Biodegradability of poly(lactic-co-glycolic acid) after femtosecond laser irradiation

Biodegradation is a key property for biodegradable polymer-based tissue scaffolds because it can provide suitable space for cell growth as well as tailored sustainability depending on their role. Ultrashort pulsed lasers have been widely used for the precise processing of optically transparent materials, including biodegradable polymers. Here, we demonstrated the change in the biodegradation of a poly(lactic-co-glycolic acid) (PLGA) following irradiation with femtosecond laser pulses at different wavelengths. Microscopic observation as well as water absorption and mass change measurement revealed that the biodegradation of the PLGA varied significantly depending on the laser wavelength. There was a significant acceleration of the degradation rate upon 400 nm-laser irradiation, whereas 800 nm-laser irradiation did not induce a comparable degree of change. The X-ray photoelectron spectroscopy analysis indicated that laser pulses at the shorter wavelength dissociated the chemical bonds effectively, resulting in a higher degradation rate at an early stage of degradation.

High-frequency (20 to 40 MHz) acoustic response of liquid-filled nanocapsules

Liquid-core nanoparticles are promising candidates for targeted ultrasound-controlled therapy, but their acoustic detection remains challenging. High-frequency (20 to 40 MHz) tone burst sequences were implemented with a programmable ultrasound biomicroscope to characterize acoustic response from perfluorooctyl bromide-core nanoparticles with thick poly(lactide-coglycolide) (PLGA) shells. Radio-frequency signals were acquired from flowing solutions of nanoparticles with two different shell-thickness-to-particle-radius ratios, solid PLGA nanoparticles, and latex nanobeads (linear controls). Normalized fundamental (20 MHz) and second-harmonic power spectral density (PSD) increased with particle concentration and was highest for the thinnest shelled particles. The second- harmonic PSD was detectable from the nanoparticles for peak rarefactional pressures (PRP) from 0.97 to 2.01 MPa at 23 cycles and for tone bursts from 11 to 23 cycles at 2.01 MPa. Their second-harmonic¿to¿fundamental ratio increased as a function of PRP and number of cycles. Within the same PRP and cycle ranges, the second-harmonic¿to¿fundamental ratios from matched concentration solutions of latex nanobeads and solid PLGA nanoparticles was more weakly detectable but also increased with PRP and number of cycles. Nanoparticles were detectable under flow conditions in vitro using the contrast agent mode of a high-frequency commercial scanner. These results characterize linear acoustic response from the nanoparticles (20 to 40 MHz) and demonstrate potential for their highfrequency detection.

Role of hydroxypropyl-β-cyclodextrin on freeze-dried and gamma-irradiated PLGA and PLGA-PEG diblock copolymer nanospheres for ophthalmic flurbiprofen delivery

Poly(D,L-lactide-co-glycolide) and poly(D,L-lactide-co-glycolide) with poly(ethylene glycol) nanospheres (NSs) incorporating flurbiprofen (FB) were freeze-dried with several cryoprotective agents and sterilized by γ-irradiation. Only when 5.0% (w/v) hydroxypropyl-β-cyclodextrin (HPβCD) was used, a complete resuspension by manual shaking and almost identical particle size of the NSs was obtained after freeze-drying. In vitro drug release and ex vivo corneal permeation of NSs with and without HPβCD were evaluated. The presence of HPβCD resulted in a reduction of burst effect, providing a more sustained release of the drug. A significant decrease in the FB transcorneal permeation of NSs containing HPβCD was obtained, related to the slower diffusion of FB observed in the in vitro results. The uptake mechanism of the NSs was examined by confocal microscopy, suggesting that NSs penetrate corneal epithelium through a transcellular pathway. Ocular tolerance was assessed in vitro and in vivo by the Eytex™ and Draize test, respectively. Long-term stability studies revealed that γ-irradiated NSs stored as freeze-dried powders maintained their initial characteristics. Stability studies of the resuspended NSs after 3 months of storage in the aqueous form showed that NSs were stable at 4°C, while formulations stored at 25°C and 40°C increased their initial particle size.

Influence of ultrasonic processing on the macromolecular properties of poly (D,L-lactide-co-glycolide) alone and in its biocomposite with hydroxyapatite

In this work poly(D,L-lactide-co-glycolide) (PLGA) and a poly(d,l-lactide-co-glycolide)/hydroxyapatite (PLGA/HAp) composite processed in an ultrasonic field at higher (25 degrees C) and lower (8 degrees C) temperatures were studied with respect to the molecular properties of the obtained materials. The processing of the PLGA and the PLGA/HAp composite in an ultrasonic field resulted in a change of molar mass averages of the polymer/polymeric part of these materials, while an amorphous structure and a 50:50 lactide-to-glycolide co-monomer ratio were preserved without the formation of crystalline oligomers. However, mobility of polymeric chains obtained after ultrasonic processing was lower indicating ordering the structure of polymeric chains as a result of processing. Additionally, it was observed that the mobility of the PLGA macromolecules was lower within the composite in comparison with the mobility of the chains within the PLGA alone in the case when both were obtained after ultrasonic processing. This was a consequence of the structure formation through the interactions between the PLGA and the HAp. Based on these results different degradation rate of PLGA in composite can be expected, which is important in the application of this material for the controlled drug delivery of medicaments.

Surface characterization by atomic force microscopy of sterilized PLGA microspheres

Atomic force microscopy (AFM) is recognized a suitable and powerful technique for surface and morphological analysis. Even if until now this technique has not been frequently used in the pharmaceutical field, it can contribute to an accurate morphologic characterization of microspheres and nanospheres. In this work, atomic force microscopy has been used to perform the surface characterization of sterilized microspheres. The aim is to investigate the morphologic modifications induced by gamma irradiation on poly(lactide-co-glycolide) microspheres loaded with ovalbumin and to compare the results obtained by AFM to those obtained by scanning electron microscopy (SEM). The results obtained show that, with respect to SEM, AFM can give some additional information regarding the modifications induced by gamma-irradiation on microspheres surface morphology. The significant changes in surface roughness after irradiation are indicative of damage due to gamma-irradiation. The unchanged surface roughness values calculated for microspheres containing PEG in their matrix, suggest that this polymer exerts a protective effect towards gamma-irradiation.

Effects of common sterilization methods on the structure and properties of poly(D,L lactic-co-glycolic acid) scaffolds

While methods for the production of scaffolds with the appropriate mechanical properties and architecture for tissue engineering are attracting much attention, the effects of subsequent sterilization processes on the scaffold properties have often been overlooked. This study sought to determine the effects of sterilization with ethanol, peracetic acid, ultraviolet irradiation, and antibiotic solution on the structure of 50:50 (mol:mol) 65:35, and 85:15 poly(D,L-lactic-co-glycolic acid [PLGA]) flat-sheet and hollow-fiber scaffolds. All methods resulted in scaffold sterilization, but scanning electron microscopy revealed deformations to the scaffold surface for all treatments. The extent of surface damage increased with treatment duration. This was further investigated by measurement of pore sizes, water flux, breaking strain, and Young's modulus. External pore size and water flux was found to be increased by all treatments in the following order: ethanol (largest), antibiotics, ultraviolet light, and peracetic acid. Pore sizes were 0.25 to 0.17 microm and water flux ranged from 0.01 kg x m(-2) x s(-1) to 3.34 kg x m(-2) x s(-1). For all samples, the Young's modulus was 1.0 to 31.1 MPa and breaking strain was 1.2 to 2.4 MPa. The results of this study suggest that antibiotic treatment shows the most potential to sterilize PLGA hollow fibers for tissue engineering.

Radiosterilisation of indomethacin PLGA/PEG-derivative microspheres: Protective effects of low temperature during gamma-irradiation

Currently, gamma-irradiation seems to be a good method for sterilising drug delivery systems made from biodegradable polymers. The gamma-irradiation of microspheres can cause several physicochemical changes in the polymeric matrix. These modifications are affected by the temperature, irradiation dose and nature of the encapsulated drug and additives. This study has aimed to evaluate the influence of temperature during the sterilisation process by gamma irradiation in indomethacin PLGA microspheres including a PEG-derivative. Microspheres were prepared by the solvent evaporation method from o/w emulsion and were then exposed to gamma-irradiation. A dose of 25 kGy was used to ensure effective sterilisation. Some microspheres were sterilised with dry ice protection that guaranteed a low temperature during the process whilst others were sterilised without such dry ice protection. The effects of gamma-irradiation on the characteristics of non-loaded PLGA/PEG-derivative and indomethacin loaded PLGA/PEG-derivative microspheres with and without protection were studied. Non-protected microspheres showed changes in their morphological surface, polymer glass transition temperature, molecular weight and release rate of indomethacin after sterilisation. However, microspheres sterilised with protection did not show significant differences after gamma-irradiation exposure. The sterilisation method was satisfactory when the indomethacin loaded microspheres including a PEG-derivative were exposed to gamma-irradiation at low temperature.

Perfusion culture enhances osteogenic differentiation of rat mesenchymal stem cells in collagen sponge reinforced with poly(glycolic Acid) fiber

The objective of this study was to obtain fundamental knowledge about in vitro culture systems to enhance the proliferation and differentiation of mesenchymal stem cells (MSCs) in collagen sponge reinforced by the incorporation of poly(glycolic acid) (PGA) fiber. A collagen solution with PGA fiber homogeneously localized at PGA:collagen weight ratios of 0.67, 1.25, 2.5, and 5 was freezedried, followed by cross-linking of combined dehydrothermal, glutaraldehyde, and ultraviolet treatment. Scanning electron microscopy revealed that collagen sponges exhibited homogeneous and interconnected pore structures with an average size of 180 microm, irrespective of PGA fiber incorporation. When rat MSCs were seeded into collagen sponge with or without PGA fiber incorporation, more attached cells were observed in collagen sponge incorporating PGA fiber than in collagen sponge without PGA fiber incorporation, irrespective of the PGA:collagen ratio. The proliferation and osteogenic differentiation of MSCs in PGA-reinforced sponge at a weight ratio of 5 were greatly influenced by the culture method and growth conditions. Alkaline phosphatase (ALP) activity and osteocalcin content of MSCs cultured in PGA-reinforced sponge by the perfusion method became maximum at a flow rate of 0.2 mL/min, although they increased with culture time period. It may be concluded that appropriate perfusion conditions enable MSCs to positively improve the extent of proliferation and differentiation.

The effect of gamma-irradiation on PLGA/PEG microspheres containing ovalbumin

Poly(ethylene glycol) (PEG) and sodium chloride (NaCl) are excipients used in PLGA microsphere preparation to stabilize proteins and reduce their burst release. No information is till now available in the literature on the effect due to the use of such excipients on the biopharmaceutical performance of gamma-irradiated microparticulate systems. On this purpose, different batches of microspheres containing ovalbumin (OVA) were prepared by using a PLGA 50:50 (average Mr: 13000), different amounts of PEG (Mr: 400 or 4000) and/or sodium chloride. The non-irradiated and irradiated microspheres were characterized in terms of morphology (SEM, particle size distribution), OVA and PEG content and in vitro OVA release. Radiolysis mechanisms of OVA and OVA loaded microspheres were investigated by EPR analysis. Gamma irradiation affects either microsphere morphology or the release of OVA as a function of the amount of PEG, and the use of NaCl. Irradiation significantly reduces release rate of protein from the microspheres containing 15% and 30% of PEG and from controls (microspheres without additives), while no significative effect on protein release rate is highlighted on microspheres containing lower amounts of PEG. EPR investigation shows that increasing amounts of PEG up to 30% have a perturbation effect on OVA radiolysis path.

The effect of freeze-drying with different cryoprotectants and gamma-irradiation sterilization on the characteristics of ciprofloxacin HCl-loaded poly(D,L-lactide-glycolide) nanoparticles

In the present study, the influence of freeze-drying with several cryoprotective agents and gamma (gamma)-irradiation sterilization on the physicochemical characteristics of ciprofloxacin HCl-loaded poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles was evaluated. Nanoparticles were prepared by W/O/W emulsification solvent evaporation followed by high-pressure homogenization. They were freeze-dried in the presence of 5.0% (w/v) mannitol, trehalose or glucose, with 5.0% (w/v) or 15.0% (w/v) dextran as cryoprotectants. The nanoparticles were irradiated at a dose of 25 kGy using a 60Co source. The following physicochemical properties of the formulations were investigated: the ratio of particle size before (initial) and after freeze-drying, the ease of reconstitution of the nanoparticle suspensions and the drug-release profiles of irradiated and non-irradiated nanoparticles. The antibacterial activity against Pseudomonas aeruginosa was measured. The freeze-drying process induced a significant increase in particle size when no cryoprotectant was employed. Similar results were observed when cryoprotectants were added to the formulation. Only when mannitol was used was no significant size increase measured. Moreover, for formulations with dextran, reconstitution after freeze-drying was difficult by manual agitation and particle size could not be determined because of aggregation. After gamma-sterilization no significant difference in mean particle size was observed, but reconstitution was more difficult and drug release was influenced negatively. Ciprofloxacin HCl incorporated in the nanoparticles was still effective against the micro-organism selected after freeze-drying and gamma-sterilization.

Impregnation of Plasmid DNA into Three-Dimensional Scaffolds and Medium Perfusion Enhancein VitroDNA Expression of Mesenchymal Stem Cells

This article describes the development of an in vitro culture system to enhance the expression of a plasmid DNA for mesenchymal stem cells (MSCs) by a combination of plasmid DNA impregnation into three-dimensional cell scaffolds and culture methods. Gelatin was cationized by introducing spermine to the carboxyl groups for complexation with the plasmid DNA. As the MSC scaffold, poly(glycolic acid) (PGA) fiber fabrics, collagen sponges, and collagen sponges reinforced by incorporation of PGA fibers were used. A complex of cationized gelatin and plasmid DNA encoding bone morphogenetic protein 2 (BMP-2) was impregnated into the scaffolds. Plasmid DNA was released from PGA-reinforced collagen sponge for longer than from the other scaffolds. MCS were seeded into each type of scaffold and cultured by static, stirring, and perfusion methods. When MSCs were cultured in PGA-reinforced sponge, the level of BMP-2 expression was significantly enhanced by perfusion culture compared with the other culture methods, and the time of expression was prolonged. Irrespective of the culture method, the expression level was significantly higher from plasmid DNA impregnated in scaffold than by plasmid DNA in medium. The alkaline phosphatase activity and osteocalcin content of MSCs cultured in PGA-reinforced sponge by the perfusion method were significantly higher compared with those of other methods, and a significantly higher amount of plasmid DNA internalized into MSCs was observed. We conclude that a combination of plasmid DNA-impregnated PGA-reinforced sponge and the perfusion method was promising to promote in vitro gene expression for MSCs.

Proliferation and Differentiation of Rat Bone Marrow Stromal Cells on Poly(glycolic acid)–Collagen Sponge

We studied the effects of dexamethasone (Dex) and basic fibroblast growth factor (bFGF) on proliferation and differentiation of rat bone marrow stromal cells (RBMSCs), using three scaffolds: collagen sponge, poly(glycolic acid) (PGA)-collagen sponge, and PGA-collagen (UV) sponge. RBMSCs were seeded into the sponges, and cultured in primary medium, primary medium with Dex, and primary medium with bFGF and Dex. Three weeks after cultivation, we examined alkaline phosphatase (ALP) activity and cell number in the sponges, and also performed macroscopic, light microscopic, and scanning electron microscopic (SEM) observations. Collagen sponge shrank considerably, but PGA-collagen and PGA-collagen (UV) sponges maintained most of their original shape. PGA-collagen (UV) sponge supplemented with bFGF and Dex together had the highest ALP activity and cell number, followed by PGA-collagen sponge. Although collagen sponge showed cell proliferation only on the surface, the other two sponges showed cell proliferation in the interior. SEM showed the best cell attachment to PGA-collagen (UV) sponge in the presence of bFGF and Dex, followed by PGA-collagen sponge. In conclusion, PGA-collagen (UV) and PGA-collagen sponges proved to be much more useful as scaffolding for bone regeneration when combined with bFGF and Dex.

Influence of electron-beam radiation on the hydrolytic degradation behaviour of poly(lactide-co-glycolide) (PLGA)

The purpose of this study is to examine the effect of electron-beam (e-beam) radiation on the hydrolytic degradation of poly(lactide-co-glycolide) (PLGA) films. PLGA films were irradiated and observed to undergo radiation-induced degradation through chain scission, as observed from a drop in its average molecular weight with radiation dose. Irradiated (5, 10 and 20 Mrad) and non-irradiated (0 Mrad) samples of PLGA were subsequently hydrolytically degraded in phosphate-buffered saline solution at 37.0 degrees C over a span of 12 weeks. It was observed that the natural logarithmic molecular weight (lnMn) of PLGA decreases linearly with hydrolytic degradation time. The rate of water uptake is higher for samples irradiated at higher radiation dose (e.g. 20 Mrad) and subsequently causing an earlier onset of mass loss. It is postulated that the increase in water uptake is due to the presence of more hydrophilic end groups, which results in the formation of microcavities because of an increase in osmotic pressure. A relationship between radiation dose and the rate of hydrolytic degradation of PLGA films, through its molecular weight was also established. This relationship allows a more accurate and precise control of the life span of PLGA through the use of e-beam radiation.

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.

Study of gamma-irradiation effects on aciclovir poly(D,L-lactic-co-glycolic) acid microspheres for intravitreal administration

Gamma-irradiation effects on aciclovir poly(D,L-lactic-co-glycolic) acid (PLGA) microspheres, with gelatin as additive, were studied. Microspheres with a 2:2:10 aciclovir:gelatin:polymer ratio were prepared by the solvent evaporation method and sterilised by gamma-irradiation at a dose of 25 kGy. Loading efficiency, morphology (particle size analysis, scanning electron microscopy (SEM)), physical chemistry (infrared (IR) absorption spectrophotometry, differential scanning calorimetry (DSC), X-ray diffraction and gel permeation chromatography (GPC)) and in vitro release assays for 73 days were performed to evaluate the sterilisation effect on microsphere characteristics. After gamma-irradiation, no surface changes were observed by SEM. Microparticle mean diameter and aciclovir loading efficiency were not affected by gamma-ray exposition. IR spectroscopy, DSC and X-ray diffraction showed no modification of the bulk properties of the microspheres or their components. The controlled release profiles of aciclovir-loaded microspheres for 73 days were not altered upon exposure to gamma-irradiation. GPC measurements showed a decrease in molecular weight of the polymer. The sterilisation method is adequate because microspheres underwent no change after exposition to gamma-irradiation. These favourable properties of the aciclovir-loaded microspheres make them a suitable system for the intravitreal treatment of herpes virus infections, in an animal model.

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

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

Release of paclitaxel from polylactide-co-glycolide (PLGA) microparticles and discs under irradiation

Paclitaxel is a promising anti-cancer drug as well as a radiosensitizer for chemotherapy and radiotherapy applications. Because of the poor solubility of paclitaxel in water and most pharmaceutical reagents, it is usually formulated with an adjuvant called Cremophor EL, which causes severe side effects. This work develops new dosage forms of paclitaxel for controlled release application, which do not require the adjuvant and, thus, can avoid its associated side effects. Paclitaxel was encapsulated into the PLGA matrix with various additives such as polyethylene glycol (PEG), isopropyl myristate (IPM) and d-alpha tocopheryl polyethylene glycol (Vitamin E TPGS). These additives were used to enhance the release rate of paclitaxel from the polymer matrix. Spray-drying and an hydraulic press were used to prepare paclitaxel-PLGA microspheres and discs. The microspheres and discs were given different irradiation doses to investigate their effects on the surface morphology (characterized by SEM, AFM and XPS) and in vitro release properties. There seems to be a small effect of the ionizing radiation on various formulations. Although the irradiation did not cause observable changes on the morphology of the polymer matrix, the release rate can be enhanced by a few per cent. It was found that PEG has the highest enhancement effect for release rate among all the additives investigated in this study.

Tissue welding with biodegradable polymer films-demonstration of acute strength reinforcement in vivo

BACKGROUND AND OBJECTIVES

To demonstrate, in vivo, acute strength reinforcement benefits of polymer film patches.

STUDY DESIGN/MATERIALS AND METHODS

Full thickness incisions created in a dorsal skin flap of Sprague-Dawley rats were closed by laser-tissue welding: albumin solder was topically applied to the incision on the dermal surface, and a poly(lactic-co-glycolic acid) (PLGA) polymer film placed on the solder as a patch (controls had no film). Breaking strength was tested acutely (15-20 minutes after sacrifice).

RESULTS

The patched incisions were statistically stronger than the controls (ANOVA, P < 0.05).

CONCLUSIONS

Polymer film patches may be a viable method to increase acute breaking strengths of welds using topically applied solder.

The effect of therapeutic irradiation on LactoSorb absorbable copolymer

Bioabsorbable implants continue to gain popularity in providing temporary internal fixation due to their many advantages over metallic internal fixation. Coincident with the presence of internal fixation devices, it may be necessary to use radiotherapy to treat tumors. While metal implants can alter the distribution of the radiotherapy beam, bioabsorbable polymer implants are, essentially, tissue equivalent. This ionizing irradiation, in sufficiently high dose, can affect polymers through chain scission and cross-linking and accelerate the hydrolysis of absorbable polymers. However, little is known about the effects of therapeutic doses on such materials. This study exposed LactoSorb (Biomet, Inc., Warsaw, IN) absorbable copolymer to doses of x-ray irradiation in a clinically relevant manner, in vitro, with individual doses of 2 Gy administered five days per week for up to eight weeks, yielding a total cumulative dose of up to 80 Gy. Specimens were tested both mechanically and for inherent viscosity. Overall, the LactoSorb specimens withstood exposure to the irradiation exceedingly well, providing empirical evidence of the suitability of this material for temporary internal fixation when subsequent radiotherapy in the region is probable.

Gamma irradiation effects and EPR investigation on poly(lactide-co-glycolide) microspheres containing bupivacaine

The effects of gamma radiation on the stability of microspheres made of a polylactide-co-glycolide 50:50 copolymer (PLGA) and loaded with 40% bupivacaine (BU) were studied. The radiolysis mechanisms of BU and BU-loaded microspheres were investigated by using electronic paramagnetic resonance (EPR) analysis. Microspheres were prepared by means of a spray drying method. Gamma Irradiation was carried out in the open, at the dose of 25 kGy, by using a 60Co source. The stability of BU-loaded microspheres was evaluated over a 1-year period on the basis of drug content and dissolution profile. Non-irradiated microspheres were stable over the whole period under consideration. Immediately after irradiation the amount of BU released after 24 h from irradiated microspheres increased from 17 to 25%; in the following 3 months of storage it increased to about 35%, and then it kept constant for 1 year. Radicals generated by BU irradiation were identified by EPR analysis; the sensitivity to gamma radiation of BU was about four times lower than that of PLGA. Furthermore, the EPR spectra of loaded microspheres showed that the relative abundance of BU radicals plus PLGA radicals was proportionate to the electronic fractions of the components; this implies that no spin transfer BU/PLGA had occurred during gamma irradiation.

PLGA-based microparticles: elucidation of mechanisms and a new, simple mathematical model quantifying drug release

The two major aims of this study were: (i) to elucidate the underlying release mechanisms from drug-loaded, erodible microparticles based on poly(lactic-co-glycolic acid) (PLGA) showing biphasic drug release behavior: an initial 'burst' effect, followed by a zero order release phase; and (ii) to develop a new, simple mathematical model that allows the quantitative description of the observed in vitro drug release patterns from this type of delivery system. PLGA-based microparticles offer various advantages, such as the possibility to control the resulting drug release rate accurately over prolonged periods of time, easiness of administration (e.g., by stereotaxic injection), good biocompatibility and complete erosion (avoiding the removal of empty remnants). Consequently, the practical importance of these advanced drug delivery systems is remarkably increasing. However, only little knowledge is yet available concerning the processes controlling the release rate of the drug out of these devices. Various chemical and physical phenomena are involved, rendering the identification of the crucial mechanisms and the mathematical description of the resulting drug release kinetics difficult. In the present study, different physicochemical characterization methods (e.g., DSC, SEM, SEC, particle size analysis) were used to monitor the changes occurring within anticancer drug-loaded PLGA microparticles upon exposure to phosphate buffer pH 7.4. Based on these experimental findings, the most important underlying drug release rate controlling mechanisms were identified and a new mathematical model was developed that allows the quantitative description of the resulting release patterns.

Resorbable polymer fibers for ligament augmentation

Resorbable augmentation devices for cruciate ligament surgery have been developed to temporarily protect healing tendon grafts or sutured ligaments against high tensile loads during the postoperative healing period. Materials available at present [e.g., polydioxanone (PDS)] show a half-life tensile strength of only 4-6 weeks, whereas the process of revitalization and recovering of the transplanted tendon graft can take up to 12 months. Therefore, a device that provides gradually decreasing mechanical properties with a half-time strength of at least 6 months would be desirable. In order to obtain a suitable material, we investigated the degradation kinetics of a variety of different resorbable fibers made of poly(L-lactide) and poly(L-lactide-co-glycolide). The fiber materials differed in processing and treatment parameters like thermal posttreatment, irradiation, and fiber diameter. The fibers were degraded in vitro and were tested for mechanical properties and molecular weight at various time points up to 72 weeks. The half-time strength of the materials ranged between 5 and 64 weeks, depending on their treatment parameters. In contrast, the stiffness did not decrease adequately. However, an augmentation stiffness that does not change much versus time could not provide a gradual increase in graft load, which is important to stimulate the orientation of the collagenous tissue. Therefore, design of an augmentation construct braided out of more than one quickly degrading fiber materials is suggested. After the breakdown of the faster-degrading fiber components the stiffness would automatically decrease by the diminution of the load-carrying fiber volume.

PLGA microsphere bioburden evaluation for radiosterilization dose selection

The aim of this study was to determine the bioburden of PLGA microspheres produced by the solvent emulsion/extraction process as a means of determining an appropriate gamma-irradiation dose for sterilization. Bioburden was evaluated on the basis of ISO specifications. The analysis of initial microbial contamination was performed on blank microspheres, prepared by a non-aseptic laboratory scale process. A mean bioburden of 36.04 CFU (colony forming units)/110 mg microspheres was determined. Most of the detected germs originated from human commensal flora. According to the ISO dose-selection method, a gamma-irradiation dose of 19.6 kGy was found sufficient to ensure a sterility level of 10(-6). The effect of the selected irradiation dose on both the molecular weight of the polymer and the kinetics of 5-fluorouracil drug release from the microspheres was compared to the European Pharmacopeia recommended irradiation dose (25 kGy). This 20% reduced dose showed a lower extent of molecular weight reduction of PLGA and a better control of 5-FU release from microparticles. This can be related to reduce polymer radiation damage.

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.

Gamma irradiation for terminal sterilization of 17beta-estradiol loaded poly-(D,L-lactide-co-glycolide) microparticles

17beta-Estradiol-loaded microparticles using poly-(D, L-lactide-co-glycolide) polymer (PLG) were prepared by a modified spray-drying method and the effects of gamma-irradiation on drug substance, polymer and microparticles were investigated. Irradiation doses ranging from 5.1 to 26.6 kGy were applied using a 60Co-radiation source. 17beta-Estradiol drug substance showed excellent stability against gamma-irradiation in the investigated dose range, whereas microencapsulated estradiol seems to be converted to conjugation products with PLG, and to a lesser extent to the degradation product 9,11-dehydroestradiol. The weight-average molecular weight of the PLG polymers decreased with increasing irradiation dose while polydispersity indices (M(w)/M(n)) remained nearly unchanged, compatible with a random chain scission mechanism in lactide/glycolide-copolymer degradation. In vitro drug release studies showed accelerated kinetics with increasing irradiation doses due to dose dependent polymer degradation. Microbiological process monitoring showed decreasing bioburden with increasing spraying time, which was successfully further reduced by applying irradiation sterilization. Microencapsulated test spore suspensions of Bacillus pumilus ATCC 27142, the official test specimen for the gamma-sterilization process, revealed effective reduction of bioburden, confirming its published D(10) value. In conclusion, our studies demonstrated efficacy of gamma-irradiation as terminal sterilization method for poly-(D,L-lactide-co-glycolide) polymer-based drug delivery systems. The sterilization conditions need to be carefully adjusted for the final dosage form.

Tetracycline-HCl-loaded poly(DL-lactide-co-glycolide) microspheres prepared by a spray drying technique: influence of gamma-irradiation on radical formation and polymer degradation

Tetracycline-HCl (TCH)-loaded microspheres were prepared from poly(lactide-co-glycolide) (PLGA) by spray drying. The drug was incorporated in the polymer matrix either in solid state or as w/o emulsion. The spin probe 4-hydroxy-2,2,6, 6-tetramethyl-piperidine-1-oxyl (TEMPOL) and the spin trap tert-butyl-phenyl-nitrone (PBN) were co-encapsulated into the TCH-loaded and placebo particles. We investigated the effects of gamma-irradiation on the formation of free radicals in polymer and drug and the mechanism of chain scission after sterilization. Gamma-Irradiation was performed at 26.9 and 54.9 kGy using a 60Co source. The microspheres were characterized especially with respect to the formation of radicals and in vitro polymer degradation. Electron paramagnetic resonance (EPR) spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), high-performance liquid chromatography (HPLC), gas chromatography-mass spectroscopy (GC-MS), and scanning electron microscopy (SEM) were used for characterization of the microspheres. Using EPR spectroscopy, we successfully detected gamma-irradiation induced free radicals within the TCH-loaded microspheres, while unloaded PLGA did not contain radicals under the same conditions. The relatively low glass transition temperature of the poly(dl-lactide-co-glycolide) (37-39 degrees C) seems to favor subsequent reactions of free radicals due to the high mobility of the polymeric chains. Because of the high melting point of TCH (214 degrees C), the radicals can only be stabilized in drug loaded microspheres. In order to determine the mechanism of polymer degradation after exposure to gamma-rays, the spin trap PBN and the spin probe TEMPOL were encapsulated in the microspheres. gamma-Irradiation of microspheres containing PBN resulted in the formation of a lipophilic spin adduct, indicating that a polymeric radical was generated by random chain scission. Polymer degradation by an unzipping mechanism would have produced hydrophilic spin adducts of PBN and monomeric radicals of lactic or glycolic acid. These degradation products were not detected by EPR. This result is confirmed by the observation that possible diamagnetic reaction products of low molecular weight, consisting of TEMPOL and lactide or glycolide monomers, could not be detected by GC-MS. While an irradiation dose-dependent decrease in molecular weight of PLGA could be verified in agreement with the literature, TCH content of the microspheres was not affected by the exposure to gamma-rays. It can be concluded that EPR spectroscopy in combination with GPC, DSC, and HPLC allows a detailed characterization of the impact of gamma-sterilization on biodegradable parenteral drug delivery systems.

Gamma irradiation effects on poly(DL-lactictide-co-glycolide) microspheres

Gamma radiation treatment plays an increasingly important role in the sterilization/sanitization of pharmaceutical products. However, irradiation may affect the stability of the product and thus its safety of use. We investigated the influence of ionizing radiation on modified release microparticulate drug delivery systems made of two types of polylactide-co-glycolide copolymers (PLG): RG 503 and RG 503H; these polymers have identical molecular weights but different chemical structures. The effect of gamma radiation on polymer stability of the raw polymers (P) and related microspheres (Ms) was evaluated. Samples were irradiated at different irradiation doses (5, 15 and 25 kGy) using 60Co as radiation source. The microspheres were prepared using the spray drying technique. Degradation of PLG and related microspheres was evaluated during six months in terms of average molecular weight (Mw) loss by gel permeation chromatography (GPC) and variation in glass transition temperature (Tg) using differential calorimetry (DSC). The presence of free radicals in the product was tested by electron paramagnetic resonance (EPR). Both P and Ms showed a trend in decreasing their Mw at time 0 as a function of irradiation dose. For RG503 the decay in Mw is always negligible for doses below 15 kGy while it is about 10% for 25 kGy. After 150 days Mw decay was 25% in the microspheres and 20% in the raw polymer. It was not possible to evaluate the radiation effect, at different storage times, for RG503H because this polymer resulted to be unstable even in the regular storage conditions without being irradiated. The concentration of radiation-induced free radicals was higher in RG 503H (both P and Ms) and they were more stable than the free radicals species observed in the case of polymer RG 503. Alterations and/or production of new radicals were observed on exposure of RG 503H microspheres to the light. Radiolytic degradation of RG 503 under vacuum is characterized by a prevalence of the chain scission events leading to a decrease of Mw. Some crosslinking can occur mainly in the post irradiation stage through the decay and coupling of the hydrogen abstraction radicals. A hydroperoxydative cycle, whose mechanism is suggested, is generated in the presence of oxygen.

Postoperative irradiation treatment and bioresorbable implants in orthopaedic surgery: an experimental in vitro study

The influence of applied radiation on the degradation of a polyglycolide (PGA) test specimen was studied in vitro. There was no significant difference in the time-dependent degradation behaviour between the irradiated test specimen and controls. Mandatory irradiation of an operation site following surgery therefore does not contradict the employment of bioresorbable implants in orthopaedic surgery.

The effect of gamma irradiation on the enzymatic degradation of polyglycolic acid absorbable sutures

The purpose of the study was to examine the effect of gamma irradiation on the enzymatic as well as the in vivo degradation of polyglycolic acid sutures. The sutures of size 2-0 were irradiated at dosage levels of 0-20 mrad. The three enzymes chosen for this study were esterase, alpha-chymotrypsin, and trypsin. The irradiated sutures were both immersed in the enzyme solutions; their corresponding buffer controls, and implanted in inbred black-and-white hooded hister rats (Liverpool strain). The degradation of PGA sutures was determined mechanically. Among the three enzymes studied, esterase showed the highest enzymatic effect on the degradation of the unirradiated and irradiated PGA sutures. Trypsin's effect on PGA sutures was not observed until 20 mrad. The findings of trypsin demonstrated the hypothesis that synthetic high molecular weight polymers, which are initially resistant to enzymatic degradation, could become prone to enzymatic attack after altering their physical and chemical structures. Implanted PGA sutures maintained a similar or slightly higher mean tensile breaking strength in in vivo degradation compared to in vitro degradation (0.1M tris buffer of pH = 7.5); these degradation profiles suggest that PGA does not display similar behavior in in vivo and in vitro degradations. The magnitude of dissimilarity depends on the radiation dosage and on the duration of degradation, and is speculated to be attributable to the specific action of enzymes with respect to the configuration and chemical structure of the PGA sutures.

Scanning electron microscopic study of the hydrolytic degradation of poly(glycolic acid) suture

This article reports the morphological observations on the surface changes of poly-(glycolic acid) sutures which have been exposed to various dosages of gamma irradiation (0, 2.5, 5.0, 10, 20 and 40 Mrad) and duration of immersion (0, 7, 14, 28, 48, 60, and 90 days) in a physiological saline buffer. The most important gross morphological characteristics of PGA suture hydrolytic degradation is the formation of surface cracks on the filaments. The regularity of the surface cracks increased with an increase in the gamma irradiation and the duration of hydrolysis. Surface cracks were not observed in irradiated sutures that had not been subjected to hydrolytic degradation. The arrangement of the surface cracks, their orientation on the filaments, and the direction of crack propagation provide very useful information for depicting the mechanism of hydrolytic degradation in this class of fibrous material. The microfibrillar model of fiber structure has been used as the basis for the proposed degradation mechanism of PGA in vitro. It is believed that hydrolysis occurs initially in the amorphous regions sandwiched between two crystalline zones, as tie-chain segments, free chain ends, and chain folds in these regions degrade into fragments. As degradation proceeds, the size of the fragments reaches the stage at which they can be dissolved into the buffer medium. This dissolution removes the fragments from the amorphous regions, and surface cracks appeared.