Crosslinking and the resultant changes in mechanical properties have been shown to influence cellular activity within collagen biomaterials. With this in mind, we sought to determine the effects of crosslinking on both the compressive modulus of collagen-glycosaminoglycan scaffolds and the activity of osteoblasts seeded within them. Dehydrothermal, 1-ethyl-3-3-dimethyl aminopropyl carbodiimide and glutaraldehyde crosslinking treatments were first investigated for their effect on the compressive modulus of the scaffolds. After this, the most promising treatments were used to study the effects of crosslinking on cellular attachment, proliferation, and infiltration. Our experiments have demonstrated that a wide range of scaffold compressive moduli can be attained by varying the parameters of the crosslinking treatments. 1-Ethyl-3-3-dimethyl aminopropyl carbodiimide and glutaraldehyde treatments produced the stiffest scaffolds (fourfold increase when compared to dehydrothermal crosslinking). When cells were seeded onto the scaffolds, the stiffest scaffolds also showed increased cell number and enhanced cellular distribution when compared to the other groups. Taken together, these results indicate that crosslinking can be used to produce collagen-glycosaminoglycan scaffolds with a range of compressive moduli, and that increased stiffness enhances cellular activity within the scaffolds.

Unmanned Aerial Vehicles (UAVs) are proliferating in both the civil and military markets. Flapping wing UAVs, or ornithopters, have the potential to combine the agility and maneuverability of rotary wing aircraft with excellent performance in the low Reynolds number flight regimes. The purpose of this paper is to present new free flight experimental results for an ornithopter equipped with single degree of freedom compliant spines. The compliant spines are designed and optimized in terms of mass, maximum von-Mises stress, and desired wing bending deflections. The spines are inserted in an experimental ornithopter wing leading edge spar, in order to achieve a set of desired kinematics during the up and down strokes of a flapping cycle. The ornithopter is flown at Wright Patterson Air Force Base in the Air Force Research Laboratory Small Unmanned Air Systems (SUAS) indoor flight facility. Vicon® motion tracking cameras are used to track the motion of the vehicle for four different wing configurations. The effect of the presence of the compliant spine on the wings and body kinematics, as well as the leading edge spar deflection during free flight is presented in this paper. Several metrics were used to evaluate the vehicle performance with various compliant spine designs inserted in the leading edge spar of the wings. Results show that passively morphing the wings, via adding compliance in the leading edge spar, does not require additional power expenditure and is beneficial to the overall vertical and horizontal propulsive force production.

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