Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. The need for a novel, cost effective treatment option for osteochondral defects has therefore never been greater.

As an emerging technology, three-dimensional (3D) bioprinting has the capacity to deposit cells, extracellular matrices and other biological materials in user-defined patterns to build complex tissue constructs from the “bottom up”. Through use of extrusion bioprinting and fused deposition modelling (FDM) 3D printing, porous 3D scaffolds were successfully created in this study from hydrogels and synthetic polymers. Mesenchymal stem cells (MSCs) seeded onto polycaprolactone scaffolds with defined pore sizes and porosity maintained viability over a 7-day period, with addition of alginate hydrogel and scaffold surface treatment with NaOH increasing cell adhesion and viability. MSC-laden alginate constructs produced via extrusion bioprinting also maintained structural integrity and cell viability over 7 days in vitro culture. Growth within osteogenic media resulted in successful osteogenic differentiation of MSCs within scaffolds compared to controls (p<0.001). MSC spheroids were also successfully created and bioprinted within a novel, supramolecular hydrogel with tunable stiffness.

In conclusion, 3D constructs capable of supporting osteogenic differentiation of MSCs were biofabricated via FDM and extrusion bioprinting. Future work will look to increase osteochondral construct size and complexity, whilst maintaining cell viability.

Adipose tissue is an attractive source of mesenchymal stem cells (MSCs) as it is largely dispensable and readily accessible through minimally invasive procedures such as lipoaspiration. Until recently MSCs could only be isolated in a process involving ex-vivo culture. Pericytes (CD45−, CD146+, and CD34−) and adventitial cells (CD45−, CD146−, CD34+) represent two populations of MSCs (collectively termed perivascular stem cells or PSCs) that can be prospectively purified using fluorescence activated cell sorting (FACS). We performed FACS on lipoaspirate samples from n=129 donors to determine the frequency and yield of PSCs and to establish patient and processing factors that influence yield.

The mean number of stromal vascular fraction (SVF) cells from 100ml of lipoaspirate was 37.8×106. Within the SVF, mean cell viability was 82%, with 31.6% of cells being heamatopoietic (CD45+). Adventitial cells and pericytes represented 31.6% and 7.9% of SVF cells respectively. As such, 200ml of lipoaspirate would theoretically yield 24.5 million MSCs –a sufficient number to enable point-of-care delivery for use in several orthopaedic applications. The yield and prevalence of PSCs were minimally affected by donor age, sex and BMI. Storing lipoaspirate samples for up to 72 hours prior to processing had no significant deleterious effects on MSC yield or viability.

Our study confirms that pure populations of MSC-precursors (PSCs) can be prospectively isolated from adipose tissue, in sufficient quantities to negate the necessity for culture expansion while widening possible applications to include trauma, where a time delay between extraction and implantation excludes their use.

A 16-year-old boy was involved in an agricultural accident in which he sustained a large wound to the right arm and forearm. Radiological examination showed loss of the distal half of the humerus. A posterior splint was applied and after two months there was regeneration of the distal humerus including the articular portion. He was able to use his arm at five months. Twenty years later, he had a painless elbow and a 70° range of movement.

Introduction

iPSCs represent a promising cell source for bone regeneration. To generate osteoprogenitor cells, most protocols use the generation of embryoid bodies (EBs). However, these protocols give rise to heterogeneous population of different cell lineage.

Background. Skeletal stem cells (SSCs) have been used for the treatment of osteonecrosis of the femoral head to prevent subsequent collapse. In isolation SSCs do not provide structural support but an innovative case series in Southampton, UK, has used SSCs in combination with impaction bone grafting (IBG) to improve both the biological and mechanical environment and to regenerate new bone at the necrotic site. Aims. Analysis of retrieved tissue-engineered bone as part of ongoing follow-up of this translational case series. Methods. With Proof-of-Concept established in vitro and in vivo, the use of a living bone composite of SSCs and allograft has been translated to four patients (five hips) for treatment of osteonecrosis of their femoral heads. Parallel in vitro culture of the implanted cell-graft construct was performed. Patient follow-up was by serial clinical and radiological examination. In one patient collapse occurred in both hips due to more advanced disease than was originally appreciated. This necessitated bilateral hip arthroplasty, but allowed retrieval of the femoral heads. These were analyzed for Type 1 Collagen production, bone morphology, bone density and mechanical strength by micro computed tomography (CT), histology (A/S stain, Collagen Type 1 immunostain, biorefringence) and mechanical testing. Representative sections of cortical, trabecular and tissue engineered bone were excised from the femoral heads using a diamond-tipped saw-blade and tested to failure by axial compression. Results. Parallel in vitro analysis demonstrated sustained cell growth and viability on the allograft. Three patients currently remain asymptomatic at up to three year follow-up. Histological analysis of the two retrieved femoral heads demonstrated, critically, Type 1 collagen production in the regenerated tissue as well as mature trabecular architecture, indicative of de novo tissue engineered bone. The trabecular morphology of regenerated bone was evident on CT, and this had a bone density of 1400 Grey scale units, (compared to 1200 for natural trabecular bone and 1800 for cortical bone). On axial compressive testing the regenerated bone on the left showed a 24.8% increase in compressive strength compared to ipsilateral normal trabecular bone, and a 22.9% increase on the left. Conclusions. Retrieval analysis data has demonstrated the translational potential of a living bone composite, while ongoing clinical follow-up shows this to be an effective new treatment for osteonecrosis of the femoral head. Regeneration of the necrotic bone may prevent subsequent collapse, thereby delaying, or possibly avoiding, the need for hip arthroplasty in early stage osteonecrosis. Evaluation of this tissue engineering construct has confirmed the potential for clinical treatment of bone defects using SSC based strategies

We reviewed 59 bone graft substitutes marketed by 17 companies currently available for implantation in the United Kingdom, with the aim of assessing the peer-reviewed literature to facilitate informed decision-making regarding their use in clinical practice. After critical analysis of the literature, only 22 products (37%) had any clinical data. Norian SRS (Synthes), Vitoss (Orthovita), Cortoss (Orthovita) and Alpha-BSM (Etex) had Level I evidence. We question the need for so many different products, especially with limited published clinical evidence for their efficacy, and conclude that there is a considerable need for further prospective randomised trials to facilitate informed decision-making with regard to the use of current and future bone graft substitutes in clinical practice.

Cite this article: Bone Joint J 2013;95-B:583–97.