Magnetic hydrogel micromachines eradicate biofilms in tubular implants

Researchers from the Chinese University of Hong Kong (CUHK) have developed magnetic hydrogel micromachines with active release of antibacterial agents for biofilm eradication in small tubular medical implants.

Biofilms, slimy layers of micro-organisms and bacteria-protecting extracellular polymeric substances (EPSs) that can grow on both teeth and medical implants, are highly related to chronic and recurrent infections. These EPSs not only provide adhesion to surfaces, but also contribute to antibiotic resistance. Biofilms are extremely difficult to eradicate, particularly when they form on medical implants, which are often located in hard-to-reach regions. [Antimicrob Resist Infect Control 2019;8:76]

Failure of traditional antibiotic therapy in eradicating biofilms has prompted the need to develop new treatment approaches. Mechanical force and antimicrobial agents are two major factors essential for successful biofilm eradication. [Front Microbiol 2020;11:566325; Adv Intell Syst 2023;doi:10.1002/aisy.202300092]

“Our rod-like magnetic hydrogel micromachines are specially designed for biofilm eradication in tiny tubular medical implants,” said Professor Tony Chan of the Chow Yuk Ho Technology Centre for Innovative Medicine, CUHK.

The magnetic hydrogel micromachine

Driven by external magnetic fields, the micromachines can precisely navigate to the desired location through planar rotation and wobbling. “These two modes of motion allow access to biofilms in hard-to-reach regions, such as narrow tubes used in many medical implants,” added Chan.

The micromachines apply mechanical force at the desired location to physically destroy the biofilm structure. Upon heating to approximately 32^oC (critical solution temperature), the micromachines can release 30 percent H₂O₂ solution to generate bacteria-killing free radicals (ie, HO•, HOO•). Subsequently, the magnetic hydrogel is retrieved using a magnet. [Adv Intell Syst 2023;doi:10.1002/aisy.202300092]

“The synergetic strategy [ie, on-demand release of antibacterial agents and mechanical disruption] eliminates the need to inject large amounts of H₂O₂ solution into the biofilm site, minimizing negative impacts on surrounding healthy tissues and treatment side effects,” highlighted the researchers.

“We tested the micromachines against Escherichia coli and Bacillus cereus biofilms in curved and tiny tubes, which simulate narrow lumens in the body such as medical implants and catheters,” said Chan. Results showed that the active release magnetic hydrogel micromachines were able to remove biofilms and kill 49.68 percent of bacterial cells within 5 minutes of treatment.

“Hydrogels are soft, wet and biocompatible, which makes them great candidates for biomedical applications,” said Professor Zhang Li from the Department of Mechanical and Automation Engineering, CUHK. Apart from biofilm treatment for a wide range of body regions (eg, biliary stents and urinary catheters), the micromachines also hold potential for targeted drug delivery in tiny and tortuous lumens.

The CUHK researchers are currently planning further animal experiments and developing human-scale magnetic actuation systems that can be used alongside clinical imaging modalities. They are also considering the possibility of utilizing magnetic hydrogel micromachines in environmental and industrial applications.