Diseases originating from narrow channels within the body, such as natural orifices, the cardiovascular system, and the cerebrovascular system, pose significant global health challenges, contributing to approximately 25 million annual deaths, and ranking among the top 10 causes of death worldwide according to the World Health Organization (WHO). Consequently, there is a pressing need to develop advanced methods and instruments for diagnosing and treating these conditions.

Small-scale continuum robots pave a new path for interventional diagnosis and treatment in the body owing to their narrow cavity-accessing ability, bringing superiorities of quick recovery, and low infection risk. Up to date, the treatment of several diseases has been demonstrated using small continuum robots, such as heart disease treatment through deploying stent or electrophysiology catheter, maxillary sinus disease treatment by natural orifice transluminal endoscopic surgery (NOTES), and cerebrovascular disease diagnosis through whole-brain angiography etc. Despite of the fruitful achievements, it remains a great challenge for a continuum robot to balance miniaturization, adaptive access, high-precision control, and multi-functional in situ operation well.

To alleviate the problem of adaptive access and high-precision manipulation, this thesis proposes a millimeter-scale soft catheter robot with hybrid actuation mode that combines tendon and magnetic driven mechanisms. With the demonstrated bending angel up to 100 degrees and high-precision dynamic tracking RMSE of about 10 µm, the proposed catheter robot shows good steering within complex constrained environments and the high-precise manipulations. With a large lumen, the catheter robot envisions further diagnosis and treatment through incorporating additional tools.

To overcome the apparent conflict between a small contour, high-precision control, and functional operations, this thesis presents an optical fiber-based submillimeter catheter robot system. By utilizing the technologies of microscale 3D printing and magnetic spray, a slim contour of the probe robot with an outer diameter of 0.95 mm has been achieved. With the imaging performance analysis, we have validated the capability of both micro-meter scale imaging and out-of-sight navigation of the proposed probe robot. Moreover, through proposing the multi-sectional magnetic actuation strategy for the continuum robotic system, we have finally demonstrated the high-precision positioning, with deviations below 30 µm, of the magnetic probe and substantially enlarged the overall endoscopic imaging region by 25 folds. By integrating a functional channel inside, the robot is also verified the capability of implementing endoscopic operations.

To demonstrate the versatile diagnosis and treatment capacities of the magnetic continuum catheter robots, this thesis showcases a series of in vitro and ex vivo trials. By incorporating additional surgical tools inside, various operations, e.g., target injection and ablation within vessels, and nasopharyngeal sampling have been implemented by the millimeter-scale soft catheter robot. On the other hand, ii through integrating different functional tools, various customized biomedical operations, such as mucus sampling, drug delivery, and laser ablation, among others, have been demonstrated by the proposed submillimeter catheter robot system within constrained channel environments.

In conclusion, this thesis innovates in the design, fabrication and control of small-scale magnetic continuum catheter robots to overcome the challenges from constrained channel environments. This work represents a remarkable advance in the small-scale magnetic continuum catheter robots, which will shed light on the design of small-scale continuum robot for accessing more hard-to-reach areas in the body and enriches broad potential biomedical applications.