In vitro release of complexed pDNA from biodegradable polymer films

The controlled delivery of low‐molecular weight drugs and proteins from biodegradable polymers has received considerable attention. However, controlled release studies of pDNA from such polymers have not been reported to date. In this study, a plasmid DNA was complexed with the cationic polymer called polyethylenimine (PEI). This gene vector has been shown to be very effective in transfecting cells. The complexed DNA were then incorporated into different types of poly‐lactic‐co‐glycolic acid (PLGA) film; PLGA 53/47 (M_w 90 kDa), 50/50 (M_w 11 kDa, end group is lauryl ester) and 75/25 (M_w 120 kDa). Their release profiles from a buffer solution were studied. An initial (small) burst release of PEI‐DNA from film was observed in PLGA 53/47 and 50/50, followed by a plateau phase and finally a rapid erosion‐controlled release. For PLGA 50/50, the rapid release started after 14 days; erosion‐controlled release for PLGA 53/47 started after 9 days; for PLGA 75/25, the release rate was governed by an initial burst release (10%) followed by a slow release controlled by diffusion. No obvious erosion‐controlled release rate was observed for this polymer up to 27 days. Thus, the controlled release of complexed DNA follows the general features exhibited by lower‐ M_w drugs. This is of significance in designing gene vector matrices that offer the promise of more lasting gene therapy compared with particulate formulations. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Spray drying technique to produce controlled release formulations of zidovudine—an anti‐HIV drug

This article explores the application of spray drying technique to produce microparticles of poly(D ,L ‐lactide‐co‐glycolic acid) (PLGA), as well as di‐block copolymer of polylactic acid (PLA) and polyethylene glycol (PEG) (PLA‐PEG), containing zidovudine (AZT), an anti‐HIV drug, to achieve its controlled release over an extended period of time. Of the two polymers studied, PLGA is hydrophobic, whereas PLA‐PEG is hydrophilic and the drug, AZT is water‐soluble. Formulations were developed containing 10 and 25 wt % of AZT giving encapsulation efficiencies (EE) of 66 to 86% for PLGA and 90 to 94% for PLA‐PEG di‐block copolymer. All the formulations were characterized by Fourier transform spectroscopy (FTIR) to investigate the interaction of AZT with polymers and to characterize PLA‐PEG. NMR was also employed to confirm the formation of PLA‐PEG. X‐ray diffraction was used to understand the molecular level dispersion of AZT within the polymeric matrices, while differential scanning calorimetry was employed to assess thermal properties. Scanning electron microscopy was employed to understand the surface morphology of AZT‐loaded microparticles. In vitro release experiments performed in pH 7.4 buffer media extended the release of AZT up to 125 h with PLGA, whereas 30 h were required for releasing AZT through PLA‐PEG microparticles. Cumulative release data were fitted to an empirical equation to understand the nature of release characteristics. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 000: 000–000, 2011     

Paclitaxel release from micro-porous PLGA disks

Micro-porous biodegradable polymeric foams have potential applications in tissue engineering and drug delivery systems. A two-stage fabrication process combining spray drying and supercritical gas foaming is presented for the encapsulation of paclitaxel in micro-porous PLGA (poly lactic glycolic acid) foams. Encapsulation of paclitaxel in the PLGA polymer matrix was achieved and these foams have potential application as a new type of surgical implant for controlled release of paclitaxel. This technique may also be applied to other hydrophobic drugs which face problems of slow release when encapsulated in a compact polymeric device. The micro-porous structure helps to increase drug release rate due to a shorter diffusion path of the drug in the polymer. The final residual organic solvent content in the polymer was low and well within safety limits due to the high miscibility of supercritical CO₂ with the organic solvent. The pore size distribution, the phase behavior, and the in vitro swelling behavior of the foams were characterized. In vitro release results showed a nearly constant release rate for up to 8 weeks. The release profiles from micro-porous foam and from compressed disks were compared to assess the performance of micro-porous foams as sustained release implants. The foams implanted intracranially in mice showed therapeutic concentrations of paclitaxel at distant regions of the brain even after 28 days of implantation.     

Polymeric sodium alginate interpenetrating network beads for the controlled release of chlorpyrifos

Novel polymeric sodium alginate (Na‐Alg) interpenetrating network (IPN) beads have been prepared by crosslinking Na‐Alg blend with gelatin (GE) or egg albumin (EA) using glutaraldehyde (GA) as the crosslinking agent. These beads were used for the controlled release of chlorpyrifos. The swelling experiments were performed in water at different temperatures, and these data were used to calculate the molecular mass (M_C) between crosslinks as well as diffusion coefficients. Diffusion coefficients calculated from desorption data were lower by about two orders of magnitude than those calculated from sorption results. Higher values of M_C were obtained for the gelatin‐based IPNs than the neat Na‐Alg and egg albumin‐based matrices. Size of the beads did not vary significantly either by the network or by increasing the exposure time to the crosslinking agent. The scanning electron microscopy (SEM) was used to understand the surface characteristics of the beads. Differential scanning calorimetry (DSC) indicated a molecular level dispersion of chlorpyrifos in the polymer matrix. The percentage entrapment efficiency showed a dependence on the type of network polymer as well as time of exposure to the crosslinking agent. The encapsulation efficiency decreased with an increase in time of exposure to the crosslinking agent. In vitro release experiments have been performed to follow the release kinetics of chlorpyrifos from the matrices. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 911–918, 2002     

Experimental problems in the application of UV/visible based methods as the quantification tool for the entrapped/released insulin from PLGA carriers

BACKGROUND: Controlled release of medicaments from biodegradable polymers remains the most convenient way for their sustained release. Although a number of articles have been published, experimental work involving the preparation of polymer‐based carriers and release procedures are not described with sufficient level of detail to allow other researchers to reproduce the experiments and to compare published results with their own. In this contribution the experimental background of the entrapment and release of insulin from PLGA carriers is described and the problems found at each step related to UV/Visible method used to quantify them are addressed in detail. RESULTS: The quantification of entrapped insulin by UV/visible methods was affected by aggregation. The design of the release experiment influenced the results regarding the entrapment efficiency (EE) and the maximum percentage of released insulin. It was also found that the presence of colloidal polymeric particles, insufficient centrifugation times and the kind of solvent used in the release test might lead to mistakes in the percentage of liberated insulin when UV/visible based methods are employed. CONCLUSIONS: This contribution demonstrates that serious discrepancies in the EE and percentage of released protein may arise if some key experimental factors are not taken into account. Therefore, the analysis presented here tries to point out important aspects of this topic currently not reported, unnoticed or not properly analyzed in the open literature. The results are useful for the entrapment of any protein on any polymeric device using UV/visible based methods to quantify them. Copyright © 2009 Society of Chemical Industry     

Preparation and delayed release of poly(lactide‐ co‐glycolide)/ketoconazole composite fiber mats

In this study, slow release materials–poly(lactide‐co‐glycolide) (PLGA) ultrafine fiber mats containing different ketoconazole (KCZ) contents were prepared and their release behaviors were investigated in vitro. PLGA/KCZ ultrafine fiber mats were prepared via electrospinning and characterized by means of scanning electron microscope, Fourier transform infrared, X‐ray diffraction (XRD), and thermal gravimetric analysis. The slow release properties of PLGA/KCZ fiber mats in vitro were studied by measuring the concentrations of KCZ dissolved in the phosphate buffered solution (pH = 4.5) at a programmed time. Results indicated that KCZ could be dispersed in PLGA very well in a wide range of KCZ content from 10 to 100% with respect to PLGA. Most KCZ in PLGA fibers were physically dispersed. The thermal decomposition temperature of PLGA was lowered due to the incorporation of KCZ. With increased drug concentration, the release amount would increase in unit time. The two‐stage releases would be sustained to achieve the effective utilization of KCZ. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Mesomomorphism enhancement of modified side‐chain liquid‐crystalline polysiloxanes by copolymerization

The liquid‐crystalline (LC) monomer 4‐allyoxybenzoyloxy‐4′‐buthylbenzoyloxy‐p‐phenyl (M₁), whose LC phase appeared at lower temperatures, from 137 to 227°C, and the modified mesogenic monomer 4‐allyoxybenzoyloxy‐4′‐methyloxybenzoyloxy‐p‐biphenyl (M₂), whose LC phase appeared at higher temperatures, from 185 to 312°C, were prepared. A series of side‐chain LC polysiloxanes containing M₁ and M₂ were prepared by graft copolymerization. Their LC properties were characterized by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. The results show that the introduction of the modified mesogenic monomer M₂ into the polymeric structure caused an additional increase in the clearing point (isotropic transition temperature) of the corresponding polysiloxanes, compared with unmodified polysiloxanes, but did not significantly affect the glass‐transition temperature. Moreover, the modified polysiloxanes exhibited nematic phases as the unmodified polymer did. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1196–1201, 2005     

New carbon nanotube–conducting polymer composite electrodes for drug delivery applications

A novel drug delivery system (DDS) based on a carbon nanotube (CNT)–poly(3,4‐ethylenedioxythiophene) (PEDOT) composite was constructed via a layering method. Single‐walled CNTs (SWNTs) were immobilized on a gold electrode using a layer‐by‐layer technique. In particular, cysteamine (Cys) was firstly bonded to the gold surface through the strong S? Au association and SWNTs were subsequently linked onto the Cys layer through condensation reaction of ? NH₂ and carboxyl groups by 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide/N‐hydroxysuccinimide coupling. X‐ray photoelectron spectroscopy and Raman spectroscopy demonstrate that this is a facile route for immobilizing CNTs on gold electrodes. Finally PEDOT was electropolymerized on the SWNT‐functionalized electrode to make a SWNT–PEDOT composite, and the modified electrode was applied as a DDS. Dexamethasone, as a model drug, was incorporated into PEDOT in the electropolymerization. Investigations of the electrochemical properties of SWNT–PEDOT demonstrate that SWNTs greatly improve the conductivity and increase the charge capacity of PEDOT. The composite exhibits a petal‐like surface structure, 20–30 nm thick and 100–200 nm wide. Compared to a DDS based on pure PEDOT synthesized under the same conditions, SWNT–PEDOT has the merits of higher drug release rate and larger release amount. The average mass release for every five voltammetry cycles increases from 1.4126 to 1.8864 mg cm^?2. Copyright © 2011 Society of Chemical Industry     

Electrical,mechanical, structural,and thermal behaviors of polymeric gel electrolyte membranes of poly(vinylidene fluoride‐co‐hexafluoropropylene) with the ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate plus lithium tetrafluoroborate

Polymeric gel electrolyte membranes based on the polymer poly(vinylidene fluoride‐co‐hexafluoropropylene) [P(VdF–HFP)] with different weight percentages of the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate plus 0.3M lithium tetrafluoroborate (LiBF₄) salt were prepared and characterized by scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, complex impedance spectroscopy, pulse echo techniques, and Vickers hardness (H) testing. After the incorporation of the IL plus the salt solution in the P(VdF–HFP) polymer, the melting temperature, glass‐transition temperature (T_g), degree of crystallinity, thermal stability, elastic modulus (E), and hardness (H) gradually decreased with increasing content of the IL–salt solution as a result of complexation between the P(VdF–HFP) and IL. This was confirmed by FTIR spectroscopy. A part of the IL and LiBF₄ were found to remain uncomplexed as well. The ionic conductivity (σ) of the polymeric gel membranes was found to increase with increasing concentration of the IL–salt solution. The temperature‐dependent σs of these polymeric gel membranes followed an Arrhenius‐type thermally activated behavior. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41456.     

Preparation,optimization, and characterization of simvastatin nanoparticles by electrospraying: An artificial neural networks study

The purpose of this study was to determine major factors impacting the size of simvastatin (SIM)‐loaded poly(d , l ‐lactic‐co‐glycolide) (PLGA) nanoparticles (NPs) that was prepared using electrospraying. Three variables including concentration of polymer and salt as well as solvent flow rate were used as input variables. Size of NPs was considered as output variable. For the first time, our findings using a systematic and experimental approach, showed the importance of salt concentration as the dominant factor determining the size with a sharp and reverse effect. Optimum formulation (i.e., flow rate 0.08 mL h^?1, polymer concentration 0.7 w/v %, and salt concentration 0.8 mM) was then evaluated for aqueous solubility, encapsulation efficiency, particle size, in vitro drug release pattern and cytotoxicity. A very appreciable encapsulation efficiency (90.3%) as well as sustained release profile, considerable enhancement in aqueous solubility (～5.8 fold) and high IC₅₀ (>600 µM of SIM‐loaded PLGA NPs) indicated PLGA as a promising nanocarrier for SIM. The optimum formulation had particle size, zeta potential value, polydispersity index (PDI) and drug loading of 166 nm, +3 mV, 0.62 and 9%, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43602.     

PLGA‐based in situ‐forming system: degradation behavior in the presence of hydroxyapatite nanoparticles

The degradation behavior of poly(lactic‐co‐glycolic acid) (PLGA) is important for its application as a biomaterial. In this work, the influence of nano‐hydroxyapatite (nano‐HA) on the degradation behavior of PLGA matrix was studied. PLGA‐based in situ forming system containing nano‐HA was prepared using the immersion precipitation method and the polymer hydrolysis was investigated in a phosphate buffer (pH 7.4) at 37°C. The pH values in the testing medium were evaluated to quantify the degradation process. Gel permeation chromatography and scanning electron microscopy techniques were employed to monitor changing of the weight‐average molecular weight (M_W) and the body structures of PLGA matrices, respectively. To model the M_W changes, a first‐order degradation model was employed. The formed PLGA matrices had different porosities that effected water penetration into the matrices following the hydrolysis process. The obtained degradation rate constant using a mathematical model for PLGA matrices with different nano‐HA content was about from 2.5 to 4.5 times lower than neat PLGA matrix. POLYM. ENG. SCI., 59:1028–1035, 2019. © 2019 Society of Plastics Engineers     

Kinetics of drug release from drug carrier of polymer/TiO2 nanotubes composite—pH dependent study

This study was to investigate the kinetics of drug release from polymer/TiO₂ nanotubes composite. Lidocaine and carprofen were selected as model drugs to represent weak base and weak acid drugs, respectively. Mathematical models used to fit the in vitro drug release experimental data indicate that at higher pH, the drug release was first order diffusion controlled. At lower pH, the release of the two drugs exhibits two staged controlled release mechanism. The first phase is due to drug diffusion and the second stage is a result of poly(lactic‐co‐glycolic acid) (PLGA) polymer degradation. The rate of drug release from polymer/TiO₂ nanotubes drug carrier was mainly controlled by three pH dependent factors: the solubility of the drug, the degree of polymer swelling/degradation, and the electrostatic force between polymer and drug. This study suggests that controlled release could be achieved for polymer/TiO₂ nanotubes drug carrier via the modulation of pK_a values of polymers and drug solubility. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41570.     

Impact of PLGA molecular behavior in the feed solution on the drug release kinetics of spray dried microparticles

The purpose of this study was to understand the impact of the poly (lactic-co-glycolic acid) (PLGA) molecular behavior in the feed solution on the drug release kinetics of PLGA microparticles prepared via spray drying. The PLGA molecular behavior in the feed solutions were characterized by using tube viscometry, which provides information about the polymer coil radius (R_coil), the Martin constant (K_m), and the overlap concentration (c*). The particle size and the drug surface enrichment were investigated by using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The drug release profiles were characterized by using the USP paddle method and analyzed by using the Crank's diffusion model to calculate the kinetic parameters. Multivariate data analysis using principal component analysis (PCA) was employed to display the relationship between the PLGA molecular behavior, particle properties and the drug release kinetics from the spray dried PLGA microparticles. Rheological studies suggested that an increased molar ratio of a poor solvent (methanol) in the solvent system resulted in a decreased R_coil, the increase in K_m and c*. The higher effective diffusion coefficient of drug calculated by using the Crank's diffusion model was observed in the polymer matrix prepared at an acetone-to-methanol molar ratio of 69:31. The PCA models indicated that the drug surface enrichment and the K_m were directly proportional to the drug burst release, while the entanglement index was inversely correlated. Further, the particle size had a less significant impact on the drug burst release. This study implies that the polymer molecular behavior would influence the microscopic connectivity and diffusivity of polymer matrix, which eventually affects the drug release kinetics.     

Controlled antibody release from a matrix of poly(ethylene-co-vinyl acetate) fractionated with a supercritical fluid

A new method is presented for controlling the rate of antibody (Ab) release from an inert matrix composed of poly(ethylene-co-vinyl acetate) (EVAc), a biocompatible polymer that is frequently used to achieve controlled release. Using supercritical propane, a parent EVAc sample (M_n = 70 kDa, M_w/M_n = 2.4) was separated into narrow fractions with a range of molecular weights (8.7 < M_n < 165 kDa, 1.4 < M_w/M_n < 1.7). Solid particles of Ab were dispersed in matrices composed of different polymer fractions and the rate of Ab release into buffered saline was measured. The rate of Ab release from the EVAc matrix depended on molecular weight: > 90% of the incorporated Ab was released from low molecular weight fractions (M_n < 40 kDa) during the first 5 days of release, while < 10% was released from the high molecular weight fraction (M_n > 160 kDa) during 14 days of release. No significant differences in polymer composition, glass-transition temperature, or crystallinity were identified in the different molecular weight fractions of EVAc. Mechanical properties of the polymer did depend on the molecular weight distribution, and correlated directly with Ab release rates. Because it permits rapid and reproducible fractionation of polymers, supercritical fluid extraction can be used to modify the performance of polymeric biomaterials. © 1993 John Wiley & Sons, Inc.     

Study on the polymerization of ϵ‐caprolactam in the interlamellar spaces of [TEACOOH]–montmorillonite intercalations complex and its characterization

The polymerization of ?‐caprolactam between the interlamellar spaces of the [TEACOOH]–montmorillonite intercalations complex was attempted using Na–montmorillonite and 10‐carboxy‐n‐decyltriethylammonium bromide to achieve [TEACOOH]–polycaprolactam–montmorillonite, in which montmorillonite (inorganic polymer) is chemically bonded with the polycaprolactam (organic polymer). The results of X‐ray and IR analysis for the samples obtained after polymerization showed that the polymerization reaction has been successfully accomplished. For the purpose of studying the polymeric reaction product more precisely, we have isolated the polymerized product from the silicate layers and analyzed it with X‐ray diffractometer and IR spectrometer. Comparison of the results of X‐ray and IR analysis between the isolated polymer and the polymer that was synthesized by the reaction of ?‐caprolactam only with the organic cation without montmorillonite showed that both obtained polymers are the same compounds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1904–1910, 2003     

In vitro degradation and drug‐release behavior of electrospun,fibrous webs of poly(lactic‐co‐glycolic acid)

Ultrafine fibrous webs of poly(lactide‐co‐glycolic acid) (PLGA) containing the bactericidal antibiotic drug rifampin were prepared by electrospinning, and their properties were investigated for wound‐dressing applications. Because PLGA is a biodegradable and biocompatible polymer, it is one of the best materials for the preparation of wound‐dressing substrates. Through this investigation of PLGA/rifampin electrospun webs, we found that the in vitro degradation reached approximately 60% in 10 days, and the drug release from the webs showed a fast and constant profile suitable for wound‐dressing applications. Also, we observed that both the web‐degradation rate and the drug‐release rate increased as the drug concentration in the PLGA/rifampin electrospun webs and the content level of glycolide units in the PLGA polymer matrix increased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Amphiphilic PLGA-PEG-PLGA triblock copolymer nanogels varying in gelation temperature and modulus for the extended and controlled release of hyaluronic acid

Different compositional parameters of poly(_D,L-lactic-co-glycolic acid)-b-poly(ethylene glycol) triblock copolymers (PLGA-PEG) were varied to analyze their effect on gel formation and mechanical properties. Parameters such as hydrophilic/hydrophobic ratio (PLGA/PEG ratio), lactic acid/glycolic acid ratio (LA/GA ratio), PEG molecular weight (PEG Mw), polymer solution concentration, copolymer molecular weight (Mw), and polydispersity index (PDI) were studied in this work. For copolymers with PEG Mw of 1500 Da, gelation temperature (34–37 °C) was affected by _D,L-LA/GA ratio and Mw; while modulus was affected by LA/GA ratio, Mw, and Mn. Based on the parametric study, an injectable, thermoresponsive hyaluronic acid (HA) delivery platform was designed for ocular applications. PLGA-PEG copolymers with _D,L-LA/GA ratio of 15/1, PLGA/PEG ratio of 2/1, PEG Mw of 1500 Da, and Mw of about 6 KDa gelled at 35 °C, were optically transparent, had a modulus less than 350 Pa and were used for HA release studies. This work also demonstrates, for the first time, an extended and controlled release of HA, beyond 2 weeks, from injectable hydrogels modified with a noncovalent interacting agent, poly(L-lysine). Smaller PLL chains slowed down the HA release kinetics, while larger PLL chains produced a release profile similar to the nonmodified hydrogels. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48678.     

Synthesis and characterization of biodegradable low molecular weight aliphatic polyesters and their use in protein‐delivery systems

Poly(lactic acid) (PLA) and poly(lactic‐co‐GA) (PLGA) with low molecular weights were synthesized by a one‐step polycondensation of lactic acid (LA) with glycolic acid (GA) molecules using stannous octoate as a catalyst at 160°C. A high yield (>80%) of all the polymers was obtained in the study. The PLA and PLGA copolymers were characterized by ¹H‐NMR, GPC, and DSC measurements, etc. We elaborated HSA‐loaded microspheres based on PLA and PLGA copolymers with different monomer ratios (LA/GA = 85:15, 75:25, 65:35, and 50:50) by the solvent‐extraction method based on the formation of double w/o/w emulsion. Microspheres were characterized in terms of the morphology, size, and encapsulation efficiency (E.E.). The highest E.E. (69.3%) of HSA was obtained for HSA‐loaded PLGA (65/35) microspheres among all the formulations. In vitro matrix degradation and protein release of these microspheres were performed in phosphate‐buffer saline (PBS; 154 mM, pH 7.4). The degradation profiles were characterized by measuring the loss of the microsphere mass and the decrease of the polymer intrinsic viscosity. The release profiles were investigated from the measurement of the protein presented in the release medium at various intervals. It was shown that the matrix degradation and protein‐release profiles were highly LA/GA ratio‐dependent. It is suggested that these matrix polymers may be optimized as carriers in protein‐ and peptide‐delivery systems for different purposes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1848–1856, 2004     

Crystal structure,curing kinetics,and thermal properties of bisphenol fluorene epoxy resin

Diglycidyl ether of 9,9‐bis(4‐hydroxyphenyl) fluorene (DGEBF) monomer was successfully synthesized and characterized in detail. The crystal structure of DGEBF was measured by single‐crystal X‐ray diffraction analysis. Curing kinetics of DGEBF with 4,4‐diaminodiphenyl sulfone (DDS), thermal properties, and decomposition kinetics were investigated using nonisothermal differential scanning calorimetry (DSC) according to Kissinger, Ozawa and Crane methods. The glass transition temperature (T_g), thermal properties of cured polymer were estimated by DSC, dynamic mechanical analysis, and thermogravimetric analyses. Epoxy value of DGEBF monomer up to theoretical value leads to higher crosslink density of cured polymers. The cured DGEBF/DDS system exhibited obvious higher T_g and better thermal stability compared to those of DGEBF/diamine systems reported previously. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Physical properties of PLGA films during polymer degradation

The rates of change of polymer properties (glass transition temperature, weight fraction sorbed water, and polymer molecular weight) were determined in poly (DL ‐lactide‐co‐glycolide) films under accelerated storage conditions. Films were stored at 70°C and 95%, 75%, 60%, 45%, or 28% relative humidity. Weight fraction sorbed water was determined by thermogravimetric analysis, the glass transition temperature (Tg_mix) of the polymer/water mixture by modulated temperature differential scanning calorimetry, and PLGA number‐average molecular weight (M_n) by size exclusion chromatography (SEC). Rates of moisture increase and Tg_mix decrease were related to the decrease in PLGA M_n through a modification of the Gordon‐Taylor equation. Understanding the relative rates of polymer physical and chemical degradation will allow for improved design of PLGA formulations that control rates of drug delivery and preserve drug stability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009