Current significance and future perspective of 3D-printed bio-based polymers for applications in energy conversion and storage system

The increasing global population has led to a surge in energy demand and the production of environmentally harmful products, highlighting the urgent need for renewable and clean energy sources. In this context, sustainable and eco-friendly energy production strategies have been explored to mitigate the adverse effects of fossil fuel consumption to the environment. Additionally, efficient energy storage devices with a long lifespan are also crucial. Tailoring the components of energy conversion and storage devices can improve overall performance. Three-dimensional (3D) printing provides the flexibility to create and optimize geometrical structure in order to obtain preferable features to elevate energy conversion yield and storage capacitance. It also serves the potential for rapid and cost-efficient manufacturing. Besides that, bio-based polymers with potential mechanical and rheological properties have been exploited as material feedstocks for 3D printing. The use of these polymers promoted carbon neutrality and environmentally benign processes. In this perspective, this review provides an overview of various 3D printing techniques and processing parameters for bio-based polymers applicable for energy-relevant applications. It also explores the advances and current significance on the integration of 3D-printed bio-based polymers in several energy conversion and storage components from the recently published studies. Finally, the future perspective is elaborated for the development of bio-based polymers via 3D printing techniques as powerful tools for clean energy supplies towards the sustainable development goals (SDGs) with respect to environmental protection and green energy conversion

Clickable and Antifouling Platform of Poly[(propargyl methacrylate)-<i>ran</i>-(2-methacryloyloxyethyl phosphorylcholine)] for Biosensing Applications

A functional copolymer platform, namely, poly­[(propargyl methacrylate)-<i>ran</i>-(2-methacryloyloxyethyl phosphorylcholine)] (PPgMAMPC), was synthesized by reversible addition–fragmentation chain-transfer polymerization. In principle, the alkyne moiety of propargyl methacrylate (PgMA) should serve as an active site for binding azide-containing molecules via a click reaction, i.e., Cu-catalyzed azide/alkyne cycloaddition (CuAAC), and 2-methacryloyloxyethyl phosphorylcholine (MPC), the hydrophilic monomeric unit, should enable the copolymer to suppress nonspecific adsorption. The copolymers were characterized using Fourier transform infrared (FTIR) and ¹H NMR spectroscopies. Thiol-terminated, PPgMAMPC-SH, obtained by aminolysis of PPgMAMPC, was immobilized on a gold-coated substrate using a “grafting to” approach via self-assembly. Azide-containing species, namely, biotin and peptide nucleic acid (PNA), were then immobilized on the alkyne-containing copolymeric platform via CuAAC. The potential use of surface-attached PPgMAMPC in biosensing applications was shown by detection of specific target molecules, i.e., streptavidin (SA) and DNA, by the developed sensing platform using a surface plasmon resonance technique. The copolymer composition strongly influenced the performance of the developed sensing platform in terms of signal-to-noise ratio in the case of the biotin–SA system and hybridization efficiency and mismatch discrimination for the PNA–DNA system

Surface-Grafted Poly(acrylic acid) Brushes as a Precursor Layer for Biosensing Applications: Effect of Graft Density and Swellability on the Detection Efficiency

Carboxyl groups along poly­(acrylic acid) (PAA) brushes attached to the surface of a gold-coated substrate served as the precursor moieties for the covalent immobilization of amino-functionalized biotin or bovine serum albumin (BSA) to form a sensing probe for streptavidin (SA) or anti-BSA detection, respectively. Surface-grafted PAA brushes were obtained by acid hydrolysis of poly­(<i>tert</i>-butyl acrylate) brushes, formerly prepared by surface-initiated atom transfer radical polymerization of <i>tert</i>-butyl acrylate. As determined by surface plasmon resonance, the PAA brushes immobilized with functionalized biotin or BSA probes not only showed good binding with the designated target analytes but also maintained a high resistance to nonspecific protein adsorption, especially those PAA brushes with a high surface graft density. Although the probe binding capacity can be raised as a function of the graft density of the PAA brushes or the amount of carboxyl groups along the PAA chains, the accessibility of the target analyte to the immobilized probe was limited at the high graft density of the PAA brushes. The effect was far more apparent for the BSA–anti-BSA probe–analyte pair than for the much smaller biotin–SA probe–analyte pair. The impact of the swellability of the PAA brushes, as tailored by the degree of carboxyl group activation, on both the sensing probe immobilization and analyte detection was also addressed. This investigation demonstrated that PAA brushes having a defined graft density have a promising potential as a precursor layer for biosensing applications

Gold Nanorods Stabilized by Biocompatible and Multifunctional Zwitterionic Copolymer for Synergistic Cancer Therapy

A zwitterionic copolymer between methacryloyloxyethyl phosphorylcholine (MPC) and methacrylic acid (MA), PMAMPC is introduced as a potential versatile polymeric stabilizer for gold nanorods (AuNRs). The MA units in the copolymer serve as built-in feature for multiple functionalization, namely introducing additional thiol groups as active sites for binding with the AuNRs and conjugating with doxorubicin (DOX), an anticancer drug via acid-labile hydrazone linkage. The MPC units, on the other hand, provide biocompatibility and antifouling characteristics. The chemically modified PMAMPC can act as an effective stabilizer for AuNRs yielding PMAMPC-DOX-AuNRs with a fairly uniform size and shape with good colloidal stability. <i>In vitro</i> cytotoxicity suggested that PMAMPC can not only improve the AuNRs biocompatibility, but also decrease DOX toxicity to a certain extent. The PMAMPC-DOX-AuNRs were efficiently internalized inside cancer cells and localized in lysosomes, where DOX was presumably acid-triggered released as monitored by confocal laser scanning microscopic analysis and flow cytometry. Furthermore, the combined photothermal-chemo treatment of cancer cells using PMAMPC-DOX-AuNRs exhibited a higher therapeutic efficacy than either single treatment alone. These results suggested that the PMAMPC-DOX-AuNRs could potentially be applied in pH-triggered drug delivery for synergistic cancer therapy

Development of a Novel Antifouling Platform for Biosensing Probe Immobilization from Methacryloyloxyethyl Phosphorylcholine-Containing Copolymer Brushes

The immobilization of thiol-terminated poly­[(methacrylic acid)-<i>ran</i>-(2-methacryloyloxyethyl phosphorylcholine)] (PMAMPC-SH) brushes on gold-coated surface plasmon resonance (SPR) chips was performed using the “grafting to” approach via self-assembly formation. The copolymer brushes provide both functionalizability and antifouling characteristics, desirable features mandatorily required for the development of an effective platform for probe immobilization in biosensing applications. The carboxyl groups from the methacrylic acid (MA) units were employed for attaching active biomolecules that can act as sensing probes for biospecific detection of target molecules, whereas the 2-methacryloyloxyethyl phosphorylcholine (MPC) units were introduced to suppress unwanted nonspecific adsorption. The detection efficiency of the biotin-immobilized PMAMPC brushes with the target molecule, avidin (AVD), was evaluated in blood plasma in comparison with the conventional 2D monolayer of 11-mercaptoundecanoic acid (MUA) and homopolymer brushes of poly­(methacrylic acid) (PMA) also immobilized with biotin using the SPR technique. Copolymer brushes with 79 mol % MPC composition and a molecular weight of 49.3 kDa yielded the platform for probe immobilization with the best performance considering its high S/N ratio as compared with platforms based on MUA and PMA brushes. In addition, the detection limit for detecting AVD in blood plasma solution was found to be 1.5 nM (equivalent to 100 ng/mL). The results have demonstrated the potential for using these newly developed surface-attached PMAMPC brushes for probe immobilization and subsequent detection of designated target molecules in complex matrices such as blood plasma and clinical samples

Poly(<i>N</i>‑isopropylacrylamide)-Stabilized Gold Nanoparticles in Combination with Tricationic Branched Phenylene-Ethynylene Fluorophore for Protein Identification

Gold nanoparticles stabilized by thermoresponsive polymer, poly­(<i>N</i>-isopropylacrylamide) (PNIPAM-AuNPs) were prepared by surface grafting of thiol-terminated PNIPAM onto citrate-stabilized AuNPs. The color change of the PNIPAM-AuNPs solution from red to blue-purple without precipitation when the solution was heated to 40 °C, above the lower critical solution temperature (LCST) of PNIPAM, indicated the thermoresponsive property of the synthesized AuNPs. PNIPAM-AuNPs were used to detect proteins by chemical nose approach based on fluorescence quenching of fluorophore by AuNPs. An array-based sensing platform for detection of six proteins, namely bovine serum albumin, lysozyme, fibrinogen, concanavalin A, hemoglobin, holo-transferrin human can be successfully developed from the PNIPAM-AuNPs having different molecular weights (4 and 8 kDa) and conformation (varied heat treatment from 25 to 40 °C) in combination with a tricationic branched phenylene-ethynylene fluorophore. From principal component analysis (PCA) followed by linear discriminant analysis (LDA), 100% accuracy of protein classification using a leave-one-out (LOO) approach can be achieved by using only two types of PNIPAM-AuNPs

Thermoresponsive and Active Functional Fiber Mats for Cultured Cell Recovery

Thermoresponsive and active functional fiber mats were prepared from random copolymer of poly­(pentafluorophenyl acrylate-<i>co</i>-<i>N</i>-isopropylacrylamide) (P­(PFPA-<i>co</i>-NIPAM)), which was synthesized by a controlled radical polymerization process based on reversible addition–fragmentation chain transfer (RAFT). As reactive sites, pentafluorophenyl ester (PFP) groups were incorporated in the copolymer to allow for a multiple post-polymerization modification. UV-cross-linkable moieties were first introduced by partially reacting PFP groups in the copolymer with <i>ortho</i>-nitrobenzyl (ONB)-protected diamine. Electrospinning the resulting ONB-containing P­(PFPA-<i>co</i>-NIPAM), followed by UV-induced cross-linking, yielded stable cross-linked thermoresponsive PNIPAM-based fiber mats. The remaining PFP active groups on the surface of copolymer fiber mats allowed for further conjugation with an H-Gly-Arg-Gly-Asp-Ser-OH (GRGDS) peptide, a well-known cell adhesive peptide sequence that was selected as a model in order to promote cell growth. At 37 °C, fibroblast cells were found to attach, spread, and proliferate well on the GRGDS-immobilized cross-linked (CL) fiber mat, as opposed to those on the GRGDS-immobilized un-cross-linked (UCL) fiber mat. By decreasing the temperature down to 20 °C, i.e. below the lower critical solution temperature (LCST) of thermoresponsive PNIPAM, cultured cells could easily be released from both GRGDS-immobilized CL and UCL fiber mats, whereas no cells were detached from tissue culture polystyrene (TCPS). These results suggest that the thermosensitive and active functional fiber mat obtained in this research represent an attractive and versatile platform for cultured cell recovery, which is beneficial for tissue engineering applications

Patterned Poly(acrylic acid) Brushes Containing Gold Nanoparticles for Peptide Detection by Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

Patterned poly­(acrylic acid) (PAA) brushes was successfully generated via photolithography and surface-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylic acid as verified by water contact angle measurements and FT-IR analysis. The carboxyl groups of PAA brushes can act as reducing moieties for in situ synthesis of gold nanoparticles (AuNPs), without the use of additional reducing agent. The formation of AuNPs was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. The glass surface-modified by PAA brushes and immobilized with AuNPs (AuNPs-PAA) can be used as a substrate for SALDI-MS analysis, which is capable of detecting both small peptides having <i>m</i>/<i>z</i> ≤ 600 (glutathione) and large peptides having <i>m</i>/<i>z</i> ≥ 1000 (bradykinin, ICNK­QDCP­ILE) without the interference from matrix signal suggesting that AuNPs were stably trapped within the PAA brushes and the carboxyl groups of PAA can serve as internal proton source. By employing AuNPs as the capture probe, the AuNPs-PAA substrate can selectively identify thiol-containing peptides from the peptide mixtures with LOD as low as 0.1 and 0.05 nM for glutathione and ICNK­QDCP­ILE, respectively. An ability to selectively detect ICNK­QDCP­ILE in a diluted human serum is also demonstrated. The patterned format together with its high sensitivity and selectivity render this newly developed substrate a potential platform for high-throughput analysis of other biomarkers, especially those with low molecular weight in complex biological samples