Mahmut Selman Sakar

École Polytechnique Fédérale de Lausanne | EPFL · Institute of Mechanical Engineering

The comprehension of physical wave phenomena is imperative for students in the fields of engineering and basic sciences. Laboratory experiments that involve generation of acoustic waves can be used to explain advanced nonlinear wave phenomena. Acoustic levitation is a method for stably suspending and trapping objects in mid-air using acoustic radia...

Cellular contractility, migration, and extracellular matrix (ECM) mechanics are critical for a wide range of biological processes including embryonic development, wound healing, tissue morphogenesis, and regeneration. Even though the distinct response of cells near the tissue periphery has been previously observed in cell-laden microtissues, includ...

Biomimetic retinas with a wide field of view and high resolution are in demand for neuroprosthetics and robot vision. Conventional neural prostheses are manufactured outside the application area and implanted as a complete device using invasive surgery. Here, a minimally invasive strategy based on in situ self-assembly of photovoltaic microdevices...

Acoustically excited microbubbles generate various nonlinear forces that can be leveraged in microscale systems for actuation and manipulation. To obtain optimal performances, bubbles should be characterized; however, so far, they were studied indirectly by measuring downstream phenomena. Here, we present a novel scheme to measure the vibrations of...

Classic microsurgical techniques, such as those used in the early 1900s by Mangold and Spemann, have been instrumental in advancing our understanding of embryonic development. However, these techniques are highly specialized, leading to issues of inter-operator variability. Here we introduce a user-friendly robotic microsurgery platform that allows...

Processes such as embryonic development and wound healing involve a complex coupled interplay between cellular contractility and migration, as well as extracellular matrix (ECM) mechanics and remodeling. Despite intense efforts to describe biomechanical interactions between cells and the surrounding extracellular matrix (ECM), the regulatory princi...

The dynamics and connectivity of neural circuits continuously change on timescales ranging from milliseconds to an animal’s lifetime. Therefore, to understand biological networks, minimally invasive methods are required to repeatedly record them in behaving animals. Here we describe a suite of devices that enable long-term optical recordings of the...

The concept of creating all-mechanical soft microrobotic systems has great potential to address outstanding challenges in biomedical applications, and introduce more sustainable and multifunctional products. To this end, magnetic fields and light have been extensively studied as potential energy sources. On the other hand, coupling the response of...

The concept of creating all-mechanical soft microrobotic systems has great potential to address outstanding challenges in biomedical applications, and introduce more sustainable and multifunctional products. To this end, magnetic fields and light have been extensively studied as potential energy sources. On the other hand, coupling the response of...

Microsurgical techniques, such as those used in the early 1900s by Mangold and Spemann, were not only foundational for experimental embryology, but are still in use today. Here, we build on these classic techniques by introducing a user-friendly robotic microsurgery platform that allows precise mechanical manipulation of soft tissues in zebrafish e...

We present a new cell culture technology for large-scale mechanobiology studies capable of generating and applying optically controlled uniform compression on single cells in 3D. Mesenchymal stem cells (MSCs) are individually encapsulated inside an optically triggered nanoactuator-alginate hybrid biomaterial using microfluidics, and the encapsulati...

One of the grand challenges in interventional cardiology and neuroradiology is to minimize the operation time and risk of damage during catheterization. These two factors drastically increase if the target location resides in small and tortuous vessels. Flow‐driven microcatheters are capable of rapidly and safely navigating small arteries with comp...

Microbubbles excited by acoustic fields inside water oscillate and generate acoustic radiation forces and drag-induced acoustic streaming. These forces can be harnessed in various biomedical applications, such as targeted drug delivery and on-chip biomanipulation. The conventional approach for using microbubbles as actuators is to trap them inside...

Malignant transformation and tumour progression are associated with cancer-cell softening. Yet how the biomechanics of cancer cells affects T-cell-mediated cytotoxicity and thus the outcomes of adoptive T-cell immunotherapies is unknown. Here we show that T-cell-mediated cancer-cell killing is hampered for cortically soft cancer cells, which have p...

Epithelia are contiguous sheets of cells that stabilize the shape of internal organs and support their structure by covering their surfaces. They acquire diverse morphological forms appropriate for their specific functions during embryonic development, such as the kidney tubules and the complex branching structures found in the lung. The maintenanc...

The dynamics and connectivity of neural circuits continuously change during an animal's lifetime on timescales ranging from milliseconds to days. Therefore, to investigate how biological networks accomplish remarkable cognitive and behavioral tasks, minimally invasive methods are needed to perform repeated measurements, or perturbations of neural c...

Microbubbles excited by acoustic fields inside water oscillate, and generate acoustic radiation forces and drag-induced acoustic streaming. These forces can be harnessed in various biomedical applications such as targeted drug delivery and on-chip biomanipulation. The conventional approach for using microbubbles as actuators is to trap them inside...

Mechanobiology explores how forces regulate cell behaviors and what molecular machinery are responsible for the sensing, transduction, and modulation of mechanical cues. To this end, probing of cells cultured on planar substrates has served as a primary experimental setting for many decades. However, native extracellular matrices (ECMs) consist of...

An autonomous robot perceives its environment, makes decisions based on acquired information and programmed routines, and then actuates a movement or performs a manipulation task within that environment. The idea of microrobotics is primarily based on teleoperated mobile micromachines equipped with manipulation capabilities such as actuated gripper...

This paper presents the design, fabrication, and operation of a soft robotic compression device that is remotely powered by laser illumination. We combined the rapid and wireless response of hybrid nanomaterials with state-of-the-art microengineering techniques to develop machinery that can apply physiologically relevant mechanical loading. The pas...

An alternative intracranial aneurysm embolic agent is emerging in the form of hydrogels due to their ability to be injected in liquid phase and solidify in situ. Hydrogels have the ability to fill an aneurysm sac more completely compared to solid implants such as those used in coil embolization. Recently, the feasibility to implement photopolymeriz...

Active biomaterials offer novel approaches to study mechanotransduction in mammalian cells. These material systems probe cellular responses by dynamically modulating their resistance to endogenous forces or applying exogenous forces on cells in a temporally controlled manner. Stimuli-responsive molecules, polymers, and nanoparticles embedded inside...

Minimally invasive medical procedures, such as endovascular catheterization, have considerably reduced procedure time and associated complications. However, many regions inside the body, such as in the brain vasculature, still remain inaccessible due to the lack of appropriate guidance technologies. Here, experimentally and through numerical simula...

Tissue morphogenesis and regeneration are essentially mechanical processes that involve coordination of cellular forces, production and structural remodeling of extracellular matrix (ECM), and cell migration. Discovering the principles of cell–ECM interactions and tissue-scale deformation in mechanically-loaded tissues is instrumental to the develo...

Minimally invasive medical procedures, such as endovascular catheterization, have drastically reduced procedure time and associated complications. However, many regions inside the body, such as in the brain vasculature, still remain inaccessible due to the lack of appropriate guidance technologies. Here, experimentally and through numerical simulat...

A design, manufacturing, and control methodology is presented for the transduction of ultrasound into frequency-selective actuation of multibody hydrogel mechanical systems. The modular design of compliant mechanisms is compatible with direct laser writing and the multiple degrees of freedom actuation scheme does not require incorporation of any sp...

The appearance of DNA in the cytosol is perceived as a danger signal that stimulates potent immune responses through cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS). How cells regulate the activity of cGAS toward self-DNA and guard against potentially damaging autoinflammatory responses is a fundamental biological question. H...

Herein, a methodology for the directed self‐assembly of untethered microactuators and soft robotic microdevices from nanoscale building blocks is presented. The building block is a multifunctional stimuli‐responsive nanoactuator that consists of a magnetized gold nanorod encapsulated by a thermoresponsive hydrogel. The metallic core serves as a pho...

Recent work is unveiling the interactions between magnetic microswimmers and cells of the immune system.

Engineered fibrous tissues consisting of cells encapsulated within collagen gels are widely used three-dimensional in vitro models of morphogenesis and wound healing. Although cell-mediated matrix remodeling that occurs within these scaffolds has been extensively studied, less is known about the mesoscale physical principles governing the dynamics...

We present a methodology for building biologically inspired, soft microelectromechanical systems (MEMS) devices. Our strategy combines several advanced techniques including programmable colloidal self-assembly, light-harvesting with plasmonic nanotransducers, and in situ polymerization of compliant hydrogel mechanisms. We synthesize optomechanical...

Gripping and holding of microscale objects are key tasks for robotic biomanipulation. However, the size and mechanical properties of biological samples show high variability, and they are sensitive to external forces. In article number 1803870, Xinling Wang, Mahmut Selman Sakar, and co‐workers present a simple yet highly adaptive engineering soluti...

Bacteria can exploit mechanics to display remarkable plasticity in response to locally changing physical and chemical conditions. Compliant structures play a notable role in their taxis behavior, specifically for navigation inside complex and structured environments. Bioinspired mechanisms with rationally designed architectures capable of large, no...

The article from this special issue was previously published in ZAMM ‐ Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, Volume 98, Issue 10, 2018. For completeness we are including the title page of the article. The full text of the article can be read in Issue 98:10 on Wiley Online Library: https:/...

In this work we introduce a theoretical and computational modeling framework for the contractile response of single cells triggered by external mechanical stimuli. The structural response due to the formation and dissociation of stress fibers is modeled following isotropic anisotropic contractile phases with an orientation that evolves with time an...

Controlled folding of tissues occurs in development and would enable advances in tissue engineering. In this issue of Developmental Cell, Hughes et al. (2018) use in vivo, in vitro, and in silico approaches to uncover blueprints of microscale mesenchymal cell distribution that robustly drives macroscopic 3D folding of tissues. Controlled folding of...

Transport of individual cells or chemical payloads on a subcellular scale is an enabling tool for the study of cellular communication, cell migration, and other localized phenomena. We present a magnetically actuated robotic system capable of fully automated manipulation of cells and microbeads. Our strategy uses autofluorescent robotic transporter...

Recent advances in smart materials and microfabrication techniques lead to the development of microrobots for on-demand and targeted therapy. Self-folded hydrogel tubes are particularly promising vehicles as they provide relatively large surface area-to-volume ratio and cargo space for therapeutic agents. In this work, we decorate these microstruct...

Phagocytes, predatory cells of the immune system, continuously probe their cellular microenvironment on the hunt for invaders. This requires prey recognition followed by the formation of physical contacts sufficiently stable for pickup. Although immune cells must apply physical forces to pick up their microbial prey, little is known about their hun...

Hydrogel-based robotic microdevices are currently investigated for minimally invasive medical procedures. Hydrogels are especially suited to targeted drug delivery applications as they are able to carry several times more drug solution than its dry weight. A major drawback of these system is that drug release takes place before reaching the targete...

Nature provides a wide range of inspiration for building mobile micromachines that can navigate through confined heterogenous environments and perform minimally invasive environmental and biomedical operations. For example, microstructures fabricated in the form of bacterial or eukaryotic flagella can act as artificial microswimmers. Due to limitat...

Planar in vitro models have been invaluable tools to identify the mechanical basis of wound closure. Although these models may recapitulate closure dynamics of epithelial cell sheets, they fail to capture how a wounded fibrous tissue rebuilds its 3D architecture. Here we develop a 3D biomimetic model for soft tissue repair and demonstrate that fibr...

The use of a single energy source for both manipulating micromachines and triggering their functionalities will result in highly integrated devices and simplify the design of the controlling platform. Here, we demonstrate this concept employing magnetoelectric Janus particle-based micromachines, which are fabricated by coating SiO2 microspheres wit...

The increasing threat of multidrug-resistant bacterial strains against conventional antibiotic therapies represents a significant worldwide health risk and intensifies the need for novel antibacterial treatments. In this work, an effective strategy to target and kill bacteria using silver-coated magnetic nanocoils is reported. The coil palladium (P...

To investigate how cells sense stiffness in settings structurally similar to native extracellular matrices, we designed a synthetic fibrous material with tunable mechanics and user-defined architecture. In contrast to flat hydrogel surfaces, these fibrous materials recapitulated cell-matrix interactions observed with collagen matrices including ste...

In this work, we have developed 3D hybrid microstructures consisting of a short ferromagnetic CoNi segment for wireless magnetic control, coupled to a photocatalytic Bi2O3/ BiOCl segment for water remediation under UV-visible light. These hybrid microstructures (pillars and helices) were fabricated using 3D photolithography and template-assisted el...

A design methodology is reported to fabricate functional compound micromachines using 3D direct laser writing and selective physical vapor deposition of magnetic materials. Microtransporters with a wirelessly controlled Archimedes screw pumping mechanism are engineered. Spatiotemporally controlled collection, transport, and delivery of microparticl...

In this article, we introduce the real-time cellular force microscope (RT-CFM), a high-throughput microrobotic platform for mechanical stimulation and characterization of single cells. We developed computer vision algorithms that fully automate the positioning of target cells and localization of the sensor tip. The control and acquisition architect...

Soft-magnetic core-multishell Fe@C NWs/AAO nanocomposites were synthesized using anodization, electrodeposition and low-pressure chemical vapour deposition (CVD) at 900 ºC. High chemical stability is achieved by the conversion of AAO from amorphous to θ- and δ-Al2O3 phases above 600 ºC. Moreover, the surface properties of the material evolve from b...

The effect of dynamic shape switching of hydrogel bilayers on the performance of self-folding microrobots is investigated, for navigation in body orifices and drug release on demand. Tubular microrobots are fabricated by coupling a thermoresponsive hydrogel nanocomposite with a poly(ethyleneglycol)diacrylate (PEGDA) layer, to achieve spontaneous an...

Here we present a quantitative approach to constructing effective 3D muscle tissues through shape optimization and load impedance matching with electrical and optical stimulation. We have constructed long, thin, fascicle-like skeletal muscle tissue and optimized their form factor through mechanical characterization. A new apparatus was designed and...

We present a microrobotic platform that combines MEMS-based capacitive force sensing technology, a dual-stage positioning system and a real-time control and acquisition architecture with computer vision automation to manipulate and mechanically characterize growing plant cells. The topography accuracy of the system, using a silicon wafer sample is...

We demonstrate noncontact transport of microscale objects in liquid environments using untethered, magnetic microrobots. The flow and vortices generated by the rotating microrobot are efficient for selective and gentle trapping, stable transport, and targeted delivery of microscale cargo. The motion of the microrobots can be precisely controlled ev...

Significance Cell-based soft robotic devices could have a transformative impact on our ability to design machines and systems that can dynamically sense and respond to a range of complex environmental signals. We demonstrate innovative advancements in biomaterials, tissue engineering, and 3D printing, as well as an integration of these technologies...

Manipulation and transport of microscale objects in 3D with high spatiotemporal resolution require precise control over the applied forces. We report a strategy that uses specially engineered microbars having engagement points and multiple helical microcarriers that can apply reversible loads onto these holders. The helical microcarriers are actuat...

The presented microrobotic platform combines the advantages of self-folding NIR light sensitive polymer bilayers, magnetic alginate microbeads, and a 3D manipulation system and introduces a solution for targeted, on-demand drug and cell delivery. First feasibility studies are presented together with the potential of the full design.

The majority of muscles, nerves, and tendons are composed of fiber-like fascicle morphology. Each fascicle has a) elongated cells highly aligned with the length of the construct, b) a high volumetric cell density, and c) a high length-to-width ratio with a diameter small enough to facilitate perfusion. Fiber-like fascicles are important building bl...

Hybrid artificial flagella (h-ABF) consisting of a ferromagnetic alloy head and a helical polymer tail can be fabricated by sequential electrodeposition of a cobalt-nickel alloy and polypyrrole inside a photoresist template patterned by 3D laser lithography. As M. A. Zeeshan, S. Pané, and co-workers report on page 1284, the h-ABFs are physically st...

Mahmut S. Sakar and co-workers, on page 952 combine the design and fabrication of near infrared light (NIR) responsive hydrogel capsules and biocompatible magnetic scaffolds for on-demand, targeted drug and cell delivery. The smart microcapsules encapsulate magnetic alginate microbeads loaded with biological materials and they can be automatically...

The presented microrobotic platform combines together the advantages of self-folding NIR light sensitive polymer bilayers, magnetic alginate microbeads, and a 3D manipulation system, to propose a solution for targeted, on-demand drug and cell delivery. First feasibility studies are presented together with the potential of the full design.