A Universal Strategy to Construct High-Performance Homo- and Heterogeneous Microgel Assembly Bioinks.

Three dimensional (3D) extrusion bioprinting aims to replicate the complex architectures and functions of natural tissues and organs. However, the conventional hydrogel and new-emerging microgel bioinks are both difficult in achieving simultaneously high shape-fidelity and good maintenance of cell viability/function, leading to limited amount of qualified hydrogel/microgel bioinks. Herein, a universal strategy is reported to construct high-performance microgel assembly (MA) bioinks by using epigallocatechin gallate-modified hyaluronic acid (HA-EGCG) as coating agent and phenylboronic acid grafted hyaluronic acid (HA-PBA) as assembling agent. HA-EGCG can spontaneously form uniform coating on the microgel surface via mussel-inspired chemistry, while HA-PBA quickly forms dynamic phenylborate bonds with HA-EGCG, conferring the as-prepared MA bioinks with excellent rheological properties, self-healing, and tissue-adhesion. More importantly, this strategy is applicable to various microgel materials, enabling the preparation of homo- and heterogeneous MA (homo-MA and hetero-MA) bioinks and the hierarchical printing of complicated structures with high fidelity by integration of different microgels containing multiple materials/cells in spatial and compositional levels. It further demonstrates the printing of breast cancer organoid in vitro using homo-MA and hetero-MA bioinks and its preliminary application for drug testing. This universal strategy offers a new solution to construct high-performance bioinks for extrusion bioprinting.

A Novel Bidirectional AlGaN/GaN ESD Protection Diode.

Despite the superior working properties, GaN-based HEMTs and systems are still confronted with the threat of a transient ESD event, especially for the vulnerable gate structure of the p-GaN or MOS HEMTs. Therefore, there is still an urgent need for a bidirectional ESD protection diode to improve the ESD robustness of a GaN power system. In this study, an AlGaN/GaN ESD protection diode with bidirectional clamp capability was proposed and investigated. Through the combination of two floating gate electrodes and two pF-grade capacitors connected in parallel between anode or cathode electrodes and the adjacent floating gate electrodes (CGA (CGC)), the proposed diode could be triggered by a required voltage and possesses a high secondary breakdown current (IS) in both forward and reverse transient ESD events. Based on the experimental verification, it was found that the bidirectional triggering voltages (Vtrig) and IS of the proposed diode were strongly related to CGA (CGC). With CGA (CGC) increasing from 5 pF to 25 pF, Vtrig and IS decreased from ~18 V to ~7 V and from ~7 A to ~3 A, respectively. The diode's high performance demonstrated a good reference for the ESD design of a GaN power system.