Technique paper for wet-spinning poly(L-lactic acid) and poly(DL-lactide-co-glycolide) monofilament fibers

A simple and repeatable method is described for wet-spinning poly(L-lactic acid) (PLLA) and poly(DL-lactic-co-glycolic acid) (PLGA) monofilament fibers. These fibers are strong, elastic, and suitable for many applications, including use as tissue-engineering scaffolds. The PLLA wet-extruded fibers do not show additional strain-induced crystallization as a result of drawing the fibers during fabrication; however, there is an apparent increase in crystallinity late in the degradation process in saline at 37 degrees C. We have measured the molecular weight degradation in saline at 37 degrees C for fibers of both PLLA and PLGA. Changing solvent systems, polymer blends, and winding rates alters mechanical and morphological properties of these fibers for specific applications. The authors discuss a possible theoretical explanation for these observed changes due to changes in polymer concentration, solvent system, and coagulation bath properties. This wet-extrusion process is simple and inexpensive enough to be carried out in almost any laboratory interested in tissue engineering.     

Degradation of poly(lactide-co-glycolide) (PLGA) and poly(L-lactide) (PLLA) by electron beam radiation

This paper seeks to examine the effects of electron beam (e-beam) radiation on biodegradable polymers (PLGA and PLLA), and to understand their radiation-induced degradation mechanisms. PLGA (80:20) and PLLA polymer films were e-beam irradiated at doses from 2.5 to 50 Mrad and the degradation of these films were studied by measuring the changes in their molecular weights, FTIR spectra, thermal and morphological properties. The dominant effect of e-beam irradiation on both PLGA and PLLA is chain scission. Chain scission occurs first through scission of the polymer main chain, followed by hydrogen abstraction. Chain scission, though responsible for the reduction in the average molecular weight, Tc, Tg and Tm of both polymers, encourages crystallization in PLGA. PLLA also undergoes chain scission upon irradiation but to a lesser degree compared to PLGA. The higher crystallinity of PLLA is the key factor in its greater stability to e-beam radiation compared to PLGA. A linear relationship is also established between the decrease in molecular weight with respect to radiation dose.     

Development of biodegradable poly(propylene fumarate)/poly(lactic-co-glycolic acid) blend microspheres. II. Controlled drug release and microsphere degradation

This article describes the effects of six processing parameters on the release kinetics of a model drug Texas red dextran (TRD) from poly(propylene fumarate)/poly(lactic-co-glycolic acid) (PPF/PLGA) blend microspheres as well as the degradation of these microspheres. The microspheres were fabricated using a double emulsion-solvent extraction technique in which the following six parameters were varied: PPF/PLGA ratio, polymer viscosity, vortex speed during emulsification, amount of internal aqueous phase, use of poly(vinyl alcohol) in the internal aqueous phase, and poly(vinyl alcohol) concentration in the external aqueous phase. We have previously characterized these microspheres in terms of microsphere morphology, size distribution, and TRD entrapment efficiency. In this work, the TRD release profiles in phosphate-buffered saline were determined and all formulations showed an initial burst release in the first 2 days followed by a decreased sustained release over a 38-day period. The initial burst release varied from 5.1 (+/-1.1) to 67.7 (+/-3.4)% of the entrapped TRD, and was affected most by the viscosity of the polymer solution used for microsphere fabrication. The sustained release between day 2 and day 38 ranged from 7.9 (+/-0.8) to 27.2 (+/-3.1)% of the entrapped TRD. During 11 weeks of in vitro degradation, the mass of the microspheres remained relatively constant for the first 3 weeks after which it decreased dramatically, whereas the molecular weight of the polymers decreased immediately upon placement in phosphate-buffered saline. Increasing the PPF content in the PPF/PLGA blend resulted in slower microsphere degradation. Overall, this study provides further understanding of the effects of various processing parameters on the release kinetics from PPF/PLGA blend microspheres thus allowing modulation of drug release to achieve a wide spectrum of release profiles.     

Degradation behaviour in vitro for poly(D,L-lactide-co-glycolide) as drug carrier

Biodegradable polymers have been extensively investigated because of regulating drug release rate easily, obviating the need to remove the device, and good biocompatibility. Among the biodegradable polymers currently under investigation, poly(D,L-lactide-co-glycolide) (PLGA) copolymers are the most widely studied because of their long history of safe clinical use as drug carrier. 50 : 50 PLGA was used as a model degradable polymer in this study to investigate the degradation behaviour on drug release from bulk degradable polymers in vitro. 5-fluorouracil (5-FU) was used as a model drug. Molecular weight change, residual mass, water uptake, morphological change of PLGA wafers, and pH of release test medium were characterized to investigate the effect of polymer degradation on drug release. The release rate of 5-FU increased with the increase of 5-FU loading amount and the release profiles of 5-FU irrespective of 5-FU loading amount followed near first order release kinetics.     

Size and temperature effects on poly(lactic-co-glycolic acid) degradation and microreservoir device performance

The component materials of controlled-release drug delivery systems are often selected based on their degradation rates. The release time of a drug from a system will strongly depend on the degradation rates of the component polymers. We have observed that some poly(lactic-co-glycolic acid) polymers (PLGA) exhibit degradation rates that depend on the size of the polymer object and the temperature of the surrounding environment. In vitro degradation studies of four different PLGA polymers showed that 150 microm thick membranes degraded more rapidly than 50 microm thick membranes, as characterized by gel permeation chromatography and mass loss measurements. Faster degradation was observed at 37 degrees C than 25 degrees C, and when the saline media was not refreshed. A biodegradable polymeric microreservoir device that we have developed relies on the degradation of polymeric membranes to deliver pulses of molecules from reservoirs on the device. Earlier molecular release was seen from devices having thicker PLGA membranes. Comparison of an in vitro release study from these devices with the degradation study suggests that reservoir membranes rupture and drug release occurs when a membrane threshold molecular weight of 5000-15000 is reached.     

Towards developing surface eroding poly(alpha-hydroxy acids)

We have prepared a library of biodegradable polyesters derived from poly(alpha-hydroxy acids) (PHAs) that appear to primarily exhibit surface erosion behavior. This was achieved by increasing the hydrophobicity of the polymers in two distinct steps, namely: macromer formation and a coupling step. In the first step, macromerdiols (MDs) with varying lipophilicities were prepared by polymerization of L-lactide or mixture of L-lactide and glycolide (3/1 by mole) to various lengths (n = 10, 20, 30, and 40) using alkanediols of increasing C-chain length (C6, C8, and C12) as initiators in the presence of Tin(II) catalyst. In the second step, the macromer diols were linked together with diacid dichlorides of varying C-chain lengths (C6, C8, C10, and C12) to yield polyesters ranging in molecular weight (Mw) from 20 to 130 KDa and polydispersity of 1.5-6. These polyesters exhibited different thermal behavior from pure PHAs that can be tuned by changing the initiator core, the lactide/glycolide chain length, and diacid dichloride type. In addition, all these polymers showed solubility in tetrahydrofuran unlike poly(L-lactic acid) (PLLA) and poly(lactide-co-glycolide) (PLGA). In contrast to PLLA and PLGA, the degradation behavior of these novel polyesters exhibited linear profiles consistent with a surface erosion behavior. Release studies using Congo red as a model drug from microspheres prepared from these polyesters showed linear release profiles with correlation constants of least-square fits approaching a value of unity. Degradable polyesters with tunable thermal and degradation behavior may find applications in drug delivery and tissue engineering, where control over these parameters is critical to ensure predictable outcomes.     

Preparation, characterization, and in vitro evaluation of physostigmine-loaded poly(ortho ester) and poly(ortho ester)/poly(D,L-lactide-co-glycolide) blend microspheres fabricated by spray drying

The physostigmine-loaded poly(ortho ester) (POE), poly(dl-lactide-co-glycolide) (PLGA) and POE/PLGA blend microspheres were fabricated by a spray drying technique. The in vitro degradation of, and physostigmine release from, the microspheres were investigated. SEM analysis showed that the POE and POE/PLGA blend particles were spherical. They were better dispersed when compared to the pure PLGA microspheres. Two glass transition temperature ( Tg ) values of the POE/PLGA blend microspheres were observed due to the phase separation of POE and PLGA in the blend system. XPS analysis proved that POE dominated the surfaces of POE/PLGA blend microspheres, indicating that the blend microspheres were coated with POE. The encapsulation efficiencies of all the microspheres were more than 95%. The incorporation of physostigmine reduced the Tg value of microspheres. The Tg value of the degrading microspheres increased with the release of physostigmine. For instance, POE blank microspheres and physostigmine-loaded POE microspheres had a Tg value of 67 degrees C and 48 degrees C, respectively. After 19 days in vitro incubation, Tg of the degrading POE microspheres increased to 55 degrees C. Weight loss studies showed that the degradation of the blend microspheres was accelerated with the presence of PLGA because its degradation products catalyzed the degradation of both POE and PLGA. The release rate of physostigmine increased with increase of PLGA content in the blend microspheres. The initial burst release of physostigmine was effectively suppressed by introducing POE to the blend microspheres. However, there was an optimized weight ratio of POE to PLGA (85:15 in weight), below which a high initial burst was induced. The POE/PLGA blend microspheres may make a good drug delivery system.     

Controlled degradation of multilayered poly(lactide-co-glycolide) films using electron beam irradiation

The ability to undergo predictable and controlled degradation allows biopolymers to release prescribed dosages of drugs locally over a sustained period. However, the bulk or homogeneous degradation of some of these polymers like poly(L-lactide) (PLLA) and poly(lactide-co-glycolide) (PLGA) work against a better controlled release of the drugs. Inducing the polymers to undergo surface erosion or layer-by-layer degradation could provide a better process of controlled drug release from the polymers. This study has demonstrated that surface erosion degradation of PLGA is possible with the use of a multilayer film system, with PPdlLGA [plasticized poly(D,L-lactide-co-glycolide) (PdlLGA)] as the surface layers and poly(L-lactide-co-glycolide) as the center layer. The use of the more hydrophilic PPdlLGA as the surface layer resulted in a faster degradation of the surface layers compared to the center layer, thus giving a surface erosion degradation effect. The rate of surface degradation could also be controlled with electron beam (e-beam) radiation, where e-beam irradiation was shown to alter the degradation time and onset of polymer mass loss. It was also shown that the more highly irradiated PPdlLGA surface layers had an earlier onset of mass loss, which resulted in a faster reduction in overall film thickness. The ability to control the rate of film thickness reduction with different radiation dose promises a better controlled release of drugs from this multilayer PLGA film system.     

Preparation of poly(L-lactic acid) and poly(DL-lactic-co-glycolic acid) foams by use of ice microparticulates

Biodegradable foams of poly(L-lactic acid) (PLLA) and poly(DL-lactic-co-glycolic acid) (PLGA) for tissue engineering were fabricated by a porogen-leaching technique using ice microparticulates as the porogen material. PLLA or PLGA solution in chloroform was mixed with ice microparticulates. The mixtures were frozen by being placed in molds in liquid nitrogen and freeze-dried to form the foams. Scanning electron microscopic observation of the PLLA and PLGA foams showed that evenly distributed and interconnected pore structures were formed in these foams. The porosity and surface area of the foams increased with an increase in the weight fraction of the ice microparticulates, while the median pore size remained unchanged. The pore structures of the foams could be manipulated by controlling processing variables such as the size and weight fraction of the ice microparticulates and polymer concentration.     

Morphological and degradation studies of sirolimus-containing poly(lactide-co-glycolide) discs

The effect of residual solvent and copolymer ratio on the in vitro degradation and drug release behavior of a bioabsorbable polymer/drug system was investigated in an effort to understand and develop the use of these excipients for controlled drug delivery devices. Sirolimus-containing poly(lactide-co-glycolide) (PLGA) discs were fabricated by a solution-casting method using dimethyl sulfoxide (DMSO) as the solvent. The residual DMSO was removed from a set of discs by supercritical carbon dioxide extraction, and reflections of crystalline sirolimus were observed in the wide-angle X-ray scattering profile observed after extraction. A correlation was not observed between the extent of drug crystallization and extraction conditions and copolymer ratio. Mass loss, molecular weight, and sirolimus release were monitored during an in vitro study of the oven-dried neat PLGA, sirolimus-containing PLGA, and extracted sirolimus-containing PLGA discs during 56 days. The sirolimus-containing PLGA discs with residual DMSO exhibited a faster sirolimus release rate compared to the extracted discs. The residual DMSO facilitated release of sirolimus. The discs that contained PLGA with higher glycolide content, particularly 50% glycolide, degraded faster and exhibited faster sirolimus release.     

Co-effect of aqueous solubility of drugs and glycolide monomer on in vitro release rates from poly(D,L-lactide-co-glycolide) discs and polymer degradation

The objective of this study was to investigate the effect of aqueous solubility of model drugs and glycolide monomer (GM) from poly(D,L-lactide-co-glycolide) (PLGA) discs on in vitro release rates and polymer degradation. 5-Fluorouracil (5-FU), a water-soluble compound, and dexamethasone in a water-insoluble base form were selected as model drugs. Glycolide monomer, that has moderate solubility in water, was a non-toxic and biodegradable additive as a derivative material of hydrolysis of PLGA in order to obtain desirable drugs release rates. PLGA discs with or without GM were formulated by means of compression molding method. The prepared polymeric discs were incubated at 37 degrees C in phosphate-buffered saline (PBS, pH 7.4) and characterized at scheduled time points for water uptake, mass loss, diameter and morphology change, molecular weight and composition change using scanning electron microscopy (SEM), gel-permeation chromatography (GPC), and H-NMR, respectively. The supernatants were taken out of the sample vials and were analyzed for drug release. The 5-FU release was found to be increasing in proportion to the drug loading amount with an initial burst for 5 days, while dexamethasone release showed inverse relationship with the increasing drug loading amount. However, the release behaviors of 5-FU and dexamethasone polymeric discs containing GM showed faster release rates than control discs (without GM) and did not show lag periods during the in vitro release test due to adding GM, which acted as a channeling agent that has moderate solubility in water. Polymer degradation was found to be affected by aqueous solubility of drugs and GM. In conclusion, we observed that drugs release rates were influenced by their aqueous solubility and loading amount and also GM plays a major role in controlling drug release rates regardless of solubility of drugs. This system appears to be promising for controlled drug delivery aimed at local therapy.     

Enzymatic degradation behavior and mechanism of poly(lactide-co-glycolide) foams by trypsin

The purpose of this study is to investigate the enzymatic degradation behaviors of porous poly(lactide-co-glycolide) (PLGA) foams in the presence of trypsin, in comparison with their hydrolytic degradation. To inspect the effect of trypsin on the degradation of PLGA, both the hydrolytic and enzymatic degradation of non-porous PLGA samples were also performed. The changes of molecular weight and molecular weight distribution (polydispersity) during the degradation were determined by gel permeation chromatograph. And the changes of weight, thickness and morphology with the degradation were also measured. The degradation of PLGA displayed as two stages. In the first stage, the molecular weight of PLGA decreased continuously with degradation time, whereas little weight loss occurred. But in the second stage, the molecular weight of PLGA had decreased to a low value and was almost unchanged with time, while the sample experienced significant weight loss. And it was found that the presence of trypsin could significantly accelerate the weight loss rates of all the PLGA samples, but it caused little difference in the decrease of molecular weight and the change of PLGA composition between the enzymatic and hydrolytic degradation. Therefore, the enzymatic degradation of PLGA was still primarily a hydrolysis process. A mechanism of enzymatic degradation was proposed that the trypsin could enhance the weight loss of PLGA by acting as surfactant to push the dispersion of degradation products into water even though they could not dissolve in water.     

Preparation of biodegradable microspheres of testosterone with poly(D,L-lactide-co-glycolide) and test of drug release in vitro

Biodegradable microspheres formulation of testosterone (T) can be used as a new physiological approach for androgen replacement in hypogonadal men. In this study, poly(D,L-lactide-co-glycolide) (PLGA) microspheres containing T were prepared by a solvent-evaporation/solvent-diffusion process and the drug release tests of the microspheres were carried out in vitro. T/PLGA microspheres with good yield, desired size and satisfied drug loading were obtained. A significant testosterone sustained release was shown in the drug release tests in vitro. Since PLGA microspheres preparations are normally sterilized by colbat-60 irradiation, the effects of 25 kGy colbat-60 irradiation on physicochemical properties and in vitro drug release profile of T/PLGA microsphere were investigated. The results showed that the irradiation didn't have any effects on the physicochemical properties of T. Though about one-third decrease in molecular weight of PLGA was caused by the irradiation, no significant changes were observed on the drug release profile in vitro.     

Designing multilayered particulate systems for tunable drug release profiles

Triple-layered microparticles comprising poly(D,L-lactide-co-glycolide, 50:50) (PLGA), poly(L-lactide) (PLLA) and poly(ethylene-co-vinyl acetate, 40 wt.% vinyl acetate) (EVA) were fabricated using a one-step solvent evaporation technique, with ibuprofen drug localized in the EVA core. The aim of this study was to investigate the drug release profiles of these triple-layered microparticles in comparison to double-layered (PLLA/EVA and PLGA/EVA) (shell/core) and single-layered EVA microparticles. Double- and triple-layered microparticles were shown to eliminate burst release otherwise observed for single-layered microparticles. For triple-layered microparticles, the migration of acidic PGA oligomers from the PLGA shell accelerated the degradation of the PLLA mid-layer and subsequently enhanced drug release in comparison to double-layered PLLA/EVA microparticles. Further studies showed that drug release rates can be altered by changing the layer thicknesses of the triple-layered microparticles, and through specific tailoring of layer thicknesses, a zero-order release can be achieved. This study therefore provides important mechanistic insights into how the distinctive structural attributes of triple-layered microparticles can be tuned to control the drug release profiles.     

Cytoplasmic delivery of a macromolecular fluorescent probe by poly(d, l-lactic-co-glycolic acid) microspheres

A macromolecular fluorescent probe encapsulated in poly(d, l-lactic-co-glycolic acid) (PLGA) microspheres was used as a model for studying cytoplasmic delivery of antigens. We hypothesized that Texas red dextran loaded in PLGA microspheres would be delivered to the cytoplasm and that cytoplasmic delivery would be affected by polymer molecular weight. Cellular localization of the Texas red dextran was investigated at two different molecular weights of PLGA: 6000 and 60,000 g/mol. Intracellular degradation and processing of Texas red dextran-loaded PLGA microspheres by mouse peritoneal macrophages was monitored both in vitro and in vivo for a 7-day period using confocal laser scanning microscopy (CLSM). The results revealed cytoplasmic delivery of the fluorescent probe at both molecular weights of PLGA. Furthermore, the CLSM images showed that both in vitro and in vivo, the kinetics of microsphere degradation and cytoplasmic delivery were more rapid for the 6000 g/mol PLGA microspheres than the 60,000 g/mol PLGA microspheres. Hence, this study provides physical evidence that PLGA microspheres are capable of cytoplasmic delivery and that delivery to the cytosol can be controlled by modifying formulation parameters such as polymer molecular weight.     

New poly(ester-carbonate) multi-block copolymers based on poly(lactic-glycolic acid) and poly(ϵ-caprolactone) segments

A new family of multi-block copolymers having the structure of poly(ester-carbonate)s was obtained by a chain-extension reaction involving poly(lactic-glycolic acid) oligomers (PLGA) and oligomeric α,ω-bishydroxy-terminated poly(ϵ-caprolactone)s (PCDT). The latter were first transformed into α,ω-bis(chloroformate)s, which were subsequently condensed in the presence of amines with both the hydroxylic and the carboxylic end-groups of PLGA oligomers. Several samples differing in the length of the PCDT segments and in the composition of the PLGA segments were prepared and characterized for their physico-chemical properties. All of them had high molecular weight, good solubility in organic solvents, and modest swellability in aqueous media. As regards their thermal behaviour, some samples showed evidence of the presence of a crystalline phase. Since these products are potentially useful as bioerodible materials in drug delivery systems, some preliminary results on their degradation behaviour under conditions mimicking those found in biological fluids are reported.     

Release of Hydrophilic Drug from Biodegradable Polymer Blends

This paper reports on the release behavior of the drug lidocaine-HCl from a immiscible polymeric blend. Biodegradable polymer blends of poly(L-lactic acid)/poly(lactic-co-glycolic acid) (PLLA/PLGA) were loaded with lidocaine-HCl, and the release of lidocaine-HCl from these blends was monitored. It was found that the release profiles were significantly affected by the affinity and subsequent partitioning of the drug into one of the two phases in the blends. It was hypothesized that the hydrophilic lidocaine-HCl seems to have a tendency to reside in the PLGA component of the PLLA/PLGA blend. This resulted in a release very much controlled by the degradation of PLGA, even when PLLA is the major phase of the blend. A mathematical model was further employed to quantify the partitioning, as well as model the lidocaine-HCl release profiles of different blend compositions.     

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

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

Sustained release of mitomycin-C from poly(DL-lactide) /poly(DL-lactide-co-glycolide) films

Mitomycin-C (MMC)-loaded poly(DL-lactide) (PLA)/poly(DL-lactide-co-glycolide) (PLGA) films which have different drug loading capacities and thicknesses were prepared by a solvent-evaporation technique. Degradation and release studies were conducted at 37 degrees C in pH 7.4 phosphate buffered saline. The results showed that both the rate and the percentage of released MMC increased as the glycolide content in the copolymer increased from 10 to 30% (w/w) and the drug load increased from 0.5 to 2 mg MMC per 300 mg of polymer. In contrast, they decreased depending upon increasing film thickness from 80 to 300 microm and polymer molecular weight. It was found that the drug release mechanism is diffusion-controlled according to a non-Fickian diffusion mechanism.     

Effects of protein molecular weight on the intrinsic material properties and release kinetics of wet spun polymeric microfiber delivery systems

Wet spun microfibers have great potential for the design of multifunctional controlled release scaffolds. Understanding aspects of drug delivery and mechanical strength, specific to protein molecular weight, may aid in the optimization and development of wet spun fiber platforms. This study investigated the intrinsic material properties and release kinetics of poly(l-lactic acid) (PLLA) and poly(lactic-co-glycolic acid) (PLGA) wet spun microfibers encapsulating proteins with varying molecular weights. A cryogenic emulsion technique developed in our laboratory was used to encapsulate insulin (5.8 kDa), lysozyme (14.3 kDa) and bovine serum albumin (BSA, 66.0 kDa) within wet spun microfibers (～100 μm). Protein loading was found to significantly influence mechanical strength and drug release kinetics of PLGA and PLLA microfibers in a molecular-weight-dependent manner. BSA encapsulation resulted in the most significant decrease in strength and ductility for both PLGA and PLLA microfibers. Interestingly, BSA-loaded PLGA microfibers had a twofold increase (8 ± 2 MPa to 16 ± 1 MPa) in tensile strength and a fourfold increase (3 ± 1% to 12 ± 6%) in elongation until failure in comparison to PLLA microfibers. PLGA and PLLA microfibers exhibited prolonged protein release up to 63 days in vitro. Further analysis with the Korsmeyer–Peppas kinetic model determined that the mechanism of protein release was dependent on Fickian diffusion. These results emphasize the critical role protein molecular weight has on the properties of wet spun filaments, highlighting the importance of designing small molecular analogues to replace growth factors with large molecular weights.