Inter-penetrating Polymer Network(IPN) tissue expanders

Self-inflating hydrogel tissue expanders have drawn great interest for generating new soft tissue in plastic and reconstructive surgeries. However, their over-rapid expansion rate can lead to tissue necrosis. Additional coatings or membranes can provide controlled swelling, but will be damaged upon crafting. This study is concerned with developing a novel inter-penetrating polymer network (IPN) tissue expander with controlled expansion and the ability to be crafted by surgeons as well. Firstly, VP/MMA-PLGA IPN has been prepared by crosslinking a secondary PLGA network in the presence of a primary VP/MMA network. The incorporation of PLGA effectively decreases the initial swelling rate and extends the swelling period. It is the only self-inflating tissue expander at present with controlled swelling and the ability to be crafted by surgeons. However, the equilibrium swelling ratio is sacrificed with increased PLGA weight fraction, which will limit the application of this IPN expander to surgeries that only need small tissue expansions, such as anophthalmia, eyelid, lip or nose reconstructions. Secondly, PLGA has been replaced with alternative secondary polymer networks, PLA and PCL to prepare IPN hydrogels. The swelling behaviour of VP/MMA-PLA IPN and VP/MMA-PCL semi-IPN is closely linked with the hydrophobicity and weight fraction of the secondary network, regardless of its glass transition temperature or crosslinking condition. At a similar weight fraction, the more hydrophobic the secondary network, the lower the initial swelling rate and the equilibrium swelling ratio, and the longer the swelling period. Thirdly, HEMA, VP/HEMA, and HEMA/SA bulk hydrogels have been prepared as alternative primary networks. Hydrogels show an increased swelling capacity with increased content of VP or SA, but at the expense of mechanical properties at the swollen state. Both HEMA and VP/HEMA show a low swelling, which might not be enough to induce tissue expansion. HEMA/SA shows superior swelling in distilled water but minimal swelling in non-polar solvents. Finally, the in vivo study of VP/MMA-PLGA IPN has been performed in a sheep model. The IPN hydrogels successfully generate tissue growth with the same quality as natural skin tissue and without any signs of serious inflammation or tissue necrosis. The rapid degradation of PLGA in vivo can cause the loss in mechanical integrity, leading to hydrogel collapsing under the restorative force of the skin. But this could be solved by tuning the ratio of lactide to glycolide in PLGA.