The mechanical properties of biomaterials play important roles in performing their specialized functions: synthesizing, storing, and transporting biomolecules; maintaining internal structures; and responding to external environments. Besides biological cells, there are also many other biomaterials that are highly deformable and have a diameter between 1μm and 100μm, comparable to that of most biological cells. For example, many polymeric microcapsules for drug delivery use are spherical particles of micrometers size. In order to mechanically characterize individual micrometer-sized biomaterials, the capability of capturing high-resolution and low-magnitude force feedback is required. This research focuses on the development of micro devices and experimental techniques for quantifying the mechanical properties of alginate-chitosan microcapsules. The micro devices include microelectromechanical systems (MEMS) capacitive force sensors and force-feedback microgrippers, capable of measuring sub-μN forces. Employing the MEMS devices, systems were constructed to perform the micro-scale compression testing of microcapsules. The force sensors are capable of resolving forces up to 110μN with a resolution of 33.2nN along two independent axes. The force sensors were applied to characterizing the mechanical properties of hydrogel microparticles without assembling additional end-effectors. The microcapsules were immobilized by a PDMS holding device and compressed between the sensor probe and holding device. Young's modulus values of individual microcapsules with 1%, 2%, and 3% chitosan coating were determined through the micro-scale compression testing in both distilled deionized (DDI) water and pH 7.4 phosphate buffered saline (PBS). The Young's modulus values were also correlated to protein release rates. Instead of compressing the microcapsule against the wall of the holding device, a force-feedback MEMS microgripper with the capability of directly compressing the microcapsule between two gripping arms has been used for characterizing both the elastic and viscoelastic properties of the microcapsules during micromanipulation. The single-chip microgripper integrates an electrothermal microactuator and two capacitive force sensors, one for contact detection (force resolution: 38.5nN) and the other for gripping force measurements (force resolution: 19.9nN). Through nanoNewton force measurements, closed-loop force control, and visual tracking, the system quantified the Young's modulus values and viscoelastic parameters of alginate microcapsules, demonstrating an easy-to-operate, accurate compression testing technique for characterizing soft, micrometer-sized biomaterials.

The mechanical properties of biomaterials play important roles in performing their specialized functions: synthesizing, storing, and transporting biomolecules; maintaining internal structures; and responding to external environments. Besides biological cells, there are also many other biomaterials that are highly deformable and have a diameter between 1μm and 100μm, comparable to that of most biological cells. For example, many polymeric microcapsules for drug delivery use are spherical particles of micrometers size. In order to mechanically characterize individual micrometer-sized biomaterials, the capability of capturing high-resolution and low-magnitude force feedback is required. This research focuses on the development of micro devices and experimental techniques for quantifying the mechanical properties of alginate-chitosan microcapsules. The micro devices include microelectromechanical systems (MEMS) capacitive force sensors and force-feedback microgrippers, capable of measuring sub-μN forces. Employing the MEMS devices, systems were constructed to perform the micro-scale compression testing of microcapsules. The force sensors are capable of resolving forces up to 110μN with a resolution of 33.2nN along two independent axes. The force sensors were applied to characterizing the mechanical properties of hydrogel microparticles without assembling additional end-effectors. The microcapsules were immobilized by a PDMS holding device and compressed between the sensor probe and holding device. Young's modulus values of individual microcapsules with 1%, 2%, and 3% chitosan coating were determined through the micro-scale compression testing in both distilled deionized (DDI) water and pH 7.4 phosphate buffered saline (PBS). The Young's modulus values were also correlated to protein release rates. Instead of compressing the microcapsule against the wall of the holding device, a force-feedback MEMS microgripper with the capability of directly compressing the microcapsule between two gripping arms has been used for characterizing both the elastic and viscoelastic properties of the microcapsules during micromanipulation. The single-chip microgripper integrates an electrothermal microactuator and two capacitive force sensors, one for contact detection (force resolution: 38.5nN) and the other for gripping force measurements (force resolution: 19.9nN). Through nanoNewton force measurements, closed-loop force control, and visual tracking, the system quantified the Young's modulus values and viscoelastic parameters of alginate microcapsules, demonstrating an easy-to-operate, accurate compression testing technique for characterizing soft, micrometer-sized biomaterials.

L’objectif de cette thèse est le développement d’un nouveau capteur de forcemulti-axes destiné à mesurer les composantes de friction impliquées dans lecontact doigt/objet lors la micromanipulation dextre. Des études théoriques etdes simulations par éléments finis ont conduit à la conception de ce capteurMEMS piézorésistif composé d’une plate-forme centrale munie d’une microbille,entourée d’une table compliante. D’après les résultats de simulations, ce capteur estcapable de mesurer indépendamment les forces normales et de frottement (couplageréciproque inférieure à 1%) avec une bonne sensibilité. Différents runs de fabricationnous ont permis d’obtenir des dispositifs exploitables. La structure mécanique de cescapteurs a été validée par la mesure des fréquences de résonance qui sont en accordavec les résultats de simulation. Des premiers résultats expérimentaux en termesde mesure de force ont ensuite été obtenus grâce au développement d’un banc detest (structure robotique, actionneurs, caméras, etc.). Nous nous sommes égalementintéressés à la problématique de l’étalonnage des capteurs de micro et nanoforceà l’aide de ressorts magnétiques reliés à des masses mesurables. Nous avons, danscette optique, mis au point une stratégie d’estimation et de compensation passivedes perturbations mécaniques en utilisant un principe différentiel. Cette approchea été appliquée à un capteur de nanoforce basé sur la lévitation diamagnétique et aabouti à des résultats prometteurs : une résolution inférieure au nanonewton a puêtre obtenue. / Sensor enabling to characterize the finger/object contact involved in dexterousmicromanipulation. Theoretical studies and finite elements simulations have lead tothe conception of this piezoresistive MEMS sensor composed of a central platformwith a micro-ball and surrounded by a compliant table. According to the simulationresults, this sensor is able to independently measure the normal and friction forces(crosstalk less than 1 %) with a good sensitivity. Several runs of fabrication allowedus to obtain usable devices. The mechanical structure of such sensors has beenvalidated by the measurement of resonance frequencies that are consistent with thesimulation results. The first experimental results in terms of force measurement werethen obtained through the development of a test bench (robotic structure, actuators,cameras, etc.). We were also interested in the problem of calibration of micro andnanoforce sensors using magnetic springs connected to measurable masses. In thiscontext, we developed an estimation strategy and a passive rejection of mechanicaldisturbances using a differential principle. This approach was applied to a nanoforcesensor based on the diamagnetic levitation and yielded promising results: a resolutionlower the nanonewton level could be obtained.