Enhanced Osseous Integration of Human Trabecular Allografts Following Surface Modification With Bioactive Lipids

In this study, we used extracellular matrix (ECM) gels and human bone allograft as matrix vehicles to deliver the sphingolipid growth factor FTY720 to rodent models of tibial fracture and a critical-sized cranial defect. We show that FTY720 released from injectable ECM gels may accelerate callous formation and resolution and bone volume in a mouse tibial fracture model. We then show that FTY720 binds directly to human trabecular allograft bone and releases over 1 week in vitro. Rat critical-sized cranial defects treated with FTY720-coated grafts show increases in vascularization and bone deposition, with histological and micro-computed topography (microCT) evidence of enhanced bone formation within the graft and defect void. Immunohistochemical analysis suggests that osteogenesis within FTY720-coated grafts is associated with reduced CD68(+) macrophage infiltration and recruitment of CD29(+) bone progenitor cells. Matrix binding of FTY720 thus represents a promising and robust bone regeneration strategy with potential clinical translatability

Alignment and Composition of Laminin-Polycaprolactone Nanofiber Blends Enhance Peripheral Nerve Regeneration

Peripheral nerve transection occurs commonly in traumatic injury, causing deficits distal to the injury site. Conduits for repair currently on the market are hollow tubes; however, they often fail due to slow regeneration over long gaps. To facilitate increased regeneration speed and functional recovery, the ideal conduit should provide biochemically relevant signals and physical guidance cues, thus playing an active role in regeneration. To that end, laminin and lamininpolycaprolactone (PCL) blend nanofibers were fabricated to mimic peripheral nerve basement membrane. In vitro assays established 10% (wt) laminin content is sufficient to retain neurite-promoting effects of laminin. In addition, modified collector plate design to introduce an insulating gap enabled the fabrication of aligned nanofibers. The effects of laminin content and fiber orientation were evaluated in rat tibial nerve defect model. The lumens of conduits were filled with nanofiber meshes of varying laminin content and alignment to assess changes in motor and sensory recovery. Retrograde nerve conduction speed at 6 weeks was significantly faster in animals receiving aligned nanofiber conduits than in those receiving random nanofiber conduits. Animals receiving nanofiber-filled conduits showed some conduction in both anterograde and retrograde directions, whereas in animals receiving hollow conduits, no impulse conduction was detected. Aligned PCL nanofibers significantly improved motor function; aligned laminin blend nanofibers yielded the best sensory function recovery. In both cases, nanofiber-filled conduits resulted in better functional recovery than hollow conduits. These studies provide a firm foundation for the use of naturalsynthetic blend electrospun nanofibers to enhance existing hollow nerve guidance conduits

Bone tissue engineering in a rotating bioreactor: A quantitative approach

In this thesis, we have undertaken a quantitative approach toward the design, construction, and functional evaluation of a new microcarrier scaffold system of osteoblast-like cell culture for in vitro tissue engineering of bone in the High Aspect Ratio Vessel (HARV) rotating bioreactor. Using novel methods of numerical simulation and in situ particle tracking, we showed that microcarriers with density greater than the surrounding fluid exhibit a periodic orbital motion equal to their sedimentation speed, and an outward, radial migration leading to repeated collisions with the bioreactor wall. In contrast, lighter-than-water microcarriers exhibit an inward migration towards the center of the bioreactor, and avoid bioreactor wall collisions and consequent damage to attached cells and tissues. To exploit this result, we fabricated novel lighter-than-water scaffolds based on hollow microcapsules of biodegradable poly(lactic-co-glycolic acid) (PLAGA). Individual microcapsules were thermally fused in predetermined size ranges to form three-dimensional (3-D) scaffolds with 25–40% internal pore volume and 100 to 300 μm median pore size. Scaffolds exhibited a controlled, collision free trajectory in the bioreactor with velocities in a range from 1 to 100 mm/s depending on scaffold properties. Peak shear stress imparted to cells on the exterior scaffold during culture ranged from 0.22 to 0.26 N/m2. Rates of internal fluid perfusion during scaffold motion were calculated using a mathematical model and ranged from 0.01–1 mm/s. Cells within interior regions of the scaffold experience peak shear stress far less (≈0.03 N/m2) than those on the exterior. Bone cells cultured on microcarrier scaffolds in the rotating bioreactor attached homogenously to the scaffolds at densities ranging from 10 4–105 cell/cm2. Cells also retained their osteoblastic phenotype and showed significant increases in mineralized bone matrix synthesis after 7 days of dynamic cultivation in the bioreactor as compared to appropriate static culture controls. In addition, cells exhibited a robust expression of key bone marker genes such as alkaline phosphatase collagen I, and early expression of osteocalcin. These results show that the microcarrier scaffold system may be utilized to quantify functional differences in osteoblastic cell function, and to enhance the phenotype development osteoblast-like cells

Bone tissue engineering in a rotating bioreactor: A quantitative approach

In this thesis, we have undertaken a quantitative approach toward the design, construction, and functional evaluation of a new microcarrier scaffold system of osteoblast-like cell culture for in vitro tissue engineering of bone in the High Aspect Ratio Vessel (HARV) rotating bioreactor. Using novel methods of numerical simulation and in situ particle tracking, we showed that microcarriers with density greater than the surrounding fluid exhibit a periodic orbital motion equal to their sedimentation speed, and an outward, radial migration leading to repeated collisions with the bioreactor wall. In contrast, lighter-than-water microcarriers exhibit an inward migration towards the center of the bioreactor, and avoid bioreactor wall collisions and consequent damage to attached cells and tissues. To exploit this result, we fabricated novel lighter-than-water scaffolds based on hollow microcapsules of biodegradable poly(lactic-co-glycolic acid) (PLAGA). Individual microcapsules were thermally fused in predetermined size ranges to form three-dimensional (3-D) scaffolds with 25–40% internal pore volume and 100 to 300 μm median pore size. Scaffolds exhibited a controlled, collision free trajectory in the bioreactor with velocities in a range from 1 to 100 mm/s depending on scaffold properties. Peak shear stress imparted to cells on the exterior scaffold during culture ranged from 0.22 to 0.26 N/m2. Rates of internal fluid perfusion during scaffold motion were calculated using a mathematical model and ranged from 0.01–1 mm/s. Cells within interior regions of the scaffold experience peak shear stress far less (≈0.03 N/m2) than those on the exterior. Bone cells cultured on microcarrier scaffolds in the rotating bioreactor attached homogenously to the scaffolds at densities ranging from 10 4–105 cell/cm2. Cells also retained their osteoblastic phenotype and showed significant increases in mineralized bone matrix synthesis after 7 days of dynamic cultivation in the bioreactor as compared to appropriate static culture controls. In addition, cells exhibited a robust expression of key bone marker genes such as alkaline phosphatase collagen I, and early expression of osteocalcin. These results show that the microcarrier scaffold system may be utilized to quantify functional differences in osteoblastic cell function, and to enhance the phenotype development osteoblast-like cells

Therapeutic Angiogenesis and Bone Regeneration with Natural and Synthetic Small Molecules

Presented on June 11, 2013 from 8:30 a.m.-9:30 a.m. at the Parker H. Petit Institute for Bioengineering & Bioscience (IBB), room 1128, Georgia Tech.Edward Botchwey is an Associate Professor in the Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology.Runtime: 68:05 minutesEndothelial cells play significant roles in conditioning the environment in local tissues after injury by the production and secretion of angiocrine factors. At least two distinct subsets of leukocytes, CD45+ CD11b+ Ly6C+Gr1+CX3CR1lo inflammatory monocytes (IM) and CD45+CD11b+Ly6CGr1-CX3CR1hi anti-inflammatory monocytes (AM), respond differentially to these angiocrine factors and promote pathogen/debris clearance and angiogenesis/wound healing, respectively. Our laboratory is currently investigating how local sphingosine 1-phosphate receptor 3 (S1P3) agonism recruits AM to remodeling vessels. We employ micron and nanoscale biomaterials to deliver FTY720, a S1P1/3 agonist, to inflamed and ischemic tissues, to reduce in pro-inflammatory cytokine secretion and an increase in regenerative cytokine secretion. The altered balance of cytokine secretion results in a reduction in inflammatory monocyte recruitment and an increase in anti-inflammatory CX3CR1hi monocyte recruitment to a pro-regenerative perivascular niche. Increased S1P3 expression and activation on AM resulted in significantly enhanced SDF-1α chemotaxis over IM. AM recruitment also enhanced arteriolar diameter expansion and increased length density of the local vasculature: classic signs of vascular remodeling. This work establishes a role for S1P receptor signaling in the local conditioning of tissues by angiocrine factors that preferentially recruit regenerative monocytes that can enhance healing outcomes, bone tissue regeneration, and biomaterial implant functionality

Impact of corporate board size and board independence on stock returns volatility in Ghana

AbstractThis paper investigates the role of corporate board size and board independence on the volatility of stock returns of Ghanaian-listed firms. A sample of 22 listed firms on the Ghana Stock Exchange was used, between 2011 and 2019. The study adopted the panel-corrected standard error (PCSE) regression technique supported by Driscoll-Kraay and robust ordinary least square (OLS) approaches as robustness measures. It was found that corporate board size of listed firms must be sizeable enough to reduce the volatility of stock returns. More specifically, the findings demonstrate that firms with large corporate board sizes are associated with lower stock returns volatility in support of the agency theory. Moreover, board independence indicates a positive and significant relationship with stock return volatility in support of the risk-seeking hypothesis. This implies that increasing the number of outside board executives on corporate boards is not enough to reduce stock return volatility perhaps due to a high level of information asymmetry between outside board members and insiders. Similarly, large firms are more volatile in terms of stock returns than smaller firms. Thus, this study recommends stricter enforcement of monitoring and disclosure of relevant market information on listed firms as well as strengthening the capacity of independent board executives via appropriate training