Final Activity Report Summary - FUNCTIONCOLLCAPS (Functionalised colloidal capsules)
The main aim of the project was creation of multifunctional biocompatible coating for hollow polyelectrolyte microcapsules which were proposed for encapsulation of drugs, drug delivery and controlled release. For the satisfactory performance of the hollow polyelectrolyte microcapsules, an adaptable coating providing good colloid stability, resistance against non-specific protein adsorption and targeted delivery is vital. The other researchers have developed graft-copolymers with poyelectrolyte backbones (e.g. poly(L-lysine), PLL) which can be electrostatically adsorbed onto such capsules and polyethyleneglycol (PEG) side chains providing a low zeta-potential, colloid stability and low adsorption of molecules from blood serum. However, these graft-copolymers have lack of reactive groups which may be needed for anchoring sensor molecules for targeting purposes and do not preserve integrity of the capsules made of weak polyelectrolytes (which are most of biodegradable polymers) at extreme pH values because the electrostatic charging of the capsule's polyelectrolyte constituents leads to unlimited swelling and dissolution. Limited swelling of the microcapsules at extreme pH is a much desired property because it allows loading them with drugs via diffusion through the pores at the post-preparation stage. Control over the swelling degree can be achieved via introduction of additional linkages between the polyelectrolyte chains within the capsules' walls.
We have proposed dextran polyaldehyde (DPA) as such a coating which is a derivative of dextran (a natural polysaccharide) and may substitute the graft-copolymers for the reasons that dextran is biocompatible, biodegradable, has many reactive alcohol groups unlike PEG (which has only two end-groups), and chemistry of dextran and its derivatives has been well studied. We demonstrated that the DPA coatings provide a good stability of the capsules against aggregation upon storage in solutions of ions having multiple charges (calcium and phosphate ions) and preserve the integrity of the capsules at both high and low pH (0.1 M NaOH and 0.1 M HCl). On the contrary, the unmodified polyelectrolyte capsules are quickly dissolved in 0.1 M NaOH. The limiting swelling degree of the DPA-coated capsules was determined by the density of the aldehyde groups along the polysaccharide chain. The swelling in 0.1M NaOH was reversible: the capsules restored their initial size at neutral pH.
We have proposed dextran polyaldehyde (DPA) as such a coating which is a derivative of dextran (a natural polysaccharide) and may substitute the graft-copolymers for the reasons that dextran is biocompatible, biodegradable, has many reactive alcohol groups unlike PEG (which has only two end-groups), and chemistry of dextran and its derivatives has been well studied. We demonstrated that the DPA coatings provide a good stability of the capsules against aggregation upon storage in solutions of ions having multiple charges (calcium and phosphate ions) and preserve the integrity of the capsules at both high and low pH (0.1 M NaOH and 0.1 M HCl). On the contrary, the unmodified polyelectrolyte capsules are quickly dissolved in 0.1 M NaOH. The limiting swelling degree of the DPA-coated capsules was determined by the density of the aldehyde groups along the polysaccharide chain. The swelling in 0.1M NaOH was reversible: the capsules restored their initial size at neutral pH.