The effect of bone microstructure on the initiation and growth of microcracks.

Osteonal bone is often compared to a composite material and to metals as discontinuities within the material may provide sites of stress concentration for crack initiation and serve as barriers to crack growth. However, little experimental data exist to back up these hypotheses. Fluorescent chelating agents were applied at specific intervals to bone specimens fatigue tested in cyclic compression at a stress range of 80 MPa. The failed specimens were sectioned and labelled microcracks identified using UV epifluorescence microscopy. Microcrack lengths were measured and their relationship to cement lines surrounding secondary osteons recorded. Microcrack length at the time of encountering a cement line was also measured. Microcracks of less than 100mum stopped growing when they encountered a cement line. Microcracks of greater than 100mum in length continued to grow after encountering a cement line surrounding an osteon. Only microcracks greater than 300mum in length were capable of penetrating osteons and these microcracks were the only ones which were observed to cause failure in the specimen. These experimental data support the hypothesis that secondary osteons act as barriers to crack propagation in compact bone. However, it shows that this microstructural barrier effect is dependent on the crack length at the time of encountering an osteon. For the vast majority of cracks, osteons act as barriers to growth but for the minority of cracks that are long enough and do break through the cement line, an osteon may actually act as a weakness in the bone and facilitate crack propagation

Future Perspectives on the Role of Stem Cells and Extracellular Vesicles in Vascular Tissue Regeneration

Vascular tissue engineering is an area of regenerative medicine that attempts to create functional replacement tissue for defective segments of the vascular network. One approach to vascular tissue engineering utilizes seeding of biodegradable tubular scaffolds with stem (and/or progenitor) cells wherein the seeded cells initiate scaffold remodeling and prevent thrombosis through paracrine signaling to endogenous cells. Stem cells have received an abundance of attention in recent literature regarding the mechanism of their paracrine therapeutic effect. However, very little of this mechanistic research has been performed under the aegis of vascular tissue engineering. Therefore, the scope of this review includes the current state of TEVGs generated using the incorporation of stem cells in biodegradable scaffolds and potential cell-free directions for TEVGs based on stem cell secreted products. The current generation of stem cell-seeded vascular scaffolds are based on the premise that cells should be obtained from an autologous source. However, the reduced regenerative capacity of stem cells from certain patient groups limits the therapeutic potential of an autologous approach. This limitation prompts the need to investigate allogeneic stem cells or stem cell secreted products as therapeutic bases for TEVGs. The role of stem cell derived products, particularly extracellular vesicles (EVs), in vascular tissue engineering is exciting due to their potential use as a cell-free therapeutic base. EVs offer many benefits as a therapeutic base for functionalizing vascular scaffolds such as cell specific targeting, physiological delivery of cargo to target cells, reduced immunogenicity, and stability under physiological conditions. However, a number of points must be addressed prior to the effective translation of TEVG technologies that incorporate stem cell derived EVs such as standardizing stem cell culture conditions, EV isolation, scaffold functionalization with EVs, and establishing the therapeutic benefit of this combination treatment

Scaffold-based delivery of nucleic acid therapeutics for enhanced bone and cartilage repair

Recent advances in tissue engineering have made progress toward the development of biomaterials capable of the delivery of growth factors, such as bone morphogenetic proteins, in order to promote enhanced tissue repair. However, controlling the release of these growth factors on demand and within the desired localized area is a significant challenge and the associated high costs and side effects of uncontrolled delivery have proven increasingly problematic in clinical orthopedics. Gene therapy may be a valuable tool to avoid the limitations of local delivery of growth factors. Following a series of setbacks in the 1990s, the field of gene therapy is now seeing improvements in safety and efficacy resulting in substantial clinical progress and a resurgence in confidence. Biomaterial scaffold‐mediated gene therapy provides a template for cell infiltration and tissue formation while promoting transfection of cells to engineer therapeutic proteins in a sustained but ultimately transient fashion. Additionally, scaffold‐mediated delivery of RNA‐based therapeutics can silence specific genes associated with orthopedic pathological states. This review will provide an overview of the current state‐of‐the‐art in the field of gene‐activated scaffolds and their use within orthopedic tissue engineering applications

2,2,5,5-Tetramethyloxolane (TMO) as a Solvent for Buchwald–Hartwig Aminations

Buchwald–Hartwig amination is one of the most important methods for the synthesis of N-arylamines and is widely employed for the synthesis of potential pharmaceuticals, natural products, and other fine chemicals. The reaction usually uses a Pd(0) catalyst such as Pd(dba)2 and (±)-BINAP in the presence of a base, and toluene is the most commonly used solvent. However, there are significant safety, toxicological, and environmental hazards associated with the use of toluene. Herein, we demonstrate the successful application of 2,2,5,5-tetramethyloxolane (TMO), a solvent with a similar property profile to toluene, for Buchwald–Hartwig amination reactions for coupling a wide range of primary and secondary amines with aryl bromides. When NaOt-Bu was used as the base, similar yields were obtained in toluene and TMO. In contrast, using Cs2CO3, TMO outperformed toluene significantly for electron-deficient aryl bromides that could be susceptible to nucleophilic attack. To showcase the use of TMO as a solvent for Buchwald–Hartwig aminations, the synthesis of a key intermediate in the route to smoothened (SMO) receptor antagonist drug candidate SEN826 was successfully accomplished in TMO. Improved metrics and reduction in residual palladium in the isolated amines demonstrate further benefits in the substitution of toluene with TMO in Buchwald–Hartwig aminations

Highly versatile cell-penetrating peptide loaded scaffold for efficient and localised gene delivery to multiple cell types: From development to application in tissue engineering

Gene therapy has recently come of age with seven viral vector-based therapies gaining regulatory approval in recent years. In tissue engineering, non-viral vectors are preferred over viral vectors, however, lower transfection efficiencies and difficulties with delivery remain major limitations hampering clinical translation. This study describes the development of a novel multi-domain cell-penetrating peptide, GET, designed to enhance cell interaction and intracellular translocation of nucleic acids; combined with a series of porous collagen-based scaffolds with proven regenerative potential for different indications. GET was capable of transfecting cell types from all three germ layers, including stem cells, with an efficiency comparable to Lipofectamine® 3000, without inducing cytotoxicity. When implanted in vivo, GET gene-activated scaffolds allowed for host cell infiltration, transfection localized to the implantation site and sustained, but transient, changes in gene expression – demonstrating both the efficacy and safety of the approach. Finally, GET carrying osteogenic (pBMP-2) and angiogenic (pVEGF) genes were incorporated into collagen-hydroxyapatite scaffolds and with a single 2μg dose of therapeutic pDNA, induced complete repair of critical-sized bone defects within 4 weeks. GET represents an exciting development in gene therapy and by combining it with a scaffold-based delivery system offers tissue engineering solutions for a myriad of regenerative indications

L&D professionals in organisations: much ambition, unfilled promise

This monograph reports a study investigating the roles of learning and development (L&D) professionals in Irish, UK European and US organisations. The study investigates the contextual factors influencing L&D roles in organisations, the strategic and operational roles that L&D professionals play in organisations, the competencies and career trajectories of L&D professionals, the perceptions of multiple internal stakeholders of the effectiveness of L&D and the relationships between context, L&D roles, competencies/expertise, and perceived effectiveness. We gathered data using multiple methods: survey (n=440), Delphi study (n=125) and semi-structured interviews (n=30). The analysis revealed that L&D professionals increasingly respond to a multiplicity of external and internal contextual influences and internal stakeholders perceived the effectiveness of L&D professionals differently with significant gaps in perceptions of what L&D contributes to organisational effectiveness. L&D professionals perform both strategic and operational roles in organisations and they progress through four career levels. Each L&D role and career level requires a distinct and unique set of foundational competencies and L&D expertise. Finally, we found that different contextual predictors were important in explaining the perceived effectiveness of L&D roles and the importance attached to different foundational competencies and areas of L&D expertise. We discuss the implications for theory, research and practice

Chitosan for gene delivery and orthopedic tissue engineering applications.

Gene therapy involves the introduction of foreign genetic material into cells in order exert a therapeutic effect. The application of gene therapy to the field of orthopaedic tissue engineering is extremely promising as the controlled release of therapeutic proteins such as bone morphogenetic proteins have been shown to stimulate bone repair. However, there are a number of drawbacks associated with viral and synthetic non-viral gene delivery approaches. One natural polymer which has generated interest as a gene delivery vector is chitosan. Chitosan is biodegradable, biocompatible and non-toxic. Much of the appeal of chitosan is due to the presence of primary amine groups in its repeating units which become protonated in acidic conditions. This property makes it a promising candidate for non-viral gene delivery. Chitosan-based vectors have been shown to transfect a number of cell types including human embryonic kidney cells (HEK293) and human cervical cancer cells (HeLa). Aside from its use in gene delivery, chitosan possesses a range of properties that show promise in tissue engineering applications; it is biodegradable, biocompatible, has anti-bacterial activity, and, its cationic nature allows for electrostatic interaction with glycosaminoglycans and other proteoglycans. It can be used to make nano- and microparticles, sponges, gels, membranes and porous scaffolds. Chitosan has also been shown to enhance mineral deposition during osteogenic differentiation of MSCs in vitro. The purpose of this review is to critically discuss the use of chitosan as a gene delivery vector with emphasis on its application in orthopedic tissue engineering

In-vivo generation of bone via endochondral ossification by in-vitro chondrogenic priming of adult human and rat mesenchymal stem cells

Background: Bone grafts are required to repair large bone defects after tumour resection or large tr