Development of Antimicrobial Surfaces Using Diamond-like Carbon or Diamond-like Carbon-Based Coatings

Abstract

The medical device market is a high-growth sector expected to sustain an annual growth rate of over 5%, even in developed countries. Daily, numerous patients have medical devices implanted or inserted within their bodies. While medical devices have significantly improved patient outcomes, as foreign objects, their wider use can lead to an increase in device-related infections, thereby imposing a burden on healthcare systems. Multiple materials with significant societal impact have evolved over time: the 19th century was the age of iron, the 20th century was dominated by silicon, and the 21st century is often referred to as the era of carbon. In particular, the development of nanocarbon materials and their potential applications in medicine are being explored, although the scope of these applications remains limited. Technological innovations in carbon materials are remarkable, and their application in medicine is expected to advance greatly. For example, diamond-like carbon (DLC) has garnered considerable attention for the development of antimicrobial surfaces. Both DLC itself and its derivatives have been reported to exhibit anti-microbial properties. This review discusses the current state of DLC-based antimicrobial surface development.

Keywords: antibacterial surface; bacterial adhesion; biofilm; diamond-like carbon; hydrophilicity; surface smoothness; ζ-potential.

Figure 1

Schematic showing the growth cycle of a biofilm formed by a single bacterial species on a solid surface. (1) Reversible attachment of single planktonic bacteria to the surface. The first attach-ment of bacteria is influenced by attractive or repulsive forces generated by nutrient levels, pH, and surface temperature. (2) Aggregation of bacteria and irreversible attachment to surfaces. (3) Formation of an external matrix of multilayered complex biomolecules, microcolony formation, and EPS secretion that constitute the external matrix. Secretion of polysaccharides by biofilm-forming strains enables aggregation, adherence, and surface tolerance, allowing for improved surface colonization. (4) Maturation of biofilms and acquisition of a three-dimensional structure as they reach maturity. These three-dimensional structures rest on self-produced extra-cellular matrix components. (5) Fully mature biofilms detach, which allows bacterial cells to take on a planktonic state once again, thereby establishing biofilms in other locations (reprinted from [20]).

Figure 2

Examples of water contact angle (free surface energy) control with DLC. (A) Water contact angle changes on ePTFE surface with DLC coating (reprinted from [5]) (B); water contact angle changes on polyurethane surface with DLC and nitrogen-doped DLC coatings (reprinted from [13]) (C); water contact angle changes on silicon surface with DLC and oxygen-doped DLC coatings (reprinted from [11]).

Figure 3

Surface smoothing of fibrous ePTFE structures using DLC coating. Application of DLC on the ePTFE surface clearly results in smoothing of each individual fiber within the fibrous structure of the ePTFE.

Figure 4

The distribution of 74 types of amorphous carbon films on a ternary diagram based on sp² bonds, sp³ bonds, and hydrogen content. The diameter of each circle corresponds to the nanoindentation hardness of each amorphous carbon film. (Reprinted from [31]).

Figure 5

Image of ζ potential.