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Background: Knee osteoarthritis (OA) is a prevalent disease that contributes to lower limb immobility and pain resulting in lost productivity in the work place. Repetitive loading of the knee joint, particularly in occupational settings, significantly increases OA risk. However, rest may promote tissue recovery and increase tissue tolerance to load. Therefore rest should be examined as a mechanism to prevent the development of knee OA. Purpose: The primary objective was to determine if rest can mitigate mechanical deformation of the stifle (knee) joint and articular cartilage damage during loading compared to an unloaded control in an intact porcine stifle model. Methods: A randomized controlled trial was conducted. Among 18 pairs of porcine hind limbs, one limb in each pair was randomly assigned to receive a loading intervention; while the matched pair served as control. Stifles in both groups were dissected, mounted into the loading apparatus, and pre-loaded. Intervention joints were then randomized into one of three loading protocols: no rest, 3:2 work:rest, and 1:1 work:rest; all of these protocols exposed joints to the same amount of cumulative load. Following loading, all joints were dissected to expose the cartilage. Cartilage damage was scored on a categorical scale. Deformation and energy dissipation were calculated for intervention limbs from data obtained from the loading apparatus. Results: Rest did not mitigate displacement or energy dissipation in the stifles exposed to loading. Rest was associated with reduced cartilage damage scores in the lateral femur in the 1:1 condition. Conclusion: Rest had little impact on joint mechanics and cartilage damage in this model. The small sample size may explain these results. Future investigations involving larger samples should assess if longer periods of rest are need to minimize joint damage as a result of loading. / Thesis / Master of Science (MSc) / Repetitive loading of the knee joint is linked to breakdown of knee cartilage leading to the development and progression of knee osteoarthritis (OA). For example, over-exposure to physically demanding tasks in the workplace (i.e. squatting, bending, lifting etc.) increases knee OA risk. However, it is possible that rest breaks can prevent cartilage damage by allowing the tissue to recover and maintain proper function. Therefore, the purpose of this work was to determine the influence of rest on knee joint mechanics and cartilage quality by repetitively loading pig knee joints and exposing them to varying periods of rest. Rest up to sixty seconds did not allow for tissue recovery, nor did it assist with joint function. This work suggests that longer periods of rest may be required to mitigate the damaging effects of loading, or that rest may not mitigate the effects of loading at all.

Back pain is the second most common neurological ailment in the United States and the leading cause of pain and disability. More than 80% of the total US population experiences back-pain during their life time and the annual back pain related healthcare costs exceed 100 billion dollars. While the exact cause of low back pain (LBP) is still unknown, degeneration of the intervertebral disc (IVD) has been suggested as a primary contributor. IVD is the largest avascular tissue in the human body and it is composed of three integrated tissues (annulus fibrosus - AF, nucleus pulposus - NP and cartilaginous end plate - CEP). IVD functions as a shock-absorber during motion and provides flexibility to motion of the spine. Maintaining IVD tissue integrity is an energy demanding process. Studies have shown that mechanical loading affects cellular biosynthesis of IVD tissue and may also promote IVD degeneration. However the path to this effect is still unknown. We propose a link between mechanical loading and cell energy production which contributes to altered cellular biosynthesis. Thus, we investigated the effects of mechanical loading on IVD cell energy metabolism under various mechanical loading regimes. Porcine AF and NP cells were isolated and seeded in 2% agarose at a 5,000,000 cells/mL cell density. A custom made bioreactor was used to conduct compression experiments. The experiment groups were: 15% static compression; 30% static compression; 0.1, 1 and 2 Hz dynamic compression at 15% strain magnitude. Experiment duration was 4 hr. ATP concentration in cell-agarose construct and culture media were measured using Luciferin-luciferase method to evaluate ATP production and ATP release from cells respectively. Lactate concentration in media was measured using lactate dehydrogenase enzymatic assay. Nitrite (stable metabolite of nitric oxide - NO) concentration in media was measured by Greiss Assay. DNA content per sample was measured using fluorometric assay. DNA content per sample was used as an internal control; all compressed samples were then normalized to unstrained control group. ATP production of AF cells was up regulated by static and dynamic mechanical loading. Data suggests that AF cell response to mechanical loading is primarily loading amplitude dependent. NP cells exhibited an increased ATP production at 1 Hz dynamic loading but remained comparable to control samples at other tested conditions. AF cells produced an increase in NO production at 1-, 2 Hz dynamic loading. NO production of NP cells was up regulated by mechanical loading at all tested conditions. ATP release was up regulated at higher frequencies in AF cells. In addition to higher frequencies (1 Hz and 2 Hz) NP cell ATP release was also up regulated by 30% static compression. Thus, this study clearly illustrates that mechanical loading affects IVD cell energy production.

Since bone tissues grow in intimate contact with implant surfaces in vivo, there is a need to investigate how bone cells respond to mechanical loads adjacent to implants under well characterized loading conditions that stimulate the bone-implant surface. Thus, the objective of this study was to demonstrate an effective means for applying known, uniform, cyclic strain to cells growing on implant materials in vitro. A cell culture strain plate device was developed based on the application of the four-point bending principle. The device uses a small electric motor to drive belts attached to shafts which turn a set of cams. The cams are attached to pins which connect to a titanium plate which rests over arched supports. When deflected and depending on which set of cams are used, strains generated range from around 200 to 1000 ìstrain. UMR-106 osteoblast-like cells were cultured on the titanium plate, and the plate was deflected at three strain magnitudes at 1.5 Hz for durations of 4 and 24 hours. Strain gages recorded average maximum strain levels of 182 ± 3, 366 ± 9, and 984 ± 7µstrain. The strain device, with attached cells, was tested in an amiable bioenvironment. Results from strain gages indicated a uniform strain field existed within the center region of the plate and culture area. Cells in the test plates stained viable, exhibited similar morphology to controls, and were assayed for alkaline phosphatase (ALP) activity, total protein production, and calcium deposition. Results also indicated that stretched cells exhibited increases in proliferation, as well as changes in ALP activity vs. unstrained controls. Thus, the device was successful in distinguishing differences in cell response to mechanical perturbations and may be used to investigate how cells respond to strains at implant-bone interfaces.

PURPOSE: To understand the influences of mechanical loading on bone adaptation, the ground reaction force (GRF) applied to the bone must be quantified. The use of force plates in a lab setting is the accepted method for quantifying GRFs; however, this is not feasible in free-living situations. Recent developments in accelerometer technology may provide the ability to evaluate the effects of mechanical loading on bone outside of laboratory settings. The purpose of this project was to validate an accelerometer for the measurement of mechanical loading by comparing its output against GRFs. METHODS: Male and female participants (n = 20 males, 20 females; 18 to 49 yr) completed 10 repetitions of 9 common everyday movements (stand, walk, jog, run, 15 cm jump, step down from curb, drop down from curb, forward hop, and side hop) on a force plate with an accelerometer worn on their right hip. Then, a subset (n = 5 males, 5 females) wore an accelerometer on their right hip and played basketball, volleyball, and dodgeball as a group. Finally, all 40 participants wore an accelerometer home for 7 days. All activities were organized into derived activity categories labeled as low-, moderate-, and high-mechanical-load-intensity and used with 59 possible accelerometer variables to predict mechanical load. Models were fit using the randomForest package in R. Model performance (coefficient of determination [R2] and median absolute error) was evaluated using cross-validation. RESULTS: The percentage of variation mechanical load intensity explained by the models ranged from 0.27 to 0.78 with median absolute errors ranging from 0.20 to 0.49. The model with R2 = 0.78 contained the known activity categories and the accelerometer variables, but this is not realistic for free-living situations where activity categories will not be known. The two free-living models with the highest R2 values included derived activity categories and accelerometer variables, and estimated, on average, 21.1 and 20.7 hours per day in low-intensity, 1.6 and 1.7 hours per day in moderate-intensity, and 0.0 and 0.5 hours per day in high-intensity osteogenic activity, respectively. CONCLUSION: It is assumed that higher intensity activities (i.e., jumping vs. jogging) result in higher GRF values, but depending on the actual execution of the movement, this is not always the case. This research demonstrated that models containing the accelerometer variables performed better in predicting GRF than those containing only the derived activity categories. This supports the hypothesis that accelerometers provide valuable objective information when evaluating mechanical loading on bone.

Mechanical loading is an integral component to maintaining bone mass during periods of disuse (i.e. bedrest or casting) or reduced weightbearing activity. Recent data has shown a direct relation between the sympathetic nervous system (SNS) and bone metabolism, however the underlying mechanisms responsible for this relationship are unknown. Furthermore, the role that beta adrenergic stimulation during disuse has on cancellous bone mass and microarchitecture have yet to be defined. The central hypothesis of this research is that resistance exercise and beta-1 adrenergic (Adrb1) receptor agonist administration attenuate disuse-associated reductions in metaphyseal bone during 28 days of rodent hindlimb unloading (HU). Study one determined whether an eccentric- (ECC) or combined isometric+eccentric- (ISO+ECC) based contraction paradigm, engaged during hindlimb unloading (HU), mitigates losses in musculoskeletal mass and strength. Both simulated resistance training (SRT) protocols inhibited reductions in disuse-sensitive cancellous bone mass and maintained plantarflexor muscle strength. Study two determined whether combining the anabolic effects of SRT with the anti-resorptive effects of alendronate (ALEN) during HU positively impacts cancellous bone in an additive or synergistic fashion. ALEN significantly inhibited the anabolic response of cancellous bone to SRT during HU. Study three determined whether an Adrb1 receptor agonist (dobutamine; DOB) mitigates disuse-associated losses in bone mass and formation rate (BFR) during HU. DOB administration significantly blunted reductions in bone mineral density (vBMD) by maintaining cancellous BFR. Study four determined if Adrb1 receptor agonist administration during HU results in an attenuation of osteocyte apoptosis within cancellous bone and whether this relates to a decrease in Bax/Bcl-2 mRNA content ratio (pro- and anti-apoptotic proteins). HU significantly increased cancellous bone osteocyte apoptosis and Bax/Bcl-2 mRNA content ratio, which was reduced by the administration of DOB. Collectively, these are the first studies to assess the role of beta-1 adrenergic signaling and resistance exercise in mitigating disuse-induced loss of cancellous bone mass in rodents. The long term goals of this research are to understand the exact molecular mechanisms by which both Adrb1 signaling and high intensity resistance exercise provide beneficial bone effects during prolonged periods of disuse and to apply these findings to current osteoporosis research.

Intervertebral disc (IVD) degeneration is a prevalent health problem that is highly linked to back pain. To understand the disease and tissue response to therapies, ex-vivo whole IVD organ culture systems have recently been introduced. The goal of this study was to develop and validate a whole spinal segment culturing system that loads the disc in complex loading similar to the in-vivo condition, while preserving the adjacent endplates and vertebral bodies. The complex loading applied to the spinal segment was achieved with three pneumatic cylinders. The pneumatic cylinders were rigidly attached to two triangular alumni plates at each corner, comprising the loading mechanism. By extending or compressing the pneumatic cylinders, three modes of loading were achieved: flexion-extension, bi-lateral bending, and cyclic compression. The cylinders were controlled via microcontroller, and the entire system was fully automated. The culture container, which housed the spinal segment during culturing, was a flexible silicone container with an aluminum base and lid. The culture container attached to the loading mechanism allows for loading of the spinal segment. It had a vent attached to the aluminum lid that allowed for gas exchange in the system. The dynamic bioreactor was able to achieve physiologic loading conditions with 100 N of applied compression and approximately 2-4 N-m of applied torque. The function of the bioreactor was validated through testing of bovine caudal IVDs with intact endplates and vertebral bodies that were isolated within 2 hours of death and cultured for 14 days under a diurnal cycle. The resulting IVD cell viability following 14 days of loading was approximately 43% and 20% for the nucleus pulposus and annulus fibrosus respectively, which was significantly higher than the unloaded controls. The loading system accurately mimicked flexion-extension, bi-lateral bending, and compression motions seen during daily activities. Results indicate that this complex dynamic bioreactor may be appropriate for extended pre-clinical testing of vertebral mounted spinal devices and therapies.

The majority of the physical properties of tissue depend directly on the interstitial or intracellular concentration of water within the epidermal and dermal layers. The relationship between skin constituent concentrations, such as water and protein, and the mechanical and optical properties of human skin is important to understand its complex nature. Localized mechanical loading has been proven to alter optical properties of tissue, but the mechanisms by which it is accomplished have not been studied in depth. In this thesis, skin's complex nature is investigated experimentally and computationally to give us better insight on how localized mechanical loading changes tissues water content and its optical properties. Load-based compression and subsequent increased optical power transmission through tissue is accomplished to explore a relationship between localized mechanical loading and tissue optical and mechanical properties. Using Optical Coherence Tomography (OCT), modification of optical properties, such as refractive index, are observed to deduce water concentration changes in tissue due to mechanical compression. A computational finite element model is developed to correlate applied mechanical force to tissue strain and water transport. Comprehensive understanding of the underlying physical principles governing the optical property changes within skin due to water concentration variation will enable future development of applications in the engineered tissue optics field. / Master of Science

Tissue optical clearing aims to increase the penetration depth of near-collimated light in biological tissue to enhance optical diagnostic, therapeutic, and cosmetic procedures. Previous studies have shown the effects of chemical optical clearing on tissue optical properties. Drawbacks associated with chemical clearing include the introduction of potentially toxic exogenous chemicals into the tissue, poor site targeting, as well as slow transport of the chemicals through tissue. Thus, alternative clearing methods have been investigated. Mechanical compression is one such alternative tissue optical clearing technique. The mechanisms of action of mechanical compression may be similar to those of chemical clearing, though they have yet to be investigated systematically. This research describes the design and execution of a number of procedures useful for the quantification of the tissue optical clearing effects of localized mechanical compression. The first experimental chapter presents the effects of compression on image resolution and contrast of a target imaged through ex vivo biological tissue. It was found that mechanical optical clearing allowed recovery of smaller targets at higher contrast sensitivity when compared to chemical clearing. Also, thickness-independent tissue clearing effects were observed. In the second experimental chapter, dynamic changes in tissue optical properties, namely scattering and absorption coefficients (?s' and ?a, respectively) were monitored during a controlled compression protocol using different indentation geometries. A reduction in ?s' and ?a was evident for all indentation geometries, with greater changes occurring with smaller surface area. Results indicate that localized mechanical compression may be harnessed as a minimally-invasive tissue optical clearing technique. / Master of Science

Critically ill patients admitted to the intensive care unit (ICU) commonly develop severe muscle wasting and weakness and consequently impaired muscle function. This not only delays respirator weaning and ICU discharge, but has deleterious effects on morbidity, mortality, financial costs, and quality of life of survivors. Acute Quadriplegic Myopathy (AQM) is one of the most common neuromuscular disorders underlying ICU muscle wasting and paralysis, and is a consequence of modern intensive care interventions, although the exact causes remain unclear. Muscle gene/protein expression, intracellular signalling, post-translational modifications, muscle membrane excitability, and contractile properties at the single muscle fibre level were explored in order to unravel the mechanisms underlying the muscle wasting and weakness associated with AQM and how this can be counteracted by specific intervention strategies. A unique experimental rat ICU model was used to address the mechanistic and therapeutic aspects of this condition, allowing time-resolved studies for a period of two weeks. Subsequently, the findings obtained from this model were translated into a clinical study. The obtained results showed that the mechanical silencing of skeletal muscle, i.e., absence of external strain (weight bearing) and internal strain (myosin-actin activation) due to the pharmacological paralysis or sedation associated with the ICU intervention, is likely to be the primary mechanism triggering the preferential myosin loss and muscle wasting, features specifically characteristic of AQM. Moreover, mechanical silencing induces a specific gene expression pattern as well as post-translational modifications in the motor domain of myosin that may be critical for both function and for triggering proteolysis. The higher nNOS expression found in the ICU patients and its cytoplasmic dislocation are indicated as a probable mechanism underlying these highly specific modifications. This work also demonstrated that passive mechanical loading is able to attenuate the oxidative stress associated with the mechanical silencing and induces positive effects on muscle function, i.e., alleviates the loss of force-generating capacity that underlie the ICU intervention, supporting the importance of early physical therapy in immobilized, sedated, and mechanically ventilated ICU patients.