Comparison of the enthalpic relaxation of poly(lactide-co-glycolide) 50:50 nanospheres and raw polymer

Utilization of Microfluidics for the Preparation of Polymeric Nanoparticles for the Antioxidant Rutin: A Comparison with Bulk Production

OBJECTIVE

To compare the characteristics of rutin-loaded PLGA (poly(lactic-coglycolic acid)) nanoparticles prepared using a single emulsion evaporation method (bulk method) and a nanoprecipitation method using microfluidics.

METHODS

Rutin-loaded PLGA nanoparticles were produced using different methods and characterized for size, zeta potential, entrapment efficiency (EE) and drug loading (DL). A design of experiments approach was used to identify the effect of method parameters to optimize the formulation. DSC was used to investigate the solid-state characteristics of rutin and PLGA and identify any interactions in the rutin-loaded PLGA nanoparticles. The release of rutin from PLGA nanoparticles was examined in biorelevant media and phosphate buffer (PBS).

RESULTS

The optimal formulation of rutin-loaded PLGA nanoparticles produced using a microfluidics method resulted in a higher entrapment efficiency of 34 ± 2% and a smaller size of 123 ± 4 nm compared to a bulk method (EE 27 ± 1%, size 179 ± 13 nm). The solidstate of rutin and PLGA changed from crystalline to amorphous with the preparation of rutin- loaded PLGA nanoparticles. More importantly, using microfluidics, rutin released faster from rutin-loaded PLGA nanoparticles in biorelevant media and PBS with higher burst release compared to the rutin release from the nanoparticles prepared by using the bulk method.

CONCLUSION

Rutin can be encapsulated in nanoparticles formulated with different methods with mean sizes of less than 200 nm. Microfluidics produced more uniform rutin-loaded PLGA nanoparticles with a higher EE, DL and faster release compared to a bulk production method.

Ozone Gas as a Benign Sterilization Treatment for PLGA Nanofiber Scaffolds

The use of electrospun nanofibers for tissue engineering and regenerative medicine applications is a growing trend as they provide improved support for cell proliferation and survival due, in part, to their morphology mimicking that of the extracellular matrix. Sterilization is a critical step in the fabrication process of implantable biomaterial scaffolds for clinical use, but many of the existing methods used to date can negatively affect scaffold properties and performance. Poly(lactic-co-glycolic acid) (PLGA) has been widely used as a biodegradable polymer for 3D scaffolds and can be significantly affected by current sterilization techniques. The aim of this study was to investigate pulsed ozone gas as an alternative method for sterilizing PLGA nanofibers. The morphology, mechanical properties, physicochemical properties, and response of cells to PLGA nanofiber scaffolds were assessed following different degrees of ozone gas sterilization. This treatment killed Geobacillus stearothermophilus spores, the most common biological indicator used for validation of sterilization processes. In addition, the method preserved all of the characteristics of nonsterilized PLGA nanofibers at all degrees of sterilization tested. These findings suggest that ozone gas can be applied as an alternative method for sterilizing electrospun PLGA nanofiber scaffolds without detrimental effects.

Recent advances in testing of microsphere drug delivery systems

INTRODUCTION

This review discusses advances in the field of microsphere testing.

AREAS COVERED

In vitro release-testing methods such as sample and separate, dialysis membrane sacs and USP apparatus IV have been used for microspheres. Based on comparisons of these methods, USP apparatus IV is currently the method of choice. Accelerated in vitro release tests have been developed to shorten the testing time for quality control purposes. In vitro-in vivo correlations using real-time and accelerated release data have been developed, to minimize the need to conduct in vivo performance evaluation. Storage stability studies have been conducted to investigate the influence of various environmental factors on microsphere quality throughout the product shelf life. New tests such as the floating test and the in vitro wash-off test have been developed along with advancement in characterization techniques for other physico-chemical parameters such as particle size, drug content, and thermal properties.

EXPERT OPINION

Although significant developments have been made in microsphere release testing, there is still a lack of guidance in this area. Microsphere storage stability studies should be extended to include microspheres containing large molecules. An agreement needs to be reached on the use of particle sizing techniques to avoid inconsistent data. An approach needs to be developed to determine total moisture content of microspheres.

Biomolecule gradient in micropatterned nanofibrous scaffold for spatiotemporal release

Controlled molecule release from scaffolds can dramatically increase the scaffold ability of directing tissue regeneration in vitro and in vivo. Crucial to the regeneration is precise regulation over release direction and kinetics of multiple molecules (small genes, peptides, or larger proteins). To this end, we developed gradient micropatterns of electrospun nanofibers along the scaffold thickness through programming the deposition of heterogeneous nanofibers of poly(ε-caprolactone) (PCL) and poly(D,L-lactide-co-glycolide) acid (PLGA). Confocal images of the scaffolds containing fluorophore-impregnated nanofibers demonstrated close matching of actual and designed gradient fiber patterns; thermal analyses further showed their matching in the composition. Using acid-terminated PLGA (PLGAac) and ester-terminated PLGA (PLGAes) to impregnate molecules in the PCL-PLGA scaffolds, we demonstrated for the first time their differences in nanofiber degeneration and molecular weight change during degradation. PLGAac nanofibers were more stable with gradual and steady increase in the fiber diameter during degradation, resulting in more spatially confined molecule delivery from PCL-PLGA scaffolds. Thus, patterns of PCL-PLGAac nanofibers were used to design versatile controlled delivery scaffolds. To test the hypothesis that molecule-impregnated PLGAac in the gradient-patterned PCL-PLGAac scaffolds can program various modalities of molecule release, model molecules, including small fluorophores and larger proteins, were respectively used for time-lapse release studies. Gradient-patterns were used as building blocks in the scaffolds to program simultaneous release of one or multiple proteins to one side or, respectively, to the opposite sides of scaffolds for up to 50 days. Results showed that the separation efficiency of molecule delivery from all the scaffolds with a thickness of 200 μm achieved >88% for proteins and >82% for small molecules. In addition to versatile spatially controlled delivery, micropatterns were designed to program sequential release of proteins. The hierarchically structured materials presented here may enable development of novel multifunctional scaffolds with defined 3D dynamic microenvironments for tissue regeneration.

Effect Of Structural Relaxation On The Preparation And Drug Release Behavior Of Poly(lactic-co-glycolic)acid Microparticle Drug Delivery Systems

Control of burst release is a major challenge in the development of poly(lactide-co-glycolide) (PLGA) microparticle drug delivery systems. It has been well-documented in previous literature that formulation and processing variables determine particle morphology, which in turn, governs drug diffusivity and burst release. However, it is not generally appreciated that PLGA polymers used for microparticle systems are typically amorphous, and as such, undergo structural relaxation during processing and storage, characterized by enthalpy and volume reduction. Volume reduction due to structural relaxation can decrease drug diffusivity within microparticles and affect burst release. The magnitude of the driving force leading to structural relaxation is linked to the rate of particle hardening, and is affected by process parameters. Studies that directly address structural relaxation in PLGA microparticles indicate that the manufacturing process and residual solvent levels, as well as the nature of the interaction between drug and polymer affect the rate of structural relaxation. Therefore, the conditions chosen for particle fabrication may be a major source of variability in the burst release and may affect the stability of the drug release profile during storage. The potential effects of structural relaxation on drug release are likely to be formulation specific. Additional work is required to understand and control the relationship between microparticle processing, structural relaxation, and performance of PLGA microparticle drug delivery systems.

Physical ageing and thermal analysis of PLGA microspheres encapsulating protein or DNA

PLGA microspheres undergo physical ageing but their ageing kinetics have not been reported, nor the effect of encapsulated protein or plasmid DNA on any associated changes to the glass transition. Differential scanning calorimetry (DSC) was used to measure the rate of ageing of various PLGA microsphere formulations, with temperature-modulated DSC used to accurately measure the associated glass transition. The Cowie-Ferguson model was applied to determine the parameters describing the enthalpy relaxation kinetics. We show that encapsulated proteins had no significant effect on the glass transition of the microspheres, whereas DNA and PVA were mild antiplasticising agents, particularly with high Mw PLGA. Physical ageing occurred through a range of enthalpy relaxation times (or modes) and was independent of both encapsulated protein and surfactant used during microsphere preparation. Analysis of accelerated ageing at 35 degrees C gave calculated enthalpy relaxation times to thermal equilibrium of 280-400 h. No ageing was observed < or = 10 degrees C and at 25 degrees C estimated relaxation times were at least one order of magnitude greater than at 35 degrees C. Ageing of PLGA microspheres therefore occurs at temperatures >10 degrees C, but relaxation will be far from equilibrium unless storage times and/or temperatures are prolonged or nearing the glass transition, respectively.

Localization of bovine serum albumin in double-walled microspheres

Phase separation of binary blends of various combinations of poly (L-lactide) (PLA), and poly (D,L-lactide-co-glycolide) (PLGA), was investigated using differential scanning calorimetry (DSC). Based on this phase separation phenomenon, double-walled microspheres were fabricated. A model agent, bovine serum albumin (BSA) labeled with fluorescein isothiocyanate (FITC-BSA) was localized in each layer. Scanning electron microscopy (SEM) and fluorescence microscopy (FM) were used to assess the formation of double-walled microspheres and the localization of the drug, respectively. When a 1:1 polymer ratio was used, the FITC-BSA was localized in the outer layer. When the relative ratio of PLGA to PLA was increased to 3:1 using the same overall polymer concentration, the FITC-BSA was localized in the inner core. Release studies were carried out to evaluate the advantage of double-walled microspheres compared to single walled microspheres. Microspheres made with FITC-BSA localized in the inner core exhibited a significantly lower initial release rate compared to microspheres where the drug was located in the outer layer, or compared to microspheres made from PLA only. Hence microspheres with a double-walled morphology have the potential for therapeutic use where a high burst might be detrimental.