A large animal model for standardized testing of bone regeneration strategies.

BACKGROUND: The need for bone graft substitutes including those being developed to be applied together with new strategies of bone regeneration such as tissue engineering and cell-based approaches is growing. No large animal model of bone regeneration has been accepted as a standard testing model. Standardization may be the key to moving systematically towards better bone regeneration. This study aimed to establish a model of bone regeneration in the sheep that lends itself to strict standardization and in which a number of substances can be tested within the same animal. To this end the caudal border of the ovine scapula was used as a consistent bed of mineralized tissue that provided sufficient room for a serial alignment of multiple experimental drill holes. RESULTS: The findings show that for the sake of standardization, surgery should be restricted to the middle part of the caudal margin, an area at least 80 mm proximal from the Glenoid cavity, but not more than 140 mm away from it, in the adult female Land Merino sheep. A distance of 5 mm from the caudal margin should also be observed. CONCLUSIONS: This standardized model with defined uniform defects and defect sites results in predictable and reproducible bone regeneration processes. Defects are placed unilaterally in only one limb of the animal, avoiding morbidity in multiple limbs. The fact that five defects per animal can be evaluated is conducive to intra-animal comparisons and reduces the number of animals that have to be subject to experimentation.

Is moisture really the most important influencing factor on the mechanical properties of claw horn? Modulus of elasticity and dry-matter content in flat and contracted claws.

The modulus of elasticity (E) and dry matter content (DMC) of horn samples from two types of claw deformity (contracted and flat claws) were determined according to EN-ISO 527 and ASTM D 638-03. The overall E values for all segments combined were 168 +/- 154 MPa (mean +/- SD, n = 79) and 248 +/- 196 (n = 90) for contracted and flat claws, respectively. These values were approximately 60% and 40% less than the E value of sound claw material. The high correlation between E and DMC, as previously found for sound claw horn material was not present in horn obtained from these types of pathologically altered claws.

Modulus of elasticity and dry-matter content of bovine claw horn affected by the changes of chronic laminitis.

The mechanical properties of horn samples from 22 hind claws with chronic laminitis were determined in adult Austrian Fleckvieh cows. The resistance to deformation was quantified as the modulus of elasticity (E). Tension tests revealed mean E values of 520MPa for the dorsal wall, 243MPa for the abaxial wall, 339MPa for the axial wall and 97MPa for the sole. E tended to be lower in laminitic horn than in sound horn in all segments tested, with the difference being largest in the abaxial wall. The mean dry-matter content (DMC) of the laminitic claws was 75.8% in the dorsal wall, 75.86% in the abaxial wall, 71.15% in the axial wall and 69.28% in the sole. These values are generally comparable to those for sound claws except in the axial wall. Further, E and DMC were only correlated in the axial wall. Chronic laminitis leads to a low resistance of claw horn to mechanical insults in the dorsal wall, abaxial wall and sole, and to the loss of a correlation between the E and DMC in these segments. The reason for these alterations is therefore not increased ingress of moisture, but must be due to changes in the microstructure, biochemical components and/or horn formation by the diseased dermis.