Construction of Bionic Porous Polyetherimide Structure by an In Situ Foaming Fused Deposition Modeling Process

Abstract

A wide variety of organisms in nature have excellent structures, which are far superior to artificial machinery. [1] Inspired by nature, the structural characteristics of biological systems were mimicked to design similar new bionic materials, [2,3] to obtain more reliable, efficient, and intelligent material. [4] Porous structure was a prevalent structure in many organisms in nature, such as leaves, [5] trees, and other plants, whose cell structure enhanced fluid transport and adsorption in plant. Porous structures in the fur of animals [6] could reduce the weight of the fur while insulating the heat to maintain the body temperature. [7] The unique hexagonal structure of honeycomb [8] had maximum space utilization and excellent mechanical properties. The porous structure in the skeleton [9] facilitated cell adhesion and growth. And the hierarchical porous structure with both macropores and micropores were more capable of fast mass transfer, [10][11][12] showing great potential for applications in catalysis, [13] adsorption, [5] lithium-ion batteries, [14] fuel cell, [15] supercapacitor, [15] etc.However, it is challenging to construct biomimetic hierarchical porous materials artificially. Most of the methods traditionally used to fabricate cell structures are selective etching, salt leaching, phase separation, foaming, freeze-drying, ice crystal template method, etc. Huang et al. [16] used thermally induced phase separation-salt leaching to prepare polyamide porous bionic scaffolds. Zhai et al. used physical foaming and bead compression molding process to prepare a variety of polymer porous foams, such as polypropylene, [17] polystyrene, [18] polylactic acid (PLA), [19] polycarbonate, [20] polyetherimide, [21] thermoplastic polyurethane (TPU) [22] foams, etc. Bai et al. prepared bone tissue scaffolds with gradient channel pores through the ice crystal template method, [23] manufactured polar bear fur bionic porous fibers via the freeze-drying technology. [24] Nevertheless, these methods are complicated to operate and face great difficulties in mimicking complex, fine, and layered porous structures.The introduction of 3D printing technology, such as direct ink writing (DIW), [25][26][27] selective laser melting (SLM), [28,29] fused deposition modeling (FDM), [30,31] and digital light processing (DLP) [32,33] has taken the design and construction of bionic structures a step further. Compared with traditional molding methods, 3D printing technology possessed extremely high degree of design freedom. However, 3D printing technology is not only limited by the printable materials, but also its limited resolution do not allow the preparation of microscopic holes. It usually also needs to be combined with conventional technologies to prepare hierarchical porous structures with both macroscopic and microscopic pores. For instance, Song et al. [34] used SLM technology

Enhanced Interfacial Adhesion and Increased Isotropy of 3D Printed Parts with Microcellular Structure Fabricated via a Micro‐Extrusion CO2‐Foaming Process

“…For the preparation of foamed samples, the PEI filaments were placed in the autoclave at 60 °C after drying at 150 °C for 4 h. According to our previous research, the adsorption and desorption rates of CO 2 in PEI are slow. [ 46 ] To achieve the adsorption equilibrium [ 23 ] and high gas content, [ 23 ] in the following 48 h step, the filaments were saturated with compressed CO 2 at 8 MPa. After saturation, PEI filaments were taken out and placed for 8–240 h for desorption before printing.…”

“…After saturation, PEI filaments were taken out and placed for 8–240 h for desorption before printing. The desorption rate of CO 2 in PEI material is very low, [ 46 ] it can meet the requirement of long‐time printing of parts. Therefore, the influence of gas content on foam morphology during the long 8–240 h desorption process was studied, while the unfoamed samples were obtained by printing directly after drying without saturation.…”

“…The infilling angles of the sample were 90°and 0°(Figure 2b). Based on the commonly used printing parameters in the literature and our previous exploration of PEI printing parameters, [31,32,46,47] the printing parameters of foamed and unfoamed samples were selected as shown in Table 1. For PEI, we used common parameters (layer height: 0.20 mm, printing temperature: 360 °C, platform temperature: 160 °C, printing speed: 50 mm s À1 ) to print the samples, and appropriately changed one of the parameters to analyze the impact of printing parameters on the printed samples.…”

A Review of the Preparation of Porous Fibers and Porous Parts by a Novel Micro-Extrusion Foaming Technique

“…Previously, PEI was used for MEF to prepare porous fibers, demonstrating its excellent foaming behavior. Afterward, Zhou et al [ 126 ] used PEI for micro-extrusion foam stacking to prepare porous parts. Research showed that as the saturation pressure decreased, desorption time was prolonged, nozzle temperature increased, cell size gradually increased, and cell density gradually decreased.…”

“…( B ) Software slicing to determine the printing path. ( C ) The physical object obtained by micro-extrusion foam stacking, honeycomb, ( D ) grid scaffold (un-foamed), ( E ) grid scaffold (foamed), ( F ) triangle scaffold, ( G ) hexagonal scaffold, ( H ) bone, ( I ) loofah, ( J ) bamboo, and ( K ) leaf [ 126 ].…”