ABSTRACT
There is a growing interest in using proteins as therapeutics agents. Unfortunately, they suffer from limited stability and bioavailability. We aimed to develop a new delivery system for proteins. ALP, a model protein, was successfully encapsulated in the physically cross-linked sodium alginate/hydroxypropylcellulose (ALG-HPC) hydrogel microparticles. The obtained objects had regular, spherical shape and a diameter of â¼4 µm, as confirmed by optical microscopy and SEM analysis. The properties of the obtained microbeads could be controlled by temperature and additional coating or crosslinking procedures. The slow, sustained release of ALP in its active form with no initial burst effect was observed for chitosan-coated microspheres at pH = 7.4 and 37 °C. Activity of ALP released from ALG/HPC microspheres was confirmed by the occurance of effectively induced mineralization. SEM and AFM images revealed formation of the interpenetrated three-dimensional network of mineral, originating from the microbeads' surfaces. FTIR and XRD analyses confirmed formation of hydroxyapatite.
Subject(s)
Alginates/chemistry , Alkaline Phosphatase/chemistry , Cellulose/analogs & derivatives , Enzymes, Immobilized/chemistry , Hydrogels/chemistry , Microspheres , Cellulose/chemistry , Delayed-Action Preparations/chemistry , Glucuronic Acid/chemistry , Hexuronic Acids/chemistryABSTRACT
"Smart" (thermosensitive) alginate-hydroxypropylcellulose (Alg/HPC) microbeads for controlled release of heparin were synthesized and the release profiles at various temperatures and for various alginate/HPC compositions were measured. Microbeads of regular spherical shape (ca. 3 microm in diameter) containing efficiently encapsulated heparin were obtained using an emulsification method. The internal structure of the bead was estimated by fluorescence microscopy using dansyl alginate as a labelled component. The microbeads surface structure and morphology were imaged in a dry state using scanning electron microscopy (SEM) and in water using atomic force microscopy (AFM). The microbead surface was shown to be covered by the regular network of pores with a mesh of ca. 30-60 nm. Lower critical solution temperature (LCST) of the Alg/HPC systems was measured spectrophotometrically (cloud point measurements). Heparin release profiles were obtained based on spectrophotometric detection of heparin complex with Azure A. Three-stage sustained release for at least 16 days was observed at 37 degrees C. This was correlated with the size of the pores present at the surface of microbeads. The release profile can be controlled by the temperature and composition of the Alg/HPC microbeads.
