International Conference and Expo on Biomechanics and Implant Design July 27-29, 2015 Florida, USA

The muscle spindle and its associated sensory neurons form the afferent sensorimotor circuit of motor function. In order to better understand the physiology of this circuit so as to use it to address its relevant diseases; this study aims to establish an in vitro model of this spindle-sensory unit by integrating the cells comprising this system with microelectromechanical (MEMS) technology. A defined cell culture system has been developed to support the in vitro differentiation of human intrafusal muscle fibers (muscle fibers inside the muscle spindle) and human proprioceptive sensory neurons as well as their connections. A BioMEMS chip has been designed and fabricated to allow for the integration and functional analysis of this biological system. Intrafusal muscle fibers have been grown and activated by controlled stretching of the cantilever sensor. This non-invasive test bed will allow for controlled and long-term monitoring, interrogation and high control analysis of the sensorimotor unit of the human neuromuscular reflex arc. It could have use for applications not only for emulation of human health and disease, but also for the construction of relevant robotic systems.

Biological micro electromechanical systems (bio-MEMS) have been engineered to replicate animal and human tissue in order to develop body-on-a-chip systems. These models are beneficial for drug development by allowing a non-invasive acquisition of cellular electrophysiological response as well as reducing ethical concerns found in traditional animal and human trials. As these systems become smaller and more intricate, the accurate positioning of droplets containing biological components onto bio-MEMS becomes more difficult. The use of a cellular bioprinter allows the user to quickly deposit micro droplets with high precision. Multiple cell types are also easily printed onto a single microchip enabling integrated cell studies. We have optimized the printing process to reliably print skeletal muscle and neurons onto silicon-based bio-MEMS for the development of in vitro tissue platforms to study various physiological disorders.

A high-content multiplexed in vitro assay system capable of interrogating functional muscle output and endurance is of paramount importance in the drug discovery and development process. We have been successful in deriving contractile skeletal muscle from an array of cell sources including rat, mouse, and most importantly human, while utilizing serum-free medium components. Force and endurance profiles of skeletal muscle have been altered chemically, utilizing an array of drug compounds as well as physically, via mechanical or electrical manipulation. These alterations to typical in vitro physiological response have resulted in significant changes in both contractile peak force and fatiguability. This multiplexed silicon based cantilever system utilizing serum-free conditions is adept at measuring both acute and chronic skeletal muscle adaptations on a high-content scale making it an ideal system for initial drug screening applications.

April 2008 - Present: Associate Professor, Dept. of Biomechatronic Engineering, SKKU, South Korea Feb. 2005 – March 2008: Senior Researcher, Korea Institute of Machinery and Materials (KIMM), South Korea. Mar. 2004 – Feb. 2005: Senior Researcher, Samsung Electronics Inc., South Korea. Dec. 2003: Ph.D. in Mechanical Engineering, Univ. of Wisconsin-Madison, USA

The natural biopolymers, collagen and alginate, have been widely used in various tissue regeneration procedures. However, their low mechanical and osteo inductive properties represent major limitations of their usage as bone tissue regenerative scaffolds. To overcome these deficiencies, biomimetic composite scaffolds were prepared using a mixture of collagen and alginate as a matrix material, and various silica weight fractions as a coating agent. The composite scaffolds were highly porous and consisted of interconnected pores, with a mesh-like structure. After incubation in simulated body fluid, various levels of bone-like hydroxyapatite (HA) on the surface of the composite scaffolds developed in proportion to the increase in silica content coating the scaffolds, indicating that the composite scaffolds have osteo inductive properties. The composite scaffolds were characterized in terms of various physical properties and biological activities using pre-osteoblasts (MC3T3-E1). The mechanical improvement of a composite scaffold in compressive mode was ~2.4-fold in the dry state compared to the collagen/alginate scaffold. Cell proliferation on the composite scaffold was significantly improved by ~1.3-fold compared to the mineralized collagen/alginate scaffold (control). These results suggest that mineralized biomimetic composite scaffolds have potential for use in tissue regeneration.

The patterning of cardiomyocytes on microelectrode arrays (MEAs) allows the in vitro measurement of conduction velocity with a defined path. However, the biomechanics of functional cardiac tissue presents unique challenges to the 2D cell culture environment. Whereas the heart allows bulk movement, the MEA surface is rigid. When beating cardiomyocytes contract, they exert a force on neighboring cells, the extracellular matrix (ECM), and proteins adsorbed to the MEA surface, creating the potential for the mechanical separation at cell to cell or cell to surface attachment points. The biomechanical durability of patterned cardiomyocytes on MEAs was studied, and the influence of long-term cell culture conditions on conduction velocity and beat frequency is reported. A combination of factors enhanced the long-term culture viability of rat and human cardiomyocytes including pattern geometry, surface modification, and protein deposition.

Ph.D. candidate: 2011~ present, Bio-Mechatronic Engineering, SKKU, South Korea
Scientist: 2012~2013, Biomedical Engineering, Cornell University, USA
MS: 2009~2011, Mechanical Engineering, Chosun University, South Korea
BS: 2005~2009, Mechanical Engineering, Chosun University, South Korea

Biomedical scaffolds have been widely investigated because they are essential for support and promotion of cell adhesion, proliferation and differentiation in three-dimensional (3D) structures. An ideal scaffold should be highly porous to enable efficient nutrient and oxygen transfer and have a 3D structure that provides optimal micro-environmental conditions for the seeded cells to obtain homogeneous growth after along culture period. In this study, new hierarchical osteoblast-like cell (MG-63)-laden scaffolds consisting of micro-sized struts/inter-layered micro-nanofibres and cell-laden hydrogel struts with mechanically stable and biologically superior properties were introduced. Poly (ethylene oxide) (PEO) was used as a sacrificial component to generate pores within the cell-laden hydrogel struts to attain a homogeneous cell distribution and rapid cell growth in the scaffold interior. The alginate-based cell-laden struts with PEO induced fast/homogeneous cell release, in contrast to nonporous cell-laden struts. Various weight fractions (0.5, 1, 2, 3 and 3.5 wt%) of PEO were used, of which 2 wt% PEO in the cell-laden strut resulted in the most appropriate cell release and enhanced biological activities (cell proliferation and calcium deposition), compared to nonporous cell-laden struts.

This study suggested a new combination therapy of using biocompatible polymer to improve the stabilization of islet and prevention of immune cell infiltration and recognition and using diverse immunosuppressive drugs with multi-layer modification to effectively decrease the immune reaction in a porcine to mouse transplantation model. Most of all, the porcine islets were modified with SH-6-arm-PEG-lipid and Gelatin-Catechol (Artificial ECM) for stabilization of fragility. Secondly, stabilized porcine islets were immobilized with three kinds of PEG derivatives (6-arm-PEG-catechol, 6-arm-PEG-SH and linear PEG-SH; PEGylation) for immunoprotection. The artificial ECM and PEG derivatives effectively cover the surface of porcine islets (Artificial ECM + PEGylation group) and help to retain the size of porcine islets. The viability and functionality of porcine islets was not affected. In addition, protein adsorption was measured using artificial ECM and PEG derivatives conjugated on collagen glass, which data has shown that multi-layer modification significantly reduced attachment of human serum albumin, fibronectin and IgG compared to control collage glass. The combined effect of multi-layer modified porcine islet and cocktailed immunosuppressive drugs on the survival time of grafted islet was assessed in a xenogeneic porcine-to-mouse model (control group, artificial ECM + PEGylation group, control + drug group, and artificial ECM + PEGylation + drug group). The median survival time (MST) of artificial ECM + PEGylation group was 4-fold increased compared to that of control group. In addition, the MST of artificial ECM+ PEGylation + drug group was 2.16-fold increased compared to control + drug group. Therefore, we proposed new porcine islet transplantation protocol using surface multi-layer modification and immunosuppressive drugs for stabilization and immunoprotection.

In vitro systems capable of measuring contractile peak force of skeletal muscle that mimic organ functionality have become increasingly important in drug development. A multiplexed atomic force microscopy based silicon cantilever system amenable to measuring myotube deflection would be invaluable in this discovery process. Human skeletal muscle was grown on silicon based cantilever arrays that deflect in response to myotube contraction. Conversion of force measurements using a modified version of Stoney’s equation closely correlates with data acquired by the more rigorous method of finite element analysis (FEA) which requires the measurement of cross-sectional area (CSA) of the myotubes. From a physiological perspective, the conclusion that myotube force generation scales with CSA validates that the in vitro data collected from the cantilever bioMEMS system matches in vivo data trends. While the best normative predictor of in vivo / in vitro correlation is CSA utilizing FEA analysis, Stoney’s equation approach is suitable for calculating the myotube force, but with only a very small increase in variation versus the FEA approach. The normalizing of functional output data to biophysical attributes facilitates closer comparisons between experimental groups, and improves the power of the statistical differences observed. These improved predictions of in vivo responses from in vitro data are likely to accelerate future drug development and toxicology studies.

Human somatosensory system is information consisting of senses of touch, pressure, temperature, pain and movement obtained from the receptors distributed on muscles, joints and skin. As somatosensory system is basic information formed in the human body to maintain a stable posture together with visual and vestibular senses, attempts to improve the postural equilibrium of the body by stimulating somatosensory system continue. In the meantime, some studies reported that a greater somatosensory stimulation than the threshold stimulation of individuals reduces postural equilibrium as the movement system for postural equilibrium in the body is disturbed. This study performed an objective measurement of personal threshold for somatosensory system from outside, and estimated the intensity of a sub-threshold stimulation that may have an effect on the body by analyzing the somatosensory evoked potentials (SEPs). It supposed that there will be an intensity of a sensory stimulation that may influence the body in spite of sub-threshold values among threshold intensities measured on fingers and the tibialis anterior tendon and evaluated the effect of the sensory stimulation on the body by analyzing the EEG when the subdivided somatosensory stimulation was applied to the body. It is expected that the objective threshold estimates of the somatosensory stimulation and the results on the setting for the sensory stimulation intensity drawn by this study, which may influence the body in spite of sub-threshold values, can be used to set a personal specific somatosensory stimulation intensity to be applied to the body to improve postural equilibrium in the next studies.

Promising pharmaceuticals frequently fail clinical trials due to cardiotoxicity or a decline in heart function not shown in pre-clinical animal models and live-dead assays on human cell lines. The development of low cost, high-throughput, and reliable in vitro human models remains a priority for pharmaceuticals to avoid costly dead ends in clinical trials. Organ-on-a-chip systems allow the creation of a functional, human tissue test bed that leverages the benefits of miniaturization and the availability of differentiable human stem cells. We report the development of a 2D cardiac platform that allows the functional interrogation of human induced pluripotent stem cell (iPSCs) derived cardiomyocytes (CM). The platform uses a laser reflected off silicon cantilevers with adhered CMs to monitor contractile force and beat frequency. Long-term cardiomyocyte culture conditions and a gravity-driven micro fluidic housing construct allow the daily and non-invasive interrogation of the cantilevers. Chips with up to 32 cantilevers can be rapidly scanned by the automated stages and cardiac output measured by a high speed detector. This enables acute and chronic drug studies with arrhythmogenic and ionotropic compounds to predict in vivo cardiac output.

The ability to efficiently monitor the functionality of neuromuscular junctions (NMJs) in vitro is essential to understanding the mechanisms that lead to their disruption during the early onset of neurodegenerative diseases. Functional in vitro NMJ systems with human cells instead of animal cells eliminate the issue of species variability in the development of new therapeutics. In this study we report a compartmentalized co-culture system that monitors the functionality of neuromuscular interactions by recording myotube contraction in response to isolated electrical stimulation of motoneurons. Motoneuron cell bodies are located on microelectrodes arrays (MEAs) in a motoneuron chamber while their axons extend through micro fluidic tunnels to a distal chamber containing skeletal muscle on surface-modified micro fabricated silicon cantilevers. While the MEAs stimulate and/or record the activity of motoneurons, cantilever deflection monitored by laser from underneath allows for measurement of the force and frequency of myotube contraction. Two-chambered micro fluidic devices have been used extensively to study neuronal function, axonal biology and synapses. However, this is the first time that this platform has been coupled with two functional Bio-MEM (biological microelectromechanical system) devices namely, MEAs and cantilevers. This elegant system allows non-invasive high-throughput interrogation of the function of NMJs, providing a valuable test bed for the etiological study and drug development of relevant neurodegenerative diseases.

Minseong Kim did his MS and is presently pursuing his PhD from 2012 to present in Bio-Mechatronic Engineering, from SKKU, South Korea. He did his BS in 2008-2012 in Biochemical Engineering from Chosun University, South Korea

In this study, we propose a new scaffold fabrication method, “direct electro-hydrodynamic jet process,” using the initial jet of an electro spinning process and ethanol media as a target. The fabricated three dimensional (3D) fibrous structure was configured with multi-layered micro sized struts consisting of randomly entangled micro/nano fibrous architecture, similar to that of native extracellular matrixes. The fabrication of the structure was highly dependent on various processing parameters, such as the surface tension of the target media, and the flow rate and weight fraction of the polymer solution. As a tissue regenerative material, the 3D fibrous scaffold was cultured with preosteoblasts to observe the initial cellular activities in comparison with a solid-freeform fabricated 3D scaffold sharing a similar structural geometry. The cell-culture results showed that the newly developed scaffold provided outstanding microcellular environmental conditions to the seeded cells (about 3.5-fold better initial cell attachment and 2.1-fold better cell proliferation).

Seongmi Song has completed her bachelor’s degree from Chonbuk National University in Biomedical Engineering and she is working towards a master’s degree from Chonbuk National University in Healthcare Engineering. She is interested in fall detection based on gait analysis and nanomaterials.

To compensate the defect of rollator based on FSR (Force Sensing Resistor) or force sensor such as velocity control problem ongait slopes, Knee joint anterior displacement was investigated to detect walking intention detection using IR (Infraed Ray) sensors. Leg muscle activities and foot pressure are also measured in order to verify our investigation. Two IR sensors are placed on the center of rollator to sense right and left legs’ walking intention. EMG signal was monitored rectus femoirs, biceps femoris, tibialis anterior, and gastrocnemius. Pedar-X system measured foot pressure (forefoot, mid foot, hindfoot, and average pressure). Twenty healthy males (age 24.3±1.5 years, height 174.7±5.3, and weight 72.6±4.6kg) were involved in experiments which had been preceded 30 minutes a week, during 3weeks. The gait slope and increasing velocity situation show that knee joint anterior displacement was increased. Based on EMG and foot pressure results, femoral region muscles’ activation increased and load activated was concentrated on hindfoot in volar titling case. On the contrary, lower leg muscles were more activated and concentrated load was located in forefoot. These results were similar to knee joint anteriordisplacement from IR sensors.

The neuromuscular system represents the major functional outputs of the central nervous system (CNS). Its dysfunction is closely related to many neurodegenerative diseases, including ALS (Amyotrophic Lateral Sclerosis). This study aims to develop a defined human-based functional neuromuscular system for the study and drug development of ALS disease. We have developed a defined in vitro system in which functional neuromuscular junctions (NMJs) can be formed with human stem cells as the sources. With the implementation of PDMS chamber system, this NMJ system is then modified by separating motoneurons and muscle cells, in which the functional analysis of NMJ formation can be better controlled. Motoneurons and muscle cells will be differentiated from the iPSCs derived from diseased patients. These patient-derived cells will then be incorporated into this functional NMJ system for the pathological and therapeutic study of disease. The outcome of this study would generate efficient functional in vitro model which would be clinically applicable to the study and treatment of various NMJ pathologies.

Wei Li has completed her PhD in 2002 from University of Sydney Australia and Postdoctoral studies from the same University. She is Australian Research Council (ARC) and Australian Reserach Fellow (ARF) since 2010. She has published more than 70 scientific articles in reputed journals.

Rapid and stable osseointegration signifies a major concern in design of implantable prostheses, which stimulates continuous development of new implant materials and structures. This paper aims to promote a computational design framework of a bead/particle coated porous surface for implants by exploring how its micromechanical features determine osseointegration through multiscale modeling technique. A typical dental implantation setting was exemplified for investigation. The global responses of a macroscale model were obtained through 48 month remodeling simulation, which forms a basis for the microscopic models created with different particle size, porosity and gradients. The osseointegration responses are evaluated in terms of bone density of peri-implant, BIC ratio and Tresca shear stress (PTS). The response surface method (RSM) was utilized to formulate the bone remodeling responses in terms of the above mentioned design parameters. The multiobjective optimisation was then performed to simultaneously (1) maximize density and uniformity; and (2) maximize BIC ratio and minimize PTS for achieving the best possible overall outcome. Due to strong competition between these two design objectives, a Pareto front is generated. To make a proper trade-off, the minimum distance selection criterion is considered for a compromised optimal solution. This study provides a novel design methodology for individual patient that allow optimizing topographical features for a desirable patient-specific biomechanical environment, thus promoting osseointegration.