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Robotization of medical acts often requires the evaluation of contacts between a robotic system and a patient, for safety or efficiency reasons. When contact occurs with a stiff environment, instabilities and vibrations can appear and a passive compliance is therefore needed. In this paper, we propose to embed compliance in a force sensor and to develop a novel force sensor with large compliance, i.e. a zero stiffness at contact transition to ease robot control. To get at the same time a satisfying measurement range and low off-axis sensitivity, an optical measurement process based on an optical line generated thanks to additive manufacturing is exploited. A compliant sensor body allowing the desired stiffness profile is presented and the specific optical measurement technique is developed. Finally, a prototype of the proposed force sensor is evaluated experimentally.

ICube / AVR - IRIS s/c IRCAD Hôpitaux Universitaires 1, place de l'hôpital 67091 Strasbourg Cedex France ASME International Design Engineering Technical Conferences, Québec city Email: laurent.barbe[at]unistra.fr; International audience; Linear actuation is a basic need in robotized manipulation of surgical instruments, that must comply with a challenging environment in terms of safety, compactness and now often compatibility with imaging modalities like CT or MRI. In this paper, we focus on needle manipulation for interventional radiology. We propose a needle driver, i.e. a linear actuator for needle insertion, based on the inchworm principle combined with pneumatic energy. Our first contribution is to propose, model and implement the device using a so-called auxetic structure. Its use increases achievable displacement under pressure and provides sufficient off-axis stiffness to use the actuator without additional guidance. Simplified modeling is introduced for the actuator synthesis. Our second contribution is to implement the actuator with multimaterial additive manufacturing combining rigid and flexible materials to increase compactness. As a third contribution, initial assessment of component sterilization and compatibility with X-ray and MRI imaging modalities is presented.

Additive manufacturing is more and more used in optics to produce opto-mechanical components as well as light transmission mediums, either for prototype evaluation or for functional part generation. It was previously shown that optical systems can benefit from the geometrical accuracy of the printed parts. Intrinsic defects such as surface roughness or volume birefringence can also be exploited for optical component design. We here present such use of particular properties of an additive manufacturing process based on photopolymerization. The final goal of the work is the design of a force sensor for collaborative robotics. More precisely, the aim is to design an optical force sensor to control the contact force between a human body and a magnetic source controlled by a robot for medical purpose. Optical sensors are known to have major interests in harsh environments where classical electrical sensors cannot be used due to, like here, electromagnetic compatibility issues. Two 3D-printed designs of optical force sensors are compared. The first one, conceptually developed in a previous work, is using polarization modulation due to force-induced birefringence to modify optical transmission in a sensor based on a monolithic original geometry. For such a case, additive manufacturing appears as a powerful production technique as the 3D part must be transparent and at the same time obtained with an accurate complex geometry. The second design is based on the volume scattering properties of printed transparent parts. For the first time to our knowledge, we show that the optical system made out of a beam expander and a cylindrical lens, necessary to achieve an optical line, can be replaced by a simple prismatic 3D-printed element. Using the Polyjet technology developed by Stratasys Ltd, a line can simply be obtained using the 1D volume light scattering inside the printed medium. The variation of line properties is then related to the mechanical strain induced by the force to be measured. In other words, the optical properties we rely on are linked to the bulk liquid material, its photopolymerization during printing and finally the impact of mechanical stress on the printed component. The sensitive element in the force sensor can be seen as a metamaterial with properties which depend on its micrometric structuration. The micro-structuration size is not related to the standard minimum feature size as claimed by the manufacturer but to the additive manufacturing process itself. In our case, a Stratasys Connex 350 printer has been used with an acrylate transparent material. Opto-mechanical properties such as birefringence, surface roughness, elasto-optic coefficients have been measured. The ability to generate an optical line using natural 1D volume light scattering in a printed parallelepiped with polished surfaces is experimentally demonstrated. As potential application, the parallelepiped is used to replace a cylindrical lens in an amplitude modulation force sensor. The sensor response is measured. Thus, additive manufacturing appears to be a promising technique to achieve optical components and to integrate optical sensors in future 3D-printed mechatronic systems.

The assessment of the three-dimensional architecture of collagen fibers inside vessel walls constitutes one of the bases for building structural models for the description of the mechanical behavior of these tissues. Multiphoton microscopy allows for such observations, but is limited to volumes of around a thousand of microns. In the present work, we propose to observe the collagenous network of vascular tissues using micro-CT. To get a contrast, three staining solutions (phosphotungstic acid, phosphomolybdic acid and iodine potassium iodide) were tested. Two of these stains were showed to lead to similar results and to a satisfactory contrast within the tissue. A detailed observation of a small porcine iliac vein sample allowed assessing the collagen fibers orientations within the medial and adventitial layers of the vein. The vasa vasorum network, which is present inside the adventitia of the vein, was also observed. Finally, the demonstrated micro-CT staining technique for the three-dimensional observation of thin soft tissues samples, like vein walls, contributes to the assessment of their structure at different scales while keeping a global overview of the tissue.

Predictive theoretical-numerical modeling of the behavior and evolution of biological tissue is a difficult task since many of the required knowledge tools (experimental, theoretical and numerical) are still not well understood. We present here some methodologies and results specific to multiscale and multiphysics numerical modeling of biological tissues applied to the predictive behavior of cortical veins depending on their local constituents' microstructure and for bone remodeling and reconstruction as a function of the local mechanobiology. Although further work is required to improve the accuracy of the developed models, the proposed approaches highlight their potential usefulness for understanding the mechanical-biological couplings, short and long term predictions of biological evolutions as well as possible further transfer to medical applications.

The collagen fibers' three-dimensional architecture has a strong influence on the mechanical behavior of biological tissues. To accurately model this behavior, it is necessary to get some knowledge about the structure of the collagen network. In the present paper, we focus on the in situ characterization of the collagenous structure, which is present in porcine jugular vein walls. An observation of the vessel wall is first proposed in an unloaded configuration. The vein is then put into a mechanical tensile testing device. As the vein is stretched, three-dimensional images of its collagenous structure are acquired using multiphoton microscopy. Orientation analyses are provided for the multiple images recorded during the mechanical test. From these analyses, the reorientation of the two families of collagen fibers existing in the vein wall is quantified. We noticed that the reorientation of the fibers stops as the tissue stiffness starts decreasing, corresponding to the onset of damage. Besides, no relevant evolutions of the out of plane collagen orientations were observed. Due to the applied loading, our analysis also allowed for linking the stress relaxation within the tissue to its internal collagenous structure. Finally, this analysis constitutes the first mechanical test performed under a multiphoton microscope with a continuous three-dimensional observation of the tissue structure all along the test. It allows for a quantitative evaluation of microstructural parameters combined with a measure of the global mechanical behavior. Such data are useful for the development of structural mechanical models for living tissues.

In this paper, we investigated the brain-sinus junction and especially the bridging veins linking these two organs. Two types of optical microscopy were used: conventional optical microscopy and digital microscopy. We used thin histological sections prepared from a human brain, and stained with Masson's trichrome, hemalun and orcein. Finally we observed the path of the bridging vein inside the brain-skull interface. At smaller scales, wavy collagen fiber bundles were found and characterized inside the vein walls. Taking into account the orientations of the different sections with reference to frontal planes, we found that the bridging vein has a very complex geometry, which increases the difficulty to determine fiber orientations in its walls. Nevertheless, we found that collagen fiber bundles are mainly circumferentially oriented in the superior sagittal sinus walls. In this paper, we were able to characterize precisely the path of the bridging vein from the brain to the sinus, with different magnifications.

We propose a second gradient, two-solids, continuum mixture model with variable masses to describe the effect of micro-structure on mechanically-driven remodelling of bones grafted with bio-resorbable materials. A one-dimensional numerical simulation is addressed showing the potentialities of the proposed generalized continuum model. In particular, we show that the used second gradient model allows for the description of some micro-structure-related size effects which are known to be important in hierarchically heterogeneous materials like reconstructed bones. Moreover, the influence of the introduced second gradient parameters on the final percentages of replacement of artificial bio-material with natural bone tissue is presented and discussed.

Medical surgery is currently rapidly improving and requires modeling faithfully the mechanical behavior of soft tissues. Various models exist in literature; some of them created for the study of biological materials, and others coming from the field of rubber mechanics. Indeed biological tissues show a mechanical behavior close to the one of rubbers. But while building a model, one has to keep in mind that its parameters should be loading independent and that the model should be able to predict the behavior under complex loading conditions. In addition, keeping physical parameters seems interesting since it allows a bottom up approach taking into account the microstructure of the material. In this study, the authors consider different existing hyperelastic models based on strain energy functions and identify their coefficients successively on single loading stress-stretch curves. The experimental data used, come from a paper by Zemanek dated 2009 and concerning uniaxial, equibiaxial and plane tension tests on porcine arterial walls taken in identical experimental conditions. To achieve identification, the strain energy function of each model is derived differently to provide an expression of the Cauchy stress associated to each loading case. Firstly the parameters of each model are identified on the uniaxial tension curve using a least squares method. Then, keeping the obtained parameters, predictions are made for the two other loading cases (equibiaxial and plane tension) using the associated expressions of stresses. A comparison of these predictions with experimental data is done and allows evaluating the predictive capabilities of each model for the different loading cases. A similar approach is used after swapping the loading types. Since the predictive capabilities of the models are really dependent on the loading chosen to determine their parameters, another type of identification procedure is set up. It consists in adding the residues over the three loading cases during identification. This alternative identification method allows a better agreement between each model and the various types of experiments. This study evaluated the ability of some classical hyperelastic models to be used for a predictive scope after being identified on a specific loading type. Besides it brought to light some existing models which can describe at best the mechanical behavior of biological tissues submitted to various loadings.

One of the specific interests of optical sensors is their compatibility with harsh environments. The polarization modulated force sensor we propose offers this advantage, in addition to low cost and ease of manufacturing thanks to its acrylate 3D printed monolithic design. All the polarization control is indeed achieved using the geometry of a single component making unnecessary future alignments. The complex geometry of the transducer is obtained thanks to the 3D printing process. This process and the resulting material optical properties are described. The sensor concept and the fabrication method are experimentally investigated. A monolithic force sensor in the required range of 20 N is exhibited for application in the field of MR-compatible robotics. The potentiality of 3D printing for optical application in the design of the force sensor is illustrated.