Optimizing Continuum Robot Tendon Routing for Minimally Invasive Brain Surgery

Tendon-driven continuum robots possess versatile application capabilities and have a robust design. The actuation of such robots with non-straight tendons that wrap around the backbone, described by a variable function, offers a lot of untapped potentials. While it has been shown that these continuum robots are able to take up complex shapes using only one actuated segment, the merits of non-straight tendon routing have not been quantified in terms of workspace and motion. In this paper, we show that one additional helically routed tendon can greatly benefit the robot's reachable workspace. For instance, the reachable workspace of a one-segment robot with 3 conventional straight tendons increases by 400 % by adding one helically routed tendon. Furthermore, the dexterity of such a continuum robot is improved, i.e. motion sequences to avoid obstacles or to twine an object for grasping. For the first time, the potential of tendon-driven continuum robots with two segments and helically routed tendons is investigated. The general findings on the merits of helical tendon routing are supported with both simulation and experimental results.

We propose a segment design that combines two distinct characteristics of tendon-driven continuum robots, i.e. variable length and non-straight tendon routing, into a single segment by enabling rotation of its backbone. As a result, this segment can vary its helical tendon routing and has four degrees-of-freedom, while maintaining a small-scale design with an overall outer diameter of 7 mm thanks to an extrinsic actuation principle. In simulation and on prototypes, we observe improved motion capabilities, as evidenced by position redundancy and follow-the-leader deployment along spatially tortuous paths. To demonstrate the latter on a physical prototype, a simple, yet effective area-based error measure for follow-the-leader deployment is proposed to evaluate the performance. Furthermore, we derive a static model which is used to underpin the observed motion capabilities. In summary, our segment design extends previous designs with minimal hardware overhead, while either archiving similar accuracy in position errors and planar follow-the-leader deployment, or exhibiting superior motion capabilities due to position redundancy and spatial follow-the-leader deployment.

Tendon-driven continuum robots offer exceptional flexibility and slenderness, making them particularly suitable for inspection and maintenance in constrained and unstructured environments as well as robotic surgery. However, their control remains challenging due to nonlinear behavior, limited sensory feedback, and a significant kinematic dissimilarity from existing controllers. These challenges make continuum robots, similarly to endoscopes, their non-robotic counterparts, require a cost- and time-expensive training for users who operate them in such critical environments. This paper addresses this point by designing and implementing a custom, user-friendly control interface for a tendon-driven continuum robot, leveraging principles from both robotics and gaming to enhance intuitiveness and accessibility. After developing a custom graphical user interface, a prototype has been manufactured to evaluate system performance in a dedicated testing environment. Twelve participants have attempted a timed navigation task using the proposed interface, with data collected to assess usability and control accuracy. Results confirmed the feasibility and effectiveness of the system: users were able to navigate the robot through the course with minimal training. Participant feedback is then analyzed to identify meaningful directions for improvement.

Generic and high-performance feedback control is still challenging for tendon-driven continuum robots. Conventional model-based controllers, based on the piecewise constant curvature (PCC) assumption, explicitly require the arc parameters (bending angle and direction angle) to link the task (in Cartesian coordinates) and actuation spaces. However, the approaches' effectiveness remains to be explored when robot shapes deviate from circular arcs. This paper proposed a hybrid scheme for novel kinematic control of continuum robots. The error led by the slack state has been avoided through tension supervision, while analytical differential kinematics is further developed to avoid the explicit call of arc parameters by importing Cylindrical coordinates into task space and applying accurate piecewise linear approximation. Comparison between a conventional PCC-based controller and the proposed controller has been done by implementing them in a twin-pivot joint-based continuum section. An overall tip positioning accuracy of ±0.35mm has been reached, and a result of root-mean-square-error (RMSE): 0.3mm and Max error: 0.97mm has been observed when running two predefined path tracking. Further, in order to evaluate the versatility of the proposed controller, a dual-revolute joint-based and a 3D-printed continuum section were used to test for path tracking to prove the effectiveness of the controller on a wide range of continuum robotic systems.

Choroid plexus epithelial cells can secrete cerebrospinal fluid into the ventricles, serving as the major structural basis of the selective barrier between the neurological system and blood in the brain. In fact, choroid plexus epithelial cells release the majority of cerebrospinal fluid, which is connected with particular ion channels in choroid plexus epithelial cells. Choroid plexus epithelial cells also produce and secrete a number of essential growth factors and peptides that help the injured cerebrovascular system heal. The pathophysiology of major neurodegenerative disorders like Alzheimer's disease, Parkinson's disease, as well as minor brain damage diseases like hydrocephalus and stroke is still unknown. Few studies have previously connected choroid plexus epithelial cells to the etiology of these serious brain disorders. Therefore, in the hopes of discovering novel treatment options for linked conditions, this review extensively analyzes the association between choroid plexus epithelial cells and the etiology of neurological diseases such as Alzheimer's disease and hydrocephalus. Finally, we review CPE based immunotherapy, choroid plexus cauterization, choroid plexus transplantation, and gene therapy.

Constrained visual predictive control of tendon-driven continuum robots

Continuum robots have the advantages of agility and adaptability. However, existing continuum robots have limitations of low stiffness and complex motion modes, and the existing variable stiffness methods cannot achieve a wide range of stiffness changes and fast switching stiffness simultaneously. A continuum robot structure, switching stiffness method, and motion principle are proposed in this article. The continuum robot is made up of three segments connected in series. Each segment comprises multiple spherical joints connected in series, and the joints can be locked by their respective airbag. A valve controls each airbag, quickly switching the segment between rigidity and flexibility. The motion of the segments is driven by three cables that run through the robot. The segment steers only when it is unlocked. When a segment becomes locked, it acts as a rigid body. As a result, by locking and unlocking each segment in sequence, the cables can alternately drive all the segments. The stiffness variation and movement of the continuum robot were tested. The segment's stiffness varies from 36.89 to 1300.95 N/m and the stiffness switching time is 0.25-0.48 s. The time-sharing control mode of segment stiffness and motion is validated by establishing a specific test platform and a mathematical model. The continuum robot's flexibility is demonstrated by controlling the fast bending of different segments sequentially.

Continuum Robots The cover illustrates three continuum robots accessing a nuclear facility through pipes, with a pneumatically actuated robot manipulating a radioactive component, a tendon-driven continuum robot performing a laser machining task on it, and a concentric tube robot monitoring the operation. In article number 2200367, recent advances, current limitations, and open challenges in the design, modeling, and control of continuum robots are discussed by Matteo Russo, Dragos Axinte, and colleagues.

This paper presents the design and evaluation of a soft hand exo-sheath integrated with a soft fabric electromyography (EMG) sensor for rehabilitation and activities of daily living (ADL) assistance of stroke and spinal cord injury (SCI) patients. This wearable robot addresses the limitations of the soft robot gloves with design considerations in terms of ergonomics and clinical practice. Its features include: this exo-sheath is based on electric actuation and has been designed to be compact and portable. It reduces the shear force and avoids kinematic singularity comparing with tendon-driven soft gloves as their tendon routings are typically in parallel with individual fingers. Disparate from conventional robotic gloves, this design optimizes a bio-inspired fin-ray structure to enhance the hand proprioception as the palm is not covered by wearable structures. With a novel self-fastening finger clasp design, wearers can self-don/doff the exoskeleton device simplifying ADL assistance. To develop more intuitive control interface, a soft fabric EMG sensor has been developed to understand human intentions. The functionality of this soft robot has been demonstrated with experimental results using the low-level position control, kinematics evaluation and reliable EMG measurements.

Continuum robots, characterized by their hyper-redundant and flexible structures, have gained significant attention in fields such as minimally invasive surgery, remote inspection, and soft manipulation. Their complex design and highly nonlinear kinematic behavior present substantial modeling and control challenges. This paper presents a complete framework encompassing the design, modeling, and inverse kinematics solution for a novel two-segment, tendon-driven continuum robot utilizing an elastic spring backbone for enhanced compliance and structural simplicity. A constant curvature forward kinematic model is presented. Subsequently, an efficient numerical approach for solving the challenging inverse kinematics problem is introduced by adapting the Jacobian-based Newton-Raphson method and incorporating the Moore-Penrose Pseudoinverse. This strategy effectively manages the robot's redundancy, ensuring smooth and reliable trajectory generation. Experimental verification confirms the robot's feasibility, demonstrating that the system successfully navigates along the trajectories computed by the inverse kinematics, thus validating the reasonableness of the kinematic model and ensuring seamless and smooth operation. These findings provide a robust foundation for improving motion planning of simple continuum robot platforms in practical applications.

Endoscopic third ventriculostomy combined with choroid plexus cauterization (ETV+CPC) has been adopted by many pediatric neurosurgeons as an alternative to placing shunts in infants with hydrocephalus. However, reported success rates have been highly variable, which may be secondary to patient selection, operative technique, and/or surgeon training. The objective of this prospective multicenter cohort study was to identify independent patient selection, operative technique, or surgical training predictors of ETV+CPC success in infants. This was a prospective cohort study nested within the Hydrocephalus Clinical Research Network's (HCRN) Core Data Project (registry). All infants under the age of 2 years who underwent a first ETV+CPC between June 2006 and March 2015 from 8 HCRN centers were included. Each patient had a minimum of 6 months of follow-up unless censored by an ETV+CPC failure. Patient and operative risk factors of failure were examined, as well as formal ETV+CPC training, which was defined as traveling to and working with the experienced surgeons at CURE Children's Hospital of Uganda. ETV+CPC failure was defined as the need for repeat ETV, shunting, or death. The study contained 191 patients with a primary ETV+CPC conducted by 17 pediatric neurosurgeons within the HCRN. Infants under 6 months corrected age at the time of ETV+CPC represented 79% of the cohort. Myelomeningocele (26%), intraventricular hemorrhage associated with prematurity (24%), and aqueductal stenosis (17%) were the most common etiologies. A total of 115 (60%) of the ETV+CPCs were conducted by surgeons after formal training. Overall, ETV+CPC was successful in 48%, 46%, and 45% of infants at 6 months, 1 year, and 18 months, respectively. Young age (< 1 month) (adjusted hazard ratio [aHR] 1.9, 95% CI 1.0-3.6) and an etiology of post-intraventricular hemorrhage secondary to prematurity (aHR 2.0, 95% CI 1.1-3.6) were the only two independent predictors of ETV+CPC failure. Specific subgroups of ages within etiology categories were identified as having higher ETV+CPC success rates. Although training led to more frequent use of the flexible scope (p < 0.001) and higher rates of complete (> 90%) CPC (p < 0.001), training itself was not independently associated (aHR 1.1, 95% CI 0.7-1.8; p = 0.63) with ETV+CPC success. This is the largest prospective multicenter North American study to date examining ETV+CPC. Formal ETV+CPC training was not found to be associated with improved procedure outcomes. Specific subgroups of ages within specific hydrocephalus etiologies were identified that may preferentially benefit from ETV+CPC.

Dandy-Walker complex (DWC) is a continuum of congenital anomalies comprising Dandy-Walker malformation (DWM), Dandy-Walker variant (DWV), Blake pouch cyst, and mega cisterna magna (MCM). Hydrocephalus is variably associated with each of these, and DWC-associated hydrocephalus has mostly been treated by shunting, often with 2-compartment shunting. There are few reports of management by endoscopic third ventriculostomy (ETV). This study is the largest series of DWC or DWM-associated hydrocephalus treated by ETV, and the first report of treatment by combined ETV and choroid plexus cauterization (ETV/CPC) in young infants with this association. A retrospective review of the CURE Children's Hospital of Uganda clinical database between 2004 and 2010 identified 45 patients with DWC confirmed by CT scanning (25 with DWM, 17 with DWV, and 3 with MCM) who were treated for hydrocephalus by ETV/CPC. Three were excluded because of other potential causes of hydrocephalus (2 postinfectious and 1 posthemorrhagic). The median age at treatment was 5 months (88% of patients were younger than 12 months). There was a 2.4:1 male predominance among patients with DWV. An ETV/CPC (ETV only in one) was successful with no further operations in 74% (mean and median follow-up 24.2 and 20 months, respectively [range 6-65 months]). The rate of success was 74% for DWM, 73% for DWV, and 100% for MCM; 95% had an open aqueduct, and none required posterior fossa shunting. Endoscopic treatment of DWC-associated hydrocephalus should be strongly considered as the primary management in place of the historical standard of creating shunt dependence.

Pediatric hydrocephalus imposes a significant clinical and financial burden in developing countries. Traditional treatment by ventricular shunting in this setting suffers a high rate of shunt infection and malfunction. This study aims at assessing the efficacy and safety of endoscopic third ventriculostomy (ETV), either alone or combined with choroid plexus cauterization (CPC), for preventing shunt dependence in pediatric hydrocephalus within a healthcare setting of a tertiary hospital in Egypt. A prospective clinical case series included patients aged 16years or younger with clinical manifestations of hydrocephalus requiring CSF diversion. Cases with active infection or brain imaging showing prohibitive anatomical distortion or multiloculated hydrocephalus were excluded. Failed ETV + / - CPC cases were categorized into early (< 3months) and late (> 3months) failure groups, each with specific management strategies. A total of 40 patients were admitted to Ain Shams University Hospital between March 2022 and August 2023 and underwent ETV/CPC (n = 32) for those younger than 2years and ETV alone (n = 8) for patients > 2years old, using a flexible neuroendoscope. Aqueductal stenosis was the most common etiology, observed in 13 patients (32.5%), followed by Chiari type 2 in 11 patients (27.5%), and post-infectious causes in 6 patients (15%). The median age of the patients was 5.05months (mean 22months; range 0.23-169.27months). The median preoperative ETV success score (ETVSS) was 50. Overall, 25 patients (62.5%) achieved successful outcomes following either ETV alone or ETV/CPC procedures, with no procedure-related morbidity or mortality. Fifteen patients (37.5%) experienced ETV failure, of whom 6 underwent ETV redo procedures. Across the entire cohort, 28 patients (70%) remained shunt-free, with a mean follow-up of 12months. The addition of CPC to ETV (for patients < 2years) using the flexible scope demonstrates effectiveness in decreasing the necessity for shunt placement in younger patients with a likelihood of ETV failure. Moreover, being a safe procedure, it supports a sustainable and cost-effective approach to hydrocephalus treatment.

Continuum robots are an attractive solution for navigation in complex and restrictive environments. However, with the existing technology, only two approaches are possible for development of high dexterity continuum robots with low compliance: (i) utilizing a fully articulated body with high number of individually actuated rigid links; (ii) employing a body consisting of flexible sections and strong spring elements. While the former requires numerous actuators, thus a heavy and expensive actuator-pack, the latter necessitates larger and costlier actuators to overcome the spring force. Moreover, the latter approach cannot achieve as low compliance due to its flexible nature. This paper introduces a novel planar continuum robot design that benefits from a fully articulated body divided into individually actuated sections of synchronized links. The kinematic modelling and motion planning of the robot arm are presented and utilized for evaluation of the proposed design. A six-section prototype, consisting of 30 links, validates the proposed designs and demonstrates its performance in both simulation and real experiments on four different paths. The validation is based on distal deviation of individual links from the intended paths. Evaluation verifies that the concepts lead to lower compliance, higher dexterity and actuator-pack size reduction (i.e. one actuator per section), as compared to existing approaches.

Minimally invasive mitral valve repair offers significant advantages over traditional open-heart surgery, yet it remains a complex procedure that exposes both patients and medical staff to radiation. To address these challenges, a significant research interest is growing in automating these manual procedures. Continuum robots represent a promising approach, thanks to their ability to navigate confined spaces. However, their nonlinear behavior presents challenges in modeling and control. In this study, we developed a robust position control method for a variable-length tendon-driven continuum robot. We designed a control system that effectively tracks the desired target positions by employing a constant curvature model and a Jacobian-based control algorithm with real-time position feedback. We assessed the stability of our system through Lyapunov analysis, demonstrating reliable convergence to these target positions. Experimental validation conducted in a cardiovascular phantom demonstrated significant improvements with respect to the state of the art. Our method achieved a trajectory following error of approximately 2.43 mm [1.63, 3.23] and a target position error of about 1.92 mm [1.73, 3.13]. Moreover, the computation time per trajectory point was reduced to approximately 0.04 seconds, highlighting enhanced computational efficiency. These results showcase improved accuracy and efficiency in minimally invasive mitral valve repair procedures.