Bioprocess‐Inspired Microscale Additive Manufacturing of Multilayered TiO₂/Polymer Composites with Enamel‐Like Structures and High Mechanical Properties

Abstract

Natural structure‐forming processes found in biological systems are fantastic and perform at ambient temperatures, in contrast with anthropogenic technologies that commonly require harsh conditions. A new research direction “bioprocess‐inspired fabrication” is proposed to develop novel fabrication techniques for advanced materials. Enamel, an organic–inorganic composite biomaterial with outstanding mechanical performance and durability, is formed by repeating the basic blocks consisting of columnar hydroxyapatite or fluorapatite and an organic matrix. Inspired by the enamel formation process, a microscale additive manufacturing method is proposed for achieving a multilayered organic–inorganic columnar structure. In this approach, rutile titanium dioxide (TiO2) nanorods, polymers, and graphene oxide (GO) are sequentially assembled in a layer‐by‐layer fashion to form an organic–inorganic structure. In particular, GO serves as a substrate for TiO2 nanorods and interacts with polymers, jointly leading to the strength of the composites. Impressively, this enamel‐like structure material has hardness (1.56 ± 0.05 GPa) and ultrahigh Young's modulus (81.0 ± 2.7 GPa) comparable to natural enamel, and viscoelastic property (0.76 ± 0.12 GPa) superior to most solid materials. Consequently, this biomimetic synthetic approach provides an in‐depth understanding for the formation process of biomaterials and also enables the exploration of a new avenue for the preparation of organic–inorganic composite materials.

Graphene Oxide Encapsulating Liquid Metal to Toughen Hydrogel

“…As shown in Figure S4 (Supporting Information), the FT‐IR spectrum of GO powder shows various oxygen‐containing functional groups, such as OH stretching (3433 and 1393 cm −1 ), CO (1729 cm −1 ), and CO stretching (1067 cm −1 ). [ 38,39 ] After encapsulating LM, the carbonyl stretching peak at 1729 cm −1 disappears, while COO − peak at 1622 cm −1 becomes stronger, indicating that the COOH on GO has been converted into COO − to coordinate with Ga 3+ in LM. New bands such as NH (3312 cm −1 ) and intramolecular bonded OH (3191 cm −1 ) are formed, and CO stretching at 1067 cm −1 weakens in the curve of P‐LMGO.…”

Bioprocess-Inspired Room-Temperature Synthesis of Enamel-like Fluorapatite/Polymer Nanocomposites Controlled by Magnesium Ions

“…Enamel is the outermost layer of a tooth and is one of the hardest mineralized tissues in living organisms . The outstanding mechanical strength and fatigue resistance of enamel are attributed to the intricate hierarchical arrangement of nanorod-like hydroxyapatite (HAP) or fluorapatite (FAP) crystals. , Decades of dedicated research were directed at replicating the columnar structure and excellent mechanical properties of enamel in vitro. , Yeom et al adopted a strategy reversing the sequence of enamel biosynthesis in nature to replicate enamel-inspired ZnO nanocomposites. The hardness and Young’s modulus values of the resultant composites were comparable to those of natural enamel.…”

“…18,19 Decades of dedicated research were directed at replicating the columnar structure and excellent mechanical properties of enamel in vitro. 20,21 Yeom et al adopted a strategy reversing the sequence of enamel biosynthesis in nature to replicate enamel-inspired ZnO nanocomposites. The hardness and Young's modulus values of the resultant composites were comparable to those of natural enamel.…”

A Selective-Response Bioinspired Strain Sensor Using Viscoelastic Material as Middle Layer

“…To fabricate these sensors, various transduction mechanisms, such as piezoresistive, capacitive, piezoelectric, triboelectric, liquid metal, etc., have been adopted. On the basis of the above mechanisms, two main types of sensors have been widely developed: particular structural types and functional material types. − The former type includes serpentine, wrinkle, pillar, crack, and interlock, offering advantages such as high sensitivity, low hysteresis, and fast response. The latter always refers to conductive polymer composites, which are comprised of various incorporated fillers, including carbon materials (e.g., CNTs, CB, graphene), metallic nanoparticles (e.g., AgNPs, AuNPs, PtNPs), nanowires (e.g., AgNWs, AuNWs), and a wide range of matrices (e.g., PDMS, Ecoflex, NR, SBR).…”