Multifunctional composite hydrogel bolus with combined self-healing, antibacterial and adhesive functions for radiotherapy.

Radiotherapy is a commonly used method for curing cancers that appear on or just below the skin. Because of the dose build-up effect of X-rays, boluses made of various materials such as silica and wax are clinically applied on patients to increase the skin dose for an enhanced therapeutic effect. However, these commercial boluses can't conform well to the skin's surface with some curvature, resulting in radiation dose attenuation/loss at the lesion location. To address this limitation, we have developed a nano-titanium dioxide (nTiO2)-incorporated polyurethane/polyacrylamide (TPU/PAAm) hydrogel with multi-functions for fabricating a desirable bolus. The obtained hydrogel exhibits excellent mechanical, adhesive and self-healing properties and can fit closely to the surface of patients with any 3D curvature, eliminating the air gap which is a common problem for commercial boluses applied on patients. In particular, it is encouraging that when using the bolus made of TPU/PAAm hydrogel, the dose distribution including dose coverage, conformability and homogeneity within the planning target volume (PTV) is far superior to that when using the commercial bolus. A sufficient dose shifts toward the surface of the head model and is located only in the lesion site, demonstrating that TPU-PAAm hydrogel can provide an optimal dose distribution and be clinically effective for treating superficial tumors. Furthermore, nTiO2 particles feature uniform dispersion at the nanometer level in hydrogel after being modified by 2,2-bis(hydroxymethyl)propionic acid (DMPA) based on coordination chemistry, endowing the hydrogel with long-acting antibacterial ability. The good cell affinity of TPU-PAAm hydrogel is also confirmed in this study, further ensuring that the TPU-PAAm hydrogel prepared here is a desirable candidate as a tissue equivalent with the advantages of convenient use and effectiveness in radiotherapy.