PRISM :: Browsing by Author "Duncan, Neil A."

Browsing by Author "Duncan, Neil A."

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Open Access
Bioprocessing of Mesenchymal Stem Cells and Their Derivatives: Toward Cell-Free Therapeutics
(2018-09-12) Phelps, Jolene; Sanati-Nezhad, Amir; Ungrin, Mark; Duncan, Neil A.; Sen, Arindom
Mesenchymal stem cells (MSCs) have attracted tremendous research interest due to their ability to repair tissues and reduce inflammation when implanted into a damaged or diseased site. These therapeutic effects have been largely attributed to the collection of biomolecules they secrete (i.e., their secretome). Recent studies have provided evidence that similar effects may be produced by utilizing only the secretome fraction containing extracellular vesicles (EVs). EVs are cell-derived, membrane-bound vesicles that contain various biomolecules. Due to their small size and relative mobility, they provide a stable mechanism to deliver biomolecules (i.e., biological signals) throughout an organism. The use of the MSC secretome, or its components, has advantages over the implantation of the MSCs themselves: (i) signals can be bioengineered and scaled to specific dosages, and (ii) the nonliving nature of the secretome enables it to be efficiently stored and transported. However, since the composition and therapeutic benefit of the secretome can be influenced by cell source, culture conditions, isolation methods, and storage conditions, there is a need for standardization of bioprocessing parameters. This review focuses on key parameters within the MSC culture environment that affect the nature and functionality of the secretome. This information is pertinent to the development of bioprocesses aimed at scaling up the production of secretome-derived products for their use as therapeutics.
Open Access
cell morphology and gap junction communication in the annulus fibrosus
(2009) McMillian, Jana Leigh; Duncan, Neil A.
Open Access
The Contribution of Endogenous and Exogenous Stem Cells in Fracture Repair
(2019-12-17) Ferrie, Leah Elizabeth; Duncan, Neil A.; Krawetz, Roman J.; Matyas, John Robert; Rancourt, Derrick E.
Throughout the lifespan, bone remodels in response to damage, such as fracture. However, diseases such as osteoporosis can cause impaired bone healing, increasing the risk of progression to non-repairing defects called fracture non-unions. Promoting the healing of fracture non-unions is a promising target for bone tissue engineering due to the limited success of current clinical treatment methods. There has been significant research on the use of stem cells with and without biomaterial scaffolds to treat bone fractures due to their promising regenerative capabilities. However, the relative roles of transplanted stem cells (exogenous stem cells) and stem cells found naturally in the body (endogenous stem cells) and their overall contribution to in vivo fracture repair is not well understood, thereby delaying the translation of new tissue engineering therapies to the clinic. The purpose of this research was to determine the interaction between exogenous and endogenous stem cells and biomaterials during bone fracture healing. This study was conducted using a burr-hole fracture model in a mesenchymal stem cell lineaging-tracing mouse. Burr-hole fractures were treated with collagen-I biomaterial loaded with and without green fluorescent protein tagged induced pluripotent stem cells. Using lineage-tracing, the roles of exogenous and endogenous stem cells during bone fracture repair could be elucidated. It was determined that in both a normal and impaired model of fracture healing treatment with exogenous stem cells did not result in improved bone formation and did not promote the recruitment of endogenous stem cells. However, treatment with exogenous stem cells in an impaired model of healing may offer healing advantages compared to in a normal model of healing. The outcomes of this study provide fundamental knowledge required for developing more effective stem cell and biomaterial therapies to treat bone fractures.
Open Access
Cyclical tensile loading and measurement of cell deformation in three-dimensional gel culture: a new method
(2002) Dussault, Chantal; Duncan, Neil A.
Open Access
Durability Performance and Life Cycle Cost Analysis of Concrete Beams Reinforced with Various Reinforcement
(2019-02) Amiri, Mouhammad Abdullah; El-Hacha, Raafat; Duncan, Neil A.; Khoshnazar, Rahil
In the context of efficiency, sustainability, and life-cycle cost, reinforcement durability became a significant concern. Long-term costs are bringing the attention of many countries and companies who aim to minimize them maximally. Subsequently, researchers started concentrating on the study of the durability of materials to enhance the sustainability and resiliency of future structures. The primary objective of this study is to examine the durability and performance of concrete beams reinforced with different types of materials exposed to identical environmental conditions and loads. Therefore, several types of corrosion-resistant reinforcing rebars including Fibre Reinforced Polymer (FRP) (Glass, Carbon, and Basalt), Martensitic Micro-Composite Formable Steel (MMFX), and Stainless steel, in addition to the conventional uncoated black steel for comparison purposes were examined. The research studied the performance of 28 beams in total, the beams were 2 metres long with 150x305 mm cross section, twenty-one beams were subjected to environmental conditions, and seven were used as controls. The exposed beams were subjected to a sustained load equivalent to 40% of their ultimate capacity, exposed to spraying salt water with 3.5% sodium chloride (NaCl) concentration, and subjected to a total of 195 freeze-thaw cycles with temperature ranging between +34°C and –34°C equivalent to 5 years in real conditions. After the exposure, the beams were acclimatized to room temperature and together with the control unexposed specimens were tested for ultimate capacity. No one material was found to be superior in all of the studied parameters, the beams presented differences in the performance such as load-deflection, deviation from linearity, ductility, crack pattern, in addition to the strength loss, and cost. The initial cost of the beams was calculated, and the results showed more than 60% difference for specific types of rebars in comparison to conventional steel reinforced beams.
Open Access
Enhanced Longitudinal Analysis of Bone Strength Estimated by 3D Bone Imaging and the Finite Element Method
(2020-10-06) Plett, Ryan Michael; Boyd, Steven Kyle; Duncan, Neil A.; Manske, Sarah Lynn; Kim, Keekyoung; Edwards, William Brent
Three-dimensional (3D) imaging with high-resolution peripheral quantitative computed tomography (HR-pQCT) and micro-finite element (FE) analysis provides important insight into bone health. Longitudinal analyses of bone morphology maximize precision by using 2D slice-matching registration (SM) or 3D rigid-body registration (3DR) to account for repositioning error between scans, however, the compatibility of these techniques with FE for longitudinal bone strength estimates is limited. This work developed and validated a FE approach for longitudinal HR-pQCT studies using 3DR to maximize reproducibility by fully accounting for misalignment between images. Using a standard imaging protocol, ex vivo (N=10) and in vivo (N=40) distal radius HR-pQCT images were acquired to estimate the efficacy of 3DR to reduce longitudinal variability due to repositioning error and assess the sensitivity of this method to detect true changes in bone strength. In our proposed approach, the full common bone volume defined by 3DR for serial scans was used for FE. Standard FE parameters were estimated by no registration (NR), SM, and 3DR. Ex vivo reproducibility was estimated by the least significant change (LSC) in each parameter with a ground truth of zero change in longitudinal estimates. In vivo reproducibility was estimated by the standard deviation of the rate of change (σ) with an ideal value that was minimized to define true changes in longitudinal estimates. Group-wise comparisons of ex vivo and in vivo reproducibility found that FE reproducibility was improved by both SM (CVRMS<0.80%) and 3DR (CVRMS<0.62%) compared to NR (CVRMS~2%), and 3DR was advantageous as repositioning error increased. Although 3D registration did not negate motion artifacts, it played an important role in detecting and reducing variability in FE estimates for longitudinal study designs. Therefore, 3D registration is ideally suited for estimating in vivo effects of interventions in longitudinal studies of bone strength.
Open Access
Functional gap junction communication and its mechanobiological role in the outer annulus fibrosus
(2006) Kelly, Elizabeth Jessica; Duncan, Neil A.
Open Access
Historic Reinforced Concrete in Alberta: Analysis and Conservation of Two Structures
(2018-09-14) Rouhi, Alireza; Shrive, Nigel; Vera, Jacqueline; Ingham, Jason Maxwell; Lissel, Shelley L.; Duncan, Neil A.
The Brooks Aqueduct and the Greenhill mine tipple structure were built in the turn of the twentieth century in southern Alberta. They were among the first reinforced concrete structures to be built in that region and are considered great engineering and construction achievements for their time. They were both built at a time when there was no standard for the design of reinforced concrete structures in North America and lots of issues about the concrete design and construction, especially from the durability point of view, were still unknown. Both structures had a great impact on the economy of their local regions and now are designated as national and provincial historic sites respectively. Frequent repair and maintenance became necessary from the early stages of operation of Brooks Aqueduct due to design and construction deficiencies. Both structures show significant signs of damage and deterioration and need to be evaluated and properly repaired and maintained. This research involves evaluation of the two structures through site inspections and laboratory tests on the samples taken from them. The work also involves numerical modelling of the structures to identify areas of possible over stress and find the main causes of damage and deterioration. Several similarities and differences are found between the concrete used in these structures and their deterioration mechanism. The main goal in evaluation and repair of Brooks Aqueduct is to maintain it as a monument and an engineering and construction achievement. In the case of the Greenhill mine tipple structure, two scenarios were studied: adaptive reuse as a restaurant and maintaining the structure as a monument. Results of the analyses show that although there was clear lack of understanding about the behaviour of concrete in the design of these structures, most of the damage and deterioration are non-structural and has happened due to durability issues mainly from exposure to freeze-thaw cycles and corrosion of the reinforcement. Service life analysis of the two structure is also performed based on theoretical models and test results. Recommendations for extending the remaining service life and conservation and retrofitting of the two structures and similar cases are provided based on the results of the tests and analyses. The research identifies common types of problems in historic reinforced concrete structures constructed in Alberta in the early twentieth century and ways to recognise and overcome these problems. The results also emphasize that in evaluation of concrete from the early twentieth century, one has to look for certain problems such as lack of resistance against durability issues (mainly freeze-thaw and carbonation), lack of precision in placement of the reinforcing steel (rebar), lack of rebar splice lengths, lack of proper cover of concrete and lack of proper grading and selection of aggregates.
Open Access
The Influence of Intracortical Microarchitecture on the Mechanical Fatigue of Bone
(2020-07-07) Loundagin, Lindsay Lessel; Edwards, William Brent; Boyd, Steven Kyle; Schmidt, Roel Kuijer Tannin; Duncan, Neil A.; Cooper, David Michael Lane; Taylor, David; Manske, Sarah Lynn
Mechanical fatigue is the predominant etiology of stress fracture, a known contributor to atypical femoral fracture, and may also play a critical role in fragility fracture. While these fatigue-related fractures are well-documented in humans, they are poorly understood. Extensive research has attempted to characterize the fatigue behavior of cortical bone; however, owing to the inherent variability in bone tissue, samples that appear identical in macrostructure can exhibit a large degree of scatter in fatigue life. The overarching hypothesis of this thesis is that the variance in fatigue-life data can be attributed to intracortical microarchitecture, including the size, spacing, and density of vascular canals and osteocyte lacunae. A series of studies were conducted that utilized ex vivo mechanical testing, high-resolution imaging, and finite element modeling to establish the relationship between intracortical microarchitecture and the fatigue life of bone in compression. Both porosity and canal diameter demonstrated a strong negative relationship with fatigue life, whereas lacunar density was positively correlated. The reduced fatigue life associated with higher porosity was a result of larger, rather than more abundant canals, indicating that canals act as stress concentrators that may impair the fatigue resistance of bone beyond increasing overall porosity. The stress concentrations caused by vascular canals were quantified as stressed volume (i.e., the volume of material above yield) which was positively correlated to porosity and canal diameter. Furthermore, stressed volume proved to be a strong predictor of fatigue-life variance across multiple loading magnitudes. The findings from this thesis suggest that a majority of the fatigue-life variance of cortical bone in compression is driven by intracortical microarchitecture, and fatigue failure may be predicted by quantifying the stress concentrations associated with vascular canals.
Open Access
Intercellular communication and in situ strains in the annulus fibrosus under high flexion loads
(2007) Desrochers, Jane; Duncan, Neil A.
Open Access
Intercellular Gap Junction Communication in the Bovine Annulus Fibrosus
(2019-02-21) McWhae, Russell; Duncan, Neil A.; Matyas, John Robert; Sen, Arindom; Li, Leping; Salo, Paul T.
The intervertebral disc has a complex, anisotropic structure. The annulus fibrosus, the fibrous outer layer of the intervertebral disc, consists of fifteen to twenty-five concentric layers of collagen fibers at alternating orientations. Cells inside and between these lamellae are known to communicate with each other through gap junctions, protein channels that directly couple the membranes of adjacent cells and form interconnected networks that may be used to coordinate a response to mechanical stimuli. These fibroblastic cells fall into three distinct morphologies: spindle-shaped lamellar cells, round lamellar cells, and interlamellar cells. With confocal microscopy methods, gap-junctional intercellular signal propagation between groups of interconnected cells was examined. While the anisotropic microenvironment of the outer annulus was hypothesized to manifest in non-homogenous signal-propagation patterns, it was demonstrated that no clear directional biases or non-homogenous behavior existed among different cell morphologies and orientations; instead, intercellular signal propagation appears to be primarily proximity based.
Open Access
Investigating the role of proteoglycans in fibril sliding
(2006) Thomas, Dorothy Ann; Duncan, Neil A.
Open Access
Linear cell arrays and cell isolation in the annulus fibrosus of the intervertebral disc
(2004) van der Werf, Marije; Duncan, Neil A.
Open Access
Methods to determine the microscopic and macroscopic swelling behaviour of the annulus fibrosus
(2002) Hulme, Paul Alexander; Duncan, Neil A.
Open Access
Modelling Hydraulic Fracturing in Tight Reservoirs Using Equivalent Continuum Approach
(2021-01-29) Atdayev, Eziz; Wong, Ron Chik Kwong; Eaton, David William S.; Davidsen, Jörn; Duncan, Neil A.
Hydraulic fracturing has transitioned into widespread use over the last few decades. There are a variety of numerical methods available to simulate hydraulic fracturing. However, most current methods require a large number of input parameters, of which the values of some parameters are poorly constrained. This research proposes a new method of modelling the hydraulically fractured region using void-ratio and strain dependent relation to define the permeability of the fractured region. This approach is computationally efficient and reduces the number of input parameters. By implementing this method with an equivalent continuum representation, uncertainties are reduced arising from heterogeneity and anisotropy of the earth materials. The computational efficiency improves modelling performance in stress-sensitive zones such as in the vicinity of the injection well or near faults.
Open Access
Physiological oxygen conditions enhance the angiogenic properties of extracellular vesicles from human mesenchymal stem cells
(2023-08-23) Phelps, Jolene; Hart, David A.; Mitha, Alim P.; Duncan, Neil A.; Sen, Arindom
Abstract Background Following an ischemic injury to the brain, the induction of angiogenesis is critical to neurological recovery. The angiogenic benefits of mesenchymal stem cells (MSCs) have been attributed at least in part to the actions of extracellular vesicles (EVs) that they secrete. EVs are membrane-bound vesicles that contain various angiogenic biomolecules capable of eliciting therapeutic responses and are of relevance in cerebral applications due to their ability to cross the blood–brain barrier (BBB). Though MSCs are commonly cultured under oxygen levels present in injected air, when MSCs are cultured under physiologically relevant oxygen conditions (2–9% O2), they have been found to secrete higher amounts of survival and angiogenic factors. There is a need to determine the effects of MSC-EVs in models of cerebral angiogenesis and whether those from MSCs cultured under physiological oxygen provide greater functional effects. Methods Human adipose-derived MSCs were grown in clinically relevant serum-free medium and exposed to either headspace oxygen concentrations of 18.4% O2 (normoxic) or 3% O2 (physioxic). EVs were isolated from MSC cultures by differential ultracentrifugation and characterized by their size, concentration of EV specific markers, and their angiogenic protein content. Their functional angiogenic effects were evaluated in vitro by their induction of cerebral microvascular endothelial cell (CMEC) proliferation, tube formation, and angiogenic and tight junction gene expressions. Results Compared to normoxic conditions, culturing MSCs under physioxic conditions increased their expression of angiogenic genes SDF1 and VEGF, and subsequently elevated VEGF-A content in the EV fraction. MSC-EVs demonstrated an ability to induce CMEC angiogenesis by promoting tube formation, with the EV fraction from physioxic cultures having the greatest effect. The physioxic EV fraction further upregulated the expression of CMEC angiogenic genes FGF2, HIF1, VEGF and TGFB1, as well as genes (OCLN and TJP1) involved in BBB maintenance. Conclusions EVs from physioxic MSC cultures hold promise in the generation of a cell-free therapy to induce angiogenesis. Their positive angiogenic effect on cerebral microvascular endothelial cells demonstrates that they may have utility in treating ischemic cerebral conditions, where the induction of angiogenesis is critical to improving recovery and neurological function.
Open Access
Poly (ε-Caprolactone)-Silk Fibroin Based Functional Repair for Annulus Fibrosus Tears
(2019-01-24) Novin, Mana; Duncan, Neil A.; Kallos, Michael S.; Salo, Paul T.; Ungrin, Mark D.; Sen, Arindom; Lü, Qingye
Intervertebral disc degeneration with an associated bulged/herniated disc is a significant cause of low back pain. Annulus fibrosus (AF) tears and defects are a major clinical problem with no current treatments available for its closure and repair, resulting in risk of re-herniation. This thesis focuses on the chemical and mechanical characterization of a newly-designed biodegradable poly(ɛ-caprolactone)-silk fibroin (PCL-SF) as a potential candidate for the closure of irregular AF defects through minimally-invasive implantation. Thermoset PCL-SF scaffolds were produced with two concentrations of the PCL-diacrylate macromer solution (40% and 60% w/v) and five PCL:SF ratios (100:0, 90:10, 80:20, 70:30, and 60:40). Chemical characterization of the scaffolds confirmed the effective blending of PCL and SF macromolecules with uniform distribution of SF throughout the scaffolds and formation of β-sheet conformation in SF. Mechanical characterization of the scaffolds showed: (i) highly interconnected pores with pore sizes of 260–265 μm, (ii) tensile moduli and yield strains of 0.22-0.31 MPa and 41-61%, respectively, and (iii) compressive moduli of 0.11- 0.27 MPa. The above-mentioned porosities were within the range that reportedly supports AF cell penetration, adhesion, and accumulation of a collagen I rich extracellular matrix. The tensile moduli of tested scaffolds were in the range of human AF tissue in radial and axial directions. The compressive moduli were slightly less than native AF tissue but approximately an order of magnitude higher than those of other AF repair biomaterials. Additionally, the in vitro biodegradation rate of scaffolds was found to be slow enough to provide mechanical support in the time frame needed for AF regeneration. However, scaffolds were unable to exhibit shape-memory capabilities suitable for self-fitting in AF defects. Further optimization of the scaffold design with respect to shape memory capability for minimally-invasive delivery and self-fitting in AF defect will be required for clinical application.
Open Access
Quantifying In Vivo Cervical Spine Kinematics: Validation of a Novel Data Collection and Processing Pipeline
(2020-07-16) Figueroa, Luis Alonso; Ronsky, Janet L.; Swamy, Ganesh; Duncan, Neil A.
Intervertebral disc (IVD) degeneration is a condition that affects a vast majority of the aging population. IVD is characterized by the decay of the joints between vertebrae and may result in pain and disability. Studying spinal kinematics has proven effective for evaluating the outcomes of surgical procedures aimed at mediating with the effects of IVD degeneration, such as cervical discectomy and fusion (ACDF) and cervical total disc arthroplasty (cTDA). However, quantifying and analyzing cervical IVD kinematics represents a challenging task when examining biomechanics of the neck. This study presents a novel data collection and processing pipeline aimed at quantifying in-vivo kinematics of the cervical spine with high-speed biplanar video-radiography (HSBV). A cadaveric pilot study was conducted to test the viability and accuracy of this methodology. Accuracy, defined as the error with respect to radiostereometric analysis (RSA) (the “gold standard”), was calculated as 1.39±0.58° in rotational error and 0.97±0.74 mm in translational error. A separate experiment was implemented to validate the RSA. It was determined that RSA techniques present accuracies of 0.09±0.01 mm and 0.35±0.05 deg/sec. The development of this valuable tool to analyze and measure the in vivo kinematics of the cervical spine will enable further understanding of cervical spine kinematics following cTDA and ACDF.
Open Access
Reference-Free Response-Only Damage Identification in Bridges Using Relative Wavelet Entropy
(2019-04-17) Moravvej Hamedani, Mohammad Hossein; El-Badry, Mamdouh; Duncan, Neil A.; Dann, Markus R.; Dilger, Walter H.; Sudak, Leszek Jozef; Narasimhan, Sriram; Khoshnazar, Rahil
Bridges are designed and built to be safe against failure and to perform satisfactorily over their service life. To ensure safety and serviceability, it is essential to evaluate the structural performance of bridges through identification of potential damage at the earliest time possible. A vibration-based damage identification technique (DIT) that can detect structural damage, determine its location, and estimate its severity has been investigated in this research. The technique combines discrete wavelet transform (DWT) – a powerful signal processing tool for decomposition of signals – and spectral entropy in a relative procedure to detect and quantify the damage-induced disturbances in the measured dynamic response of bridges under ambient vibration. This relative wavelet entropy (RWE)-based DIT is a practical means for damage identification in in-situ cases, where the normal operation of bridges cannot be interrupted to perform dynamic excitation tests, and the data obtained from a reference (undamaged) state of the bridges are not available for comparison with the data measured from their current (damaged) state. Through its relative procedure, the technique has the advantage of mitigating undesirable effects of varying operational and environmental conditions on the damage detection process. In this research, the theoretical bases of the technique are presented, and its efficacy has been experimentally validated against false damage indications under varying operational and environmental conditions, such as the location of input dynamic excitation, location and extent of damage, support conditions, and temperature levels. The technique has also been implemented in small- and large-scale bridge specimens of various structural systems tested under different loading conditions. The test specimens included push-off columns, reinforced concrete beams, strengthened beams, precast concrete truss girders, slab-on-truss girder bridges, and post-tensioned concrete girders. The RWE-based DIT showed successful performance in identifying a wide variety of test-induced damage, including fracture in shear reinforcement, concrete cracking/crushing, debonding of strengthening sheets, rupture of truss elements’ confining tubes, and failure in truss connections. The technique has also been used to investigate the effects of pre-stressing on the dynamic behaviour of post-tensioned concrete girders to address the disagreement in the research community about the effectiveness of vibration-based DITs in pre-stress force identification.
Open Access
Studies of Structural and Mechanical Properties of Skin and Treated Split Thickness Skin Autografts
(2018-09-06) Tarraf, Samar Andrea; Di Martino, Elena S.; Biernaskie, Jeff A.; Duncan, Neil A.; Matyas, John Robert
Split-thickness skin autografts (STSGs) are the gold standard treatment for full thickness burn wounds. Healthy skin from the patient is harvested and transplanted onto the wound. The graft, comprised of epidermis and superficial dermis, is missing cellular components adversely affecting functionality. One major contributor to reduced functionality is decreased elasticity. Understanding the biomechanical properties of grafts can help assess the efficacy of treatments. We hypothesize that combining STSGs with dermal stem cells could stimulate tissue remodeling, generation of neodermis and improve functionality. Coupling mechanics with microscopy assays gives a more encompassing understanding of the changes in mechanical properties. This study provides an initial comparison between skin tissue types and between graft treatments. We established differences between healthy and grafted skin and showed shortcomings of the xenograft model used. We also demonstrated the effects of graft treatment on mechanical response. Treatment cannot fully recover healthy skin behavior, but improves graft functionality.