Pulsatile protein release and protection using radiation-crosslinked polypeptide hydrogel delivery devices

In the recent years recombinant technology has identified numerous protein based therapeutics. Their
effective delivery, though, can be challenging due to the poor stability of most proteins along their pathway
to the target site in the body. Hydrogels have been identified as good candidates for protein encapsulation
and delivery thanks to both material and manufacturing process advantages. In this work we
propose high energy irradiation as a synthetic methodology of choice to engineer hydrogel-based
delivery devices for encapsulation and pulsatile release of proteins, triggered by pH, and for prevention
of their denaturation when encapsulated. In particular, maleic anhydride functionalised poly(N-2-
HydroxyEthyl)-DL-Aspartamide (PHEA-MA) hydrogels have been crosslinked without the use of toxic
reagents or catalysts and in mild conditions via gamma irradiation. At the variance of the irradiation conditions,
hydrogels with dramatically different crosslinked structure, thus rheological properties and
swelling behaviour, have been obtained. The ability to swell and shrink cyclically upon repeated pH
jumps and the absence of cytotoxicity have been demonstrated for all the hydrogels produced. Moreover
some of the variants exhibited full degradability at 37 C with degradation products that are not-toxic for
the cell. Depending on the networks average mesh size, as derived by the treatment of rheological data
with simple rubber elasticity equations, with respect to the characteristic dimension of the chosen model
protein, substantial loading of the protein and its retention or release, controlled by pH, have been
achieved. These results, coupled with the versatility of the synthetic platform, suggest the possibility
to use these materials as components of intelligent/programmable devices specifically designed as to
release theoretically any protein based therapeutic.