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Injectable polyurethane-based hydrogels for smart drug release in the treatment of chronic skin wounds

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Injectable polyurethane-based hydrogels for smart drug release in the treatment of chronic skin wounds

R. Laurano1, A. Torchio1, M. Boffito1, G. Ciardelli1

1Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Torino, Italy. rossella.laurano@polito.it

1. Introduction

Chronic skin wounds affect more than 40 million patients worldwide. Their treatment represents a growing burden for healthcare systems due to the increasing health care costs, the population aging and the rise in diabetes and obesity incidence. The ideal wound dressing should (i) provide a moist wound environment, (ii) protect from external agents, (iii) remove exudate from the wound, and (iv) enhance tissue regeneration. However, no existing treatment fulfils all these demands [1].

Hence, the design of innovative, smart and effective wound dressings represents a current and important challenge. In this work, we developed a thermo-responsive polyurethane- based hydrogel able to transfer pH changes from the biological milieu (pH in the range 7.4-8.5) to its core, triggering the release of anti- inflammatory drugs.

2. Methods

An amphiphilic polyurethane (PU) (CHP407) was synthesized starting from Poloxamer P407, 1,6- hexamethylene diisocyanate and 1,4-cycloexane dimethanol [2]. CHP407 powder was plasma treated with Acrylic Acid vapours to introduce carboxylic groups along the polymer chains (PCHP407), thus enhancing hydrogel sensitivity to basic pH. PUs were characterized by Size Exclusion Chromatography, Attenuated Total Reflectance Fourier transform Infrared spectroscopy (ATR-FTIR), Proton Nuclear Magnetic Resonance (1H-NMR) and Toluidine Blue O assay (TBO). CHP407 and PCHP407 hydrogels were characterized in terms of sensitivity to temperature (tube inverting and gelation time tests, rheology) and external pH (swelling tests in the presence of basic or acid buffers). pH- triggered release of hydrophilic and hydrophobic anti-inflammatory drugs was studied. Cytotoxicity was assessed according to ISO10993.

3. Results

Chemical characterization assessed the successful synthesis of CHP407 with a final number average molecular weight of 50 kDa and a polydispersity index of 1.3. TBO assay, 1H-NMR and ATR-FTIR demonstrated the introduction of carboxylic groups along the polymer chains and evidenced a high intra- and inter-synthesis repeatability of

plasma treatment. Tube inverting, gelation time and rheological tests showed the ability of 15%w/v concentrated PU solutions to undergo a sol-to-gel transition at about 27°C within few minutes. No differences in gelation kinetics of CHP407- and PCHP407-based hydrogels were reported and both systems were in a complete gel state at 37°C, demonstrating that plasma treatment does not affect hydrogel thermo- sensitivity. Concerning sensitivity to basic pH, PCHP407-based hydrogels transferred basic pH of the surrounding environment to the gel core with a significantly faster kinetics and a significantly higher swelling if compared to CHP407 gels. On the other hand, CHP407- and PCHP407-based hydrogels showed a similar behaviour in the presence of acid buffers. Hence, the introduction of -COOH groups along CHP407 chains increased hydrogel sensitivity to basic pH. These data were also confirmed by studying the pH-triggered release of hydrophobic and hydrophilic drugs.

Cytotoxicity tests performed on hydrogel extracts with NIH-3T3 murine fibroblasts showed no cytotoxicity.

4. Discussion and Conclusion

PU-based hydrogels are promising candidates in chronic skin wound treatment as they are characterized by (i) easy injectability, (ii) a sol-to- gel transition within few minutes at 37°C, (iii) a moist environment and (iv) capability to fill cavities without causing pressure. Furthermore, COOH-modified PU-based (i.e. PCHP407) hydrogels showed faster inner pH variations and higher swelling with respect to native ones (i.e.

based on CHP407), resulting in pH-triggered and accelerated release kinetics of encapsulated drugs.

5. Acknowledgements

This work was supported by the Horizon 2020 European Union funding for Research &

Innovation project “MOZART” (MesopOrous matrices for localiZed pH-triggered releAse of theRapeuTic ions and drugs) (H2020-NMP6- 2015).

References

[1] L.I.F. Moura, A.M.A. Dias, E. Carvalho, H.C. de Sousa, “Recent advances on the development of wound dressings for diabetic foot ulcer treatment - a review”, Acta Biomateriala, vol. 9, p.

7093-7114, 2013

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[2] M. Boffito, E. Gioffredi, V. Chiono, S. Calzone, E. Ranzato, S.

Martinotti, G. Ciardelli, “Novel polyurethane-based thermo- sensitive hydrogels as drug release and tissue engineering platforms: design and in vitro characterization”, Polymer International, vol. 65, p. 756 – 769, 2016

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