Atomic layer deposition (ALD) has emerged as a powerful technique for fabricating thin films with precise control over thickness, composition, and conformality. In biomedical applications, ALD is particularly valuable for creating functional coatings that enhance the performance of medical devices, implants, and surgical tools. By enabling nanoscale surface modifications, ALD coatings can impart antibacterial properties, improve biocompatibility, and reduce adverse immune responses without altering the bulk material properties of the underlying substrate.

One of the key advantages of ALD in biomedical coatings is its ability to deposit uniform and pinhole-free films even on complex geometries. This is critical for medical implants, where surface uniformity directly influences performance. For instance, orthopedic implants, cardiovascular stents, and dental prosthetics often require coatings that promote tissue integration while preventing bacterial colonization. ALD achieves this by allowing atomic-level control over film growth, ensuring consistent coverage across intricate surfaces.

Titanium dioxide (TiO2) and zinc oxide (ZnO) are among the most widely studied ALD-deposited materials for biomedical coatings due to their multifunctional properties. TiO2 coatings are known for their excellent biocompatibility, corrosion resistance, and photocatalytic antibacterial activity. When exposed to ultraviolet (UV) light, TiO2 generates reactive oxygen species (ROS) that disrupt bacterial cell membranes, making it effective against pathogens such as Staphylococcus aureus and Escherichia coli. Additionally, TiO2 films exhibit high chemical stability, reducing ion leaching and ensuring long-term performance in physiological environments.

ZnO, another promising ALD material, offers inherent antibacterial properties even without external activation. The release of zinc ions from ZnO coatings disrupts bacterial cell walls and inhibits biofilm formation. Studies have demonstrated that ZnO thin films can significantly reduce bacterial adhesion on surfaces, making them suitable for catheters, wound dressings, and other infection-prone medical devices. Furthermore, ZnO’s biocompatibility and ability to promote osteogenesis make it attractive for bone implants.

Substrate compatibility is a critical consideration when applying ALD coatings in biomedical settings. Common substrates include metals (titanium, stainless steel), polymers (polyethylene, polyetheretherketone), and ceramics (alumina, hydroxyapatite). ALD’s low-temperature processing (typically below 200°C) allows deposition on temperature-sensitive polymers without causing thermal degradation. For example, ALD-coated polymer-based implants benefit from enhanced surface hardness and reduced wear while retaining their mechanical flexibility.

Metallic implants, such as titanium alloys used in joint replacements, often require surface modifications to prevent corrosion and improve osseointegration. ALD coatings of TiO2 or Al2O3 provide a protective barrier against corrosive body fluids while maintaining the substrate’s mechanical integrity. The conformal nature of ALD ensures that even porous or textured surfaces, such as those found in bone scaffolds, receive uniform coverage.

In addition to antibacterial and biocompatible coatings, ALD is used to deposit films that modulate cellular responses. For instance, hydroxyapatite (HA) coatings applied via ALD mimic the mineral component of bone, promoting osteoblast adhesion and accelerating bone regeneration. By fine-tuning the crystallinity and stoichiometry of HA films, ALD can optimize their bioactivity for specific orthopedic applications.

Another emerging application is the use of ALD to create antifouling coatings that prevent protein adsorption and thrombus formation on blood-contacting devices. Thin films of Al2O3 or TiO2 can reduce platelet adhesion on cardiovascular stents, lowering the risk of thrombosis without the need for systemic anticoagulants. The precise thickness control offered by ALD ensures that these coatings do not interfere with the device’s mechanical functionality.

Despite its advantages, ALD faces challenges in biomedical coating applications. The slow deposition rate and high precursor costs can limit scalability for large-scale medical devices. However, advances in plasma-enhanced ALD (PEALD) and spatial ALD have improved throughput while maintaining film quality. Additionally, the long-term stability of ALD coatings under physiological conditions requires further investigation, particularly for biodegradable implants where coating degradation must align with tissue healing rates.

Future directions for ALD in biomedical coatings include the development of multicomponent and nanostructured films. For example, doping TiO2 with nitrogen or silver nanoparticles can enhance its visible-light photocatalytic activity, broadening its antibacterial utility. Similarly, gradient coatings that transition from antibacterial to pro-regenerative properties could optimize implant performance over time.

In summary, ALD offers unparalleled precision in fabricating biomedical coatings that address critical challenges in infection control, biocompatibility, and device performance. By leveraging materials like TiO2 and ZnO and ensuring compatibility with diverse substrates, ALD enables next-generation surface modifications for medical applications. Continued research into scalable deposition techniques and advanced material designs will further expand the role of ALD in improving healthcare outcomes.