Researchers have developed a novel type of microrobot, termed ‘bubble bots’, demonstrating potential for targeted drug delivery in surgical applications.
Published in Nature Nanotechnology, the study highlights a simplified, biocompatible design that combines autonomous movement with highly effective tumour targeting.
Developed by a team led by Wei Gao at Caltech and the University of Southern California, this method previously used ultrasound imaging and magnetic guidance to deliver 3D-printed microscale robots to tumours in animal models, releasing chemotherapeutic agents directly at the tumour site.
Building on this work, they devised a radically simplified approach: making the bubble itself a self-propelled robot.
These microbubbles, produced by an ultrasound probe that agitates bovine serum albumin (BSA) solutions, form a protein shell that can be chemically modified for various functions.
By attaching enzymes such as urease and catalase to the bubble surface, the team enabled autonomous motility and chemotactic behaviour.
Urease catalyses a reaction with urea, generating ammonia and carbon dioxide, thereby creating an asymmetric chemical environment that propels the bubble forward.
The addition of magnetic nanoparticles enabled external magnetic steering, guiding bubble bots to specific locations within the body via ultrasound imaging.
To enhance targeting specificity, the researchers engineered a second version of the bubble bots by binding catalase to their surface. Catalase reacts with elevated hydrogen peroxide levels – common in tumour and inflamed tissues – producing water and oxygen.
This chemotactic response enables the bubbles to autonomously seek out and accumulate at tumour sites, eliminating the need for external control or imaging guidance.
Once at the target, focused ultrasound can rupture the bubbles, releasing their cargo directly into the tumour microenvironment. This on-demand triggering results in deeper drug penetration compared to previous hydrogel-based microsystems.
Preclinical studies in mice demonstrated promising results: a 60% reduction in bladder tumour size over 21 days when using bubble bots to deliver therapeutics, outperforming drug administration alone. This innovative platform combines biocompatibility, controllable motion, imaging guidance, and autonomous targeting into a compact and efficient design.
Gao said: ‘Our goal is to move microrobots closer to clinical use for surgical applications. The simplicity and effectiveness of bubble bots could revolutionise targeted therapy in surgery, providing precise, minimally invasive treatment options.’
