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Molecular mechanics of mineralized collagen fibrils in bone.

Nair AK, Gautieri A, Chang SW, Buehler MJ - Nat Commun (2013)

Bottom Line: Here we perform full-atomistic calculations of the three-dimensional molecular structure of a mineralized collagen protein matrix to try to better understand its mechanical characteristics under tensile loading at various mineral densities.We find that as the mineral density increases, the tensile modulus of the network increases monotonically and well beyond that of pure collagen fibrils.These findings reveal the mechanism by which bone is able to achieve superior energy dissipation and fracture resistance characteristics beyond its individual constituents.

View Article: PubMed Central - PubMed

Affiliation: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

ABSTRACT
Bone is a natural composite of collagen protein and the mineral hydroxyapatite. The structure of bone is known to be important to its load-bearing characteristics, but relatively little is known about this structure or the mechanism that govern deformation at the molecular scale. Here we perform full-atomistic calculations of the three-dimensional molecular structure of a mineralized collagen protein matrix to try to better understand its mechanical characteristics under tensile loading at various mineral densities. We find that as the mineral density increases, the tensile modulus of the network increases monotonically and well beyond that of pure collagen fibrils. Our results suggest that the mineral crystals within this network bears up to four times the stress of the collagen fibrils, whereas the collagen is predominantly responsible for the material's deformation response. These findings reveal the mechanism by which bone is able to achieve superior energy dissipation and fracture resistance characteristics beyond its individual constituents.

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Related in: MedlinePlus

Analysis of stress fields for different mineral contents.(a) View of the cross-section of the y–z plane of the unit cell used to perform the stress analysis. The principal stress contours for an applied stress of 100 MPa in collagen microfibril show a nearly uniform stress distribution, whereas the data for 20 and 40% mineral-density cases clearly reveals significantly higher stress regions in the HAP mineral. (b) Quantification of the overall average stress in the collagen and mineral phases at 100 MPa applied stress, showing that the mineral phase features about four times the stress level compared with collagen.
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f6: Analysis of stress fields for different mineral contents.(a) View of the cross-section of the y–z plane of the unit cell used to perform the stress analysis. The principal stress contours for an applied stress of 100 MPa in collagen microfibril show a nearly uniform stress distribution, whereas the data for 20 and 40% mineral-density cases clearly reveals significantly higher stress regions in the HAP mineral. (b) Quantification of the overall average stress in the collagen and mineral phases at 100 MPa applied stress, showing that the mineral phase features about four times the stress level compared with collagen.

Mentions: To understand the distribution of stress inside the microfibril, we compute the stress distribution in the cross sectional y–z plane (Fig. 6a). The virial stresses33 are computed for an applied stress of 100 MPa for 0%, 20% and 40% mineral-density cases, respectively. To visualize and quantify the stresses in the unit cell, we compute the principal stresses for a region with a finite thickness of 15 Å in the x direction. For the 0% case we choose the overlap region, and for the 20 and 40% mineral-density cases we chose the gap region for principal stress computation. As observed from Fig. 6a, the 0% case has a nearly uniform stress distribution with maximum stresses reaching ~15 MPa, indicating that the collagen backbone gets stretched and the three chains take the load. The mineralized cases show higher stress in HAP compared with collagen, with maximum stress reaching 50 MPa, hence suggesting that the load is predominantly carried by the mineral phase. To validate this finding, we plot the average stress in collagen and the mineral phase for 20 and 40% mineral densities. Figure 6b shows that the HAP phase takes approximately four times the stress compared with collagen. This leads to the conclusion that as the mineral content increases, there is a stronger interaction between the mineral and the collagen, and that the applied load is distributed among collagen and mineral phases in a particular pattern.


Molecular mechanics of mineralized collagen fibrils in bone.

Nair AK, Gautieri A, Chang SW, Buehler MJ - Nat Commun (2013)

Analysis of stress fields for different mineral contents.(a) View of the cross-section of the y–z plane of the unit cell used to perform the stress analysis. The principal stress contours for an applied stress of 100 MPa in collagen microfibril show a nearly uniform stress distribution, whereas the data for 20 and 40% mineral-density cases clearly reveals significantly higher stress regions in the HAP mineral. (b) Quantification of the overall average stress in the collagen and mineral phases at 100 MPa applied stress, showing that the mineral phase features about four times the stress level compared with collagen.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3644085&req=5

f6: Analysis of stress fields for different mineral contents.(a) View of the cross-section of the y–z plane of the unit cell used to perform the stress analysis. The principal stress contours for an applied stress of 100 MPa in collagen microfibril show a nearly uniform stress distribution, whereas the data for 20 and 40% mineral-density cases clearly reveals significantly higher stress regions in the HAP mineral. (b) Quantification of the overall average stress in the collagen and mineral phases at 100 MPa applied stress, showing that the mineral phase features about four times the stress level compared with collagen.
Mentions: To understand the distribution of stress inside the microfibril, we compute the stress distribution in the cross sectional y–z plane (Fig. 6a). The virial stresses33 are computed for an applied stress of 100 MPa for 0%, 20% and 40% mineral-density cases, respectively. To visualize and quantify the stresses in the unit cell, we compute the principal stresses for a region with a finite thickness of 15 Å in the x direction. For the 0% case we choose the overlap region, and for the 20 and 40% mineral-density cases we chose the gap region for principal stress computation. As observed from Fig. 6a, the 0% case has a nearly uniform stress distribution with maximum stresses reaching ~15 MPa, indicating that the collagen backbone gets stretched and the three chains take the load. The mineralized cases show higher stress in HAP compared with collagen, with maximum stress reaching 50 MPa, hence suggesting that the load is predominantly carried by the mineral phase. To validate this finding, we plot the average stress in collagen and the mineral phase for 20 and 40% mineral densities. Figure 6b shows that the HAP phase takes approximately four times the stress compared with collagen. This leads to the conclusion that as the mineral content increases, there is a stronger interaction between the mineral and the collagen, and that the applied load is distributed among collagen and mineral phases in a particular pattern.

Bottom Line: Here we perform full-atomistic calculations of the three-dimensional molecular structure of a mineralized collagen protein matrix to try to better understand its mechanical characteristics under tensile loading at various mineral densities.We find that as the mineral density increases, the tensile modulus of the network increases monotonically and well beyond that of pure collagen fibrils.These findings reveal the mechanism by which bone is able to achieve superior energy dissipation and fracture resistance characteristics beyond its individual constituents.

View Article: PubMed Central - PubMed

Affiliation: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

ABSTRACT
Bone is a natural composite of collagen protein and the mineral hydroxyapatite. The structure of bone is known to be important to its load-bearing characteristics, but relatively little is known about this structure or the mechanism that govern deformation at the molecular scale. Here we perform full-atomistic calculations of the three-dimensional molecular structure of a mineralized collagen protein matrix to try to better understand its mechanical characteristics under tensile loading at various mineral densities. We find that as the mineral density increases, the tensile modulus of the network increases monotonically and well beyond that of pure collagen fibrils. Our results suggest that the mineral crystals within this network bears up to four times the stress of the collagen fibrils, whereas the collagen is predominantly responsible for the material's deformation response. These findings reveal the mechanism by which bone is able to achieve superior energy dissipation and fracture resistance characteristics beyond its individual constituents.

Show MeSH
Related in: MedlinePlus