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  • 1.
    Atif, Abdul Raouf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Carter, Sarah-Sophia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Pujari-Palmer, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Tenje, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Mestres, Gemma
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Bone Cement Embedded in a Microfluidic Device2018Conference paper (Refereed)
    Abstract [en]

    Calcium phosphate cements (CPCs) have a great potential in the treatment of bone disorders due to their excellent biocompatibility. Although CPCs are promising when implanted in vivo, there is poor correlation between in vitro and in vivo studies. This could be because most conventional in vitro systems lack a 3D architecture, or dynamic conditions (i.e. a continuous refreshment stream). The aim of this work is to embed CPCs into a microfluidic system and evaluate ion and protein exchange at different flow rates.

  • 2.
    Atif, Abdul Raouf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Pujari-Palmer, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Tenje, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Mestres, Gemma
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Evaluation of Ionic Interactions of Bone Cement-on-Chip2019Conference paper (Other academic)
    Abstract [en]

    INTRODUCTION: Biomaterials are synthetic materials that can be incorporated into the body to replace an impaired physiological function. Apatite calcium phosphate cements (CPCs), used for bone regeneration, give calcium-deficient hydroxyapatite (CDHA) as an end-product after a dissolution-precipitation reaction during fabrication. CDHA has a tendency to uptake calcium and release phosphate into cell culture medium. Potentially, this leads to depletion of calcium ions in solution, which can be detrimental to cell survival. The aim of this work is to embed CDHA in a microfluidic system and evaluate ion exchange at different flow rates.

    METHODS: CPC paste was cast into a 0.8mm pocket within a Polydimethylsiloxane (PDMS, cured at 60°C for 2h) mould. CPCs were set in 0.9% w/v NaCl at 37°C for 10 days resulting in CDHA. The PDMS containing the CDHA was then bonded to glass, leaving a 0.5mm channel gap. Minimum Essential Media (MEM, 1ml) was pumped through the channel at low (2µl/min), medium (8µl/min) and high (14µl/min) flow rates. A CDHA disc (ø=15mm, h=2mm) was immersed in MEM (1ml) at static conditions (0µl/min) for 24h. Stock Media was taken as control. Calcium and phosphorus concentrations were analysed using Inductively Coupled Plasma Optical Emission Spectroscopy.

    RESULTS & CONCLUSIONS: CDHA was successfully embedded in a microfluidic chip (Fig. 1A). Observed [Ca] and [P] levels were closer to levels in stock MEM at higher flow rates (Fig. 1B). We anticipate that osteoblast viability will improve when grown under flow, as opposed to static conditions, due to continuous replenishment of cell medium.

  • 3.
    Procter, Philip
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Pujari-Palmer, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University.
    Hulsart Billström, Gry
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Insley, Gerard
    Larsson, Sune
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Orthopaedics.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    A new ex-vivo murine model for evaluation of adhesiveness of a novel biomimetic bone glue2018Conference paper (Refereed)
  • 4.
    Procter, Philip
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Pujari-Palmer, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University.
    Hulsart Billström, Gry
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Larsson, Sune
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Orthopaedics.
    Insley, Gerard
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Designing A Commercial Biomaterial For A Specific Unmet Clinical Need –: An Adhesive Odyssey2018Conference paper (Refereed)
    Abstract [en]

    There are clinical situations in fracture repair, e.g. osteochondral fragments, where current implant hardware is insufficient. The proposition of an adhesive enabling fixation and healing has been considered but no successful candidate has emerged thus far. The many preclinical and few clinical attempts include fibrin glue, mussel adhesive and even “Kryptonite” (US bone void filler). The most promising recent attempts are based on phosphorylating amino acids, part of a common cellular adhesion mechanism linking mussels, caddis fly larvae, and mammals. Rapid high bond strength development in the wetted fatty environment of fractured bone, that is sustained during biological healing, is challenging to prove both safety and efficacy. Additionally, there are no “predicate” preclinical animal and human models which led the authors to develop novel evaluations for an adhesive candidate “OsStictm” based on calcium salts and amino acids. Adhesive formulations were evaluated in both soft (6/12 weeks) and hard tissue (3,7,10,14 & 42 days) safety studies in murine models. The feasibility of a novel adhesiveness test, initially proven in murine cadaver femoral bone, is being assessed in-vivo (3,7,10,14 & 42 days) in bilateral implantations with a standard tissue glue as the control. In parallel an ex-vivo human bone model using freshly harvested human donor bone is under development to underwrite the eventual clinical application of such an adhesive. This is part of a risk mitigation project bridging between laboratory biomaterial characterisation and a commercial biomaterial development where safety and effectiveness have to meet today´s new medical device requirements.

  • 5.
    Procter, Philip
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Pujari-Palmer, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Hulsart-Billstrom, Gry
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Wenner, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Insley, Gerard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Larsson, Sune
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Orthopaedics.
    Engqvsit, Hakan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    A biomechanical test model for evaluating osseous and osteochondral tissue adhesives.In: BMC Biomedical engineering, ISSN 2524-4426Article in journal (Refereed)
  • 6.
    Pujari-Palmer, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. Uppsala University.
    The biological and physical performance of high strength dicalcium phosphate cement in physiologically relevant models2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The chemical properties of calcium phosphate cements (CPCs) are very similar to the mineral phase of bone. CPCs are, consequently, very effective substrates (scaffolds) for tissue engineering; bone and stem cells attach readily, and can proliferate and differentiate to form new bone tissue. Unlike other CPCs that may remain largely unchanged in the body for years, such as hydroxyapatite, dicalcium phosphates are remodelled by the body and rapidly converted to new bone. Unfortunately, the dicalcium phosphates are also typically too weak to support load bearing in the human body. Our laboratory has recently developed a novel, high strength brushite CPC, (hsCPC), which can reach 10-50 fold higher failure strength than many commercially available CPCs. The aim of this thesis was to investigate the physical, chemical and biological performance of hsCPCs in physiologically relevant model of drug release, load bearing, osteoconductivity, and as a scaffold for bone tissue engineering.

    Multiple CPCs were compared in a model of screw augmentation to determine whether the physical properties of the cement, such as bulk strength and porosity, affected orthopedic screw holding strength. In an in vitro model of bone regeneration stem cells were grown on macroporous scaffolds that were fabricated from hsCPC. Drug releasing scaffolds were fabricated to examine whether the low porosity of hsCPC impeded drug release during a 4 week incubation period. The biological activity of an incorporated drug, Rebamipide, was examined after acute and chronic incubation periods. In the drug release study it was noted that the biological response to hsCPC was significantly better than tissue culture grade polystyrene, even in groups without drug. The mechanism underlying this biological response was further investigated by testing the effect of pyrophosphate, a common cement additive, on bone cell proliferation and differentiation. This thesis concludes that a high strength cement can produce significant improvement in screw augmentation strength, if there is sufficient cortical bone near the augmentation site. The hsCPC is also cytocompatible, and can support bone and stem cell proliferation and differentiation. hsCPC scaffolds stimulated osteogenic gene expression comparable to native bone scaffolds. hsCPC scaffolds are also capable of delivering drug for up to 4 weeks, in vitro. Finally, a cement additive, pyrophosphate, stimulated differentiation, but not proliferation of bone cells.

    List of papers
    1. Rebamipide Delivered by Brushite Cement Enhances Osteoblast and Macrophage Proliferation
    Open this publication in new window or tab >>Rebamipide Delivered by Brushite Cement Enhances Osteoblast and Macrophage Proliferation
    2015 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 5Article in journal (Refereed) Published
    Abstract [en]

    Many of the bioactive agents capable of stimulating osseous regeneration, such as bone morphogenetic protein-2 (BMP-2) or prostaglandin E2 (PGE2), are limited by rapid degradation, a short bioactive half-life at the target site in vivo, or are prohibitively expensive to obtain in large quantities. Rebamipide, an amino acid modified hydroxylquinoline, can alter the expression of key mediators of bone anabolism, cyclo-oxygenase 2 (COX-2), BMP-2 and vascular endothelial growth factor (VEGF), in diverse cell types such as mucosal and endothelial cells or chondrocytes. The present study investigates whether Rebamipide enhances proliferation and differentiation of osteoblasts when delivered from brushite cement. The reactive oxygen species (ROS) quenching ability of Rebampide was tested in macrophages as a measure of bioactivity following drug release incubation times, up to 14 days. Rebamipide release from brushite occurrs via non-fickian diffusion, with a rapid linear release of 9.70%+/- 0.37% of drug per day for the first 5 days, and an average of 0.5%-1% per day thereafter for 30 days. Rebamipide slows the initial and final cement setting time by up to 3 and 1 minute, respectively, but does not significantly reduce the mechanical strength below 4% (weight percentage). Pre-osteoblast proliferation increases by 24% upon exposure to 0.4uM Rebamipide, and by up to 73% when Rebamipide is delivered via brushite cement. Low doses of Rebamipide do not adversely affect peak alkaline phosphatase activity in differentiating pre-osteoblasts. Rebamipide weakly stimulates proliferation in macrophages at low concentrations (118 +/- 7.4% at 1uM), and quenches ROS by 40-60%. This is the first investigation of Rebamipide in osteoblasts.

    National Category
    Other Engineering and Technologies
    Identifiers
    urn:nbn:se:uu:diva-257022 (URN)10.1371/journal.pone.0128324 (DOI)000355319400083 ()26023912 (PubMedID)
    Available from: 2015-06-29 Created: 2015-06-29 Last updated: 2018-02-08Bibliographically approved
    2. Fabrication of rnacroporous cement scaffolds using PEG particles: In vitro evaluation with induced pluripotent stem cell-derived mesenchymal progenitors
    Open this publication in new window or tab >>Fabrication of rnacroporous cement scaffolds using PEG particles: In vitro evaluation with induced pluripotent stem cell-derived mesenchymal progenitors
    Show others...
    2016 (English)In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 69, p. 640-652Article in journal (Refereed) Published
    Abstract [en]

    Calcium phosphate cements (CPCs) have been extensively used in reconstructive dentistry and orthopedics, but it is only recently that CPCs have been combined with stem cells to engineer biological substitutes with enhanced healing potential. In the present study, macroporous CPC scaffolds with defined composition were fabricated using an easily reproduced synthesis method, with minimal fabrication and processing steps. Scaffold pore size and porosity, essential for cell infiltration and tissue ingrowth, were tuned by varying the content and size of polyethylene glycol (PEG) particles, resulting in 9 groups with different architectural features. The scaffolds were characterized for chemical composition, porosity and mechanical properties, then tested in vitro with human mesenchymal progenitors derived from induced pluripotent stem cells (iPSC-MPs). Biomimetic decellularized bone scaffolds were used as reference material in this study. Our manufacturing process resulted in the formation of macroporous monetite scaffolds with no residual traces of PEG. The size and content of PEG particles was found to affect scaffold porosity, and thus mechanical properties. Irrespective of pore size and porosity, the CPC scaffolds fabricated in this study supported adhesion and viability of human iPSC-MPs similarly to decellularized bone scaffolds. However, the architectural features of the scaffolds were found to affect the expression of bone specific genes, suggesting that specific scaffold groups could be more suitable to direct human iPSC-MPs in vitro toward an osteoblastic phenotype. Our simplistic fabrication method allows rapid, inexpensive and reproducible construction of macroporous CPC scaffolds with tunable architecture for potential use in dental and orthopedic applications.

    Keywords
    Bioinaterial scaffold, Calcium phosphate cement, Macroporosity, Mesenchymal progenitors, Induced pluripotent stem cells, Tissue engineering
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:uu:diva-306232 (URN)10.1016/j.msec.2016.06.075 (DOI)000383930900076 ()27612757 (PubMedID)
    Funder
    EU, FP7, Seventh Framework Programme, 262948
    Available from: 2016-10-27 Created: 2016-10-26 Last updated: 2018-02-08Bibliographically approved
    3. Pyrophosphate Stimulates Differentiation, Matrix Gene Expression and Alkaline Phosphatase Activity in Osteoblasts
    Open this publication in new window or tab >>Pyrophosphate Stimulates Differentiation, Matrix Gene Expression and Alkaline Phosphatase Activity in Osteoblasts
    Show others...
    2016 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 10, article id e0163530Article in journal (Refereed) Published
    Abstract [en]

    Pyrophosphate is a potent mitogen, capable of stimulating proliferation in multiple cell types, and a critical participant in bone mineralization. Pyrophosphate can also affect the resorption rate and bioactivity of orthopedic ceramics. The present study investigated whether calcium pyrophosphate affected proliferation, differentiation and gene expression in early (MC3T3 pre-osteoblast) and late stage (SAOS-2 osteosarcoma) osteoblasts. Pyrophosphate stimulated peak alkaline phosphatase activity by 50% and 150% at 100 mu M and 0.1 mu M in MC3T3, and by 40% in SAOS-2. The expression of differentiation markers collagen 1 (COL1), alkaline phosphatase (ALP), osteopontin (OPN), and osteocalcin (OCN) were increased by an average of 1.5, 2, 2 and 3 fold, by high concentrations of sodium pyrophosphate (100 mu M) after 7 days of exposure in MC3T3. COX-2 and ANK expression did not differ significantly from controls in either treatment group. Though both high and low concentrations of pyrophosphate stimulate ALP activity, only high concentrations (100 mu M) stimulated osteogenic gene expression. Pyrophosphate did not affect proliferation in either cell type. The results of this study confirm that chronic exposure to pyrophosphate exerts a physiological effect upon osteoblast differentiation and ALP activity, specifically by stimulating osteoblast differentiation markers and extracellular matrix gene expression.

    National Category
    Biomaterials Science Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-307554 (URN)10.1371/journal.pone.0163530 (DOI)000385696900011 ()27701417 (PubMedID)
    Available from: 2016-11-17 Created: 2016-11-17 Last updated: 2018-02-08Bibliographically approved
    4. Influence of cement compressive strength and porosity on augmentation performance in a model of orthopedic screw pull-out
    Open this publication in new window or tab >>Influence of cement compressive strength and porosity on augmentation performance in a model of orthopedic screw pull-out
    Show others...
    2018 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 77, p. 624-633Article in journal (Refereed) Published
    Abstract [en]

    Disease and injuries that affect the skeletal system may require surgical intervention and internal fixation, i.e. orthopedic plate and screw insertion, to stabilize the injury and facilitate tissue repair. If the surrounding bone quality is poor the screws may migrate, or the bone may fail, resulting in screw pull-out. Though numerous studies have shown that cement augmentation of the interface between bone and implant can increase screw holding strength in bone, the physical properties of cement that influence pull-out force have not been investigated. The present study sought to determine how the physical properties of calcium phosphate cements (CPCs), and the strength of the biological or synthetic material surrounding the augmented screw, affected the corresponding orthopedic screw pull-out force in urethane foam models of healthy and osteoporotic bone (Sawbones). In the simplest model, where only the bond strength between screw thread and cement (without Sawbone) was tested, the correlation between pull-out force and cement compressive strength (R2 = 0.79) was weaker than correlation with total cement porosity (R2 = 0.89). In open pore Sawbone that mimics “healthy” cancellous bone density the stronger cements produced higher pull-out force (50-60% increase). Higher strength, lower porosity, cements also produced higher pull-out forces (50-190% increase) in Sawbones with cortical fixation if the failure strength of the cortical material was similar to (bovine tibial bone), or greater than (metal shell), actual cortical bone. This result is of particular clinical relevance where fixation with a metal plate implant is indicated, as the nearby metal can simulate a thicker cortical shell and, thereby, increase the pull-out force of screws augmented with stronger cements. The improvement in pull-out force was apparent even at low augmentation volumes of 0.5 ml (50% increase), which suggest that in clinical situations where augmentation volume is limited the stronger, lower porosity CPCs may still produce a significant improvement in screw holding strength. When correlations of all the tested models were compared both cement porosity and compressive strength accurately predicted pull-out force (R2=1.00, R2=0.808), though prediction accuracy depended upon the strength of the material surrounding the Sawbone. The correlations strength was low for bone with no, or weak, cortical fixation. Higher strength and lower porosity CPCs also produced greater pull-out force (1-1.5 kN) than commercial CPC (0.2-0.5kN), but lower pull-out force than PMMA (2-3 kN). The results of this study suggest that the likelihood of screw fixation failure may be reduced by selecting calcium phosphate cements with lower porosity and higher bulk strength, in patients with healthy bone mineral density and/or sufficient cortical thickness. This is of particular clinical relevance when fixation with metal plates is indicated, or where the augmentation volume is limited.

    Place, publisher, year, edition, pages
    Elsevier, 2018
    Keywords
    Screw pull-out, Orthopedic screw augmentation, Calcium phosphate cement, Bioceramic, Bone biomechanics, Sawbones, Cortical fixation
    National Category
    Medical Materials Ceramics Applied Mechanics Biomaterials Science
    Research subject
    Engineering Science with specialization in Materials Science
    Identifiers
    urn:nbn:se:uu:diva-320157 (URN)10.1016/j.jmbbm.2017.10.016 (DOI)000418309500073 ()29100205 (PubMedID)
    Funder
    Swedish Research Council, 621–2011-3399EU, FP7, Seventh Framework Programme, 262948
    Available from: 2017-04-16 Created: 2017-04-16 Last updated: 2018-02-16Bibliographically approved
  • 7.
    Pujari-Palmer, Michael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. 0000-0001-7004-2853.
    Guo, Hua
    Stockholm Univ, Dept Mat & Environm Chem, Stockholm, Sweden.
    Wenner, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Autefage, Hélène
    Karolinska Inst, Dept Med Biochem & Biophys, Stockholm, Sweden.
    Spicer, Christopher D.
    Karolinska Inst, Dept Med Biochem & Biophys, Stockholm, Sweden.
    Stevens, Molly M.
    Karolinska Inst, Dept Med Biochem & Biophys, Stockholm, Sweden; Imperial Coll London, Dept Bioengn, Dept Mat, London, England; Imperial Coll London, Inst Biomed Engn, London, England.
    Omar, Omar
    Univ Gothenburg, Inst Clin Sci, Dept Biomat, Gothenburg, Sweden.
    Thomsen, Peter
    Univ Gothenburg, Inst Clin Sci, Dept Biomat, Gothenburg, Sweden.
    Edén, Mattias
    Stockholm Univ, Dept Mat & Environm Chem, Stockholm, Sweden.
    Insley, Gerard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Procter, Philip
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    A Novel Class of Injectable Bioceramics that Glue Tissues and Biomaterials2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 12, article id 2492Article in journal (Refereed)
    Abstract [en]

    Calcium phosphate cements (CPCs) are clinically effective void fillers that are capable of bridging calcified tissue defects and facilitating regeneration. However, CPCs are completely synthetic/inorganic, unlike the calcium phosphate that is found in calcified tissues, and they lack an architectural organization, controlled assembly mechanisms, and have moderate biomechanical strength, which limits their clinical effectiveness. Herein, we describe a new class of bioinspired CPCs that can glue tissues together and bond tissues to metallic and polymeric biomaterials. Surprisingly, alpha tricalcium phosphate cements that are modified with simple phosphorylated amino acid monomers of phosphoserine (PM-CPCs) bond tissues up to 40-fold stronger (2.5–4 MPa) than commercial cyanoacrylates (0.1 MPa), and 100-fold stronger than surgical fibrin glue (0.04 MPa), when cured in wet-field conditions. In addition to adhesion, phosphoserine creates other novel properties in bioceramics, including a nanoscale organic/inorganic composite microstructure, and templating of nanoscale amorphous calcium phosphate nucleation. PM-CPCs are made of the biocompatible precursors calcium, phosphate, and amino acid, and these represent the first amorphous nano-ceramic composites that are stable in liquids.

  • 8.
    Pujari-Palmer, Michael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Robo, Céline
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Persson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Procter, Philip
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Engqvist, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Influence of cement compressive strength and porosity on augmentation performance in a model of orthopedic screw pull-out2018In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 77, p. 624-633Article in journal (Refereed)
    Abstract [en]

    Disease and injuries that affect the skeletal system may require surgical intervention and internal fixation, i.e. orthopedic plate and screw insertion, to stabilize the injury and facilitate tissue repair. If the surrounding bone quality is poor the screws may migrate, or the bone may fail, resulting in screw pull-out. Though numerous studies have shown that cement augmentation of the interface between bone and implant can increase screw holding strength in bone, the physical properties of cement that influence pull-out force have not been investigated. The present study sought to determine how the physical properties of calcium phosphate cements (CPCs), and the strength of the biological or synthetic material surrounding the augmented screw, affected the corresponding orthopedic screw pull-out force in urethane foam models of healthy and osteoporotic bone (Sawbones). In the simplest model, where only the bond strength between screw thread and cement (without Sawbone) was tested, the correlation between pull-out force and cement compressive strength (R2 = 0.79) was weaker than correlation with total cement porosity (R2 = 0.89). In open pore Sawbone that mimics “healthy” cancellous bone density the stronger cements produced higher pull-out force (50-60% increase). Higher strength, lower porosity, cements also produced higher pull-out forces (50-190% increase) in Sawbones with cortical fixation if the failure strength of the cortical material was similar to (bovine tibial bone), or greater than (metal shell), actual cortical bone. This result is of particular clinical relevance where fixation with a metal plate implant is indicated, as the nearby metal can simulate a thicker cortical shell and, thereby, increase the pull-out force of screws augmented with stronger cements. The improvement in pull-out force was apparent even at low augmentation volumes of 0.5 ml (50% increase), which suggest that in clinical situations where augmentation volume is limited the stronger, lower porosity CPCs may still produce a significant improvement in screw holding strength. When correlations of all the tested models were compared both cement porosity and compressive strength accurately predicted pull-out force (R2=1.00, R2=0.808), though prediction accuracy depended upon the strength of the material surrounding the Sawbone. The correlations strength was low for bone with no, or weak, cortical fixation. Higher strength and lower porosity CPCs also produced greater pull-out force (1-1.5 kN) than commercial CPC (0.2-0.5kN), but lower pull-out force than PMMA (2-3 kN). The results of this study suggest that the likelihood of screw fixation failure may be reduced by selecting calcium phosphate cements with lower porosity and higher bulk strength, in patients with healthy bone mineral density and/or sufficient cortical thickness. This is of particular clinical relevance when fixation with metal plates is indicated, or where the augmentation volume is limited.

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