the copolymer employed (PLGA 85:15, 75:25 or 50:50) and the type of protein loaded. Using this rapid production process, emulsifying/stabilising agents (such as polyvinyl alcohol) are not required. We also incorporate in-line purification systems and at-line particle size monitoring. Our results demonstrate the microfluidic control parameters that can be adopted to control particle size and the impact of PLGA copolymer type on the characteristics of the produced particles. With these nanoparticles, protein encapsulation efficiency varies from 8 to 50% and is controlled by the copolymer of choice and the production parameters employed; higher flow rates, combined with medium flow rate ratios (3:1), should be adopted to promote higher protein loading (% wt/wt). In conclusion, herein, we outline the process controls for the fabrication of PLGA polymeric nanoparticles incorporating proteins in a rapid and scalable manufacturing process. Scale-independent production of polymer nanoparticles.

Combined Poly(Lactide-Co-Glycolide) Microspheres Containing Diphtheria Toxoid for a Single-shot Immunization

To develop a single-shot vaccine containing diphtheria toxoid (DT) with a sufficient immune response, poly(lactide-co-glycolide) (PLGA) microspheres were prepared by water-in-oil-in-water double emulsification and solvent extraction techniques using low or high-molecular-weight PLGA (LMW-MS or HMW-MS). Stearic acid (SA) was introduced to HMW-MS (HMW/SA-MS) as a release modulator. Mean particle sizes (dvs, μm) varied between the prepared microspheres, with LMW-MS, HMW-MS, and HMW/SA-MS having the sizes of 29.83, 110.59, and 69.5 μm, respectively; however, the protein entrapment and loading efficiency did not vary, with values of 15.2-16.8 μg/mg and 61-75%, respectively. LMW-MS showed slower initial release (~ 2 weeks) but faster and higher release of antigen during weeks 3~7 than did HMW-MS. HMW/SA-MS showed rapid initial release followed by a continuous release over an extended period of time (~ 12 weeks). Mixed PLGA microspheres (MIX-MS), a combination of HMW/SA-MS and LMW-MS (1:1), demonstrated a sufficient initial antigen release and a subsequent boost release in a pulsatile manner. Serum antibody levels were measured by ELISA after DT immunization of Balb/c mice, and showed a greater response to MIX-MS than to alum-adsorbed DT (control). A lethal toxin challenge test with MIX-MS (a DT dose of 18 Lf) using Balb/c mice revealed complete protection, indicating a good candidate delivery system for a single-shot immunization.

Multilayered Inorganic Microparticles for Tunable Dual Growth Factor Delivery

There is an increasing need to control the type, quantity, and timing of growth factors released during tissue healing. Sophisticated delivery systems offering the ability to deliver multiple growth factors with independently tunable kinetics are highly desirable. Here, a multilayered, mineral coated micro-particle (MCMs) platform that can serve as an adaptable dual growth factor delivery system is developed. Bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) are bound to the mineral coatings with high binding efficiencies of up to 80%. BMP-2 is firstly bound onto a 1st mineral coating layer; then VEGF is bound onto a 2nd mineral coating layer. The release of BMP-2 is sustained over a period of 50 days while the release of VEGF is a typical two-phase release with rapid release in the first 14 days and more sustained release for the following 36 days. Notably, the release behaviors of both growth factors can be independently tailored by changing the intrinsic properties of the mineral coatings. Furthermore, the release of BMP-2 can be tuned by changing the thickness of the 2nd layer. This injectable microparticle based delivery platform with tunable growth factor release has immense potential for applications in tissue engineering and regenerative medicine.

Method for preparation, programming, and characterization of miniaturized particulate shape-memory polymer matrices

Their capability to change their shape on demand has created significant interest for shape-memory polymers (SMPs) in minimally invasive surgery. To evaluate the miniaturization of SMP matrices for small-sized implants or controlled release systems, a strategy to prepare and evaluate microsized SMP model particles is required. This methodological study reports the emulsion-based preparation of ~30 μm microparticles (MPs) from a phase-segregated SMP, poly(ε-caprolactone) [PCL] and poly(ω-pentadecalactone) [PPDL], with a particular focus on the effects of process parameters such as polymer solvents or stabilizer type/concentration on formation and size distribution of SMP MPs. Processes for the preparation of SMP MP-loaded water-soluble polymer films with tailored mechanical properties were developed and applied for programming the SMP MP to a temporary ellipsoid shape by film stretching. For the functional evaluation of shape recovery of MPs, a light microscopy-based setup with temperature control is proposed by which the stimuli-induced switching of the microsized SMP matrices could be confirmed. Overall, by applying this methodological strategy to various thermoplastic SMPs, a routine to identify and characterize the microscale functionality of SMPs in miniaturized applications will be broadly accessible.

Lysozyme release and polymer erosion behavior of injectable implants prepared from PLGA-PEG block copolymers and PLGA/PLGA-PEG blends

PURPOSE

We evaluated the controlled release of lysozyme from various poly(D,L-lactic-co-glycolic acid) (PLGA) 50/50-polyethylene glycol (PEG) block copolymers relative to PLGA 50/50.

METHODS

Lysozyme was encapsulated in cylindrical implants (0.8 mm diameter) by a solvent extrusion method. Release studies were conducted in phosphate buffered saline +0.02% Tween 80 (PBST) at 37°C. Lysozyme activity was measured by a fluorescence-based assay. Implant erosion was evaluated by kinetics of polymer molecular weight decline, water uptake, and mass loss.

RESULTS

Lysozyme release from an AB15 di-block copolymer (15% 5 kDa PEG, PLGA 28 kDa) was very fast, whereas an AB10 di-block copolymer (with 10% 5 kDa PEG, PLGA 45 kDa) and ABA10 tri-block copolymer (with 10% 6 kDa PEG, PLGA 27 kDa) showed release profiles similar to PLGA. We achieved continuous lysozyme release for up to 4 weeks from AB10 and ABA10 by lysozyme co-encapsulation with the pore-forming and acid-neutralizing MgCO3, and from AB15 by co-encapsulation of MgCO3 and blending AB15 with PLGA. Lysozyme activity was mostly recovered during 4 weeks.

CONCLUSIONS

These block co-polymers may have utility either alone or as PLGA blends for the controlled release of proteins.

Shape-memory effect of micro-/nanoparticles from thermoplastic multiblock copolymers

The miniaturization and retained full shape-memory functionality with particle switching to different predefined shapes is reported for semi-crystalline multiblock copolymer matrices with all dimensions in the low micrometer-range. A matrix size-induced reduction of crystallinity suggests limitations of functionality in the low nanometer range. Applications as actuators in microdevices or as microcarriers with switchable shapes for modulated biorecognition are suggested.

Effect of MgO nanofillers on burst release reduction from hydrogel nanocomposites

In this study, MgO nanoparticles are applied to control the initial burst release by modification of matrix structure, thereby affecting the release mechanism. The effects of MgO nanofiller loading on the in vitro release of a model drug are investigated. Surface topography and release kinetics of hydrogel nanocomposites are also studied in order to have better insight into the release mechanism. It was found that the incorporation of MgO nanofillers can significantly decrease the initial burst release. The effect of genipin (GN) on burst release was also compared with MgO nanoparticles, and it was found that the impact of MgO on burst release reduction is more obvious than GN; however, GN cross-linking caused greater final release compared to blanks and nanocomposites. To confirm the capability of nanocomposite hydrogels to reduce burst release, the release of β-carotene in Simulated Gastric Fluid and Simulated Intestinal Fluid was also carried out. Thus, the application of MgO nanoparticles seems to be a promising strategy to control burst release.

Synthesis and properties of a star-shaped poly(ϵ-caprolactone)-ibuprofen conjugate

A series of novel star-shaped poly(ϵ-caprolactone) (PCL) biodegradable polyesters were synthesized through ring-opening polymerization of ϵ-caprolactone in the presence of a poly(amidoamine) (PAMAM) dendrimer initiator. The polymers (PAMAM/PCLs) were obtained with a high yield (92%) and a number-average molecular weight of up to 14 000 g/mol. The nonlinear structure of PAMAM/PCLs was confirmed by nuclear magnetic resonance, gel-permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. Thermal analysis indicated that the star-shaped PAMAM/PCLs had a melting point, degree of crystallinity, glass transition temperature and maximum decomposition temperature all lower than those of linear PCL. Ibuprofen (IBU), a popular non-steroidal anti-inflammatory drug, was co-valently (ester) bonded to the PAMAM/PCL molecules using the DCC/DMAP coupling method (DCC, N,N'-dicyclohexylcarbodiimide; DMAP, 4-(dimethylamino)pyridine). A high drug content (33.1 mol%) in the conjugate was obtained. The in-vitro drug-release profiles of IBU from the PAMAM/PCL/IBU conjugate were examined and found adequate for drug-carrier applications of our star-shaped polymers.

Suppression of cell attachment and protein adsorption onto amphiphilic polylactide-grafted dextran films

To develop novel biodegradable biomedical materials, polylactide-grafted dextrans (Dex-g-PLA)s having various lengths, numbers of graft chains and sugar units were synthesized using the trimethylsilyl (TMS) protection method. To explore the possibility of using Dex-g-PLA as a biomedical soft-material, the contact angle, cell attachment and protein adsorption properties of the films prepared from these biodegradable and amphiphilic graft co-polymers were investigated. The poly-L-lactide (PLLA) film did not absorb water at all because of its high hydrophobicity, while the graft co-polymer films started immediately to swell after immersion in PBS. The percentage of water absorption at equilibrium increased with increasing sugar unit content. The receding contact angle of the Dex-g-PLA films against water was smaller than that of the PLLA film. The receding contact angle of Dex-g-PLA films against water decreased with increasing the sugar unit content. The top surface of the Dex-g-PLA film was suggested to be covered with hydrophilic Dex segments by means of annealing in water and to afford the wettable surface. Such a wettable surface led to the suppression of cell attachment and protein adsorption onto the film.

Polyanhydride microparticles enhance dendritic cell antigen presentation and activation

The present study was designed to evaluate the adjuvant activity of polyanhydride microparticles prepared in the absence of additional stabilizers, excipients or immune modulators. Microparticles composed of varying ratios of either 1,6-bis(p-carboxyphenoxy)hexane (CPH) and sebacic acid or 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane and CPH were added to in vitro cultures of bone marrow-derived dendritic cells (DCs). Microparticles were efficiently and rapidly phagocytosed by DCs in the absence of opsonization and without centrifugation or agitation. Within 2h, internalized particles were rapidly localized to an acidic, phagolysosomal compartment. By 48 h, only a minor reduction in microparticle size was observed in the phagolysosomal compartment, indicating minimal particle erosion consistent with being localized within an intracellular microenvironment favoring particle stability. Polyanhydride microparticles increased DC surface expression of major histocompatability complex class II, the co-stimulatory molecules CD86 and CD40, and the C-type lectin CIRE (murine DC-SIGN; CD209). In addition, microparticle stimulation of DCs also enhanced secretion of the cytokines IL-12p40 and IL-6, a phenomenon found to be dependent on polymer chemistry. DCs cultured with polyanhydride microparticles and ovalbumin induced polymer chemistry-dependent antigen-specific proliferation of both CD4(+) OT-II and CD8(+) OT-I T cells. These data indicate that polyanhydride particles can be tailored to take advantage of the potential plasticity of the immune response, resulting in the ability to induce immune protection against many types of pathogens.

Hydrophilic polyester microspheres: effect of molecular weight and copolymer composition on release of BSA

Purpose

To study the release of a model protein, bovine serum albumin (BSA), from microspheres of an hydroxylated aliphatic polyester, poly(lactic-co-hydroxymethyl glycolic acid) (PLHMGA).

Methods

BSA-loaded microspheres were prepared by a double emulsion solvent evaporation method. The effect of copolymer composition and the molecular weight of the copolymer on in vitro release and degradation were studied. The integrity of the released BSA was studied by fluorescence spectroscopy and size exclusion chromatography (SEC).

Results

Microspheres prepared from PLHMGA with 50% hydroxymethyl glycolic acid (HMG) showed a burst release followed by a sustained release in 5–10 days. PLHMGA microspheres prepared from a copolymer with 35% and 25% HMG showed a sustained release of BSA up to 80% for 30 and 60 days, respectively. The release of BSA was hardly affected by the molecular weight of the polymer. Fluorescence spectroscopy and SEC showed that the released BSA preserved its structural integrity. Microspheres were fully degradable, and the degradation time increased from ~20 days to 60 days when the HMG content decreased from 50% to 25%.

Conclusions

Taking the degradation and release data together, it can be concluded that the release of BSA from PLHMGA microspheres is governed by degradation of the microspheres.

Effect of polymer chemistry and fabrication method on protein release and stability from polyanhydride microspheres

The release kinetics and stability of ovalbumin encapsulated into polyanhydride microspheres with varying chemistries were studied. Polymers based on the anhydride monomers sebacic acid (SA), 1,6-bis(p-carboxyphenoxy)hexane (CPH), and 1,8-bis (p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) were utilized. Microspheres were fabricated using two non-aqueous methods: a solid/oil/oil double emulsion technique and cryogenic atomization. The studies showed that the two fabrication methods did not significantly affect the release kinetics of ovalbumin, even though the burst release of the protein was a function of the fabrication method and the polymer chemistry. Antigenic stability of ovalbumin released from microspheres prepared by cryogenic atomization was studied by western blot analysis. These studies indicate that the amphiphilic CPTEG:CPH polyanhydrides preserved protein structure and enhanced protein stability by preserving the immunological epitopes of released protein.

One-step electrohydrodynamic production of drug-loaded micro- and nanoparticles

The objective of this work was to produce drug-loaded nanometre- and micrometre-scale particles using a single-step process that provides control over particle size and size distribution. Co-axial electrohydrodynamic processing was used, at ambient temperature and pressure, with poly(lactic-co-glycolic acid) as the polymeric coating material and oestradiol as the encapsulated drug. The particle diameter was varied from less than 120 nm to a few micrometres, by simple methodical adjustments in the processing parameters (polymer concentration and applied voltage). In vitro studies were performed to determine the drug release profile from the particles during unassisted and ultrasound-stimulated degradation in simulated body fluid. An encapsulation efficiency of approximately 70% was achieved and release of the drug was sustained for a period of over 20 days. Exposing the particles to ultrasound (22.5 kHz) increased the rate of release by approximately 8 per cent. This processing method offers several advantages over conventional emulsification techniques for the preparation of drug-loaded particles. Most significantly, process efficiency and the drug's functionality are preserved, as complex multistep processing involving harsh solvents, other additives and elevated temperatures or pressures are avoided. Production rates of 10(12) particles min(-1) can be achieved with a single pair of co-axial needles and the process is amenable to being scaled up by using multiple sets.

Cationic poly(VCL-AETA) hydrogels and ovalbumin (OVA) release in vitro

The objective of this research is to explore the synthesis of a new family of water soluble polycationic copolymeric precursors that could be photo-crosslinked into hydrogels. The in vitro control release of ovalbumin protein (OVA) from this family of hydrogels was also studied to assess the biomedical potential of this new family polycationic hydrogels. A series of novel poly(VCL-AETA) copolymer hydrogels was fabricated in an aqueous medium via photo-induced polymerization and crosslinking of hydrophobic N-vinylcaprolactam (VCL) and hydrophilic [2-(acryloxy)ethyl]trimethylammonium chloride (AETA) monomers over a wide range of VCL to AETA feed molar ratios of 2:1, 1:1, 1:2, 1:5. N,N'-methylene bisacrylamide (MBA) was used as a crosslinker. Ovalbumin (OVA), a model antigen, was preloaded into poly(VCL-AETA) hydrogel precursors and its release profiles in pH 7.4 PBS at 37 degrees C were investigated as a function of VCL to AETA monomer feed ratios over a period of 4 weeks. The in vitro results showed that OVA initial burst and subsequent sustained releases could be controlled by 3 material parameters: the hydrophobic VCL to hydrophilic AETA monomer feed ratios, crosslinking density and hydrogel degradation rate. Thus, the hydrophobic-hydrophilic VCL-AETA hydrogel network for controlled OVA release could offer advantages over organic solvent-based single component polymer system. However, these in vitro OVA release profiles may change in an in vivo environment.

Reduction in burst release of PLGA microparticles by incorporation into cubic phase-forming systems

A high initial burst release of an phosphorothioate oligonucleotide drug from poly(lactide-co-glycolide) (PLGA) microparticles prepared by the w/o/w solvent extraction/evaporation was reduced by incorporating the microparticles into the following glycerol monooleate (GMO) formulations: 1) pure molten GMO, 2) preformed cubic phase (GMO+water) or 3) low viscosity in situ cubic phase-forming formulations (GMO+water+cosolvent). The in situ cubic phase-forming formulations had a low viscosity in contrast to the first two formulations resulting in good dispersability of the microparticles and good syringability/injectability. Upon contact with an aqueous phase, a highly viscous cubic phase formed immediately entrapping the microparticles. A low initial burst and a continuous extended release over several weeks was obtained with all investigated formulations. The drug release profile could be well controlled by the cosolvent composition with the in situ systems.

Materials in particulate form for tissue engineering. 2. Applications in bone

Materials in particulate form have been the subjects of intensive research in view of their use as drug delivery systems. While within this application there are still issues to be addressed, these systems are now being regarded as having a great potential for tissue engineering applications. Bone repair is a very demanding task, due to the specific characteristics of skeletal tissues, and the design of scaffolds for bone tissue engineering presents several difficulties. Materials in particulate form are now seen as a means of achieving higher control over parameters such as porosity, pore size, surface area and the mechanical properties of the scaffold. These materials also have the potential to incorporate biologically active molecules for release and to serve as carriers for cells. It is believed that the combination of these features would create a more efficient approach towards regeneration. This review focuses on the application of materials in particulate form for bone tissue engineering. A brief overview of bone biology and the healing process is also provided in order to place the application in its broader context. An original compilation of molecules with a documented role in bone tissue biology is listed, as they have the potential to be used in bone tissue engineering strategies. To sum up this review, examples of works addressing the above aspects are presented.

Effect of various formulation parameters on the properties of polymeric nanoparticles prepared by multiple emulsion method

This work evaluates and interprets underlying mechanisms behind various aspects related to preparation and physical characteristics of polymeric nanoparticles (NP). These were prepared from different biodegradable polymers according to a water-in-oil-in-water emulsion solvent evaporation method. Polymers used were poly(lactic-co-glycolic) acid (PLGA), poly (lactic acid) (PLA), (PLA-PEG-PLA) triblock and (PLA-PEG-PLA)n multi-block co-polymers. A model DNA, as an example of a hydrophilic drug, was encapsulated in the internal aqueous phase. The primary emulsion was prepared using a high shear turbine mixer. The secondary emulsion was prepared by high-pressure homogenization. Surface morphology and internal structure were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Influence of process variables on the physical properties of NP has been studied. Release of DNA was evaluated. In addition, changes occurring to NP porosity and surface area during degradation were followed. Nanoparticle size was ranging between 200-700 nm, according to the preparation conditions. Homogenizing pressure, concentration of the emulsifying agent used, polymer concentration and type and the concentration of a cryoprotectant had variable effects on NP size, surface area and porosity. Batches of NP where no emulsifying agent was added were obtained successfully. The release rate of the DNA from NP was mainly dependent on porosity, which varied significantly among used polymers. The preparation technique was efficient in encapsulating the model DNA and will be used for plasmid encapsulation in a future work.

Synthesis of poly(sebacic anhydride)-indomethacin controlled release composites via supercritical carbon dioxide assisted impregnation

Poly(sebacic anhydride), PSA and indomethacin drug composite (DC) formulations were prepared using supercritical CO(2) (sc-CO(2)) aided mixing. The effect of the experimental temperature and sebacic acid purity on the physical properties of PSA-indomethacin DCs was investigated using a range of analytical techniques. The nature of the PSA-indomethacin interaction in composites after processing in sc-CO(2) under various conditions was investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and powder X-ray diffraction (XRD) methods, respectively. The results indicate that processing at 130 degrees C of a 4:1 (w/w) ratio PSA-indomethacin mixture, renders the indomethacin amorphous and dispersed within the polymer matrix. The primary interaction between PSA and indomethacin appears to be hydrogen bonding between the carboxylic acid OH of indomethacin and the carbonyl group of PSA. In vitro dissolution studies revealed that the processed composites exhibit a substantially enhanced dissolution rate compared to the physical mixtures. Also, through the control of experimental conditions, the initial burst effect of the drug release was largely alleviated. Instead, the erosion of PSA (zero order degradation) became the dominant factor in controlling the drug release rate.

Self-assembled supramolecular hydrogels formed by biodegradable PEO–PHB–PEO triblock copolymers and α-cyclodextrin for controlled drug delivery

A materials design of a new supramolecular hydrogel self-assembled between alpha-cyclodextrin and a biodegradable poly(ethylene oxide)-poly[(r)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer was demonstrated. The cooperation effect of complexation of PEO segments with alpha-cyclodextrin and the hydrophobic interaction between PHB blocks resulted in the formation of the supramolecular hydrogel with a strong macromolecular network. The in vitro release kinetics studies of fluorescein isothiocyanate labeled dextran (dextran-FITC) model drug from the hydrogel showed that the hydrogel was suitable for relatively long-term sustained controlled release of macromolecular drugs, which many simple triblock copolymer hydrogel systems could not achieve. The hydrogel was found to be thixotropic and reversible, and can be applied as a promising injectable drug delivery system.

Investigation of Drug Release and Matrix Degradation of Electrospun Poly(dl-lactide) Fibers with Paracetanol Inoculation

This study was aimed at assessing the potential use of electrospun fibers as drug delivery vehicles with focus on the different diameters and drug contents to control drug release and polymer fiber degradation. A drug-loaded solvent-casting polymer film was made with an average thickness of 100 microm for comparative purposes. DSC analysis indicated that electrospun fibers had a lower T(g) but higher transition enthalpy than solvent-casting polymer film due to the inner stress and high degree of alignment and orientation of polymer chains caused by the electrospinning process. Inoculation of paracetanol led to a further slight decrease in the T(g) and transition enthalpy. An in vitro drug release study showed that a pronounced burst release or steady release phase was initially observed followed by a plateau or gradual release during the rest time. Fibers with a larger diameter exhibited a longer period of nearly zero order release, and higher drug encapsulation led to a more significant burst release after incubation. In vitro degradation showed that the smaller diameter and higher drug entrapment led to more significant changes of morphologies. The electrospun fiber mat showed almost no molecular weight reduction, but mass loss was observed for fibers with small and medium size, which was characterized with surface erosion and inconsistent with the ordinarily polymer degrading form. Further wetting behavior analysis showed that the high water repellent property of electrospun fibers led to much slower water penetration into the fiber mat, which may contribute to the degradation profiles of surface erosion. The specific degradation profile and adjustable drug release behaviors by variation of fiber characteristics made the electrospun nonwoven mat a potential drug delivery system rather than polymer films and particles.

Synthesis and characterization of novel polyanhydrides with tailored erosion mechanisms

We have designed a new synthesis route to create polyanhydrides based on monomers that contain hydrophilic entities within highly hydrophobic backbones. The method results in polyanhydrides that can be easily processed into drug-containing tablets. The synthesis, characterization, and erosion studies of polyanhydride copolymers based on 1,6-bis(p-carboxyphenoxy)hexane (CPH), which is highly hydrophobic, and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG), which has hydrophilic oligomeric ethylene glycol segments in the monomer unit, was performed using a combination of molecular spectroscopy, thermal analysis, gravimetry, and scanning electron microscopy. The studies demonstrate that by increasing the CPH content in the CPTEG:CPH copolymers, the erosion of the system can be tailored from bulk-eroding to surface-eroding mechanism. These systems have promise as protein carriers.

Biodegradable PLGA Microspheres as a Sustained Release System for a New Luteinizing Hormone-Releasing Hormone (LHRH) Antagonist

A sustained release poly(DL-lactide-co-glycolide) (PLGA) microsphere delivery system to treat prostate cancer for a luteinizing hormone-releasing hormone (LHRH) antagonists, LXT-101 was prepared and evaluated in the paper. LXT-101 microspheres were prepared from PLGA by three methods: (1) double-emulsion solvent extraction/evaporation technique, (2) single-emulsion solvent extraction/evaporation technique, and (3) S/O/O (solid-in-oil-in-oil) method. The microspheres were investigated on drug loading, particle size, surface morphology and in vitro release profiles. An accelerated release approach was also established in order to expedite the evaluation periods. The in vivo evaluation of the microspheres was made by monitoring testosterone levels after subcutaneous administration to rats. The LXT-101 PLGA microspheres showed smooth and round surfaces according to a scanning electron microscopic investigation, and average particle size of ca. 30 mum according to laser diffractometry. The drug encapsulation efficiency of microspheres was influenced by LA/GA ratio of PLGA, salt concentrations, solvent mixture and preparation methods. Moreover, LA/GA ratio of PLGA, different preparation methods and different peptide stabilizers affected in vitro release of drugs. In vivo study, the testosterone levels were suppressed to castration up to 42 d as for the 7.5 mg/kg dose. And in vivo performance of LXT-101 microspheres was dose-dependent. The weights of rat sexual organs decreased and histopathological appearance of testes had little changes after 4-month microspheres therapy. This also testified that LXT-101 sustained release microspheres could exert the efficacy to suppress the testosterone level to castration with little toxicity. In conclusion, the PLGA microspheres could be a well sustained release system for LXT-101.

Current advances in sustained-release systems for parenteral drug delivery

Major progresses in the development of parenteral sustained-release systems have been made in recent years as evidenced by the regulatory approval and market launch of several new products. Both the availability of novel carrier materials and the advances in method of fabrication have contributed to these commercial successes. With the formulation challenges associated with biologics, new delivery systems have also been evolved specifically to address the unmet needs in the parenteral sustained release of proteins. In this review paper, different new carriers systems and preparation methods are discussed with special focus on their applications to biologicals.

New properties from PLA-PEO-PLA hydrogels

Polymeric materials are important in many medical applications. Regenerative medicine offers the potential to repair or replace damaged tissue and polymers are an essential component of many tissue engineering approaches. Hydrogels have many advantageous properties but, generally, lack robust mechanical properties. At the same time, mounting evidence points to the importance of the matrix modulus when constructing devices. In this context, triblock copolymers made from poly(-lactide)-poly(ethylene glycol)-poly(-lactide) have been prepared and formulated into hydrogels. Investigations into their mechanical properties found the elastic modulus to be greater than 10 kPa which is at least one order of magnitude stiffer than previously reported from macromolecules composed of similar monomers. Part of the reason is the presence of crystalline lactide domains. Creating hydrogels with tailored modulus across the kPa range will likely have important ramifications in regenerative medicine.

Enzymatic degradation of PLLA-PEOz-PLLA triblock copolymers

The enzymatic degradation of poly(L-lactide)-block- poly(2-ethyl-2-oxazoline)-block-poly(L-lactide) triblock copolymer (PLLA-PEOz-PLLA) was investigated using efficient enzyme proteinase K. PLLA-PEOz-PLLA solution-cast film lost a considerable amount of hydrophilic copolymers in the first 2 h, and the degradation after 2 h proceeded predominantly by surface erosion. The two faces of the hydrolyzed film exhibited different morphologies following enzymatic degradation. The lower face showed many spherulites, which are the superstructural morphology of polymer crystals. Porous spheres based on crystalline PLLA were observed on the upper face, because they were more resistant to enzymatic attack. The crystallinity of the films increased monotonously with the hydrolysis time, thus, the absorption of water gradually decreased. The analysis of degradation residues revealed that many colloids of poly(2-ethyl-2-oxazoline)-co-polyethylenimine (PEOz-co-PEI) copolymers were dispersed in the buffer solution. The average diameter, 1 microm, of the colloids was reduced to 200 nm by advanced degradation. The proteinase K exhibited remarkable hydrolysis not only at the ester bond but also the amide bond.