Name Prof.dr. P.J. Dijkstra
Phone +31 (0)53-489 3004
Function Associate professor
RESPONSIVE BLOCK COPOLYMER HYDROGELS
Hydrogels do mimic the properties of soft tissues, are in general highly biocompatible, and therefore do find a lot of interest for biomedical and pharmaceutical applications. Combining a preformed hydrogel with cells or active drugs is a way to introduce a construct in the human body or locally deliver drugs. A more attractive method to introduce hydrogels in the human body is the use of injectable hydrogels because a minimally invasive procedure is employed. These injectable hydrogels can be formed in different ways and a few examples are given hereafter. But first let us focus on the materials we use.
POLYMERS FOR INJECTABLE HYDROGELS
In case of temporary need of a construct preferably biodegradable or bio-absorbable polymers are used. Poly(lactic acid)s as an example are well-known biodegradable polymers used widely for biomedical, pharmaceutical and ecological applications. Combining poly(lactic acid) blocks (hydrophobic) with poly(ethylene glycol) blocks (hydrophilic) in linear, star, graft or hyperbranched copolymers biodegradable thermo-responsive hydrogels, thus with a transition from solution to gel, are formed depending on the hydrophilic to hydrophobic weight ratio. Nowadays we design and play around with polymer architectures to tune the properties we need in certain biomedical applications. A few examples are:
Block copolymer hydrogels
Lactic acid is a chiral molecule and thus two forms (D and L; or R and S in modern notation) do exist. An example how to use the difference in chirality in injectable hydrogels is shown in the picture below. Two aqueous copolymer solutions containing star type block-copolymers composed of a central PEG and stereo-regular polylactide blocks form networks (hydrogels) by stereocomplexation of the hydrophobic polylactide blocks.
Chemically crosslinked injectable hydrogels
In our recent research injectable hydrogels are prepared by chemical crosslinking of polymer conjugates using enzymes. Chemically crosslinked hydrogels are stronger, do slower degrade and can be potentially used in load bearing applications like in the regeneration of damaged cartilage.
Enzymatic crosslinking of conjugates (black lines are hydrophilic polysaccharide chains)
Filling a cartilage defect with an injectable hydrogel. Using a double syringe a chemically crosslinked hydrogel is formed in situ in the defect. One chamber of the syringe contains a polymer solution and the other chamber an enzyme acting as catalyst in the crosslinking reaction.
Depending on the intended application hydrogel properties can be regulated by proper design of their structure. Novel methods are explored and their influence on cells and tissues evaluated.
When you are interested in working on the cutting edge of macromolecular chemistry and supramolecular chemistry in combination with developmental bioengineering, especially tissue regeneration of cartilage, we have some challenges for you.