ABSTRACT
The interaction between genipin and a model protein bovine serum albumin (BSA), with and without the addition of acetic acid, has been studied experimentally and by modelling. The number of amino groups available to react was determined to be 5.6â¯% of the total number of amino acid building blocks on BSA. Fluorescence intensity was used to record the progress of the reaction over the 24â¯h, while the modelling study focused on capturing the kinetic profiles of the reaction. The experiments revealed a slow start to the BSA and genipin interaction, that subsequently accelerated in an S-shaped curve which the modelling study linked with the existence of the feedback cycle for both reactive amino groups and genipin. At BSA concentrations ≥30â¯mg/mL the reaction was accelerated in the presence of acid, while below 30â¯mg/mL the acidified conditions delayed the onset of the reaction. Contrary to the reaction mechanisms previously proposed, a degree of breakdown of the fluorescent links in the products formed was denoted both experimentally and in a modelling study. This indicated the reversibility of the processes forming fluorescent product/s and suggested feasibility of the successful release of the protein following prospective encapsulation within the genipin-crosslinked hydrogel structure.
ABSTRACT
We report a simple and reproducible micromoulding technique that dynamically fills microneedle moulds with a liquid formulation, using a plastic syringe, triggered by the application of vacuum ('vac-and-fill'). As pressure around the syringe drops, air inside the syringe pushes the plunger to uncover an opening in the syringe and fill the microneedle mould without manual intervention, therefore removing inter-operator variability. The technique was validated by monitoring the plunger movement and pressure at which the mould would be filled over 10 vacuum cycles for various liquid formulation of varying viscosity (water, glycerol, 20 % polyvinylpyrrolidone (PVP) solution or 40 % PVP solution). Additionally, the impact of re-using the disposable syringes on plunger movement, and thus the fill pressure, was investigated using a 20 % PVP solution. The fill pressure was consistent at 300-450 mbar. It produced well-formed and mechanically robust PVP, poly(methylvinylether/maleic anhydride) and hydroxyethylcellulose microneedles from liquid formulations. This simple and inexpensive technique of micromoulding eliminated the air entrapment and bubble formation, which prevent reproducible microneedle formation, in the resultant microneedle arrays. It provides a cost-effective alternative to the conventional micromoulding techniques, where the application of vacuum ('fill-and-vac') or centrifugation following mould-filling may be unsuitable, ineffective or have poor reproducibility.
Subject(s)
Drug Delivery Systems , Syringes , Vacuum , Reproducibility of Results , Drug Delivery Systems/methods , NeedlesABSTRACT
Self-crystallisation of 45S5 Bioglass® powder and scaffolds was observed one year after their fabrication. Plate- and acicular-shape crystals, identified as calcium and sodium carbonates, grew at room temperature and atmospheric pressure, without any further treatment.
ABSTRACT
Composite scaffolds formed from polymers and bioglasses have been widely explored for applications in regenerative medicine as they have suitable organic/inorganic structures and properties similar to human hard tissue. Yet, these materials have only been used for non-load-bearing or low load-bearing purposes as they have limited mechanical strength while research is focused on improving their properties. One method of improving mechanical strength is by covalently bonding the organic and inorganic phases. This has been successfully achieved in Class ll hybrids which have covalent bonding between polymers and bioglasses. As well as improving mechanical strength, the chemical connection of the two phases results in simultaneous degradation. The currently available composite scaffolds use collagen for the polymer phase which can cause allergic reactions and transmit pathogens. An alternative natural polymer is chitosan which has been used to create scaffolds with bioglass avoiding the issues arising from collagen. Additionally, using cross-linking agents has been shown to strengthen chitosan hydrogels improving their mechanical properties. A promising natural cross-linker is genipin which has lower toxicity than other cross-linking agents while producing hydrogels with improved mechanical properties compared to pure chitosan. In this paper we offer an overview of requirements, structures and currently available composite scaffolds for tissue engineering applications. We discuss the limitations of the currently available materials and consider the potential of covalently bonded hybrids particularly in relation to chitosan-based materials and the added benefits of genipin cross-linking.
