Strong, macroporous, and in situ-setting calcium phosphate cement-layered structures

Biomaterials. 2007 Sep;28(26):3786-96. doi: 10.1016/j.biomaterials.2007.05.015. Epub 2007 May 26.

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.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adhesiveness
  • Bone Cements / chemistry*
  • Calcium Phosphates / chemistry*
  • Chitosan / chemistry*
  • Compressive Strength
  • Computer Simulation
  • Crystallization / methods
  • Elasticity
  • Hardness
  • Materials Testing
  • Models, Chemical*
  • Nanostructures / chemistry*
  • Nanostructures / ultrastructure
  • Particle Size
  • Porosity
  • Tensile Strength

Substances

  • Bone Cements
  • Calcium Phosphates
  • Chitosan
  • calcium phosphate