title: Strong, macroporous, and in situ-setting calcium phosphate cement-layered structures.
abstract: Calcium phosphate cement (CPC) is highly promising for clinical uses due to its in situ-setting ability, excellent osteoconductivity and bone-replacement capability. However, the low strength limits its use to non-load-bearing applications. The objectives of this study were to develop a layered CPC structure by combining a macroporous CPC layer with a strong CPC layer, and to investigate the effects of porosity and layer thickness ratios. The rationale was for the macroporous layer to accept tissue ingrowth, while the fiber-reinforced strong layer would provide the needed early-strength. A biopolymer chitosan was incorporated to strengthen both layers. Flexural strength, S (mean+/-sd; n=6) of CPC-scaffold decreased from (9.7+/-1.2) to (1.8+/-0.3) MPa (p<0.05), when the porosity increased from 44.6% to 66.2%. However, with a strong-layer reinforcement, S increased to (25.2+/-6.7) and (10.0+/-1.4) MPa, respectively, at these two porosities. These strengths matched/exceeded the reported strengths of sintered porous hydroxyapatite implants and cancellous bone. Relationships were established between S and the ratio of strong layer thickness/specimen thickness, a/h:S=(17.6 a/h+3.2) MPa. The scaffold contained macropores with a macropore length (mean+/-sd; n=147) of (183+/-73) microm, suitable for cell infiltration and tissue ingrowth. Nano-sized hydroxyapatite crystals were observed to form the scaffold matrix of CPC with chitosan. In summary, a layered CPC implant, combining a macroporous CPC with a strong CPC, was developed. Mechanical strength and macroporosity are conflicting requirements. However, the novel functionally graded CPC enabled a relatively high strength and macroporosity to be simultaneously achieved. Such an in situ-hardening nano-apatite may be useful in moderate stress-bearing applications, with macroporosity to enhance tissue ingrowth and implant resorption.
authors.affiliation: Paffenbarger Research Center, American Dental Association Foundation, National Institute of Standards and Technology, 100 Bureau Drive Stop 8546, Gaithersburg, MD 20899-8546, USA. hockin.xu@nist.gov
authors.forename: Hockin H K
authors.initials: HH
authors.lastname: Xu
authors.forename: Elena F
authors.initials: EF
authors.lastname: Burguera
authors.forename: Lisa E
authors.initials: LE
authors.lastname: Carey
mesh_terms: D000268:Adhesiveness; D001843:Bone Cements / Q000737:chemistry*; D002130:Calcium Phosphates / Q000737:chemistry*; D048271:Chitosan / Q000737:chemistry*; D019245:Compressive Strength; D003198:Computer Simulation; D003460:Crystallization / Q000379:methods; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing; D008956:Models, Chemical; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D016062:Porosity; D013718:Tensile Strength
chemical_list: D001843:Bone Cements; D002130:Calcium Phosphates; D048271:Chitosan; C020243:calcium phosphate