Large bone defects can not be recovered by self-repair meanwhile, bone scaffold with biomimetic material is needed. The biomimetic materials are hydroxyapatite/collagen as inorganic and organic material. The study on printed hydroxyapatite/collagen has been conducted. However, the Crack occurred after printing and drying. The novelty of the research is addition of nanocrystalline cellulose (NCC) into the HA/collagen composite to reduce MicroCrack. The hydroxyapatite/collagen/NCC composite scaffold was printed with 3D bioprinting which was a modification in bracket and cartridge with  print speed and layer height of 10 mm/min and 0.5 mm. The Cracking process that occurred in the hydroxyapatite/collagen material was investigated using Mi-View Microscope. Furthermore, the scaffold of hydroxyapatite/collagen/NCC composite with composition 70/15/15 (%w/v) was examined using the Vickers hardness test, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron Microscope (TEM), scanning electron Microscope (SEM), energy dispersive X-ray (EDX), and thermogravimetric analysis/derivative thermogravimetry (TGA/DTG). After the printing process, shrinkage occurs on the X, Y, and Z axes with values of 14, 15.1 and 20.5%. Moreover, the hardness value was  0.002 to 0.003 HV with the detection of hydroxyapatite, collagen, and NCC. The crystallinity of hydroxyapatite/collagen/NCC was 28%. The presence of NCC in the composite material can maintain a uniform three-dimensional network structure with a dominant composition of oxygen (47.77%), calcium (36.62%), and phosphate (12.8%). The TGA/DTG represented the amount of weight loss of 23.46% with an initial temperature of 610 °C and maximum temperature of 650 °C. Therefore, hydroxyapatite/collagen/NCC is  promising material for bone tissue engineering.

In the present work the pull-in voltage of a Micro Cracked cantilever beam subjected to nonlinear electrostatic pressure was studied. Two mathematical models were employed for modeling the problem: a lumped mass model and a classical beam model. The effect of Crack in the lumped mass model is the reduction of the effective stiffness of the beam and in the beam model; the Crack is modeled as a massless rotational spring the compliance of which is related to the Crack depth. Using these two models the pull-in voltage is extracted in the static and dynamic cases. Stability analysis is also accomplished. It has been observed that the pull-in voltage decreases as the Crack depth increases and also when the Crack approaches the clamped support of the beam. The finding of this research can further be used as a non-destructive test procedure for detecting Cracks in Micro-beams.

A model of the equations of two dimensional problems in a half space, whose surface in free of Micro polar thermoplastic medium possesses cubic symmetry as a result of a Mode-I Crack is studied. There acts an initial magnetic field parallel to the plane boundary of the half- space. The Crack is subjected to prescribed temperature and stress distribution. The formulation in the context of the Lord-shulman theory LS includes one relaxation time and Green-Lindsay theory GL with two relaxation times, as well as the classical dynamical coupled theory CD. The normal mode analysis is used to obtain the exact expressions for the displacement, Micro rotation, stresses and temperature distribution. The variations of the considered variables with the horizontal distance are illustrated graphically. Comparisons are made with the results in the presence of magnetic field. A comparison is also made between the three theories for different depths.

In this paper, the pull-in phenomenon is suppressed using a range of values of amplitude and frequency of high- frequency voltage excitations in the post pull- in condition of the Cracked Micro- electromechanical systems. These specified ranges are named as stable zones. It is investigated the effects of the Crack parameters (depth and location) on changes of these zones, in the post pull-in condition. It is shown that these zones have different areas for different Crack parameters. The Cracked Micro-beam is modeled as a single- degree-of- freedom systems consist of mass- spring- damper and the motion equation of the Cracked Micro- beam is extracted. The method of direct partition of motion is used to split the fast and slow dynamics. By means of slow dynamic part, the effects of the Crack on the averaged position of vibration of Cracked Micro- beam are investigated versus voltage amplitude and frequency of the high-frequency AC. By approaching the Crack to the fixed end or increasing the depth of Crack, the stability zone reduced. Therefore, the pull- in instability can be suppressed in the lower range of amplitude and frequency. This method can be used in sensors’ health- monitoring and one can predict the parameters of the Crack using this method.