Culture of insect cells contracting spontaneously; research moving toward an environmentally robust hybrid robotic system

Biohybrid robots: recent progress, challenges, and perspectives

The past ten years have seen the rapid expansion of the field of biohybrid robotics. By combining engineered, synthetic components with living biological materials, new robotics solutions have been developed that harness the adaptability of living muscles, the sensitivity of living sensory cells, and even the computational abilities of living neurons. Biohybrid robotics has taken the popular and scientific media by storm with advances in the field, moving biohybrid robotics out of science fiction and into real science and engineering. So how did we get here, and where should the field of biohybrid robotics go next? In this perspective, we first provide the historical context of crucial subareas of biohybrid robotics by reviewing the past 10+ years of advances in microorganism-bots and sperm-bots, cyborgs, and tissue-based robots. We then present critical challenges facing the field and provide our perspectives on the vital future steps toward creating autonomous living machines.

Living Materials Herald a New Era in Soft Robotics

Living beings have an unsurpassed range of ways to manipulate objects and interact with them. They can make autonomous decisions and can heal themselves. So far, a conventional robot cannot mimic this complexity even remotely. Classical robots are often used to help with lifting and gripping and thus to alleviate the effects of menial tasks. Sensors can render robots responsive, and artificial intelligence aims at enabling autonomous responses. Inanimate soft robots are a step in this direction, but it will only be in combination with living systems that full complexity will be achievable. The field of biohybrid soft robotics provides entirely new concepts to address current challenges, for example the ability to self-heal, enable a soft touch, or to show situational versatility. Therefore, "living materials" are at the heart of this review. Similarly to biological taxonomy, there is a recent effort for taxonomy of biohybrid soft robotics. Here, an expansion is proposed to take into account not only function and origin of biohybrid soft robotic components, but also the materials. This materials taxonomy key demonstrates visually that materials science will drive the development of the field of soft biohybrid robotics.

An Ultralightweight and Living Legged Robot

In this study, we describe the most ultralightweight living legged robot to date that makes it a strong candidate for a search and rescue mission. The robot is a living beetle with a wireless electronic backpack stimulator mounted on its thorax. Inheriting from the living insect, the robot employs a compliant body made of soft actuators, rigid exoskeletons, and flexure hinges. Such structure would allow the robot to easily adapt to any complex terrain due to the benefit of soft interface, self-balance, and self-adaptation of the insect without any complex controller. The antenna stimulation enables the robot to perform not only left/right turning but also backward walking and even cessation of walking. We were also able to grade the turning and backward walking speeds by changing the stimulation frequency. The power required to drive the robot is low as the power consumption of the antenna stimulation is in the order of hundreds of microwatts. In contrast to the traditional legged robots, this robot is of low cost, easy to construct, simple to control, and has ultralow power consumption.

Bio-hybrid cell-based actuators for microsystems

As we move towards the miniaturization of devices to perform tasks at the nano and microscale, it has become increasingly important to develop new methods for actuation, sensing, and control. Over the past decade, bio-hybrid methods have been investigated as a promising new approach to overcome the challenges of scaling down robotic and other functional devices. These methods integrate biological cells with artificial components and therefore, can take advantage of the intrinsic actuation and sensing functionalities of biological cells. Here, the recent advancements in bio-hybrid actuation are reviewed, and the challenges associated with the design, fabrication, and control of bio-hybrid microsystems are discussed. As a case study, focus is put on the development of bacteria-driven microswimmers, which has been investigated as a targeted drug delivery carrier. Finally, a future outlook for the development of these systems is provided. The continued integration of biological and artificial components is envisioned to enable the performance of tasks at a smaller and smaller scale in the future, leading to the parallel and distributed operation of functional systems at the microscale.

Atmospheric-operable bioactuator powered by insect muscle packaged with medium

Despite attempts in a number of studies to utilize muscle tissue and cells as microactuators, all of the biohybrid microdevices have been operable only in the culture medium and none have worked in air due to the dry environment. This paper demonstrates an atmospheric-operable bioactuator (AOB) fabricated by packaging an insect dorsal vessel (DV) tissue with a small amount of culture medium inside a capsule. The AOB, consisting of microtweezers and the capsule, was designed based on a structural simulation that took into account the capillary effect. The base part of the microtweezers was deformed by spontaneous contractions of the DV tissue in the medium inside the capsule, by which the front edges of the microtweezer arms projecting above the medium surface were also deformed. First, we confirmed in the medium that the DV tissue was able to reduce the gap between the arm tips of the microtweezers. After taking the AOB out of the medium, as we expected, the AOB continued to work in air at room temperature. The gap reduction in air became larger than the one in the medium due to a surface tension effect, which was consistent with the simulation findings on the surface tension by the phase-field method. Second, we demonstrated that the AOB deformed a thin-wall ring placed between its tips in air. Third, we measured the lifetime of the AOB. The AOB kept working for around 40 minutes in air, but eventually stopped due to medium evaporation. As the evaporation progressed, the microtweezers were pressed onto the capsule wall by the surface tension and opening and closing stopped. Finally, we attempted to prevent the medium from evaporating by pouring liquid paraffin (l-paraffin) over the medium after lipophilic coating of the capsule. As a result, we succeeded in prolonging the AOB lifetime to more than five days. In this study, we demonstrated the significant potential of insect muscle tissue and cells as a bioactuator in air and at room temperature. By integrating insect tissue and cells not only into a microspace but also onto a substrate, we expect to realize a biohybrid MEMS device with various functions in the near future.

Room temperature operable autonomously moving bio-microrobot powered by insect dorsal vessel tissue

Living muscle tissues and cells have been attracting attention as potential actuator candidates. In particular, insect dorsal vessel tissue (DVT) seems to be well suited for a bio-actuator since it is capable of contracting autonomously and the tissue itself and its cells are more environmentally robust under culturing conditions compared with mammalian tissues and cells. Here we demonstrate an autonomously moving polypod microrobot (PMR) powered by DVT excised from an inchworm. We fabricated a prototype of the PMR by assembling a whole DVT onto an inverted two-row micropillar array. The prototype moved autonomously at a velocity of 3.5 × 10(-2) µm/s, and the contracting force of the whole DVT was calculated as 20 µN. Based on the results obtained by the prototype, we then designed and fabricated an actual PMR. We were able to increase the velocity significantly for the actual PMR which could move autonomously at a velocity of 3.5 µm/s. These results indicate that insect DVT has sufficient potential as the driving force for a bio-microrobot that can be utilized in microspaces.

Advanced technologies for gastrointestinal endoscopy

The gastrointestinal tract is home to some of the most deadly human diseases. Exacerbating the problem is the difficulty of accessing it for diagnosis or intervention and the concomitant patient discomfort. Flexible endoscopy has established itself as the method of choice and its diagnostic accuracy is high, but there remain technical limitations in modern scopes, and the procedure is poorly tolerated by patients, leading to low rates of compliance with screening guidelines. Although advancement in clinical endoscope design has been slow in recent years, a critical mass of enabling technologies is now paving the way for the next generation of gastrointestinal endoscopes. This review describes current endoscopes and provides an overview of innovative flexible scopes and wireless capsules that can enable painless endoscopy and/or enhanced diagnostic and therapeutic capabilities. We provide a perspective on the potential of these new technologies to address the limitations of current endoscopes in mass cancer screening and other contexts and thus to save many lives.

Isolation and maintenance-free culture of contractile myotubes from Manduca sexta embryos

Skeletal muscle tissue engineering has the potential to treat tissue loss and degenerative diseases. However, these systems are also applicable for a variety of devices where actuation is needed, such as microelectromechanical systems (MEMS) and robotics. Most current efforts to generate muscle bioactuators are focused on using mammalian cells, which require exacting conditions for survival and function. In contrast, invertebrate cells are more environmentally robust, metabolically adaptable and relatively autonomous. Our hypothesis is that the use of invertebrate muscle cells will obviate many of the limitations encountered when mammalian cells are used for bioactuation. We focus on the tobacco hornworm, Manduca sexta, due to its easy availability, large size and well-characterized muscle contractile properties. Using isolated embryonic cells, we have developed culture conditions to grow and characterize contractile M. sexta muscles. The insect hormone 20-hydroxyecdysone was used to induce differentiation in the system, resulting in cells that stained positive for myosin, contract spontaneously for the duration of the culture, and do not require media changes over periods of more than a month. These cells proliferate under normal conditions, but the application of juvenile hormone induced further proliferation and inhibited differentiation. Cellular metabolism under normal and low glucose conditions was compared for C2C12 mouse and M. sexta myoblast cells. While differentiated C2C12 cells consumed glucose and produced lactate over one week as expected, M. sexta muscle did not consume significant glucose, and lactate production exceeded mammalian muscle production on a per cell basis. Contractile properties were evaluated using index of movement analysis, which demonstrated the potential of these cells to perform mechanical work. The ability of cultured M. sexta muscle to continuously function at ambient conditions without medium replenishment, combined with the interesting metabolic properties, suggests that this cell source is a promising candidate for further investigation toward bioactuator applications.

Long-term and room temperature operable bioactuator powered by insect dorsal vessel tissue

We present a bioactuator powered by insect dorsal vessel tissue which can work for a long time at room temperature without maintenance. Previously reported bioactuators which exploit contracting ability of mammalian heart muscle cell have required precise environmental control to keep the cell alive and contracting. To overcome this problem, we propose a bioactuator using dorsal vessel tissue. The insect tissue which can grow at room temperature is generally robust over a range of culture conditions compared to mammalian tissues and cells. First, we confirm that a dorsal vessel tissue of lepidoptera larva Ctenoplusia agnata contracts spontaneously for at least 30 days without medium replacement at 25 degrees C. Using the dorsal vessel tissue cultured under the same conditions, we succeed in driving micropillars 100 microm in diameter and 1000 microm in height for more than 90 days. The strongest displacement of the micropillar top occurs on the 42(nd) day and is 23 microm. Based on these results, the contracting force is roughly estimated as 4.7 microN which is larger than that by a few mammalian cardiomyocytes (3.4 microN). Definite displacements of more than 10 microm are observed for 58 days from the 15(th) to the 72(nd) days. The number of life cycles can be roughly calculated as 7.5 x 10(5) times for the average frequency of about 0.15 Hz, which is no less than that of conventional mechanical actuators. These results suggest that the insect dorsal vessel tissue is a more promising material for bioactuators used at room temperature than other biological cell-based materials.