Anti-breaking Superhydrophobic and Photocatalytic Active Films used as Blood Repellent Dressing

The common method for stopping bleeding is bandaging using a medical dressing which in general is hydrophilic. During bandaging, blood is lost by adsorption into the hydrophilic wound dressings. In contrast, blood repellent superhydrophobic films could prevent blood loss while stopping bleeding. However, the practical use of superhydrophobic surfaces for blood-repellency in medical applications still poses some problems which are related to limited chemical and mechanical stability, flexibility and biocompatibility of the used materials. In particular there are concerns about using highly fluorinated substances for medical and other applications.

Prof. Hans-Jürgen Butt an coworkers at the MPI for Polymer Research in Mainz developed a method to prepare blood-repellent superhydrophobic surfaces by using hierarchical structures composed of biocompatible titanium dioxide (TiO₂) nanoparticles crosslinked with poly-(dimethylsiloxane) (PDMS).

PDMS can be easily grafted onto the surface of TiO₂ photocatalysts under the illumination of UV-A light. The resulting modified TiO₂ nanoparticles were mixed with vinyl-terminated PDMS and Pt-catalyst (concentration relative to vinyl-PDMS: 0.005 wt%) which drives the assembly and connection of particles by the vinyl-terminated PDMS with a covalent bond (Figure 1).

The resulting PDMS/TiO₂ films possess self-cleaning properties under UV illumination that can deal with both physical (sand contamination) and chemical contamination, additionally they also show antibacterial properties under UV-A illumination.

Selected substrates, e.g., textiles, were immersed in the reacting mixture for 2 h at 60 °C after treating them with oxygen plasma. Afterwards a superhydrophobic micro/nano-hierarchical structure of PDMS/TiO₂ film has formed on the chosen substrate.

The PDMS/TiO₂ film coated textile showed a static contact angle bigger than 150° for human blood and a sliding angle of around 3° for a 20 μL blood droplet. The blood repellency of the PDMS/TiO₂ film modified wound dressing is still maintained when the film is stretched. There was no blood adhesion when flowing blood impacted onto wound dressing, even when it was stretched by 200%. After twisting the dressing tens of times, it still maintained its blood repellency.

The blocking effect of blood effectively reduces the loss of blood from a wound. In addition, the PDMS/TiO₂ film modified wound dressing offers good air permeability in a water environment. Efficient air permeability provides sufficient oxygen to the wound and promotes healing. In contrast with a continuously bleeding wound bandaged up with an unmodified wound dressing, the modified wound dressing can efficiently stop the bleeding.

• highly elastic and mechanically robust superhydrophobic film
• based on biocompatible TiO₂ and PDMS
• photocatalytic activity provides self-cleaning and antibacterial properties under UV-A light
• different materials such as glass, PU and polyester textiles can be easily modified
• hemostasis function of resulting medical wound dressings is enhanced
• leakage of blood is effectively blocked while maintaining gas permeability even under water

Jie Liu, Werner Steffen, Michael Kappl, Hans-Jürgen Butt et al: "Elastic Superhydrophobic and Photocatalytic Active Films Used as Blood Repellent Dressing", Adv. Mater. 2020, 32, 1908008

PCT priority patent application WO2021089110A1 filed November 4th 2019