Author: Tien Thanh Nguyen
Nguyen, Tien Thanh, 2023 Battling Infections for bone scaffold via Novel Antimicrobial and Biocompatible Silk Sericin-Gallium-Silver Particle-Based Coatings, Flinders University, College of Medicine and Public Health
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The management of infected bone defects is a significant challenge in orthopaedics, requiring effective infection control and bone defect repair. Implant-associated osteomyelitis (IAO) has infection rates of 5-15% in fracture immobilizers and 0.3-5% in joint prostheses. Currently, antibiotics are the primary method of controlling infections in bone transplants, but overuse has led to the emergence of antibiotic-resistant bacterial strains. Metals like gallium, silver, magnesium, copper, zinc, and iron are potential antibacterial agents, but metal ions can cause toxicity in the human body. Worm silk is a natural polymer with biocompatibility, biodegradability, and non-toxic properties, making it a promising solution for mitigating metal toxicity.
In this project, researchers investigated a biomaterial to address the challenges of creating an antibacterial coating on bone scaffolds, including infection, biomaterial instability, and toxicity. Biomaterial coatings were developed for application on bone scaffold surfaces, consisting of silk sericin formed into particles and immobilized on the scaffold surface using plasma-deposited polyoxazoline. Gallium and silver particles were generated by encapsulating them with silk sericin, resulting in a biodegradable and biocompatible coating. Two types of particles were produced: gallium-silk particles (Ga-Silk Ps) and gallium-silver-silk particles (GaAg-silk Ps). These were coated onto the bone scaffold surface via a reaction between carboxylic acid groups (derived from silk sericin-encapsulated Ga and GaAg particles) and the oxazoline ring deposited by plasma technology.
SEM and TEM analyses revealed that both Ga-Silk and GaAg-Silk Ps had average particle sizes of approximately 650 nm and 800 nm, respectively, and a thin silk sericin coating of approximately 12.3 ± 3.2 nm. XPS and FTIR results showed that the amide functional groups on the particle surfaces remained structurally unchanged. Silver nanoparticle crystals were also detected and confirmed to be attached to the surface of gallium particles when reacted with silver nitrate. The Ga-Silk and GaAg-Silk Ps particles were found to inhibit bacteria (Pseudomonas aeruginosa and Staphylococcus aureus) effectively at a concentration of 2.5 mg/ml and 2.5 mg Ga + 0.25 mg Ag/ml (with a Ga:Ag ratio of 10:1), respectively.
The antibacterial surface tests of immobilized Ga-Silk and GaAg-Silk Ps particles for 4 hours showed that the antibacterial activity of Ga-Silk and GaAg-Silk Ps particles against S. aureus was 62.7% and 82.5%, respectively, while for P. aeruginosa, it was 89.7% and 95.8%, respectively. The antibacterial mechanism was attributed to ROS generation within bacterial cells, changes in the membrane potential, and the disruptive adhesion of particles to the bacterial cell membrane. The coatings showed no toxicity towards MG-63 cells and THP-1 macrophages after being cultured for 24 hours. The cell viability of both particles was over 95% when compared to the control group (tissue culture plate). In summary, the plasma polymerization technology used to coat the surface of Ga-Silk and GaAg-Silk Ps particles resulted in effective antibacterial activity and high biocompatibility with bone and immune cells, suggesting that these particles could have potential use in bone scaffold applications.
Keywords: Liquid metal, Gallium particles, Silver nanoparticles, Silk sericin, Scaffolds, Plasma polymerisation, Polyoxazoline.
Subject: Medical Biochemistry thesis
Thesis type: Masters
Completed: 2023
School: College of Medicine and Public Health
Supervisor: Vi-Khanh Truong