Phillip Chivers
University of York
Phillip R. A. Chivers graduated from the University of York in 2015 with a first class MChem degree with distinction, carrying out his Masters research project in inorganic materials chemistry at Johnson Matthey. He is now a PhD student in the research group of Professor David K. Smith at the University of York, where his research focus is on the development of novel soft materials with biological applications.
Introduction
Interpenetrating polymer network (IPN) gels comprising two orthogonally assembled polymer networks are of great interest in the pharmaceutical industry for active pharmaceutical ingredient (API) delivery because they can demonstrate desirable properties of the individual networks whilst mitigating the drawbacks of each.1,2 Reports of IPNs comprising two polymer gelator (PG) networks have become increasingly common,3 however reports where low-molecular-weight gelator (LMWG) and PG networks are combined are surprisingly limited. LMWG hydrogels are of significant interest in applications as diverse as tissue engineering, drug release and environmental remediation because of changes in material structure in response to external stimuli including pH, light and temperature.4,5 By harnessing the pH-dependent API release of a LMWG (DBS-CONHNH2)6 in combination with the mechanical robustness of a photopatternable PG (PEGDM), we are able to demonstrate the ‘best of both’ gels in one material (Figure 1).
Methods
DBS-CONHNH2/PEGDM networks incorporating non-steroidal anti-inflammatory drug naproxen (NPX) were formed sequentially to yield hybrid materials. LMWGs were assembled by heat/cool cycle followed by UV-patterning of the PG network. PG formation was spatially controlled using a photomask. These materials have been fully characterised by NMR spectroscopy, rheology and thermal analysis.
Results
The mechanical properties of the material were tuned by varying PG content. At 10% wt/v PEGDM, material stiffness increased dramatically and the gels became self-supporting. Breaking strain also increased much beyond that of the LMWG. These robust materials released NPX selectively into buffers above the drug pKa with similar preference to the LMWG alone. By photopatterning a NPX-loaded hybrid gel band, we generated a self-supporting material which demonstrated unidirectional release into a compartment of pH 7 buffer rather than into pH 2.8 buffer (Figure 2)
Discussion
We have developed for the first time a photopatternable LMWG/PG hybrid material which demonstrates great potential for targeted delivery and tissue engineering by selective release of drugs/growth factors into a suitable environment. Crucially, each gelator plays an important role in determining the material properties. The PG is necessary to enable photopatterned shaping of the material and provide mechanical robustness, whilst spatial resolution and pH-dependent release are not possible in the absence of the LMWG.
