The scale-up of a tissue engineered porous hydroxyapatite polymer composite scaffold for use in bone repair: an ovine femoral condyle defect study

The development of an osteogenic bone graft substitute has important practical and cost implications in many branches of medicine where bone regeneration is required. Previous in vitro and small animal (murine) in vivo studies highlighted a porous hydroxyapatite/poly (dl‐lactic acid) composite scaffold in combination with skeletal stem cells (SSCs) as a potential bone graft substitute candidate. The aim of the current study was to scale up the bone cell‐scaffold construct to large animals and examine the potential for repair of a critical‐sized defect via an ovine model. SSC seeded scaffolds (and unseeded scaffold controls) were implanted bilaterally into ovine femoral condyle critical defects for 3 months. A parallel in vitro analysis of ovine SSC seeded scaffolds was also performed. Post mortem mechanical indentation testing showed the bone strengths of the defect sites were 20% (controls) and 11% (SSC seeded scaffolds) those of normal cancellous bone (p < 0.01). MicroCT analysis demonstrated new bone formation within all defects with a mean increase of 13.4% in the control scaffolds over the SSC seeded scaffolds (p = 0.14). Histological examination confirmed these findings, with enhanced quality new bone within the control defects. This study highlights important issues and steps to overcome in scale‐up and translation of tissue engineered products. The scaffold demonstrated encouraging results as an osteoconductive matrix; however, further work is required with cellular protocols before any human trials

Skeletal Regeneration: application of nanotopography and biomaterials for skeletal stem cell based bone repair

The application of selected skeletal progenitor cells and appropriate biomimetic microenvironments and nanotopographical surfaces offer the potential for innovative approaches to bone disease treatment and bone regeneration. Skeletal stem cells, commonly referred to as mesenchymal stem cells or human bone marrow stromal stem cells are multipotent progenitor cells with the ability to generate the stromal lineages of bone, cartilage, muscle, tendon, ligament and fat. This review will examine i) the application of innovative nanotopography surfaces that provide cues for human stem cell differentiation in the absence of chemical cues, ii) unique biomimetic microenvironments for skeletal tissue repair as well as iii) data from translational studies from the laboratory through to the clinic demonstrating the potential of skeletal cell based repair using impaction bone grafting as an exemplar. The development of protocols, tools and above all multidisciplinary approaches that integrate biomimetic materials, nanotopography, angiogenic, cell and clinical techniques for skeletal tissue regeneration for de novo tissue formation offers an opportunity to improve the quality of life of many

Skeletal tissue regeneration: current approaches, challenges, and novel reconstructive strategies for an aging population

Loss of skeletal tissue as a consequence of trauma, injury, or disease is a significant cause of morbidity with often wide-ranging socioeconomic impacts. Current approaches to replace or restore significant quantities of lost bone come with substantial limitations and inherent disadvantages that may in themselves cause further disability. In addition, the spontaneous repair capacity of articular cartilage is limited; thus, investigation into new cartilage replacement and regeneration techniques are warranted. Along with the challenges of an increasingly aging demographic, changing clinical scenarios and rising functional expectations provide the imperative for new, more reliable skeletal regeneration strategies. The science of tissue engineering has expanded dramatically in recent years, notably in orthopedic applications, and it is clear that new approaches for de novo skeletal tissue formation offer exciting opportunities to improve the quality of life for many, particularly in the face of increasing patient expectations. However, significant scientific, financial, industrial, and regulatory challenges should be overcome before the successful development of an emergent tissue engineering strategy can be realized. We outline current practice for replacement of lost skeletal tissue and the innovative approaches in tissue regeneration that have so far been translated to clinical use, along with a discussion of the significant hurdles that are presented in the process of translating research strategies to the clinic

A tissue engineering strategy for the treatment of avascular necrosis of the femoral head

BACKGROUND & PURPOSE: Skeletal stem cells (SSCs) and impaction bone grafting (IBG) can be combined to produce a mechanically stable living bone composite. This novel strategy has been translated to the treatment of avascular necrosis of the femoral head. Surgical technique, clinical follow-up and retrieval analysis data of this translational case series is presented.METHODS: SSCs and milled allograft were impacted into necrotic bone in five femoral heads of four patients. Cell viability was confirmed by parallel in vitro culture of the cell-graft constructs. Patient follow-up was by serial clinical and radiological examination. Tissue engineered bone was retrieved from two retrieved femoral heads and was analysed by histology, microcomputed tomography (?CT) and mechanical testing.RESULTS: Three patients remain asymptomatic at 22- to 44-month follow-up. One patient (both hips) required total hip replacement due to widespread residual necrosis. Retrieved tissue engineered bone demonstrated a mature trabecular micro-architecture histologically and on ?CT. Bone density and axial compression strength were comparable to trabecular bone.CONCLUSIONS: Clinical follow-up shows this to be an effective new treatment for focal early stage avascular necrosis of the femoral head. Unique retrieval analysis of clinically translated tissue engineered bone has demonstrated regeneration of tissue that is both structurally and functionally analogous to normal trabecular bone

Large animal in vivo evaluation of a binary blend polymer scaffold for skeletal tissue-engineering strategies: translational issues

Binary blend polymers offer the opportunity to combine different desirable properties into a single scaffold, to enhance function within the field of tissue engineering. Previous in vitro and murine in vivo analysis identified a polymer blend of poly(l‐lactic acid)–poly(ε‐caprolactone) (PLLA:PCL 20:80) to have characteristics desirable for bone regeneration. Polymer scaffolds in combination with marrow‐derived skeletal stem cells (SSCs) were implanted into mid‐shaft ovine 3.5 cm tibial defects, and indices of bone regeneration were compared to groups implanted with scaffolds alone and with empty defects after 12 weeks, including micro‐CT, mechanical testing and histological analysis. The critical nature of the defect was confirmed via all modalities. Both the scaffold and scaffold/SSC groups showed enhanced quantitative bone regeneration; however, this was only found to be significant in the scaffold/SSCs group (p = 0.04) and complete defect bridging was not achieved in any group. The mechanical strength was significantly less than that of contralateral control tibiae (p < 0.01) and would not be appropriate for full functional loading in a clinical setting. This study explored the hypothesis that cell therapy would enhance bone formation in a critical‐sized defect compared to scaffold alone, using an external fixation construct, to bridge the scale‐up gap between small animal studies and potential clinical translation. The model has proved a successful critical defect and analytical techniques have been found to be both valid and reproducible. Further work is required with both scaffold production techniques and cellular protocols in order to successfully scale‐up this stem cell/binary blend polymer scaffold

Effects of setting bone cement on tissue-engineered bone graft: a potential barrier to clinical translation?

Background: Strategies to improve mechanical strength, neovascularization, and the regenerative capacity of allograft include both the addition of skeletal stemcells and the investigation of novel biomaterials to reduce and ultimately obviate the need for allograft altogether. Use of bone cement is a common method of stabilizing implants in conjunction with impacted allograft. Curing cement, however, can reach temperatures in excess of 70°C, which is potentially harmful to skeletal stem cells. The aim of this study was to investigate the effects of setting bone cement on the survival of human adult skeletal stem cells within tissue-engineered allograft and a novel allograft substitute.Methods: Milled allograft and a polymer graft substitute were seeded with skeletal stemcells, impacted into a graduated chamber, and exposed to curing bone cement. Sections were removed at 5-mm increments from the allograft-cement interface. A quantitative WST-1 assay was performed on each section as a measure of remaining cell viability. A second stage of the experiment involved assessment of methods to potentially enhance cell survival, including pretreating the allograft or polymer by either cooling to 5°C or coating with 1% Laponite, or both.Results: There was a significant drop in cellular activity in the sections taken from within 0.5 cm of the cement interface in both the allograft and the polymer (p < 0.05), although there was still measurable cellular activity. Pretreatment methods did not significantly improve cell survival in any group.Conclusions: While the addition of bone cement reduced cellular viability of tissue-engineered constructs, this reduction occurred only in close proximity to the cement and measurable numbers of skeletal stem cells were observed, confirming the potential for cell population recovery.Clinical Relevance: These studies highlight a potential pitfall when translating tissue-engineering strategies, but indicate that the use of bone cement should not necessarily be ruled out during the application of cell populations andbiomaterials in tissue regeneration

Taking tissue engineering principles into theatre: retrieval analysis from a clinically translated case

This study has provided detailed ex vivo analysis of retrieved human tissue engineered bone and possible reasons for the observed construct failure are discussed in this article. The impacted bone displayed some evidence of remodeled trabecular structure, although the bone marrow aspirate that was initially combined with the allograft contained a relatively low concentration of osteoprogenitor cells. Cellular augmentation was insufficient to overcome the osteoclastic process associated with renewed cyst formation. Concentration or culture expansion of osteoprogenitor cells from aspirated bone marrow is recommended for biological augmentation of bone graft