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Lysozyme distribution and conformation in a biodegradable polymer matrix as determined by FTIR techniques
M van de Weert1, R van 't Hof1, J van der Weerd
1Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences (UIPS), Utrecht University, Sorbonnelaan 16, 3584 CA, Utrecht, The Netherlands. m.vandeweert@pharm.uu.nl
Summary
Lysozyme is evenly distributed within poly(lactic-co-glycolic acid) microspheres, not on the surface. This suggests burst release is due to internal pore diffusion, not surface adsorption, with some protein aggregation observed.
Area of Science:
- Biomaterials Science
- Drug Delivery Systems
- Spectroscopy
Background:
- Poly(lactic-co-glycolic acid) (PLGA) microspheres are widely used for controlled drug delivery.
- Understanding protein distribution and conformation within these microspheres is crucial for optimizing release profiles.
- Lysozyme is a model protein frequently encapsulated in PLGA systems.
Purpose of the Study:
- To investigate the distribution and conformation of lysozyme within PLGA microspheres.
- To correlate the internal structure with the observed burst release phenomenon.
- To assess potential protein aggregation during microsphere formulation.
Main Methods:
- Infrared microscopy and confocal laser scanning microscopy for spatial distribution analysis.
- Attenuated total reflectance (ATR) and photoacoustic spectroscopy (PAS) for surface analysis.
- Fourier-transform infrared (FTIR) spectroscopy, including second derivative analysis, for conformational assessment.
Main Results:
- Lysozyme was homogeneously distributed within internal cavities of PLGA microspheres, not predominantly at the surface.
- A significant burst release (approx. 50%) was observed, inconsistent with surface-adsorbed protein.
- Evidence of non-covalent lysozyme aggregates (band at 1625 cm⁻¹) was detected within the microspheres, potentially adsorbed to cavity walls.
Conclusions:
- The burst release of lysozyme from PLGA microspheres is likely mediated by rapid diffusion through pores in the matrix, not surface release.
- Lysozyme is primarily located within internal cavities, with some aggregation possibly occurring at cavity walls.
- Spectroscopic techniques confirmed the internal distribution and revealed potential conformational changes without significant sample preparation artifacts.