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Bhakta G, Ekaputra AK, Rai B, Abbah SA, Tan TC, Le BQ, Chatterjea A, Hu T, Lin T, Arafat MT, van Wijnen AJ, Goh J, Nurcombe V, Bhakoo K, Birch W, Xu L, Gibson I, Wong HK, Cool SM. Fabrication of polycaprolactone-silanated β-tricalcium phosphate-heparan sulfate scaffolds for spinal fusion applications. Spine J 2018; 18:818-830. [PMID: 29269312 DOI: 10.1016/j.spinee.2017.12.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2017] [Revised: 11/08/2017] [Accepted: 12/11/2017] [Indexed: 02/03/2023]
Abstract
BACKGROUND CONTEXT Interbody spinal fusion relies on the use of external fixation and the placement of a fusion cage filled with graft materials (scaffolds) without regard for their mechanical performance. Stability at the fusion site is instead reliant on fixation hardware combined with a selected cage. Ideally, scaffolds placed into the cage should both support the formation of new bone and contribute to the mechanical stability at the fusion site. PURPOSE We recently developed a scaffold consisting of silane-modified PCL-TCP (PCL-siTCP) with mechanical properties that can withstand the higher loads generated in the spine. To ensure the scaffold more closely mimicked the bone matrix, we incorporated collagen (Col) and a heparan sulfate glycosaminoglycan sugar (HS3) with increased affinity for heparin-binding proteins such as bone morphogenetic protein-2 (BMP-2). The osteostimulatory characteristic of this novel device delivering exogenous BMP2 was assessed in vitro and in vivo as a prelude to future spinal fusion studies with this device. STUDY DESIGN/SETTING A combination of cell-free assays (BMP2 release), progenitor cell-based assays (BMP2 bioactivity, cell proliferation and differentiation), and rodent ectopic bone formation assays was used to assess the osteostimulatory characteristics of the PCL-siTCP-based scaffolds. MATERIALS AND METHODS Freshly prepared rat mesenchymal stem cells were used to determine reparative cell proliferation and differentiation on the PCL-siTCP-based scaffolds over a 28-day period in vitro. The bioactivity of BMP2 released from the scaffolds was assessed on progenitor cells over a 28-day period using ALP activity assays and release kinetics as determined by enzyme-linked immunosorbent assay. For ectopic bone formation, intramuscular placement of scaffolds into Sprague Dawley rats (female, 4 weeks old, 120-150 g) was achieved in five animals, each receiving four treatments randomized for location along the limb. The four groups tested were (1) PCL-siTCP/Col (5-mm diameter×1-mm thickness), PCL-siTCP/Col/BMP2 (5 µg), (3) PCL-siTCP/Col/HS3 (25 µg), and (4) PCL-siTCP/Col/HS3/BMP2 (25 and 5 µg, respectively). Bone formation was evaluated at 8 weeks post implantation by microcomputed tomography (µCT) and histology. RESULTS Progenitor cell-based assays (proliferation, mRNA transcripts, and ALP activity) confirmed that BMP2 released from PCL-siTCP/Col/HS3 scaffolds increased ALP expression and mRNA levels of the osteogenic biomarkers Runx2, Col1a2, ALP, and bone gla protein-osteocalcin compared with devices without HS3. When the PCL-siTCP/Col/HS3/BMP2 scaffolds were implanted into rat hamstring muscle, increased bone formation (as determined by two-dimensional and three-dimensional µCTs and histologic analyses) was observed compared with scaffolds lacking BMP2. More consistent increases in the amount of ectopic bone were observed for the PCL-siTCP/Col/HS3/BMP2 implants compared with PCL-siTCP/Col/BMP2. Also, increased mineralizing tissue within the pores of the scaffold was seen with modified-tetrachrome histology, a result confirmed by µCT, and a modest but detectable increase in both the number and the thickness of ectopic bone structures were observed with the PCL-siTCP/Col/HS3/BMP2 implants. CONCLUSIONS The combination of PCL-siTCP/Col/HS3/BMP2 thus represents a promising avenue for further development as a bone graft alternative for spinal fusion surgery.
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Affiliation(s)
- Gajadhar Bhakta
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore
| | - Andrew K Ekaputra
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore
| | - Bina Rai
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore
| | - Sunny A Abbah
- Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, NUHS Tower Block, Level 11, 1E Kent Ridge Rd, Singapore 119288, Singapore
| | - Tuan Chun Tan
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore
| | - Bach Quang Le
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore
| | - Anindita Chatterjea
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore
| | - Tao Hu
- Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, NUHS Tower Block, Level 11, 1E Kent Ridge Rd, Singapore 119288, Singapore
| | - Tingxuan Lin
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore
| | - M Tarik Arafat
- Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1 Block EA, 07-08, Singapore 117576, Singapore
| | - Andre J van Wijnen
- Department of Orthopedic Surgery, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA
| | - James Goh
- Department of Biomedical Engineering, National University of Singapore, 4 Engineering Drive 3, E4 #04-08, Singapore 117583, Singapore
| | - Victor Nurcombe
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore
| | - Kishore Bhakoo
- Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, NUHS Tower Block, Level 11, 1E Kent Ridge Rd, Singapore 119288, Singapore; Singapore Bioimaging Consortium, 11 Biopolis Way, #01-02 Helios, Singapore 138667, Singapore
| | - William Birch
- Institute of Materials Research & Engineering, #08-03, 2 Fusionopolis Way, Innovis, 138634, Singapore
| | - Li Xu
- Institute of Materials Research & Engineering, #08-03, 2 Fusionopolis Way, Innovis, 138634, Singapore
| | - Ian Gibson
- Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1 Block EA, 07-08, Singapore 117576, Singapore
| | - Hee-Kit Wong
- Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, NUHS Tower Block, Level 11, 1E Kent Ridge Rd, Singapore 119288, Singapore
| | - Simon M Cool
- Institute of Medical Biology, A*STAR, 8A Biomedical Grove, #06-06 Immunos, Singapore 138648, Singapore; Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, NUHS Tower Block, Level 11, 1E Kent Ridge Rd, Singapore 119288, Singapore.
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Manton KJ, Sadasivam M, Cool SM, Nurcombe V. Bone-specific heparan sulfates induce osteoblast growth arrest and downregulation of retinoblastoma protein. J Cell Physiol 2006; 209:219-29. [PMID: 16826571 DOI: 10.1002/jcp.20727] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The heparan sulfate (HSs) sugars of the extracellular matrix (ECM) play a key role during both development and wound repair in regulating the flow of growth and adhesive factors across their cell surface receptors. The aim of this study was to assess the structural and functional differences of HS chains extracted from the conditioned media (soluble), cell surface, and ECM of primary human osteoblast cultures, and to analyze their effects on osteoblast cell growth. HS chains from these compartments were characterized through a combination of enzymatic degradation, anion exchange chromatography, and molecular sieving. Although the chains were all approximately the same size, they varied systematically in their sulfate content, suggesting differences in their protein-binding domains. When added to pre-confluent hFOB1.19 osteoblast cultures, HS doses exceeding 500 ng/ml inhibited proliferation, without affecting viability, irrespective of their origin. Furthermore, HS doses of 500 ng/ml also downregulated retinoblastoma, Cyclin A and CDK1 protein expression, indicating that high doses of osteoblast HS negatively regulate cell cycle, resulting in growth arrest; when high doses of HS were withdrawn after a prolonged period, linear cell growth was reestablished. Thus, despite differences in sulfation, HS from either the soluble, cell surface, or matrix compartments of primary human osteoblast cultures are functionally similar with respect to their effects on growth. Binding assays revealed that the HS chains bound TGFbeta1, a known inhibitor of osteoprogenitor growth, at higher affinity than a suite of other bone-related, heparin-binding growth factors. Overcoming such sugar-mediated inhibition may prove important for wound repair.
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Affiliation(s)
- Kerry J Manton
- Institute of Molecular and Cell Biology, Proteos, Singapore
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