Self-assembly of proteins on surfaces is utilized in many fields to integrate intricate biological structures and diverse functions with engineered materials. Controlling proteins at bio-solid interfaces relies on establishing key correlations between their primary sequences and resulting spatial organizations on substrates. Protein self-assembly, however, remains an engineering challenge. As a novel approach, we demonstrate here that short dodecapeptides selected by phage display are capable of self-assembly on graphite and form long-range ordered biomolecular nanostructures. Using atomic force microscopy and contact angle studies, we identify three amino-acid domains along the primary sequence that steer peptide ordering and lead to nanostructures with uniformly displayed residues. The peptides are further engineered via simple mutations to control fundamental interfacial processes, including initial binding, surface aggregation and growth kinetics, and intermolecular interactions. Tailoring short peptides via their primary sequence offers versatile control over molecular self-assembly, resulting in well-defined surface properties essential in building engineered, chemically rich, bio-solid interfaces.

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Prevention of bacterial colonization and consequent biofilm formation remains a major challenge in implantable medical devices. Implant-associated infections are not only a major cause of implant failures but also their conventional treatment with antibiotics brings further complications due to the escalation in multidrug resistance to a variety of bacterial species. Owing to their unique properties, antimicrobial peptides (AMPs) have gained significant attention as effective agents to combat colonization of microorganisms. These peptides have been shown to exhibit a wide spectrum of activities with specificity to a target cell while having a low tendency for developing bacterial resistance. Engineering biomaterial surfaces that feature AMP properties, therefore, offer a promising approach to prevent implant infections. Here, we engineered a chimeric peptide with bifunctionality that both forms a robust solid-surface coating while presenting antimicrobial property. The individual domains of the chimeric peptides were evaluated for their solid-binding kinetics to titanium substrate as well as for their antimicrobial properties in solution. The antimicrobial efficacy of the chimeric peptide on the implant material was evaluated in vitro against infection by a variety of bacteria, including Streptococcus mutans, Staphylococcus. epidermidis, and Escherichia coli, which are commonly found in oral and orthopedic implant related surgeries. Our results demonstrate significant improvement in reducing bacterial colonization onto titanium surfaces below the detectable limit. Engineered chimeric peptides with freely displayed antimicrobial domains could be a potential solution for developing infection-free surfaces by engineering implant interfaces with highly reduced bacterial colonization property.

Cerium oxide nanoparticles (or nanoceria) have demonstrated great potential as antioxidants in various cell culture models. Despite such promise for reducing reactive oxygen species and ability for surface functionalization, nanoceria has not been extensively studied for cancer applications to date. Herein, we engineered the surface of nanoceria with dextran and observed its activity in the presence bone cancer cells (osteosarcoma cells) at different pH values resembling the cancerous and non-cancerous environment. We found that dextran coated nanoceria was much more effective at killing bone cancer cells at slightly acidic (pH=6) compared to physiological and basic pH values (pH=7 and pH=9). In contrast, minimal toxicity was observed for healthy (noncancerous) bone cells when cultured with nanoceria at pH=6 after one day of treatment in the concentration range of 10-1000 µg/mL. Although healthy bone cancer cell viability decreased after treatment with high ceria nanoparticle concentrations (250-1000 µg/mL) for longer time periods at pH=6 (3 days and 5 days), approximately 2-3 fold higher healthy bone cell viabilities were observed compared to osteosarcoma cell viability at similar conditions. Very low toxicity was observed for healthy osteoblasts cultured with nanoceria for any concentration at any time period at pH=7. In this manner, this study provides the first evidence that nanoceria can be a promising nanoparticle for treating bone cancer without adversely affecting healthy bone cells and, thus, deserves further investigation.