Kris Partridge

Induction of human osteoprogenitor chemotaxis, proliferation, differentiation, and bone formation by osteoblast stimulating factor-1/pleiotrophin: osteoconductive biomimetic scaffolds for tissue engineering.

The process of bone growth, regeneration, and remodeling is mediated, in part, by the immediate cell‐matrix environment. Osteoblast stimulating factor‐1 (OSF‐1), more commonly known as pleiotrophin (PTN), is an extracellular matrix‐associated protein, present in matrices, which act as targets for the deposition of new bone. However, the actions of PTN on human bone progenitor cells remain unknown. We examined the effects of PTN on primary human bone marrow stromal cells chemotaxis, differentiation, and colony formation (colony forming unit‐fibroblastic) in vitro, and in particular, growth and differentiation on three‐dimensional biodegradable porous scaffolds adsorbed with PTN in vivo. Primary human bone marrow cells were cultured on tissue culture plastic or poly(DL‐lactic acid‐co‐glycolic acid) (PLGA; 75:25) porous scaffolds with or without addition of recombinant human PTN (1 pg‐50 ng/ml) in basal and osteogenic conditions. Negligible cellular growth was observed on PLGA scaffold alone, generated using a super‐critical fluid mixing method. PTN (50 μg/ml) was chemotactic to human osteoprogenitors and stimulated total colony formation, alkaline phosphatase‐positive colony formation, and alkaline phosphatase‐specific activity at concentrations as low as 10 pg/ml compared with control cultures. The effects were time‐dependent. On three‐dimensional scaffolds adsorbed with PTN, alkaline phosphatase activity, type I collagen formation, and synthesis of cbfa‐1, osteocalcin, and PTN were observed by immunocytochemistry and PTN expression by in situ hybridization. PTN‐adsorbed constructs showed morphologic evidence of new bone matrix and cartilage formation after subcutaneous implantation as well as within diffusion chambers implanted into athymic mice. In summary, PTN has the ability to promote adhesion, migration, expansion, and differentiation of human osteoprogenitor cells, and these results indicate the potential to develop protocols for de novo bone formation for skeletal repair that exploit cell‐matrix interactions.

Gene Delivery in Bone Tissue Engineering: Progress and Prospects Using Viral and Nonviral Strategies

Bone tissue loss as a consequence of the natural aging process or as a result of trauma and degenerative disease has led to the need for procedures to generate cartilage and bone for a variety of orthopedic applications. The ability to transfer genes into multipotential mesenchymal stem cells, while still in its infancy, offers considerable therapeutic hope in a variety of musculoskeletal disorders. However, the choice of gene delivery method is key. This review examines the various techniques and methods currently available to enable gene transfer into a target population from viral methods (transduction) to nonviral (transfection) methods and the limitations associated with each method. The potential applications and current understanding of each method are presented. Given the demographic challenge of an aging population, the ultimate goal remains the development of simple, safe, and reproducible strategies for gene delivery that will address the pressing orthopedic clinical imperatives of many.

Immunoselection and adenoviral genetic modulation of human osteoprogenitors: in vivo bone formation on PLA scaffold.

The aim of this study was to examine the potential of immunoselected genetically modified human osteoprogenitors to form bone in vivo on porous PLA scaffolds. Human osteoprogenitors from bone marrow were selected using the antibody STRO-1 utilising a magnetically activated cell separation system. The STRO-1(+) fraction isolated 7% of nucleated marrow cells and increased fibroblastic colony formation by 300% and alkaline phosphatase activity by 190% over unselected marrow cell cultures. To engineer bone tissue, STRO-1(+) culture-expanded cells were transduced with AxCAOBMP-2, an adenovirus carrying the human BMP-2 gene, injected into diffusion chambers containing porous PLA scaffolds, and implanted in vivo. After 11 weeks the presence of bone mineral was observed by X-ray analysis and confirmed for mineral by von Kossa, as well as bone matrix composition by Sirius red staining, birefringence, and type I collagen immunohistochemistry. Bone formation in vivo indicates the potential of using immunoselected progenitor cells and ex vivo gene transfer with biodegradable scaffolds, for the development of protocols for the treatment of a wide variety of musculo-skeletal disorders.

Gene therapy used for tissue engineering applications

This review highlights the advances at the interface between tissue engineering and gene therapy. There are a large number of reports on gene therapy in tissue engineering, and these cover a huge range of different engineered tissues, different vectors, scaffolds and methodology. The review considers separately in‐vitro and in‐vivo gene transfer methods. The in‐vivo gene transfer method is described first, using either viral or non‐viral vectors to repair various tissues with and without the use of scaffolds. The use of a scaffold can overcome some of the challenges associated with delivery by direct injection. The ex‐vivo method is described in the second half of the review. Attempts have been made to use this therapy for bone, cartilage, wound, urothelial, nerve tissue regeneration and for treating diabetes using viral or non‐viral vectors. Again porous polymers can be used as scaffolds for cell transplantation. There are as yet few comparisons between these many different variables to show which is the best for any particular application. With few exceptions, all of the results were positive in showing some gene expression and some consequent effect on tissue growth and remodelling. Some of the principal advantages and disadvantages of various methods are discussed.

Biological and mechanical enhancement of impacted allograft seeded with human bone marrow stromal cells: potential clinical role in impaction bone grafting

With the demographics of an aging population the incidence of revision surgery is rapidly increasing. Clinical imperatives to augment skeletal tissue loss have brought mesenchymal stem cells to the fore in combination with the emerging discipline of tissue engineering. Impaction bone grafting for revision hip surgery is a recognized technique to reconstitute bone, the success of which relies on a combination of mechanical and biological factors. The use of morsellized allograft is currently the accepted clinical standard providing a good mechanical scaffold with little osteoinductive biological potential. We propose that applying the principles of a tissue engineering paradigm, the combination of human bone marrow stromal cells (hBMSCs) with allograft to produce a living composite, offers a biological and mechanical advantage over the current gold standard of allograft alone. This study demonstrates that hBMSCs combined with allograft can withstand the forces equivalent to a standard femoral impaction and continue to differentiate and proliferate along the bony lineage. In addition, the living composite provides a biomechanical advantage, with increased interparticulate cohesion and shear strength when compared with allograft alone.

Taking tissue-engineering principles into theater: augmentation of impacted allograft with human bone marrow stromal cells

Human bone marrow contains bone progenitor cells that arise from multipotent mesenchymal stem cells. Seeding bone progenitor cells onto a scaffold can produce a 3D living composite with significant mechanical and biological potential. This article details laboratory and clinical findings from two clinical cases, where different proximal femoral conditions were treated using impacted allograft augmented with marrow-derived autogenous progenitor cells. Autologous bone marrow was seeded onto highly washed morselized allograft and impacted. Samples of the impacted graft were also taken for ex vivo analysis. Both patients made an uncomplicated clinical recovery. Imaging confirmed defect filling with encouraging initial graft incorporation. Histochemical and alkaline phosphatase staining demonstrated that a live composite graft with osteogenic activity had been introduced into the defects. These studies demonstrate that marrow-derived cells can adhere to highly washed morselized allograft, survive the impaction process and proliferate with an osteoblastic phenotype, thus creating a living composite.