Objective To analyze the influence of different backpack types and loads on kinematics and plantar pressure of college students during stair climbing, so as to provide references for choosing the appropriate backpack and carrying mode. Methods The Nokov infrared light point motion capture system and Podome plantar pressure system were used to analyze the differences in the range of motion ( ROM) of the trunk and lower limb joints, the kinematic parameters at the peak time, the peak pressure of each plantar partition, the contact time, the maximum pressure of the whole foot, the average pressure and the maximum contact area for 15 male college students during the support period of stair climbing. Results The 5% BW and 10% BW backpack loads reduced ROM of trunk rotation, increased ROM of ankle flexion/ extension and varus / valgus. The 10% BW backpack loads increased the peak pressure of the 1st and 3rd metatarsals bones and the maximum pressure of the whole foot ( P < 0. 05). Single-shoulder bag and handbag reduced ROM of trunk tilting and rotation, and increased ROM of ankle flexion and extension, hip flexion angle, peak pressure of foot arch and medial heel (P<0. 05). The double-shoulder bag loads increased peak pressure in the toe area (P<0. 05). Conclusions During walking on the stairs, the 5% BW and 10% BW backpack loads limited trunk rotation and increased ankle ROM. The 10% BW loads also increased the load in metatarsal area. The unilateral weight-bearing mode would make the trunk tilt to the unload side and rotate to the weight-bearing side. The pressure in toe area was higher when carrying double-shoulder bag, while single-shoulder bag and handbag mainly increased the pressure of arch foot and medial heel. It is suggested that college students choose symmetrical backpack scheme, and wisely allocate back weight to avoid the injury of foot area.

Objective To fabricate a foldable microplate for single cell culture and establish finite element model of the folding microplate, so as to calculate traction force of single cells during contraction in three-dimensional (3D) state.Methods The folding angle of the microplate casued by cell traction force was calculated. Then the relation between bending moment and folding angle as well as the relation between traction force and bending moment were derived by using finite element simulation, so as to realize the characterization of traction force for singel cell in 3D state.Results The folding angles of the microplate with HSF and MC3T3-E1 cells in 3D state were 73°-173° and 49°-138°, respectively. The single cell traction forces of HSF and MC3T3-E1 cells were 55-210 nN and 52-161 nN, respectively.Conclusions The proposed method for measuring traction force of single cells in 3D state by fabricating the foldable microplate for single cell culture will provide some references for further development of calculating traction forces in 3D cell adhesion, spreading and migration.