Effect of Degradation in Small Intestinal Fluids on Mechanical Properties of Polycaprolactone and Poly-l-lactide-co-caprolactone.

Polycaprolactone and poly-l-lactide-co-caprolactone are promising degradable biomaterials for many medical applications. Their mechanical properties, especially a low elastic modulus, make them particularly interesting for implantable devices and scaffolds that target soft tissues like the small intestine. However, the specific environment and mechanical loading in the intestinal lumen pose harsh boundary conditions on the design of these devices, and little is known about the degradation of those mechanical properties in small intestinal fluids. Here, we perform tensile tests on injection molded samples of both polymers during in vitro degradation of up to 70 days in human intestinal fluids. We report on yield stress, Young's modulus, elongation at break and viscoelastic parameters describing both materials at regular time steps during the degradation. These characteristics are bench-marked against degradation studies of the same materials in other media. As a result, we offer time dependent mechanical properties that can be readily used for the development of medical devices that operate in the small intestine.

Nonlinear Inflatable Actuators for Distributed Control in Soft Robots.

As soft robotic systems grow in complexity and functionality, the size and stiffness of the needed control hardware severely limits their application potential. Alternatively, functionality can be embodied within actuator characteristics, drastically reducing the amount of peripherals. Functions such as memory, computation, and energy storage then result from the intrinsic mechanical behavior of precisely designed structures. Here, actuators are introduced with tunable characteristics to generate complex actuation sequences from a single input. Intricate sequences are made possible by harnessing hysteron characteristics encoded in the buckling of a cone-shaped shell incorporated in the actuator design. A large variety of such characteristics are generated by varying the actuator geometry. This dependency is mapped and used for creating a tool to determine the actuator geometry that yields a desired characteristic. Using this tool, a system with six actuators is created that plays the final movement of Beethoven's Ninth Symphony with a single pressure supply.

Innovative Fabrication of Hollow Microneedle Arrays Enabling Blood Sampling with a Self-Powered Microfluidic Patch.

Microneedles are gaining a lot of attention in the context of sampling cutaneous biofluids such as capillary blood. Their minimal invasiveness and user-friendliness make them a prominent substitute for venous puncture or finger-pricking. Although the latter is suitable for self-sampling, the impracticality of manual handling and the difficulty of obtaining enough qualitative sample is driving the search for better solutions. In this context, hollow microneedle arrays (HMNAs) are particularly interesting for completely integrating sample-to-answer solutions as they create a duct between the skin and the sampling device. However, the fabrication of sharp-tipped HMNAs with a high aspect ratio (AR) is challenging, especially since a length of ≥1500 µm is desired to reach the blood capillaries. In this paper, we first described a novel two-step fabrication protocol for HMNAs in stainless steel by percussion laser drilling and subsequent micro-milling. The HMNAs were then integrated into a self-powered microfluidic sampling patch, containing a capillary pump which was optimized to generate negative pressure differences up to 40.9 ± 1.8 kPa. The sampling patch was validated in vitro, showing the feasibility of sampling 40 µL of liquid. It is anticipated that our proof-of-concept is a starting point for more sophisticated all-in-one biofluid sampling and point-of-care testing systems.

Out-of-Plane Soft Lithography for Soft Pneumatic Microactuator Arrays.

Elastic pneumatic actuators are fueling new devices and applications in soft robotics. Actuator miniaturization is critical to enable soft microsystems for applications in microfluidics and micromanipulation. This work proposes a fabrication technique to make out-of-plane bending microactuators entirely by soft lithography. The only bonding step required is to seal the embedded fluidic channels, assuring the structural integrity of the microactuators. The process consists of fabricating two SU8 mold halves using different lithographic layers. Polydimethilsiloxane is poured on the bottom mold, which is subsequently aligned and assembled with the top mold. The process allows for out-of-plane actuators with a diameter of 300 µm and for fabricating arrays of up to 36 actuators that are row addressable. These active micropillars have an aspect ratio of 1:1.5 and, when pressurized at 1 bar, show a bending angle of ∼30°.

Multi-Ion-Based Modelling and Experimental Investigations on Consistent and High-Throughput Generation of a Micro Cavity Array by Mask Electrolyte Jet Machining.

The controllability and consistency in the fabrication of micro-textures on large-scale remains a challenge for existing production processes. Mask electrolyte jet machining (MEJM) is an alternative to Jet-ECM for controllable and high-throughput surface microfabrication with more consistency of dimensional tolerances. This hybrid configuration combines the high-throughput of masked-ECM and the adjustable flow-field of jet-ECM. In this work, a duckbill jet nozzle was introduced to make MEJM more capable of batch micro-structuring. A multiphysics model was built to simulate the distribution of electrochemical reaction ions, the current density distribution, and the evolution of the shape of the machined cavity. Experimental investigations are presented showing the influence of the machining voltage and nozzle moving speed on the micro cavity. Several 35×35 micro cavity arrays with a diameter of 11.73-24.92 µm and depth of 7.24-15.86 µm are generated on 304 stainless steel.

Robotic Endoscope Control Via Autonomous Instrument Tracking.

Many keyhole interventions rely on bi-manual handling of surgical instruments, forcing the main surgeon to rely on a second surgeon to act as a camera assistant. In addition to the burden of excessively involving surgical staff, this may lead to reduced image stability, increased task completion time and sometimes errors due to the monotony of the task. Robotic endoscope holders, controlled by a set of basic instructions, have been proposed as an alternative, but their unnatural handling may increase the cognitive load of the (solo) surgeon, which hinders their clinical acceptance. More seamless integration in the surgical workflow would be achieved if robotic endoscope holders collaborated with the operating surgeon via semantically rich instructions that closely resemble instructions that would otherwise be issued to a human camera assistant, such as "focus on my right-hand instrument." As a proof of concept, this paper presents a novel system that paves the way towards a synergistic interaction between surgeons and robotic endoscope holders. The proposed platform allows the surgeon to perform a bimanual coordination and navigation task, while a robotic arm autonomously performs the endoscope positioning tasks. Within our system, we propose a novel tooltip localization method based on surgical tool segmentation and a novel visual servoing approach that ensures smooth and appropriate motion of the endoscope camera. We validate our vision pipeline and run a user study of this system. The clinical relevance of the study is ensured through the use of a laparoscopic exercise validated by the European Academy of Gynaecological Surgery which involves bi-manual coordination and navigation. Successful application of our proposed system provides a promising starting point towards broader clinical adoption of robotic endoscope holders.

Micro-EDM Drilling/Milling as a Potential Technique for Fabrication of Bespoke Artificial Defects on Bearing Raceways.

The fabrication of bespoke artificial defects on bearing raceways helps in mimicking incipient faults during real application or for directly validating the diagnostic technology depending on their shapes and sizes. This is particularly useful when run-to-failure experiments are time-consuming and even difficult in some cases. However, there has been limited systematic research on the design and fabrication of artificial defects on bearing raceways, particularly for the purpose of accelerated testing. In this work, micro-EDM is put forward as a potential technique for the fabrication of artificial defects using drilling/milling mode. A methodology is developed, not only to achieve the full control of the dimension and distribution of defects on a bearing element, but also to qualitatively and quantitatively perform the efficient characterization of the defect surface. A linear regression model with the inclusion of two-way interactions based on an analysis of variance (ANOVA) is presented to optimally select the process parameters. The verification experiments show that this mathematical model obtains a good fit for approximately 80% of the observed data. Through a combination of optical microscopy and confocal microscopy, the morphology and topography of the artificial defects was measured and compared. To conclude, micro-EDM evidences its great potential in terms of machining efficiency, e.g., with an MRR of 0.060 mm3/min, TWR of 0.032 mm3/min and dimensional controllability, e.g., the standard deviation of pitting diameter and depth being 0.5 µm and 0.8 µm, respectively, to achieve a desirable feature shape for bearing defects.

3D Printing of Monolithic Capillarity-Driven Microfluidic Devices for Diagnostics.

Rapid diagnostic testing at the site of the patient is essential when a fully equipped laboratory is not accessible. To maximize the impact of this approach, low-cost, disposable tests that require minimal user-interference and external equipment are desired. Fluid transport by capillary wicking removes the need for bulky ancillary equipment to actuate and control fluid flow. Nevertheless, current microfluidic paper-based analytical devices based on this principle struggle with the implementation of multistep diagnostic protocols because of fabrication-related issues. Here, 3D-printed microfluidic devices are demonstrated in a proof-of-concept enzyme-linked immunosorbent assay in which a multistep assay timeline is completed by precisely engineering capillary wetting within printed porous bodies. 3D printing provides a scalable route to low-cost microfluidic devices and obviates the assembly of discrete components. The resulting rapid and seamless transition between digital data and physical objects allows for rapid design iterations, and opens up perspectives on distributed manufacturing.

A Novel Method for Surface Exploration by 6-DOF Encountered-Type Haptic Display Towards Virtual Palpation.

Surface exploration in virtual reality has a large potential to enrich the user's experience. It could for example be used to train and simulate medical palpation. During palpation, users tap, indent, and rub the surface of a sample to estimate the underlying properties. However, up to now there is no good approach to render such intricate interaction realistically. This paper introduces 6 degrees of freedom (DoF) encountered-type haptic display technology for simulating surface exploration tasks. Among the different phases of exploration, this article focuses on the 'in-contact sliding' phase. Two novel control approaches to render sliding over a virtual surface are elaborated. A first rendering method generates lateral frictional forces as the finger slides over the surface. A second method adjusts the inclination of the end-effector to render tissue properties. With both methods a stiff nodule embedded in a soft tissue was prepared. User experiments were carried out to find proper parameter and intensity ranges and to confirm the feasibility of the new rendering schemes. Participants indicated that both rendering schemes felt realistic. Compared to earlier work, where only the vertical stiffness was altered, lower thresholds to detect and localise embedded virtual nodules were found. Users also made fewer errors in detecting nodule edges. Furthermore, the method that used end-effector inclination allowed faster discovery of the nodule's edges. It is expected that approaches that combine both rendering methods could provide an even more realistic feel.

Morphological Control of Cilia-Inspired Asymmetric Movements Using Nonlinear Soft Inflatable Actuators.

Soft robotic systems typically follow conventional control schemes, where actuators are supplied with dedicated inputs that are regulated through software. However, in recent years an alternative trend is being explored, where the control architecture can be simplified by harnessing the passive mechanical characteristics of the soft robotic system. This approach is named "morphological control", and it can be used to decrease the number of components (tubing, valves and regulators) required by the controller. In this paper, we demonstrate morphological control of bio-inspired asymmetric motions for systems of soft bending actuators that are interconnected with passive flow restrictors. We introduce bending actuators consisting out of a cylindrical latex balloon in a flexible PVC shell. By tuning the radii of the tube and the shell, we obtain a nonlinear relation between internal pressure and volume in the actuator with a peak and valley in pressure. Because of the nonlinear characteristics of the actuators, they can be assembled in a system with a single pressure input where they bend in a discrete, preprogrammed sequence. We design and analyze two such systems inspired by the asymmetric movements of biological cilia. The first replicates the swept area of individual cilia, having a different forward and backward stroke, and the second generates a travelling wave across an array of cilia.

Phase I trial on robot assisted retinal vein cannulation with ocriplasmin infusion for central retinal vein occlusion.

PURPOSE: To evaluate the safety and feasibility of robot-assisted retinal vein cannulation with Ocriplasmin infusion for central retinal vein occlusion. METHODS: Prospective phase I trial including four patients suffering from central retinal vein occlusion (CRVO). Diagnosis was confirmed by preoperative fluo-angiography and followed by a standard three-port pars plana vitrectomy. Afterwards, a custom-built microneedle was inserted into a branch retinal vein with robotic assistance and infusion of Ocriplasmin started. Primary outcomes were the occurrence of intra-operative complications and success of cannulation. Secondary outcomes were change in visual acuity, central macular thickness (CMT) and venous filling times (VFT) during fluo-angiography two weeks after the intervention. RESULTS: Cannulation with infusion of ocriplasmin was successful in all four eyes with a mean total infusion time of 355 ± 204 seconds (range 120-600 seconds). Best corrected visual acuity (BCVA) remained counting fingers (CF) in case 3 and 4, increased in case 1 from CF to 0.9LogMAR and decreased in case 2 from 0.4 to 1.3 LogMAR. CMT and VFT both showed a trend towards significant decrease comparing preoperative measurements with two weeks postintervention (1061 ± 541 µm versus 477 ± 376 µm, p = 0.068) and 24 ll 4 seconds versus 15 ± 1 seconds, p = 0.068, respectively). In one eye a needle tip broke and could be removed with an endoforceps. There were no other intervention-related complications. CONCLUSION: Robot-assisted retinal vein cannulation is feasible and safe. Local intravenous infusion with Ocriplasmin led to an improved retinal circulation.

Micro-patterned membranes prepared via modified phase inversion: Effect of modified interface on water fluxes and organic fouling.

The introduction of patterns on a membrane-solute interface has been suggested as an effective method to tackle the reduced flux and fouling issues. Herein, the effectiveness of using spray-modified non-solvent induced phase separation (s-NIPS) to create a variety of micrometer-level structured interfaces is now studied. Circular, triangular and rectangular patterns with different dimensions were successfully created on polyacrylonitrile membranes. The rectangular pattern height was varied from 500 to 1500 µm, which resulted in a proportional increase in clean water permeance from 590 ± 47 L m-2 h-1 bar-1 to 1345 ± 108 L m-2 h-1 bar-1 respectively. This coincided with some BSA rejection loss for the highest patterns, indicating the fragile nature of these tall features. No significant rejection losses were found for the smaller pattern heights (145-250 µm) as compared to flat membranes, while fluxes more than doubled still. The critical pressure was also increased substantially for patterned membranes and showed a proportionality with the pattern height. These experimental findings were correlated with the reduced foulant adhesion due to a shear-induced slip boundary layer at the membrane-solution interface. Computational fluid dynamics simulations further showed higher shear stress values due to flow constriction within the membrane's valley regions. These findings indicate the high potential of s-NIPS patterned membranes in long-term industrial applications by requiring less membrane area for a given application and reducing cleaning interventions.

Metachronal patterns in artificial cilia for low Reynolds number fluid propulsion.

Cilia are hair-like organelles, present in arrays that collectively beat to generate flow. Given their small size and consequent low Reynolds numbers, asymmetric motions are necessary to create a net flow. Here, we developed an array of six soft robotic cilia, which are individually addressable, to both mimic nature's symmetry-breaking mechanisms and control asymmetries to study their influence on fluid propulsion. Our experimental tests are corroborated with fluid dynamics simulations, where we find a good agreement between both and show how the kymographs of the flow are related to the phase shift of the metachronal waves. Compared to synchronous beating, we report a 50% increase of net flow speed when cilia move in an antiplectic wave with phase shift of -π/3 and a decrease for symplectic waves. Furthermore, we observe the formation of traveling vortices in the direction of the wave when metachrony is applied.

Real-time on-machine observations close to interelectrode gap in a tool-based hybrid laser-electrochemical micromachining process.

A tool-based hybrid laser-electrochemical micromachining process involves concurrent application of two process energies i.e. electrochemical and laser in the same machining zone by means of a hybrid tool which serves as an ECM tool as well as a multimode waveguide. It is a relatively novel process finding applications in defect-free machining of difficult-to-cut materials without affecting their microstructure. In order to understand the physical phenomena occurring during this process, in-situ observations are required. Therefore, in this work, a real time observation was carried out of a novel tool-based hybrid laser electrochemical micromachining process. A combination of high-speed imaging and Large Scale Particle Image Velocimetry (LSPIV) was used to visualize the tool-based hybrid laser-ECM process in real time. It also allowed to carry out experimental investigations on the by-products and bubble generation which have a direct effect on process performance in terms of accuracy and efficiency. The real-time on-machine observations are unique of its kind and they will facilitate the understanding of underlying mechanisms governing this hybrid laser-electrochemical micromachining process. This will ultimately help in improving the quality of parts manufactured. This research is also a step forward towards making these physics-based hybrid processes deterministic by employing high-speed imaging in a closed loop control.

Fast Fabrication of Complex Surficial Micro-Features Using Sequential Lithography and Jet Electrochemical Machining.

This paper presents fabrication of complex surficial micro-features employing a cross-innovative hybrid process inspired from lithography and Jet-ECM. The process is referred here as mask electrolyte jet machining (MEJM). MEJM is a non-contact machining process which combines high resolution of lithography and greater flexibility of Jet-ECM. It is a non-contact process which can fabricate variety of microstructures on difficult-to-machine materials without need of expensive tooling. The presented work demonstrates the process performance of this technology by statistical analysis and multivariate kernel density estimation (KDE) based on probabilistic density function. Micro-letters are fabricated as an example of complex surficial structure comprising of multiple intersecting, straight and curved grooves. The processing response is characterized in terms of geometrical size, similarity ratio, and cumulative shape deviation. Experimental results demonstrated that micro letters with good repeatability (minimum SD of shape error ratio 0.297%) and shape accuracy (minimum shape error of 0.039%) can be fabricated with this technology. The results suggest MEJM could be a promising technology for batch manufacturing of surface microstructures with high productivity.

Shaping Soft Robotic Microactuators by Wire Electrical Discharge Grinding.

Inflatable soft microactuators typically consist of an elastic material with an internal void that can be inflated to generate a deformation. A crucial feature of these actuators is the shape of ther inflatable void as it determines the bending motion. Due to fabrication limitations, low complex void geometries are the de facto standard, severely restricting attainable motions. This paper introduces wire electrical discharge grinding (WEDG) for shaping the inflatable void, increasing their complexity. This approach enables the creation of new deformation patterns and functionalities. The WEDG process is used to create various moulds to cast rubber microactuators. These microactuators are fabricated through a bonding-free micromoulding process, which is highly sensitive to the accuracy of the mould. The mould cavity (outside of the actuator) is defined by micromilling, whereas the mould insert (inner cavity of the actuator) is defined by WEDG. The deformation patterns are evaluated with a multi-segment linear bending model. The produced microactuators are also characterised and compared with respect to the morphology of the inner cavity. All microactuators have a cylindrical shape with a length of 8 mm and a diameter of 0.8 mm. Actuation tests at a maximum pressure of 50 kPa indicate that complex deformation patterns such as curling, differential bending or multi-points bending can be achieved.

Process Fingerprint in Micro-EDM Drilling.

The micro electrical discharge machining (micro-EDM) process is extensively used in aerospace, automotive, and biomedical industries for drilling small holes in difficult-to-machine materials. However, due to the complexity of the electrical discharge phenomena, optimization of the processing parameters and quality control are time-consuming operations. In order to shorten these operations, this study investigates the applicability of a process fingerprint approach in micro-EDM drilling. This approach is based on the monitoring of a few selected physical quantities, which can be controlled in-line to maximize the drilling speed and meet the manufacturing tolerance. A Design of Experiments (DoE) is used to investigate the sensitivity of four selected physical quantities to variations in the processing parameters. Pearson's correlation is used to evaluate the correlation of these quantities to some main performance and hole quality characteristics. Based on the experimental results, the potential of the process fingerprint approach in micro-EDM drilling is discussed. The results of this research provide a foundation for future in-line process optimization and quality control techniques based on machine learning.

Evaluation of Haptic Feedback on Bimanually Teleoperated Laparoscopy for Endometriosis Surgery.

Robotic minimal invasive surgery is gaining acceptance in surgical care. In contrast with the appreciated three-dimensional vision and enhanced dexterity, haptic feedback is not offered. For this reason, robotics is not considered beneficial for delicate interventions such as the endometriosis. Overall, haptic feedback remains debatable and yet unproven except for some simple scenarios such as fundamentals of laparoscopic surgery exercises. OBJECTIVE: This work investigates the benefits of haptic feedback on more complex surgical gestures, manipulating delicate tissue through coordination between multiple instruments. METHODS: A new training exercise, "endometriosis surgery exercise" (ESE) has been devised approximating the setting for monocular robotic endometriosis treatment. A bimanual bilateral teleoperation setup was designed for laparoscopic laser surgery. Haptic guidance and haptic feedback are, respectively, offered to the operator. User experiments have been conducted to assess the validity of ESE and examine possible advantages of haptic technology during execution of bimanual surgery. RESULTS: Content and face validity of ESE were established by participating surgeons. Surgeons suggested ESE also as a mean to train lasering skills, and interaction forces on endometriotic tissue were found to be significantly lower when a bilateral controller is used. Collisions between instruments and the environment were less frequent and so were situations marked as potentially dangerous. CONCLUSION: This study provides some promising results suggesting that haptics may offer a distinct advantage in complex robotic interventions were fragile tissue is manipulated. SIGNIFICANCE: Patients need to know whether it should be incorporated. Improved understanding of the value of haptics is important as current commercial surgical robots are widely used but do not offer haptics.

Design and evaluation of a new bioelectrical impedance sensor for micro-surgery: application to retinal vein cannulation.

PURPOSE: Nowadays, millions of people suffer from retinal vein occlusion, a blind-making eye disease. No curative treatment currently exists for this vascular disorder. However, a promising treatment consists in injecting a thrombolytic drug directly inside the affected retinal vessel. Successfully puncturing miniature vessels with diameters between 50 and 400 [Formula: see text] remains a real challenge, amongst others due to human hand tremor, poor visualisation and depth perception. As a consequence, there is a significant risk of double-puncturing the targeted vessel. Sub-surfacic injection of thrombolytic agent could potentially lead to severe retinal damage. METHODS: A new bio-impedance sensor has been developed to visually display the instant of vessel puncture. The physical working principle of the sensor has been analysed, and a representative electrical model has been derived. Based on this model, the main design parameters were derived to maximise the sensor sensitivity. A detailed characterisation and experimental validation of this concept were conducted. RESULTS: Stable, repeatable and robust impedance measurements were obtained. In an experimental campaign, 35 puncture attempts on ex vivo pig eyes vessels were conducted. A confusion matrix shows a detection accuracy of 80% if there is a puncture, a double puncture or no puncture. The 20% of inaccuracy most probably comes from the limitations of the employed eye model and the experimental conditions. CONCLUSIONS: The developed bio-impedance sensor has shown great promise to help in avoiding double punctures when cannulating retinal veins. Compared to other puncture detection methods, the proposed sensor is simple and therefore potentially more affordable. Future research will include validation in an in vivo situation involving vitreoretinal surgeons.

Hardware Sequencing of Inflatable Nonlinear Actuators for Autonomous Soft Robots.

Soft robots are an interesting alternative for classic rigid robots in applications requiring interaction with organisms or delicate objects. Elastic inflatable actuators are one of the preferred actuation mechanisms for soft robots since they are intrinsically safe and soft. However, these pneumatic actuators each require a dedicated pressure supply and valve to drive and control their actuation sequence. Because of the relatively large size of pressure supplies and valves compared to electrical leads and electronic controllers, tethering pneumatic soft robots with multiple degrees of freedom is bulky and unpractical. Here, a new approach is described to embed hardware intelligence in soft robots where multiple actuators are attached to the same pressure supply, and their actuation sequence is programmed by the interaction between nonlinear actuators and passive flow restrictions. How to model this hardware sequencing is discussed, and it is demonstrated on an 8-degree-of-freedom walking robot where each limb comprises two actuators with a sequence embedded in their hardware. The robot is able to carry pay loads of 800 g in addition to its own weight and is able to walk at travel speeds of 3 body lengths per minute, without the need for complex on-board valves or bulky tethers.