Biology subjects

Alshareef, A. A.

Publications and source records attributed to Alshareef, A. A..

3 recordsLinked to original sources

bioRxiv2025

Characterization of mechanical tissue properties in post-mortem human brain using magnetic resonance elastography

Traumatic brain injury (TBI) is a serious health condition that can cause neurological dysfunction to varying degrees depending on the nature of the mechanical insult. In biomechanical studies of TBI under high loading conditions, post-mortem human subjects (PMHS) are often used since ethical concerns prohibit such experiments in living human subjects. Because PMHS brains undergo significant changes following death, it is important to understand the relationship between the mechanical properties of PMHS brain tissue and living tissue. In this study, we performed magnetic resonance elastography (MRE) on three PMHS specimens to estimate the material properties of the cadaveric brain, namely the storage modulus and the loss modulus, as well as the resulting shear stiffness and damping ratio. We also performed longitudinal MRE scans on one of the PMHS over the span of two months to investigate the evolution of tissue properties with post-mortem degradation. In comparison to in vivo subjects of age range 70-75 years, a substantially higher stiffness (mean: 5.96kPa) and lower damping ratio (mean: 0.09) were found in PMHS models. This study also revealed an initial increase in shear stiffness up to the seventh day post-mortem, followed by a steady decrease by the fifty-eighth day. However, the damping ratio displayed an opposite trend to that of shear stiffness. These changes were heterogeneous across brain regions. The collected measurements and analysis elucidate the changes in mechanical properties in post-mortem subjects, and can be used to build and validate computational models of TBI.

neuroscience↗

bioRxiv2025

Influence of exoskeleton stiffness on primary afferent feedback during stretch perturbations of isolated muscle-tendon unit

Exoskeletons assist and augment movement, but their effects on proprioceptive feedback remain poorly understood due to challenges in making direct measures of sensory signals in humans. Here, we leveraged a benchtop animal model to begin to explore how mechanical context akin to an elastic exoskeleton operating on a human lower limb joint may influence primary muscle spindle firing. In an anesthetized rat preparation, we applied controlled stretches to the medial gastrocnemius with engineered springs (0-0.5 N/mm) attached in parallel to the muscle-tendon unit (MTU) while modulating muscle activation to maintain overall system stiffness. Fascicle length was measured with sonomicrometry, force and MTU length with a servo motor, and spindle instantaneous firing rate (IFR) using dorsal root recordings. Trading off increases in parallel exoskeleton stiffness with reductions in muscle activation decreased biological muscle force (3.1 {+/-} 0.6 N to 1.6 {+/-} 0.6 N, p < 0.001) and stiffness (4.4 {+/-} 1.5 N/mm to 2.3 {+/-} 1.3 N/mm, p < 0.01), and increased fascicle length (7.9 {+/-} 1.3 mm to 8.3 {+/-} 1.5 mm, p < 0.005). We found significant correlations between spindle firing and each independent muscle fascicle kinematic and kinetic factor we investigated (p < 0.005). Thus, parallel stiffness emulating a passive elastic exoskeleton modifies muscle fascicle dynamics but does not alter spindle firing, possibly due to internal trade-offs in the salient muscle fascicle kinetic and kinematic features that drive spindle behavior. Leveraging in situ experimental frameworks that enable monitoring of primary afferent feedback during active contractions in complex mechanical contexts such as added parallel stiffness can provide a window into the effects of wearable devices on underlying sensory systems.

neuroscience↗

bioRxiv2023

A Vibrating Ingestible BioElectronic Stimulator Modulates Gastric Stretch Receptors for Illusory Satiety

Effective therapies for obesity either require invasive surgical or endoscopic interventions or high patient adherence, making it challenging for the nearly 42% of American adults who suffer from obesity to effectively manage their disease. Gastric mechanoreceptors sense distension of the stomach and perform volume-dependent vagal signaling to initiate the gastric phase and influence satiety. In this study, we developed a new luminal stimulation modality to specifically activate these gastric stretch receptors to elicit a vagal afferent response commensurate with mechanical distension. Here we developed the Vibrating Ingestible BioElectronic Stimulator (VIBES) pill - an ingestible device that performs luminal vibratory stimulation to activate mechanoreceptors and stroke mucosal receptors, which induces serotonin release as well as yields a hormonal metabolic response commensurate with a fed state. We evaluated VIBES across 108 meals in swine which consistently led to diminished food intake ([~]40%, p< 0.0001) and minimized the weight gain rate (p< 0.03) as compared to untreated controls. Application of mechanoreceptor biology could transform our capacity to help patients suffering from nutritional disorders.

pathology↗