November 14, 2018 by admin 0 Comments

3D‐Printed MOF‐Derived Hierarchically Porous Frameworks for Practical High‐Energy Density Li–O2 Batteries

Authors
Zhiyang Lyu, Gwendolyn J. H. Lim, Rui Guo, Zongkui Kou, Tingting Wang, Cao Guan, Jun Ding, Wei Chen, John Wang
Abstract
protic Li–O2 batteries are promising candidates for next‐generation energy storage technologies owing to their high theoretical energy densities. However, their practically achievable specific energy is largely limited by the need for porous conducting matrices as cathode support and the passivation of cathode surface by the insulating Li2O2 product. Herein, a self‐standing and hierarchically porous carbon framework is reported with Co nanoparticles embedded within developed by 3D‐printing of cobalt‐based metal–organic framework (Co‐MOF) using an extrusion‐based printer, followed by appropriate annealing. The novel self‐standing framework possesses good conductivity and necessary mechanical stability, so that it can act as a porous conducting matrix. Moreover, the porous framework consists of abundant micrometer‐sized pores formed between Co‐MOF‐derived carbon flakes and meso‐ and micropores formed within the flakes, which together significantly benefit the efficient deposition of Li2O2 particles and facilitate their decomposition due to the confinement of insulating Li2O2 within the pores and the presence of Co electrocatalysts. Therefore, the self‐standing porous architecture significantly enhances the cell's practical specific energy, achieving a high value of 798 Wh kg−1cell. This study provides an effective approach to increase the practical specific energy for Li–O2 batteries by constructing 3D‐printed framework cathodes.

October 16, 2018 by admin 0 Comments

Dual Sacrificial Molding: Fabricating 3D Microchannels with Overhang and Helical Features

Authors
Wei Huang Goh ¹, Michinao Hashimoto ¹,²,*
Abstract
Fused deposition modeling (FDM) has become an indispensable tool for 3D printing of molds used for sacrificial molding to fabricate microfluidic devices. The freedom of design of a mold is, however, restricted to the capabilities of the 3D printer and associated materials. Although FDM has been used to create a sacrificial mold made with polyvinyl alcohol (PVA) to produce 3D microchannels, microchannels with free-hanging geometries are still difficult to achieve. Herein, dual sacrificial molding was devised to fabricate microchannels with overhang or helical features in PDMS using two complementary materials. The method uses an FDM 3D printer equipped with two extruders and filaments made of high- impact polystyrene (HIPS) and PVA. HIPS was initially removed in limonene to reveal the PVA mold harboring the design of microchannels. The PVA mold was embedded in PDMS and subsequently removed in water to create microchannels with 3D geometries such as dual helices and multilayer pyramidal networks. The complementary pairing of the HIPS and PVA filaments during printing facilitated the support of suspended features of the PVA mold. The PVA mold was robust and retained the original design after the exposure to limonene. The resilience of the technique demonstrated here allows us to create microchannels with geometries not attainable with sacrificial molding with a mold printed with a single material.

June 1, 2018 by admin 0 Comments

The Arrival of Commercial Bioprinters – Towards 3D Bioprinting Revolution!

Authors
Deepak Choudhury*, Shivesh Anand, May Win Naing*
Abstract
The dawn of commercial bioprinting is rapidly advancing the tissue engineering field. In the past few years, new bioprinting approaches as well as novel bioinks formulations have emerged, enabling biological research groups to demonstrate the use of such technology to fabricate functional and relevant tissue models. In recent years, several companies have launched bioprinters pushing for early adoption and democratisation of bioprinting. This article reviews the progress in commercial bioprinting since the inception, with a particular focus on the comparison of different available printing technologies and important features of the individual technologies as well as various existing applications. Various challenges and potential design considerations for next generations of bioprinters are also discussed.

September 5, 2017 by admin 0 Comments

Robocasting of dense yttria-stabilized zirconia structures

Authors
Erwin Peng, Xiangxia Wei, Ulf Garbe, Dehong Yu, Brunet Edouard, Aihong Liu & Jun Ding
Abstract
Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose.

May 22, 2017 by admin 0 Comments

Ferrite-based soft and hard magnetic structures by extrusion free-forming

Authors
Erwin Peng (a), Xiangxia Wei (a), Tun Seng Herng (a), Ulf Garbe (b), Dehong Yu (b), Jun Ding (*, a)
Abstract
Functional ceramic materials, especially those with unique magnetic properties, with complex geometries have become increasingly important for various key technologies in industry. Herein, ferrite-based soft (NiFe2O4) and hard (BaFe12O19) bulk magnetic structures with three-dimensional morphologies are successfully fabricated from inexpensive metal oxide powder (NiO/Fe2O3 and BaCO3/Fe2O3) precursors through a simple extrusion free-forming (EFF) technique coupled with a high temperature solid-state reaction process. Dense polycrystalline microstructures with negligible porosity are observed for samples sintered above 1200 °C and highly crystalline NiFe2O4 and BaFe12O19 phases are successfully formed. The printed structures also exhibit either soft or hard magnetic material behavior with (i) saturation magnetization values up to approximately 86% and 95% of the NiFe2O4 and BaFe12O19 theoretical bulk magnetization values, respectively, and (ii) high densities up to ∼93% of their respective theoretical bulk density. Bulk magnetic structures with unique geometries (e.g. mesh, gear, ring and cylinder) are successfully fabricated. The EFF technique demonstrated in this work can be readily extended to other functional ferrite or titanate ceramic materials simply by changing the metal oxide powder precursors.

November 1, 2016 by admin 0 Comments

Fabrication of YBa2Cu3O7−x (YBCO) superconductor bulk structures by extrusion freeforming

Authors
Xiangxia Wei, Ragavendran Sundaram Nagarajan, Erwin Peng, Junmin Xue, John Wang, Jun Ding
Abstract
Practical applications of high temperature superconductors may require them to be processed into complex geometries. In this work, slurry-based extrusion freeforming coupled with high temperature treatment was attempted for the fabrication of bulk YBa2Cu3O7−x (YBCO) superconducting structures. YBCO parts with approximately 93% of the theoretical density were successfully fabricated after sintering at 940 °C for 60 h, with the obtained constituent phases strongly dependent on the heat treatment temperature and duration. A high critical transition temperature (TC=92 K) and good magnetic levitation ability could be obtained after optimization of the heat treatment conditions. Overall, the experimental results demonstrate that extrusion freeforming is a feasible and effective technique for fabricating YBCO superconductors that have desirable configurations and good superconductivity properties.

September 7, 2016 by admin 0 Comments

3D bioprinting of skin: a state-of-the-art review on modelling, materials, and processes

Authors
S Vijayavenkataraman¹, W F Lu¹ and J Y H Fuh¹,²
Abstract
The skin is the largest organ of the body, having a complex multi-layered structure and guards the underlying muscles, bones, ligaments, and internal organs. It serves as the first line of defence to any external stimuli, hence it is the most vulnerable to injury and warrants the need for rapid and reliable regeneration methods. Tissue engineered skin substitutes help overcome the limitations of traditional skin treatment methods, in terms of technology, time, and cost. While there is commendable progress in the treating of superficial wounds and injuries with skin substitutes, treatment of full-thickness injuries, especially with third or fourth degree burns, still looks murkier. Engineering multi-layer skin architecture, conforming to the native skin structure is a tougher goal to achieve with the current tissue engineering methods, if not impossible, restoring all the functions of the native skin. The testing of drugs and cosmetics is another area, where engineered skins are very much needed, with bans being imposed on product testing on animals. Given this greater need, 3D bioprinting is a promising technology that can achieve rapid and reliable production of biomimetic cellular skin substitutes, satisfying both clinical and industrial needs. This paper reviews all aspects related to the 3D bioprinting of skin, right from imaging the injury site, 3D model creation, biomaterials that are used and their suitability, types of cells and their functions, actual bioprinting technologies, along with the challenges and future prospects.