Abstract
For spinal fusions and the treatment of non-union fractures, biological substrates, scaffolds, or carriers often are applied as a graft to support regeneration of bone. The selection of an appropriate material critically influences cellular function and, ultimately, patient outcomes. Human bone marrow mesenchymal stem cells (BMSCs) are regarded as a critical component of bone healing. However, the interactions of BMSCs and commercial bone matrices are poorly reported. BMSCs were cultured with several commercially available bone substrates (allograft, demineralized bone matrix (DBM), collagen, and various forms of calcium phosphates) for 48 h to understand their response to graft materials during surgical preparation and the first days following implantation (cell retention, gene expression, pH). At 30 and 60 min, bone chips and inorganic substrates supported significantly more cell retention than other materials, while collagen-containing materials became soluble and lost their structure. At 48 h, cells bound to β-tricalcium phosphate-hydroxyapatite (βTCP-HA) and porous hydroxyapatite (HA) granules exhibited osteogenic gene expression statistically similar to bone chips. Through 24 h, the DBM strip and βTCP-collagen became mildly acidic (pH 7.1–7.3), while the DBM poloxamer-putties demonstrated acidity (pH < 5) and the bioglass-containing carrier became basic (pH > 10). The dissolution of DBM and collagen led to a loss of cells, while excessive pH changes potentially diminish cell viability and metabolism. Extracts from DBM-poloxamers induced osteogenic gene expression at 48 h. This study highlights the role that biochemical and structural properties of biomaterials play in cellular function, potentially enhancing or diminishing the efficacy of the overall therapy.
Highlights
The practice of medicine in orthopedic surgery has included bone regeneration since the earliest bone grafts and bone marrow transfers nearly a century ago [1,2,3,4,5,6]
Of the numerous cell sources that have been tested for bone tissue engineering, mesenchymal stem or stromal cells (MSCs) have received the most attention
2 mL of iliac crest bone marrow was processed by discontinuous density-gradient centrifugation and 20 million cells of the mononuclear fraction were cultured in complete culture media (CCM) consisting of alpha-minimal essential media (Invitrogen, Carlsbad, CA, USA) containing standard concentrations of penicillin and streptomycin (Invitrogen) and 20% (v/v) fetal bovine serum (FBS, Atlanta Biologicals, Norcross, GA, USA)
Summary
The practice of medicine in orthopedic surgery has included bone regeneration since the earliest bone grafts and bone marrow transfers nearly a century ago [1,2,3,4,5,6]. The disciplines of tissue engineering and regenerative medicine have permitted systematic evaluation of combinations of scaffolds or graft materials with stem and progenitor cells The overall consensus of these studies is that regardless of the cell source employed, it is the cells that are directly responsible for tissue formation, not the scaffold, drug, or surgical instrumentation. Scientists and clinicians have attempted to supplement or replace cells by administration of potent growth factors, including bone morphogenetic proteins (e.g., BMP-2, BMP-7) [11,12]. Of the numerous cell sources that have been tested for bone tissue engineering, mesenchymal stem or stromal cells (MSCs) have received the most attention. Of the countless studies performed exploring the potential for MSCs for the repair bone tissue, some have demonstrated that they have remarkable efficacy in the absence of a scaffold [34,35,36,37,38,39] but the general consensus is that a scaffold may be required for confinement of MSCs at the site of injury during initial stages of healing [1,7,10,26,37,38,40,41,42]
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