Robert G. Dennis

A swimming robot actuated by living muscle tissue

Biomechatronics is the integration of biological components with artificial devices, in which the biological component confers a significant functional capability to the system, and the artificial component provides specific cellular and tissue interfaces that promote the maintenance and functional adaptation of the biological component. Based upon functional performance, muscle is potentially an excellent mechanical actuator, but the larger challenge of developing muscle-actuated, biomechatronic devices poses many scientific and engineering challenges. As a demonstratory proof of concept, we designed, built, and characterized a swimming robot actuated by two explanted frog semitendinosus muscles and controlled by an embedded microcontroller. Using open loop stimulation protocols, the robot performed basic swimming maneuvers such as starting, stopping, turning (turning radius ~400 mm) and straight-line swimming (max speed >1/3 body lengths/second). A broad spectrum antibiotic/antimycotic ringer solution surrounded the muscle actuators for long term maintenance, ex vivo. The robot swam for a total of 4 hours over a 42 hour lifespan (10% duty cycle) before its velocity degraded below 75% of its maximum. The development of functional biomechatronic prototypes with integrated musculoskeletal tissues is the first critical step toward the long term objective of controllable, adaptive and robust biomechatronic robots and prostheses.

Bioengineered Internal Anal Sphincter Derived From Isolated Human Internal Anal Sphincter Smooth Muscle Cells

BACKGROUND & AIMS The internal anal sphincter (IAS) is a specialized circular smooth muscle that maintains rectoanal continence. In vitro models are needed to study the pathophysiology of human IAS disorders. We bioengineered sphincteric rings from human IAS smooth muscle cells (SMC) and investigated their response to cholinergic stimulation as well as investigated whether protein kinase C (PKC) and Rho kinase signaling pathways remain functional. METHODS 3-Dimensional bioengineered ring (3DBR) model of the human IAS was constructed from isolated human IAS SMC obtained from surgery. Contractile properties and force generation in response to acetylcholine, PKC inhibitor calphostin-C, Rho/ROCK inhibitor Y-27632, permeable Rho/ROCK inhibitor c3-exoenzyme, and PKC activator PdBU was measured. RESULTS The human IAS 3DBR has the essential characteristics of physiologically functional IAS; it generated a spontaneous myogenic basal tone, and the constructs were able to relax in response to relaxants and contract in response to contractile agents. The constructs generated dose-dependent force in response to acetylcholine. Basal tone was significantly reduced by calphostin-C but not with Y-27632. Acetylcholine-induced force generation was also significantly reduced by calphostin-C but not with Y-27632. PdBU generated force that was equal in magnitude to acetylcholine. Thus, calphostin-C inhibited PdBU-induced force generation, whereas Y-27632 and c3 exoenzyme did not. CONCLUSIONS These data indicate that basal tone and acetylcholine-induced force generation depend on signaling through the PKC pathway in human IAS; PKC-mediated force generation is independent of the Rho/ROCK pathway. This human IAS 3DBR model can be used to study the pathophysiology associated with IAS malfunctions.

Altered Central Sensitization in Subgroups of Women With Vulvodynia

ObjectiveTo investigate the clinical correlates of central nervous system alterations among women with vulvodynia. Altered central sensitization has been linked to dysfunction in central nervous system-inhibitory pathways (eg, &ggr;-aminobutyric acidergic), and metrics of sensory adaptation, a centrally mediated process that is sensitive to this dysfunction, could potentially be used to identify women at risk of treatment failure using conventional approaches. MethodsTwelve women with vulvodynia and 20 age-matched controls participated in this study, which was conducted by sensory testing of the right hands index and middle fingers. The following sensory precepts were assessed: (1) vibrotactile detection threshold; (2) amplitude discrimination capacity (defined as the ability to detect differences in intensity of simultaneously delivered stimuli to 2 fingers); and (3) a metric of adaptation (determined by the impact that applying conditioning stimuli have on amplitude discriminative capacity). ResultsParticipants did not differ on key demographic variables, vibrotactile detection threshold, and amplitude discrimination capacity. However, we found significant differences from controls in adaptation metrics in 1 subgroup of vulvodynia patients. Compared with healthy controls and women with a shorter history of pain [n=5; duration (y)=3.4±1.3], those with a longer history [n=7; duration (y)=9.3±1.4)] were found to be less likely to have adaptation metrics similar to control values. DiscussionChronic pain is thought to lead to altered central sensitization, and adaptation is a centrally mediated process that is sensitive to this condition. This report suggests that similar alterations exist in a subgroup of vulvodynia patients.

Effects of adaptation on the capacity to differentiate simultaneously delivered dual-site vibrotactile stimuli

The capacity of 20 healthy adult subjects for detecting differences in the amplitude of two simultaneously delivered 25 Hz vibrotactile stimuli was assessed both in the absence and presence of prior exposure to different conditions of adapting stimulation. Results obtained from this study demonstrate that increasing durations of adapting stimulation at one of the two skin sites, in the range of 0.2 to 2.0 s, lead to a systematic and progressive decrease in a subjects ability to accurately discriminate between the two different amplitudes. Delivery of adapting stimuli to both of the sites of skin stimulation prior to simultaneous delivery of the test and standard stimuli, however, leads to an improvement in amplitude discrimination performance--a finding which is consistent with prior published psychophysical studies that demonstrate improvements in discriminatory capacity with much longer durations of adaptation. Striking parallels between the results obtained in this study and those reported in a prior study of the effects of vibrotactile adaptation on the optical response of squirrel monkey contralateral SI cortex to vibrotactile stimulation [Simons, S.B., Chiu, J., Favorov, O.V., Whitsel, B.L., Tommerdahl, M., 2007. Duration-dependent response of SI to vibrotactile stimulation in squirrel monkey. J Neurophysiol. 97, 2121-9, Simons, S.B., Tannan, V., Chiu, J., Favorov, O.V., Whitsel, B.L., Tommerdahl, M., 2005. Amplitude-dependency of response of SI cortex to flutter stimulation. BMC Neurosci. 6, 43] suggest that the perceptual effects detected in this study could be attributable to adaptation-induced alterations of SI response.

Somatosensory information processing in the aging population.

While it is well known that skin physiology – and consequently sensitivity to peripheral stimuli – degrades with age, what is less appreciated is that centrally mediated mechanisms allow for maintenance of the same degree of functionality in processing these peripheral inputs and interacting with the external environment. In order to demonstrate this concept, we obtained observations of processing speed, sensitivity (thresholds), discriminative capacity, and adaptation metrics on subjects ranging in age from 18 to 70. The results indicate that although reaction speed and sensory thresholds change with age, discriminative capacity, and adaptation metrics do not. The significance of these findings is that similar metrics of adaptation have been demonstrated to change significantly when the central nervous system (CNS) is compromised. Such compromise has been demonstrated in subject populations with autism, chronic pain, acute NMDA receptor block, concussion, and with tactile–thermal interactions. If the metric of adaptation parallels cortical plasticity, the results of the current study suggest that the CNS in the aging population is still capable of plastic changes, and this cortical plasticity could be the mechanism that compensates for the degradations that are known to naturally occur with age. Thus, these quantitative measures – since they can be obtained efficiently and objectively, and appear to deviate from normative values significantly with systemic cortical alterations – could be useful indicators of cerebral cortical health.

Bioreactors for Guiding Muscle Tissue Growth and Development

Muscle tissue bioreactors are devices which are employed to guide and monitor the development of engineered muscle tissue. These devices have a modern history that can be traced back more than a century, because the key elements of muscle tissue bioreactors have been studied for a very long time. These include barrier isolation and culture of cells, tissues and organs after isolation from a host organism; the provision of various stimuli intended to promote growth and maintain the muscle, such as electrical and mechanical stimulation; and the provision of a perfusate such as culture media or blood derived substances. An accurate appraisal of our current progress in the development of muscle bioreactors can only be made in the context of the history of this endeavor. Modern efforts tend to focus more upon the use of computer control and the application of mechanical strain as a stimulus, as well as substrate surface modifications to induce cellular organization at the early stages of culture of isolated muscle cells.

A portable tactile sensory diagnostic device

Current methods for applying multi-site vibratory stimuli to the skin typically involve the use of two separate vibrotactile stimulators, which can lead to difficulty with positioning of stimuli and in ensuring that stimuli are delivered perfectly in phase at the same amplitude and frequency. Previously, we reported a two-point stimulator (TPS) that was developed in order to solve the problem of delivering two-point stimuli to the skin at variable distances between the sites of stimulation. Because of the success of the TPS, we designed and fabricated a new stimulator with four significant improvements over our original device. First, the device is portable, lightweight and can be used in a variety of non-laboratory settings. Second, the device consists of two independently controlled stimulators which allow delivery of stimuli simultaneously to two distinct skin sites with different amplitude, frequency and/or phase. Third, the device automatically detects the skin surface and thus allows for much better automated control of stimulus delivery. Fourth, the device is designed for rapid manufacture and, therefore, can be made readily available to other research (non-laboratory) settings. To demonstrate the device, a modified Bekesy tracking method was used to evaluate the simultaneous amplitude discrimination capacity of 20 subjects.

A novel device for delivering two-site vibrotactile stimuli to the skin

Current methods for applying two-site vibration stimuli to the skin typically involve the use of two separate vibrotactile stimulators, which can lead to difficulty with positioning of stimuli and in ensuring that stimuli are delivered perfectly in phase at the same amplitude and frequency. This report describes the Two-Point Stimulator (TPS) that was developed in order to deliver two-point stimuli to the skin at variable distances between the sites of stimulation on a trial-by-trial basis. The apparatus attaches to a vibrotactile stimulator, modifying it from the standard single probe tip to two probe tips. Each of the two probe tips can be independently positioned to set the tip-to-tip spacing. Both points of the TPS are driven by the single vibrotactile stimulator and distances between the two sites can be varied on a trial-by-trial basis. To test the device, a modified Bekesy tracking method was developed and used for two-point limen testing under stimulus conditions of varying amplitude and frequency. Data collected were consistent with previously published reports, suggesting that one possible use of the device would be to provide a means for improved measures of spatio-tactile acuity.

A novel device for the study of somatosensory information processing.

Current methods for applying multi-site vibratory stimuli to the skin typically involve the use of multiple, individual vibrotactile stimulators. Limitations of such an arrangement include difficulty with both positioning the stimuli as well as ensuring that stimuli are delivered in a synchronized and deliberate manner. Previously, we reported a two-site tactile stimulator that was developed in order to solve these problems (Tannan et al., 2007a). Due to both the success of that novel stimulator and the limitations that were inherent in that device, we designed and fabricated a four-site stimulator that provides a number of advantages over the previous version. First, the device can stimulate four independent skin sites and is primarily designed for stimulating the digit tips. Second, the positioning of the probe tips has been re-designed to provide better ergonomic hand placement. Third, the device is much more portable than the previously reported stimulator. Fourth, the stimulator head has a much smaller footprint on the table or surface where it resides. To demonstrate the capacity of the device for delivering tactile stimulation at four independent sites, a finger agnosia protocol, in the presence and absence of conditioning stimuli, was conducted on seventeen healthy control subjects. The study demonstrated that with increasing amplitudes of vibrotactile conditioning stimuli concurrent with the agnosia test, inaccuracies of digit identification increased, particularly at digits D3 and D4. The results are consistent with prior studies that implicated synchronization of adjacent and near-adjacent cortical ensembles with conditioning stimuli in impacting TOJ performance (Tommerdahl et al., 2007a,b).

Neurosensory assessments of concussion

The purpose of this research was to determine if cortical metrics-a unique set of sensory-based assessment tools-could be used to characterize and differentiate concussed individuals from nonconcussed individuals. Cortical metrics take advantage of the somatotopic relationship between skin and cortex, and the protocols are designed to evoke interactions between adjacent cortical regions to investigate fundamental mechanisms that mediate cortical-cortical interactions. Student athletes, aged 18 to 22 years, were recruited into the study through an athletic training center that made determinations of postconcussion return-to-play status. Sensory-based performance tasks utilizing vibrotactile stimuli applied to tips of the index and middle fingers were administered to test an individuals amplitude discrimination, temporal order judgment, and duration discrimination capacity in the presence and absence of illusion-inducing conditioning stimuli. Comparison of the performances in the presence and absence of conditioning stimuli demonstrated differences between concussed and nonconcussed individuals. Additionally, mathematically combining results from the measures yields a unique central nervous system (CNS) profile that describes an individuals information processing capacity. A comparison was made of CNS profiles of concussed vs. nonconcussed individuals and demonstrated with 99% confidence that the two populations are statistically distinct. The study established solid proof-of-concept that cortical metrics have significant potential as a quantitative biomarker of CNS status.