On the adhesion of a-C:H coatings deposited by PECVD on PDMS for biomedical applications

Polydimethylsiloxane (PDMS) is widely used in biomedical devices. Despite its well-recognized hemocompatibility, elasticity, and overall stability, it remains prone to bacterial colonization, which can lead to severe infections and even to device failure. Hydrogenated amorphous carbon (a-C:H) coatings have emerged as a versatile route to enhance biomaterial surfaces, and can serve as platforms for the controlled release of antibacterial agents. However, adhesion of a-C:H coatings to soft polymers such as PDMS remains a critical bottleneck limiting clinical success. This study investigates how substrate bias and hydrogen incorporation during plasma-enhanced chemical vapor deposition affect adhesion, morphology, and interface integrity of a-C:H coatings on PDMS. Coatings deposited without bias were termed polymer-like carbon (PLC), and those deposited at −300 V as diamond-like carbon (DLC). The incorporation of hydrogen during deposition produced the hydrogenated counterparts, PLCH (non-biased + H ₂) and DLCH (biased + H ₂). Time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiling revealed thicker coatings and sharper interfaces for non-biased coatings. In contrast, biased coatings were thinner and showed evidence of intermixing with substrate components. Regarding hydrogen incorporation, a decrease in coating thickness and surface roughness was observed, as well as a 65.5 % reduction in crack density comparing PLC and PLCH after tensile deformation. Furthermore, immersion tests under pseudo-physiological conditions demonstrated that PLCH remained stable for 21 days, with only localized cracks and no significant delamination under either static or dynamic conditions. These results suggest that these coatings can withstand physiological stresses while maintaining mechanical integrity. Therefore, among the variants studied, PLCH emerges as the most promising coating for flexible PDMS-based biomedical devices, offering an optimal balance of thickness, adhesion, flexibility, and chemical durability.