Faculty Bibliography

Vertically and laterally driven MEMS inertia switches are designed. The solid modeling and finite element dynamics analysis of the Nickel micro-spring in the switch are conducted. The stress distribution and the displacement-time response curve of the micro-spring under dynamic load are obtained. The influence of configuration parameters on the spring constants (including klevel and kvertic) are compared under static and dynamic loads. The finite element dynamics analysis is considered to be a useful method in evaluating the spring constant in MEMS devices, especially for the spring in inertia micro devices working under the dynamic load.

A novel MEMS inertia micro-switch has been designed basing on non-silicon surface micromachining technology. The switch mainly consists of a thicker mass block as mobile electrode and a suspended elastic beam as fixed electrode locating above the mass block. The designed switch structure not only benefits the improvement of the sensitivity and the contact effect, but also protects the switch against shock damage owing to too much deviation of the mass block and the snake springs. The dynamics finite element contact simulation about the designed switch has been done. The results show that the response time and the contact time of the switch is about 0.24ms and 10 μs respectively when 100g acceleration was applied, which is relatively better sensitivity and contact effect. The response time of the inertia micro-switch would decrease when applied acceleration was increased, and the contact effect between two electrodes would be enhanced.

A novel design of MEMS electrical inertia micro-switch was proposed. In the design, an elastic beam with holes was used as the fixed electrode, and a suspended thicker mass block with conjoined snake springs was used as the mobile electrode locating between the supporting layer and the elastic beam. This designed switch structure benefits the improvement of the sensitivity, the contact effect, and protects the switch against intensive shock damage. The micro-switch had been fabricated using cost-effective electroplating nickel and tested subsequently. The result indicates that the response time and the contact time of the micro-switch are about 0.40 ms and 12 μs respectively when 100 g acceleration is applied, which shows relatively better sensitivity and contact effect. This result has an agreement with that of dynamics finite element contact simulation about the designed micro-switch.

The vessel-stabilizing effect of angiopoietin-1 (Ang1)/Tie2 receptor signaling is a potential target for pro-angiogenic therapies as well as anti-angiogenic inhibition of tumor growth. We explored the endothelial and vascular specific activities of the Ang1 monomer, i.e. dissociated from its state as an oligomer. A truncated monomeric Ang1 variant (i.e. DeltaAng1) containing the isolated fibrinogen-like receptor-binding domain of Ang1 was created and recombinantly produced in insect cells. DeltaAng1 ligated the Tie2 receptor without triggering its phosphorylation. Moreover, monomeric DeltaAng1 was observed to bind alpha(5)beta(1) integrin with similar affinity compared with Tie2. Unexpectedly, in vitro treatment of endothelial cells with DeltaAng1 showed some of the known effects of full-length Ang1, including inhibition of basal endothelial cell permeability and stimulation of cell adhesion as well as activation of MAPKs. Local treatment of the microvasculature of the developing chicken chorioallantoic membrane with the DeltaAng1 protein led to profound reduction of the mean vascular length density, thinning of vessels, and reduction of the number of vessel branching points. Similar effects were observed in side-by-side experiments with the recombinant full-length Ang1 protein. These effects of simplification of the vessel branching pattern were confirmed through local gene transfer with lentiviral particles encoding DeltaAng1 or full-length Ang1. Together, our findings suggest a potential use for exogenous Ang1 in reducing rather than increasing vascular density. Furthermore, we show that the isolated receptor-binding domain of Ang1 is capable of mediating some effects of full-length Ang1 independently of Tie2 phosphorylation, possibly through integrin ligation.