Mechanical characterization of bone allografts, enriched with mesenchymal cells

Abstract

Bone allografts, which are used as bone regeneration material, must satisfy two functions: a biologic function and a mechanical function. The biologic task is satisfied by enrichment of the osseous reconstructive material with mesenchymal cells, radio-sterilized and lyophilized, which helps to a more efficient formation of new bone. Regarding the mechanical function, the allografts must be as rigid and strong as intact bone for immediate load-bearing capability. Consequently, a good mechanical characterization is needed to guarantee the structural integrity of the allografts in the host tissue. Thus, in this work results are presented from compression testing of cancellous and cortical/cancellous allograft tissue chips, as well as results on flexure and pure shear testing of cortical allograft strips. The test specimens were fabricated according to standard procedures. For the cancellous graft chips, different elastic moduli were obtained a long the three perpendicular directions, 32.2, 98.2, and 162.4 MPa, showing orthotropic behavior. For the cortical/cancellous chips, compression loads were only applied along the longitudinal and transversal directions of the cortical phase; the corresponding elastic moduli displayed were 518.6 and 384.8 MPa. On the other hand, for the cortical graft strips, the flexure elastic modulus obtained was 38.9 GPa; reported flexure elastic modulus in the literature for fresh human bone are between 1.525 and 31.5 GPa. Finally the shear strength exhibited by the cortical graft was 43.6 MPa.

Standardizing compression testing for measuring the stiffness of human bone

“…Certain studies used a combination of a fixed platen paired with an adjustable, rotating platen. 38 , 43 - 45 , 69 , 101 , 104 , 107 , 113 , 118 , 119 , 146 , 157 , 161 - 163 A few studies used variations of the standard machine setup such as use of grooved platens, 154 custom-built compression machines, 82 , 122 , 132 , 164 , 165 and drop tower 159 or hand-loaded testing machines. 141 Some studies tested bone specimens in water baths filled with saline solution.…”