Fused deposition modeling is a fast growing additive manufacturing technology with advantages of low cost, low operation temperature, consistent prototype accuracy, and flexible material change. Fiber-reinforced plastic composite parts have been developed by the fused deposition modeling process to improve the mechanical properties of fused deposition modeling-fabricated pure thermoplastic parts which cannot be used as load-bearing parts in the actual applications. However, porosity found at the fracture interfaces of fused deposition modeling-fabricated fiber-reinforced plastic composite parts may limit their potential for direct replacement in the functional applications. The problem may result from the larger length–diameter ratio of the chopped thin fibers used in fiber-reinforced plastic composite parts fabricating. One of the possible methods to reduce the porosity is employing small length–diameter ratio particles/flakes (such as graphite) instead of chopped thin fibers as reinforcements. However, mechanical performances of the graphite-reinforced thermoplastic composites are still unknown. In this article, comparisons on porosity and tensile properties between the specimens of carbon fiber-reinforced thermoplastic and graphite-reinforced thermoplastic fabricated by fused deposition modeling process were conducted in order to test the effects of reinforcements. Fracture interfaces of the specimens after tensile testing were observed.
Homogeneous polyelectrolyte complex
(PEC) hydrogels made from chitosan
and carboxymethylcellulose were prepared in the LiOH/KOH/urea aqueous
system through a freeze–thawing method. Following the treatments
of sequential chemical and physical cross-linking, the resulting hydrogels
with supertough mechanical strength can operate as fast response actuators
under electrical stimulus in salt aqueous solutions. The electromechanical
behaviors of the hydrogels are strongly dependent on experimental
parameters such as electric voltage, solvent constituents, pH, and
ionic strength. It is proposed that the electromechanical deformation
of hydrogel originates from a dynamic osmotic equilibrium effect taking
place at the interface between the hydrogel and the surrounding medium,
which is induced by the migration of ions throughout the gel network.
In addition, programmable 3D shape transformations were obtained by
using the PEC hydrogel with designed 2D geometric patterns. Moreover,
the bending actuation behavior of the PEC hydrogel can propel an adjacent
object to move forward. These hydrogels are expected to be used as
underwater actuators for soft robotics and other smart biomimetic
systems.
Metallic microneedles are attractive for painless transdermal drug-delivery. However, fabrication techniques for metal microneedles are often complex and multi-step. In this study, a scalable manufacturing of metallic microneedle arrays is presented using thermoplastic drawing of metallic glasses. Microneedles with tunable lengths and tips are produced by controlling the rheology and fracture of metallic glass. The same drawing process can generate solid and hollow microneedles simply by varying the thickness of metallic glass. The mechanism of thickness dependent transition from solid to hollow profiles is described by the viscous buckling of metallic liquid. In vitro skin insertion tests demonstrate that both solid and hollow metallic glass microneedles can pierce porcine skin and deliver model drugs.
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