Delivery systems made of natural-origin polymers for tissue engineering and regenerative medicine applications

There is an emergent need in the development of more specific and effective therapeutic agent carriers to help on the regeneration of a plethora of tissues. The ultimate aim of bioactive factors delivery systems development is to improve the human health with the fewest possible adverse reactions. While there have been many polymeric scaffolds and matrices with different forms and compositions developed to load and deliver bioactive factors, the delivery strategy should be established based on the type of molecules to deliver and mechanisms to control their release. As most bioactive factors such as proteins and genes are water-soluble, natural polymers are more favored than synthetic ones for this purpose. A core-shell structuring of biomaterials (in the cases of particles or fibers) where water-based polymers being placed in the inner core part may be the most common design principal to secure bioactive factors during the processing of synthetic drug delivery scaffolds.(undefined)info:eu-repo/semantics/submittedVersio

Structure and morphology of poly(vinyl alcohol) gels prepared by freezing and thawing processes

The structure and Morphology of poly(vinyl alcohol) (PVA) gels prepared by repeated cycles of 8 hour freezing at –20°C and 4 hour thawing at 25°C were examined. Long-term morphological changes of such gels were determined upon swelling in water at 37°C for 6 months. The preparation conditions were examined by varying such parameters as the number of freezing and thawing cycles, the concentration of aqueous solution, and the PVA molecular weight. The overall structure and stability were examined in terms of water content, fractional PVA dissolution, degree of crystallinity, and crystal size distribution. The analysis was applied to determine the appropriateness of the gels for various biomedical and pharmaceutical applications. An increase in the number of freezing and thawing cycles served to reinforce existing crystals within the structure. Increased initial concentrations of aqueous PVA solutions resulted in hydrogels that contained initially higher crystallinity and added stability upon swelling. An increase in the PVA molecular weight resulted in crystals of higher lamellar thickness and a broadening of the crystal size distribution due to an increase in PVA chain length. The phenomenon of secondary crystallization was found to be more pronounced for more loosely crosslinked samples. An increase in the free volume and mobility within the network allowed for additional crystallization to proceed during swelling. A molecular model was developed to describe the overall dissolution kinetics as a three-step mechanism: detachment-, diffusion-, and disentanglement-controlled dissolution. The lamellar thickness of a PVA crystal was found to significantly change the rate of unfolding and, thus, the overall dissolution kinetics. Modified PVA gels prepared in the presence of NaCl demonstrated enhanced swelling as indicated by an increase in the initial rate of swelling and the overall water content. The addition of linear poly(ethylene glycol) was investigated to enhance the stability of freeze-thawed PVA gels. The diffusional characteristics of freeze-thawed PVA gels were examined for controlled release applications. A model protein was successfully incorporated into thin films and released. Through a feasibility study, the design of novel, freeze-thawed PVA laminates was introduced