Head injury is a leading cause of morbidity and death in both industrialized and developing countries. It is estimated that brain injuries account for 15% of the burden of fatalities and disabilities, and represent the leading cause of death in young adults. Brain injury may be caused by an impact or a sudden change in the linear and/or angular velocity of the head. However, the woodpecker does not experience any head injury at the high speed of 6–7 m/s with a deceleration of 1000 g when it drums a tree trunk. It is still not known how woodpeckers protect their brain from impact injury. In order to investigate this, two synchronous high-speed video systems were used to observe the pecking process, and the force sensor was used to measure the peck force. The mechanical properties and macro/micro morphological structure in woodpecker's head were investigated using a mechanical testing system and micro-CT scanning. Finite element (FE) models of the woodpecker's head were established to study the dynamic intracranial responses. The result showed that macro/micro morphology of cranial bone and beak can be recognized as a major contributor to non-impact-injuries. This biomechanical analysis makes it possible to visualize events during woodpecker pecking and may inspire new approaches to prevention and treatment of human head injury.

Consider the 1+1-dimensional quasi-linear diffusion equations with convection and source term u t = [u m (u x ) n ] x + P(u)u x + Q(u), where P and Q are both smooth functions. We obtain conditions under which the equations admit the Lie Bäcklund conditional symmetry with characteristic η = u xx + H (u)u 2x + G(u)(u x ) 2−n + F(u)u 1−n x and the Hamilton-Jacobi sign-invariant J = u t + A(u)u n+1x + B(u)u x + C(u) which preserves both signs, ≥0 and ≤0, on the solution manifold. As a result, the corresponding solutions associated with the symmetries are obtained explicitly, or they are reduced to solve two-dimensional dynamical systems.

Biodegradable polymers have been widely used in tissue engineering for their good biocompatibility, controlled mechanical properties and processability. Among them, poly(glycerol sebacate) (PGS) is a promising biodegradable polymer that has been used in diverse tissue engineering applications such as skin, muscle, cornea, nerve, vessel, cartilage, and so on. However, one of the synthesis parameters, curing time on PGS properties is still a confusing problem waiting to be resolved. In this article, PGS was cured for 0, 24, 36, 48, 60, 72, 84, and 96 h at 130°C and their properties were characterized by a series of techniques. Differential scanning calorimetry results indicated that the melting point, crystallization temperature, melting enthalpy and crystallization enthalpy of PGS decreased with the increase of curing time. Curing time was positively correlated to the degree of crosslinking. Longer curing time not only enhanced Young's modulus of PGS but also reduced its hydrophilicity. The Young's modulus of PGS curing for 96 h was about 5 times higher than that of PGS curing for 36 h. This study suggests that the effect of curing time on PGS properties provides detailed reference for potential applications.

No abstract