Performance of Smart Materials-Based Instrumentation for Force Measurements in Biomedical Applications: A Methodological Review

The introduction of smart materials will become increasingly relevant as biomedical technologies progress. Smart materials sense and respond to external stimuli (e.g., chemical, electrical, mechanical, or magnetic signals) or environmental circumstances (e.g., temperature, illuminance, acidity, or humidity), and provide versatile platforms for studying various biological processes because of the numerous analogies between smart materials and biological systems. Several applications based on this class of materials are being developed using different sensing principles and fabrication technologies. In the biomedical field, force sensors are used to characterize tissues and cells, as feedback to develop smart surgical instruments in order to carry out minimally invasive surgery. In this regard, the present work provides an overview of the recent scientific literature regarding the developments in force measurement methods for biomedical applications involving smart materials. In particular, performance evaluation of the main methods proposed in the literature is reviewed on the basis of their results and applications, focusing on their metrological characteristics, such as measuring range, linearity, and measurement accuracy. Classification of smart materials-based force measurement methods is proposed according to their potential applications, highlighting advantages and disadvantages

Development of novel micropneumatic grippers for biomanipulation

Microbjects with dimensions from 1 μm to 1 mm have been developed recently for different aspects and purposes. Consequently, the development of handling and manipulation tools to fulfil this need is urgently required. Micromanipulation techniques could be generally categorized according to their actuation method such as electrostatic, thermal, shape memory alloy, piezoelectric, magnetic, and fluidic actuation. Each of which has its advantage and disadvantage. The fluidic actuation has been overlooked in MEMS despite its satisfactory output in the micro-scale. This thesis presents different families of pneumatically driven, low cost, compatible with biological environment, scalable, and controllable microgrippers. The first family demonstrated a polymeric microgripper that was laser cut and actuated pneumatically. It was tested to manipulate microparticles down to 200 microns. To overcome the assembly challenges that arise in this family, the second family was proposed. The second family was a micro-cantilever based microgripper, where the device was assembled layer by layer to form a 3D structure. The microcantilevers were fabricated using photo-etching technique, and demonstrated the applicability to manipulate micro-particles down to 200 microns using automated pick-and-place procedure. In addition, this family was used as a tactile-detector as well. Due to the angular gripping scheme followed by the above mentioned families, gripping smaller objects becomes a challenging task. A third family following a parallel gripping scheme was proposed allowing the gripping of smaller objects to be visible. It comprises a compliant structure microgripper actuated pneumatically and fabricated using picosecond laser technology, and demonstrated the capability of gripping microobject as small as 100 μm microbeads. An FEA modelling was employed to validate the experimental and analytical results, and excellent matching was achieved

Piezoelectric Transducers Based on Aluminum Nitride and Polyimide for Tactile Applications

The development of micro systems with smart sensing capabilities is paving the way to progresses in the technology for humanoid robotics. The importance of sensory feedback has been recognized the enabler of a high degree of autonomy for robotic systems. In tactile applications, it can be exploited not only to avoid objects slipping during their manipulation but also to allow safe interaction with humans and unknown objects and environments. In order to ensure the minimal deformation of an object during subtle manipulation tasks, information not only on contact forces between the object and fingers but also on contact geometry and contact friction characteristics has to be provided. Touch, unlike other senses, is a critical component that plays a fundamental role in dexterous manipulation capabilities and in the evaluation of objects properties such as type of material, shape, texture, stiffness, which is not easily possible by vision alone. Understanding of unstructured environments is made possible by touch through the determination of stress distribution in the surrounding area of physical contact. To this aim, tactile sensing and pressure detection systems should be integrated as an artificial tactile system. As illustrated in the Chapter I, the role of external stimuli detection in humans is provided by a great number of sensorial receptors: they are specialized endings whose structure and location in the skin determine their specific signal transmission characteristics. Especially, mechanoreceptors are specialized in the conversion of the mechanical deformations caused by force, vibration or slip on skin into electrical nerve impulses which are processed and encoded by the central nervous system. Highly miniaturized systems based on MEMS technology seem to imitate properly the large number of fast responsive mechanoreceptors present in human skin. Moreover, an artificial electronic skin should be lightweight, flexible, soft and wearable and it should be fabricated with compliant materials. In this respect a big challenge of bio-inspired technologies is the efficient application of flexible active materials to convert the mechanical pressure or stress into a usable electric signal (voltage or current). In the emerging field of soft active materials, able of large deformation, piezoelectrics have been recognized as a really promising and attractive material in both sensing and actuation applications. As outlined in Chapter II, there is a wide choice of materials and material forms (ceramics: PZT; polycrystalline films: ZnO, AlN; polymers and copolymers: PVDF, PVDF-TrFe) which are actively piezoelectric and exhibit features more or less attractive. Among them, aluminum nitride is a promising piezoelectric material for flexible technology. It has moderate piezoelectric coefficient, when available in c-axis oriented polycrystalline columnar structure, but, at same time, it exhibits low dielectric constant, high temperature stability, large band gap, large electrical resistivity, high breakdown voltage and low dielectric loss which make it suitable for transducers and high thermal conductivity which implies low thermal drifts. The high chemical stability allows AlN to be used in humid environments. Moreover, all the above properties and its deposition method make AlN compatible with CMOS technology. Exploiting the features of the AlN, three-dimensional AlN dome-shaped cells, embedded between two metal electrodes, are proposed in this thesis. They are fabricated on general purpose Kapton™ substrate, exploiting the flexibility of the polymer and the electrical stability of the semiconductor at the same time. As matter of fact, the crystalline layers release a compressive stress over the polymer, generating three-dimensional structures with reduced stiffness, compared to the semiconductor materials. In Chapter III, a mathematical model to calculate the residual stresses which arise because of mismatch in coefficient of thermal expansion between layers and because of mismatch in lattice constants between the substrate and the epitaxially grown films is adopted. The theoretical equation is then used to evaluate the dependence of geometrical features of the fabricated three-dimensional structures on compressive residual stress. Moreover, FEM simulations and theoretical models analysis are developed in order to qualitative explore the operation principle of curved membranes, which are labelled dome-shaped diaphragm transducers (DSDT), both as sensors and as piezo-actuators and for the related design optimization. For the reliability of the proposed device as a force/pressure sensor and piezo-actuator, an exhaustive electromechanical characterization of the devices is carried out. A complete description of the microfabrication processes is also provided. As shown in Chapter IV, standard microfabrication techniques are employed to fabricate the array of DSDTs. The overall microfabrication process involves deposition of metal and piezoelectric films, photolithography and plasma-based dry and wet etching to pattern thin films with the desired features. The DSDT devices are designed and developed according to FEM and theoretical analysis and following the typical requirements of force/pressure systems for tactile applications. Experimental analyses are also accomplished to extract the relationship between the compressive residual stress due to the aluminum nitride and the geometries of the devices. They reveal different deformations, proving the dependence of the geometrical features of the three-dimensional structures on residual stress. Moreover, electrical characterization is performed to determine capacitance and impedance of the DSDTs and to experimentally calculate the relative dielectric constant of sputtered AlN piezoelectric film. In order to investigate the mechanical behaviour of the curved circular transducers, a characterization of the flexural deflection modes of the DSDT membranes is carried out. The natural frequency of vibrations and the corresponding displacements are measured by a Laser Doppler Vibrometer when a suitable oscillating voltage, with known amplitude, is applied to drive the piezo-DSDTs. Finally, being developed for tactile sensing purpose, the proposed technology is tested in order to explore the electromechanical response of the device when impulsive dynamic and/or long static forces are applied. The study on the impulsive dynamic and long static stimuli detection is then performed by using an ad hoc setup measuring both the applied loading forces and the corresponding generated voltage and capacitance variation. These measurements allow a thorough test of the sensing abilities of the AlN-based DSDT cells. Finally, as stated in Chapter V, the proposed technology exhibits an improved electromechanical coupling with higher mechanical deformation per unit energy compared with the conventional plate structures, when the devices are used as piezo-actuator. On the other hand, it is well suited to realize large area tactile sensors for robotics applications, opening up new perspectives to the development of latest generation biomimetic sensors and allowing the design and the fabrication of miniaturized devices

NASA SBIR abstracts of 1991 phase 1 projects

The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

New generation of interactive platforms based on novel printed smart materials

Programa doutoral em Engenharia Eletrónica e de Computadores (área de Instrumentação e Microssistemas Eletrónicos)The last decade was marked by the computer-paradigm changing with other digital devices suddenly becoming available to the general public, such as tablets and smartphones. A shift in perspective from computer to materials as the centerpiece of digital interaction is leading to a diversification of interaction contexts, objects and applications, recurring to intuitive commands and dynamic content that can proportionate more interesting and satisfying experiences. In parallel, polymer-based sensors and actuators, and their integration in different substrates or devices is an area of increasing scientific and technological interest, which current state of the art starts to permit the use of smart sensors and actuators embodied within the objects seamlessly. Electronics is no longer a rigid board with plenty of chips. New technological advances and perspectives now turned into printed electronics in polymers, textiles or paper. We are assisting to the actual scaling down of computational power into everyday use objects, a fusion of the computer with the material. Interactivity is being transposed to objects erstwhile inanimate. In this work, strain and deformation sensors and actuators were developed recurring to functional polymer composites with metallic and carbonaceous nanoparticles (NPs) inks, leading to capacitive, piezoresistive and piezoelectric effects, envisioning the creation of tangible user interfaces (TUIs). Based on smart polymer substrates such as polyvinylidene fluoride (PVDF) or polyethylene terephthalate (PET), among others, prototypes were prepared using piezoelectric and dielectric technologies. Piezoresistive prototypes were prepared with resistive inks and restive functional polymers. Materials were printed by screen printing, inkjet printing and doctor blade coating. Finally, a case study of the integration of the different materials and technologies developed is presented in a book-form factor.A última década foi marcada por uma alteração do paradigma de computador pelo súbito aparecimento dos tablets e smartphones para o público geral. A alteração de perspetiva do computador para os materiais como parte central de interação digital levou a uma diversificação dos contextos de interação, objetos e aplicações, recorrendo a comandos intuitivos e conteúdos dinâmicos capazes de tornarem a experiência mais interessante e satisfatória. Em simultâneo, sensores e atuadores de base polimérica, e a sua integração em diferentes substratos ou dispositivos é uma área de crescente interesse científico e tecnológico, e o atual estado da arte começa a permitir o uso de sensores e atuadores inteligentes perfeitamente integrados nos objetos. Eletrónica já não é sinónimo de placas rígidas cheias de componentes. Novas perspetivas e avanços tecnológicos transformaram-se em eletrónica impressa em polímeros, têxteis ou papel. Neste momento estamos a assistir à redução da computação a objetos do dia a dia, uma fusão do computador com a matéria. A interatividade está a ser transposta para objetos outrora inanimados. Neste trabalho foram desenvolvidos atuadores e sensores e de pressão e de deformação com recurso a compostos poliméricos funcionais com tintas com nanopartículas (NPs) metálicas ou de base carbónica, recorrendo aos efeitos capacitivo, piezoresistivo e piezoelétrico, com vista à criação de interfaces de usuário tangíveis (TUIs). Usando substratos poliméricos inteligentes tais como fluoreto de polivinilideno (PVDF) ou politereftalato de etileno (PET), entre outos, foi possível a preparação de protótipos de tecnologia piezoelétrica ou dielétrica. Os protótipos de tecnologia piezoresistiva foram feitos com tintas resistivas e polímeros funcionais resistivos. Os materiais foram impressos por serigrafia, jato de tinta, impressão por aerossol e revestimento de lâmina doctor blade. Para terminar, é apresentado um caso de estudo da integração dos diferentes materiais e tecnologias desenvolvidos sob o formato de um livro.This project was supported by FCT – Fundação para a Ciência e a Tecnologia, within the doctorate grant with reference SFRH/BD/110622/2015, by POCH – Programa Operacional Capital Humano, and by EU – European Union

Sensitivities of rheological properties of magnetoactive foam for soft sensor technology

Magnetoactive (MA) foam, with its tunable mechanical properties and magnetostriction, has the potential to be used for the development of soft sensor technology. However, researchers have found that its mechanical properties and magnetostriction are morphologically dependent, thereby limiting its capabilities for dexterous manipulation. Thus, in this work, MA foam was developed with additional capabilities for controlling its magnetostriction, normal force, storage modulus, shear stress and torque by manipulating the concentration of carbonyl iron particles (CIPs) and the magnetic field with regard to morphological changes. MA foams were prepared with three weight percentages of CIPs, namely, 35 wt.%, 55 wt.% and 75 wt.%, and three different modes, namely, zero shear, constant shear and various shears. The results showed that the MA foam with 75 wt.% of CIPs enhanced the normal force sensitivity and positive magnetostriction sensitivity by up to 97% and 85%, respectively. Moreover, the sensitivities of the storage modulus, torque and shear stress were 8.97 Pa/mT, 0.021 µN/mT, and 0.0096 Pa/mT, respectively. Meanwhile, the magnetic dipolar interaction between the CIPs was capable of changing the property of MA foam from a positive to a negative magnetostriction under various shear strains with a low loss of energy. Therefore, it is believed that this kind of highly sensitive MA foam can potentially be implemented in future soft sensor systems. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Universiti Teknologi Malaysia through Collaborative Research Grant (CRG) [08G79]; Professional Development Research University (PDRU) [05E21]; Universitas Sebelas Maret, Hibah Non APBN 2021, LPPM-UNS; Ministry of Education, Youth and Sports of the Czech RepublicMinistry of Education, Youth & Sports - Czech Republic [RP/CPS/2020/006]05E21; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT; Universiti Teknologi Malaysia, UTM: 08G79; Universitas Sebelas Maret, UNS: RP/CPS/2020/00

Advanced instrumented stamps for micro transfer printing and novel application areas

Transfer printing refers to a set of techniques for deterministic assembly of functional micro/nano scale devices into two and three dimensional spatial arrangements. It provides a versatile route for realizing multifunctional heterogeneously integrated systems such as flexible electronics, biocompatible sensing and therapeutic devices, transparent and curved optoelectronic systems etc. Micro-transfer printing is an automated process that implements deterministic micro scale assembly using a molded viscoelastic stamp typically made out of PDMS. The process relies upon the control of adhesion and fracture at the interfaces between the stamp and the devices being assembled to pick up and release them. A widely exploited strategy to achieve variable adhesion from the stamp is to use the rate dependent effects of the viscoelastic stamp material. It is a very versatile process and has been used in the realization of many novel heterogeneously integrated systems. The process has been implemented industrially to assemble ultra-high concentration photovoltaic panels. This body of work presents the development of new stamp technologies to address the challenges associated with increasing parallelism and shortcomings associated with fixed geometry stamps. Starting from the concept of an active composite material with distributed sensing, actuation and compliance tuning, new stamp architectures are developed. These novel stamps replace the compliance of a bulk PDMS stamp with active functional structures with tunable stiffness; without effecting the ability of the stamps to be used for transfer printing. The new stamp architecture enables active monitoring and control of the micro transfer printing process. Using instrumentation to sense deflections/forces at each post allows detection, measurement and compensation of misalignments between the stamp and donor/receiving substrates. Furthermore this information is used to detect pick up and printing errors at individual posts, allowing for error handling to increase process robustness. Moreover the ability to selectively actuate allows to engage/disengage individual posts. This enables new transfer printing modes such as collect and place. Finally results of pilot experiments conducted to test the feasibility of using micro transfer printing in novel application areas are presented