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Lignin is a versatile biomass that possesses many different desirable properties such as antioxidant, antibacterial, anti-UV, and good biocompatibility. Natural lignin can be processed through several chemical processes. The processed lignin can be modified into functionalized lignin through chemical modifications to develop and enhance biomaterials. Thus, lignin is one of the prime candidate for various biomaterial applications such as drug and gene delivery, biosensors, bioimaging, 3D printing, tissue engineering, and dietary supplement additive. This review presents the potential of developing and utilizing lignin in the outlook of new and sustainable biomaterials. Thereafter, we also discuss on the challenges and outlook of utilizing lignin as a biomaterial., Graphical abstract Image 1, Highlights • Lignin's antioxidant, antibacterial, anti-UV and biocompatibility properties can be harnessed. • Modification and functionalization of lignin allows synthesis of enhanced biomaterials. • Biomedical applications of lignin-derived biomaterials include drug and gene delivery, biosensors, and tissue engineering.

The cathode materials for sodium ion batteries (SIBs) are intrinsically unstable due to their oxidation by electrolyte solution at high voltage; thus, developing novel solid permeable interfaces as passivation layers is critical to avoid these side oxidation reactions and increase the cycling durability of SIBs. Nevertheless, the abuse of passivation layers can hinder the Na+ transfer and further impact the rate capability. Herein, we demonstrated an effective approach that utilized konjac glucomannan (KGM) biopolymer as a multifunctional binder to build stable solid permeable interface films to achieve high-performance for Na3V2(PO4)3/C (NVP) cathodes. Compared with polyvinylidene difluoride (PVDF), the strong adhesion and solid permeable interface films of KGM protect the integrity of the electrodes. The unique conductive network and rich polar functional groups enable KGM to enhance the transfer of electrons and Na+ ions at the interfaces. Thanks to the multiple functions of KGM offering adhesion strength, a conductive network and a solid permeable interface, the NVP cathode exhibited a reversible capacity of 108.0 mA h g−1 at 0.5C (1C = 117 mA g−1). At a high rate of 50C, NVP profited from KGM to show a good capacity of 63.1 mA h g−1 and a high durability of 10 000 cycles with a small fading rate of 0.00259% per cycle. Hard carbon‖NVP full batteries, using KGM as the cathode binder, possessed a high specific energy of 137.7 W h kg−1, indicating the potential applications of KGM as an environmentally friendly binder for achieving high-rate capacity and long-term cycling durability of SIBs.

Scaffolds for stem cell-based therapy of cartilage defect require bioactivity and stiffness mimicking to the native cartilage matrix. In this study, we fabricated electrospun nanofibers composited of cartilage matrix components (collagen or chondroitin sulfate) and poly(e-caprolactone)-polytetrahydrofuran (PCL-PTHF). PCL-PTHF with rat tail derived collagen was named PR and PCL-PTHF with chondroitin sulfate (PS) termed PS, which have a modulus of 7.5 MPa and 3.6 MPa, respectively, within the range of cartilage matrix. Their chondrogenic potential for guiding chondrogenic differentiation and promoting cartilage regeneration were investigated based upon mesenchymal stem cells (MSCs). Results showed that both PR and PS nanofibers have the ability to induce chondrogenesis of MSCs and accelerate the regeneration of injured cartilage surface, probably via the suppression of Tumor necrosis factor (TNF) signaling pathway as evidenced by microarray profiles. Comparatively, PR showed better chondrogenic potential both in vitro and in vivo than that of PS, which may induce chondrogenesis through Hypoxia inducing factor-1 (HIF-1) signaling pathway. This study may provide reference for MSC based therapy of cartilage defects.

Large amounts of spent coffee grounds (SCGs) are often discarded and there is a need to find alternative disposal methods due to environmental concerns. This project aims to develop sustainable materials by re-purposing spent coffee grounds (SCGs). Oil extraction was performed using different organic solvents and yielded approximately 10% coffee oil. Coffee oil contains potentially useful chemical compounds such as fatty acids and caffeine. They also exhibited antioxidant properties. Extracted SCGs (ESCGs) were blended with epoxy resin to form composites. ESCG composites displayed a general decrease in mechanical properties relative to epoxy. However, improvements were observed when comparing ESCG composites and SCG composites. The greatest improvement belongs to epoxy composite filled with acetone-ESCGs, where the tensile strength, flexural modulus and flexural strength increased to 23.4 MPa, 3.02 GPa and 42.9 MPa respectively. This study presents a way to exploit waste materials which contributes to the goal of sustainability.

Drug therapy of osteoarthritis (OA) is limited by the short retention and lacking of stimulus-responsiveness after intra-articular (IA) injection. The weak acid microenvironment in joint provides a potential trigger for controlled drug release systems in the treatment of OA. Herein, we developed an pH-responsive metal − organic frameworks (MOFs) system modified by hyaluronic acid (HA) and loaded with an anti-inflammatory protocatechuic acid (PCA), designated as MOF@HA@PCA, for the therapy of OA. Results demonstrated that MOF@HA@PCA could smartly respond to acidic conditions in OA microenvironment and gradually release PCA, which could remarkably reduce synovial inflammation in both IL-1β induced chondrocytes and the OA joints. MOF@HA@PCA also down-regulated the expression of inflammatory markers of OA and promoted the expression of cartilage-specific makers. This work may provide a new insight for the design of efficient nanoprobes for precision theranostics of OA .

Poly(3-hydroxybutyrate) (PHB) is a sustainable and biodegradable biopolymer from bacteria, but its brittle nature greatly limits its applications. In this study, we developed a lignin-PHB copolymer to enhance the mechanical properties of PHB. β-Butyrolactone was grafted onto the lignin core by using solvent-free ring-opening polymerization (ROP). Then different amounts of lignin-PHB copolymers were blended into PHB and then engineered into nanofibers via electrospinning. The composite nanofibers with lignin-PHB copolymer exhibit much stronger mechanical properties than pure PHB fibers. Composite nanofibers with 2% lignin copolymer demonstrate the best mechanical performance with tensile strength increasing from 1.45 ± 0.36 MPa to 5.61 ± 0.63 MPa, Young's modulus increasing from 54.7 ± 1.2 MPa to 84.6 ± 10.0 MPa, and elongation increasing from 9.6 ± 2.2% to 93.5 ± 7.6%. Moreover, PHB/lignin nanofibers demonstrate tunable antioxidant activity, allowing the neutralization of excess free radicals in our body. Animal studies also demonstrate that the PHB/lignin nanofibers are nonirritating and biocompatible. Hence, these new PHB/lignin nanofibers hold great potential for biomedical applications.

Cartilage cannot self-repair and thus regeneration is a promising approach to its repair. Here we developed new electrospun nanofibers , made of poly (e-caprolactone)/polytetrahydrofuran (PCL-PTHF urethane) and collagen I from calf skin (termed PC), to trigger the chondrogenic differentiation of mesenchymal stem cells (MSCs) and the cartilage regeneration in vivo . We found that the PC nanofibers had a modulus (4.3 Mpa) lower than the PCL-PTHF urethane nanofibers without collagen I from calf skin (termed P) (6.8 Mpa) although both values are within the range of the modulus of natural cartilage (1–10 MPa). Both P and PC nanofibers did not show obvious difference in the morphology and size. Surprisingly, in the absence of the additional chondrogenesis inducers, the softer PC nanofibers could induce the chondrogenic differentiation in vitro and cartilage regeneration in vivo more efficiently than the stiffer P nanofibers. Using mRNA-sequence analysis, we found that the PC nanofibers outperformed P nanofibers in inducing chondrogenesis by specifically blocking the NF–kappa B signaling pathway to suppress inflammation. Our work shows that the PC nanofibers can serve as building blocks of new scaffolds for cartilage regeneration and provides new insights on the effect of the mechanical properties of the nanofibers on the cartilage regeneration.

Poly(3-hydroxybutyrate) (PHB) is an attractive biopolymer potential for various applications, but its brittle nature is a big handicap. In this study, we proposed lignin copolymers as mechanical reinforcement agents for PHB. A series of lignin copolymers (random and block) were synthesized via the solvent free ring-opening polymerization (ROP) of β-butyrolactone and/or e-caprolactone onto lignin core. The lignin copolymers were characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Next, these lignin copolymers were incorporated into PHB nanofibers as reinforcement fillers, in order to improve their mechanical properties. It is found that the lignin block copolymer with poly(e-caprolactone) (PCL) segment followed by PHB segment (LPC + H) displayed the best mechanical improvement. Tensile strength of PHB nanofibers enhanced from 1.81 MPa to 3.13 MPa, and elongation at break increased from 15% of 55%. In the reinforced system, lignin plays as a rigid core, PCL acts a rubbery layer and PHB segment forms strong bonding with fiber matrix. Moreover, PHB/lignin nanofibers were demonstrated with superior biodegradability and biocompatibility, indicating that the new nanofibrous system holds great potential for biomedical applications.

CpG oligodeoxynucleotides (CpG ODNs) bind to toll-like receptor 9 (TLR9) and activate the immune system. Thus, CpG ODNs have attracted considerable interest as immunotherapeutic agents or adjuvants for many diseases. Herein we report that polyethylenimine (PEI) functions as a multifunctional vector for both enhancing and regulating the immunostimulatory activity of CpG ODNs. PEI and CpG ODNs formed nanopolyplexes (NPs), which possessed good biocompatibility. PEI-CpG ODN NPs facilitated the internalization of CpG ODNs and induced increasing amounts of cytokines. Most importantly, PEI-CpG ODN NPs induced interleukin-6 (IL-6) and interferon-α (IFN-α) simultaneously, while class B CpG ODNs induced only IL-6. In contrast to class C CpG ODNs, which also simultaneously induce IFN-α and IL-6, the ratio of IFN-α and IL-6 induced by PEI-CpG ODN NPs could be regulated by changing the N/P ratio. This flexible bifurcated cytokine is promising for treating diseases such as cancer that require IL-6 and IFN-α simultaneously. Our findings propose a regulatory effect of PEI on the immunostimulatory activity of CpG ODNs, which will shed light on the development of highly efficient nonviral vectors for CpG ODN-based immunotherapy.

Rational design of new wound dressing materials aims to accelerate wound healing. Traditional hydrophilic wound dressings, however, tend to cause retention of wound exudate retention, which increases the risk of bacterial infection, resulting in slower wound healing. Herein, a multifunctional amphiphilic wound dressing nanofibrous materials with Janus superhydrophilic/ superhydrophobic feature is designed to accelerate wound healing. In this design, the top superhydrophilic polycaprolactone (PCL)-Gelatin (PCL-Gelatin, WCA ~ 0°) fibers function as a pump-like suction layer that can effectively isolate wound exudate from the wound site, thereby providing drier condition which lowers the risk of wound infection. More importantly, the superhydrophobic PCL-poly(perfluorodecyl methacrylate)-block-poly(dimethylsiloxane)-block-poly(perfluorodecyl methacrylate) (PFMA-b-PDMS-b-PFMA) (PCL-PFMA, WCA ~ 140°) in contact with the wound site showed excellent anti-adhesion effect to bacterial, cells and tissues, thereby further lowering the risk of bacterial infection and preventing the secondary injuries caused by dressing changes. Sprague-Dawley (SD) rat skin lesion model demonstrated significant improvement in wound healing of the Janus amphipathic PCL-Gelatin / PCL-PFMA fiber films compared with the conventional hydrophilic- and hydrophobic-only wound dressing materials. After 14 days of treatment, the wound healing area in this group was close to 100%. To the best our acknowledge, this is a pioneer exploration of Janus amphipathic wound dressing with unidirectional drainage function and anti-adhesive ability, which may have great potential for real life usage on clinical patients.

Upconversion of light has attracted intensive studies for biomedical research, because it enables deeper tissue analysis owing to the longer wavelength of incident light, compared with conventional downconversion fluorescent materials. Triplet-triplet annihilation (TTA), as a typical mechanism of upconversion, does not necessitate high power excitation and exhibits a higher quantum yield than rare earth upconversion owing to more sensitizer options with higher absorption coefficients. A desirable wavelength range of excitation and emission can be realized by careful selection of the combination of sensitizer and activator. Therefore, TTA-UC is worth exploring further for biorelated applications, such as bioimaging and biodetection. Recent developments are reviewed in this article.

Lignin polymerization has been considered as an effective approach for lignin valorization. Herein we report the synthesis of a series of new lignin-based copolymers (lignin–poly(e-caprolactone-co-lactide), lignin–PCLLA) via solvent-free ring-opening polymerization. Lignin–PCLLA copolymers with tunable molecular weights (10 to 16 kDa) and glass transition temperatures (−40 to 40 °C) were obtained. Such copolymers were engineered into ultrafine nanofibers by blending with polyesters (polycaprolactone, PCL and poly(l-lactic acid), PLLA) via electrospinning. Both PCL/lignin–PCLLA and PLLA/lignin–PCLLA nanofibers displayed uniform and beadless nanofibrous morphology. The size (diameters ranging from 300 to 500 nm) and tensile tests of the obtained nanofibers indicated that the lignin copolymers are miscible with the polyester matrices and can significantly improve the mechanical properties of the nanofibers. Moreover, good antioxidant activity and biocompatibility of the lignin nanofibers were demonstrated in...

TiO2-based nanomaterials are among the most promising photocatalysts for degrading organic dye pollutants. In this work, Au–TiO2 nanofibers were fabricated by the electrospinning technique, followed by calcination in air at 500 °C. Morphological and structural analyses revealed that the composite consists of TiO2 nanofibers with embedded Au nanoparticles that are extensively distributed throughout the porous fibrous structure of TiO2. The photocatalytic performance of these Au-embedded TiO2 nanofibers was evaluated in the photodegradation of Rhodamine B and methylene blue under solar simulator irradiation. Compared with pristine TiO2 nanofibers, the Au-embedded TiO2 nanofibers displayed far better photocatalytic degradation efficiency. The plasmon resonance absorption of Au nanoparticles in the visible spectral region and the effective charge separation at the heterojunction of the Au–TiO2 hybrid are the key factors that have led to the considerable enhancement of the photocatalytic activity. The results of this study clearly demonstrate the potential of Au–TiO2 electrospun nanofibers as solar-light-responsive photocatalysts for the effective removal of dye contaminants from aquatic environments.

Biodegradable poly(lactic acid) (PLA)–lignin composites are considered to be promising renewable plastic materials toward a sustainable world. The addition of lignin to PLA may assist to combat the oxidative stress induced by PLA as biomaterials. In this study, PLA–lignin copolymers with various contents of alkylated lignin (10–50%) were synthesized by ring-opening polymerization. The molecular weight of such copolymers ranged from 28 to 75 kDa, while the PLA chain length varied from 5 to 38. These PLA–lignin copolymers were further blended with poly(l-lactide) (PLLA) and fabricated into nanofibrous composites by electrospinning. The PLLA/PLA–lignin nanofibers displayed uniform and bead-free nanostructures with fiber diameter of 350–500 nm, indicating the miscibility of PLLA and lignin copolymers in nanoscale. Unlike bulk materials, incorporation of PLA–lignin copolymers did not enhance the mechanical properties of the nanofibrous composites. Antioxidant assay showed that the lignin copolymers and PLLA/PL...

In situ gel delivery systems are preferred over conventional systems due to sustained and prolonged release action of therapeutic payload onto the targeted site. Thermogel, a form of in situ gel-forming polymeric formulation, undergoes sol-gel transition after administration into the body. At room temperature, the system is an aqueous polymer solution that easily entraps therapeutic payload by mixing. Upon injection, the higher physiological temperature causes gelation in situ because of the presence of thermosensitive polymers. The gel degrades gradually over time, allowing sustained release of therapeutics localized to the site of interest. This minimizes systemic toxicity and improved efficacy of drug release to the targeted site. Thermogel properties can be easily altered for specific applications via substitution and modification of components in diblock and triblock copolymer systems. The feasibility of fine-tuning allows modifications to biodegradability, biocompatibility, biological functionalization, mechanical properties, and drug release profile. This review summarized recent development in thermogel research with a focus on synthesis and self-assembly mechanisms, gel biodegradability, and applications for drug delivery, cell encapsulation and tissue engineering. This review also assessed inadequacy of material properties as a stand-alone factor on therapeutic action efficacy in human trials, with a focus on OncoGel, an experimental thermogel that demonstrated excellent individual or synergistic drug delivery system in preclinical trials but lacked therapeutic impact in human trials. Detailed analysis from all aspects must be considered during technology development for a successful thermogel platform in drug delivery and tissue engineering.

With an ever-increasing attention on the climate change and the growing amount of plastic wastes generated, the search for an alternative to the petroleum-based plastics has never been as imperative. Inspired by the structure of natural wood, we aim to reproduce artificial equivalent using modified lignin and cellulose acetate. As natural wood are made up of an aggregation of fibers, electrospinning was used to produce the fiber component. Besides exploring the influence of various polymers on the properties of the eventual fibers, its properties were also examined in terms of its orientation – random and aligned. The addition of lignin copolymers was shown to remarkably improve the tensile strength and the Young’s modulus of cellulose acetate fibers up to 500% and 7,000% respectively. In contrast to the random fibers, the aligned fibers demonstrated better tensile strength and Young’s modulus which could be attributed to the higher crystallinity. Among the fibers, the longitudinal aligned C.A. + Lig-PHB fibers exhibited the best tensile strength and Young’s modulus which could be explored for load bearing applications.

Electrospinning is a common method to prepare nanofiber scaffolds for tissue engineering. One of the common cellulose esters, cellulose acetate butyrate (CAB), has been electrospun into nanofibers and studied. However, the intrinsic hydrophobicity of CAB limits its application in tissue engineering as it retards cell adhesion. In this study, the properties of CAB nanofibers were improved by fabricating the composite nanofibers made of CAB and hydrophilic polyethylene glycol (PEG). Different ratios of CAB to PEG were tested and only the ratio of 2:1 resulted in smooth and bead-free nanofibers. The tensile test results show that CAB/PEG composite nanofibers have 2-fold higher tensile strength than pure CAB nanofibers. The hydrophobicity of the composite nanofibers was also reduced based on the water contact angle analysis. As the hydrophilicity increases, the swelling ability of the composite nanofiber increases by 2-fold with more rapid biodegradation. The biocompatibility of the nanofibers was tested with normal human dermal fibroblasts (NHDF). The cell viability assay results revealed that the nanofibers are non-toxic. In addition to that, CAB/PEG nanofibers have better cell attachment compared to pure CAB nanofibers. Based on this study, CAB/PEG composite nanofibers could potentially be used as a nanofiber scaffold for applications in tissue engineering.

Osteoarthritis (OA) is one of the most common musculoskeletal disorders worldwide. Oxidative stress initiated by excessive free radicals such as reactive oxygen species (ROS) is a leading cause of cartilage degradation and OA. However, conventional injection or oral intake of antioxidants usually cannot provide effective treatment due to rapid clearance and degradation or low bioavailability. Here, a new strategy is proposed based on nanofibers made of poly (ε-caprolactone) (PCL) and PCL-grafted lignin (PCL-g-lignin) copolymer. Lignin offers intrinsic antioxidant activity while PCL tailors the mechanical properties. Electrospun PCL-lignin nanofibers show excellent antioxidant activity, low cytotoxicity and excellent anti-inflammatory effects as demonstrated using both H2O2-stimulated human chondrocytes and an OA rabbit model. PCL-lignin nanofibers inhibit ROS generation and activate antioxidant enzymes through autophagic mechanism. Arthroscopic implantation of nanofibrous membrane of PCL-lignin is effective to OA therapy because it is biocompatible, biodegradable and able to provide sustained antioxidant activity. Agency for Science, Technology and Research (A*STAR) This study was financially supported by National key R&D program of China (2018YFC1105900), the Guangxi Science and Technology Base and Talent Special Project (Grant No. GuikeAD17129012), and the local Science and Technology Development Project leading by the central government (the three-D printing and digital medical platform, Grant No. GuikeZY18164004), High level innovation teams and outstanding scholars in Guangxi Universities (The third batch). The authors gratefully acknowledge the financial support from the Institute of Materials Research and Engineering (IMRE) under the Agency of Science, Technology and Research (A*STAR).

Artificial skin devices are able to mimic the flexibility and sensory perception abilities of the skin. They have thus garnered attention in the biomedical field as potential skin replacements. This Review delves into issues pertaining to these skin-deep devices. It first elaborates on the roles that these devices have to fulfill as skin replacements, and identify strategies that are used to achieve such functionality. Following which, a comparison is done between the current state of these skin-deep devices and that of natural skin. Finally, an outlook on artificial skin devices is presented, which discusses how complementary technologies can create skin enhancements, and what challenges face such devices.

Cationic polymers remain attractive tools for non-viral gene transfer. The effectiveness of these vectors rely on the ability to deliver plasmid DNA (pDNA) into the nucleus of cells. While we have previously demonstrated the potential of Lignin-PGEA-PEGMA as a non-viral gene delivery vector, alterations of cellular phenotype and cytotoxicity were observed post transfection. The present study aims to explore transfection conditions for high efficiency and low toxicity of the Lignin-PGEA-PEGMA based gene delivery system. Cellular toxicity was significantly reduced by using the centrifugation protocol, which enables rapid deposition of DNA complexes. Replacement of media post centrifugation resulted in minimal exposure of cells to excess polymers, which were toxic to cells. At an optimized DNA amount (500–750 ng) and molar ratios of nitrogen (N) in polymer to phosphate (P) in pDNA (N/P = 30–40), with the use of a novel transfection enhancer that facilitates endosomal escape and nuclear trafficking, the efficiency of gene delivery was increased significantly 24 h post transfection. The present study demonstrated an appropriately optimized protocol that enabled the utility of a novel cationic polymer blend with a mixture of fusogenic lipids and a histone deacetylate inhibitor in non-viral transfection, thereby providing an attractive alternative to costly commercial gene carriers.

Polyester elastomers are soft, biodegradable and biocompatible and are commonly used in various biomedical applications, especially in tissue engineering. These synthetic polyesters can be easily fabricated using various techniques such as solvent casting, particle leaching, molding, electrospinning, 3-dimensional printing, photolithography, microablation etc. A large proportion of tissue engineering research efforts have focused on the use of allografts, decellularized animal scaffolds or other biological materials as scaffolds, but they face the major concern of triggering immunological responses from the host, on top of other issues. This review paper will introduce the recent developments in elastomeric polyesters, their synthesis and fabrication techniques, as well as their application in the biomedical field, focusing primarily on tissue engineering in ophthalmology, cardiac and vascular systems. Some of the commercial and near-commercial polyesters used in these tissue engineering fields will also be described.

Antioxidant is critical for the successful of nerve tissue regeneration, and biomaterials with antioxidant activity might be favorable for peripheral nerve repair. Lignin, a biopolymer from wood with excellent antioxidant properties, is still “unexplored” as biomaterials. To design an antioxidative bioscaffold for nerve regeneration, here we synthesized lignin-polycaprolactone (PCL) copolymers via solvent free ring-opening polymerization (ROP). Then such lignin-PCL copolymers were incorporated with PCL and engineered into nanofibrous scaffolds for supporting the growth of neuron and Schwann cell. Our results showed that the addition of lignin-PCL enhanced the mechanical properties of PCL nanofibers and endowed them with good antioxidant properties (up to 98.3 ± 1.9% free radical inhibition within 4 h). Cell proliferation assay showed that PCL/lignin-PCL nanofibers increased cell viability compared to PCL fibers, especially after an oxidative challenge. Moreover, Schwann cells and dorsal root ganglion (DRG) neurons cultured on the nanofibers to assess their potential for nerve regeneration. These results suggested that nanofibers with lignin copolymers promoted cell proliferation of both BMSCs and Schwann cells, enhanced myelin basic protein expressions of Schwann cells and stimulated neurite outgrowth of DRG neurons. In all, these sustainable, intrinsically antioxidant nanofibers may be a potential candidate for nerve TE applications.

Electronic devices have become ubiquitous in modern society and are prevalent in every facet of human activities. Although electronic devices have brought much convenience and value, the insatiable appetite for newer and more attractive devices has also created a growing ecological problem: managing electronic waste or e-waste. As the lifetime of electronic devices gets shorter and shorter, the pressure on e-waste management systems is mounting with no abate in sight. Therefore, an alternative to traditional electronics must be sought. Bio-degradable electronics have thus emerged as the most viable and ideal replacement to address the issue of uncontrollable e-waste. Bio-degradability will ensure that the waste generated will be at least non-toxic and even environmentally friendly. Furthermore, bio-degradable organic materials have also been shown to be biocompatible and human-friendly, being able to be metabolized safely in the body without causing adverse physiological reactions. As such, this developing class of “green” electronics is not only able to alleviate the growing e-waste problem, but also fulfils niche applications interfacing with the human body. This Review will introduce various bio-degradable organic materials that can serve as substitutes for the different components of an electronic device, highlight recent research achievements and applications in implementing such bio-degradable devices as well as present an overview of the printing technologies available that provide the low-cost and high throughput advantages of solution-processable organic materials over the traditional inorganic materials.

The desire for protection against UV exposure has resulted in the development of an increasing number of sunscreen agents. Lignin-based polymers have potential to serve as promising sunscreen agents as they have good UV absorption and antioxidant properties contributing towards the reduction of UV-induced skin damage. In this study, a series of lignin–poly(ethylene glycol) methacrylate (PEGMA) copolymers were synthesized via atom transfer radical polymerization (ATRP) to enhance the dispersion efficiency of lignin in the commercial creams. These copolymers showed tunability in both molecular weight (10–25 kDa) and particle size (100–200 nm), as well as excellent antioxidant properties. Different amounts of such copolymers were blended into commercial creams to investigate their sunscreen performance. Results indicated that adding lignin–PEGMA copolymers into sunblock creams improved their SPF values from 15.36 ± 2.44 to 38.53 ± 0.26. In summary, such lignin-based polymers with good UV protection and antioxidant properties offer a green alternative for developing the next generation of sunscreen creams.

In light of the incessant consumption of raw materials in the world today, the search for sustainable resources is ever pressing. Lignin, the second most naturally abundant biomass, which makes up 15% to 35% of the cell walls of terrestrial plants, has always been treated as waste and used in low-value applications such as heat and electricity generation. However, its abundance in nature could potentially solve the problem of the rapidly depleting resources if it was successfully translated into a renewable resource or valorized to higher value materials. Advanced lignin modification chemistry has generated a number of functional lignin-based polymers, which integrate both the intrinsic features of lignin and additional properties of the grafted polymers. These modified lignin and its copolymers display better miscibility with other polymeric matrices, leading to improved performance for these lignin/polymer composites. This review summarizes the progress in using such biopolymers as reinforcement fillers, antioxidants, UV adsorbents, antimicrobial agents, carbon precursors and biomaterials for tissue engineering and gene therapy. Recent developments in lignin-based smart materials are discussed as well.

Natural polysaccharide pectin has for the first time been grafted with polyhydroxybutyrate (PHB) via ring-opening polymerization of β-butyrolactone. This copolymer, pectin-polyhydroxybutyrate (pec-PHB), was blended with PHB in various proportions and electrospun to produce nanofibers that exhibited uniform and bead-free nanostructures, suggesting the miscibility of PHB and pec-PHB. These nanofiber blends exhibited reduced fiber diameters from 499 to 336–426 nm and water contact angles from 123.8 to 88.2° on incorporation of pec-PHB. They also displayed 39–335% enhancement of elongation at break relative to pristine PHB nanofibers. pec-PHB nanofibers were found to be noncytotoxic and biocompatible. Human retinal pigmented epithelium (ARPE-19) cells were seeded onto pristine PHB and pec-PHB nanofibers as scaffold and showed good proliferation. Higher proportions of pec-PHB (pec-PHB10 and pec-PHB20) yielded higher densities of cells with similar characteristics to normal RPE cells. We propose, therefore, that nanofibers of pec-PHB have significant potential as retinal tissue engineering scaffold materials.

A porous shape memory scaffold with both biomimetic structures and electrical conductivity properties is highly promising for nerve tissue engineering applications. In this study, a new shape memory polyurethane polymer which consists of inorganic polydimethylsiloxane (PDMS) segments with organic poly(e-caprolactone) (PCL) segments was synthesized. Based on this poly(PCL/PDMS urethane), a series of electrically conductive nanofibers were electrospun by incorporating different amounts of carbon-black. Our results showed that after adding carbon black into nanofibers, the fiber diameters increased from 399 ± 76 to 619 ± 138 nm, the crystallinity decreased from 33 to 25% and the resistivity reduced from 3.6 GΩ/mm to 1.8 kΩ/mm. Carbon black did not significantly influence the shape memory properties of the resulting nanofibers, and all the composite nanofibers exhibited decent shape recovery ratios of >90% and shape fixity ratios of >82% even after 5 thermo-mechanical cycles. PC12 cells were cultured on the shape memory nanofibers and the composite scaffolds showed good biocompatibility by promoting cell-cell interactions. Our study demonstrated that the poly(PCL/PDMS urethane)/carbon-black nanofibers with shape memory properties could be potentially used as smart 4-dimensional (4D) scaffolds for nerve tissue regeneration.

Nerve tissue engineering (TE) requires biomimetic scaffolds providing essential chemical and topographical cues for nerve regeneration. Poly(glycerol sebacate) (PGS) is a biodegradable and elastic polymer that has gained great interest as a TE scaffolding biomaterial. However, uncured PGS is difficult to be electrospun into nanofibers. PGS would, therefore, require the addition of electrospinning agents. In this study, we modified PGS by using atom transfer radical polymerization (ATRP) to synthesize PGS-based copolymers with methyl methacrylate (MMA). The synthesized PGS-PMMA copolymer showed a molecular weight of 82kDa and a glass transition temperature of 115°C. More importantly, the PGS-PMMA could be easily electrospun into nanofiber with a fiber diameter of 167±33nm. Blending gelatin into PGS-PMMA nanofibers was found to increase its hydrophilicity and biocompatibility. Rat PC12 cells were seeded onto the PGS-PMMA/gelatin nanofibers to investigate their potential for nerve regeneration. It was found that gelatin-containing PGS-based nanofibers promoted cell proliferation. The elongated cell morphology observed on such nanofibers indicated that the scaffolds could induce the neurite outgrowth of the nerve stem cells. Overall, our study suggested that the synthesis of PGS-based copolymers might be a promising approach to enhance their processability, and therefore advancing bioscaffold engineering for various TE applications.

A new drug concentration meter is developed. In vivo drug release can be monitored precisely via a self-indicating drug delivery system consisting of a new aggregation-induced emission thermoresponsive hydrogel. By taking the advantage of a self-indicating system, one can easily detect the depletion of drugs, and reinject to maintain a dosage in the optimal therapeutic window. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

A porous shape memory scaffold with biomimetic architecture is highly promising for bone tissue engineering applications. In this study, a series of new shape memory polyurethanes consisting of organic poly(e-caprolactone) (PCL) segments and inorganic polydimethylsiloxane (PDMS) segments in different ratios (9 : 1, 8 : 2 and 7 : 3) was synthesised. These PCL-PDMS copolymers were further engineered into porous fibrous scaffolds by electrospinning. With different ratios of PCL: PDMS, the fibers showed various fiber diameters, thermal behaviour and mechanical properties. Even after being processed into fibrous structures, these PCL-PDMS copolymers maintained their shape memory properties, and all the fibers exhibited excellent shape recovery ratios of >90% and shape fixity ratios of >92% after 7 thermo-mechanical cycles. Biological assay results corroborated that the fibrous PCL-PDMS scaffolds were biocompatible by promoting osteoblast proliferation, functionally enhanced biomineralization-relevant alkaline phosphatase expression and mineral deposition. Our study demonstrated that the PCL-PDMS fibers with excellent shape memory properties are promising substrates as bioengineered grafts for bone regeneration.

Further developing on the technique originally intended for the purpose of forming tough hydrogels, we showed in this study that the double-network system can also be used to synthesize an injectable gel. The gel was made up of poly(ethylene glycol) methyl ether methacrylate, sodium alginic acid, and calcium chloride, and two networks, consisting of ionic and covalent networks, were found to co-exist in the gel. Additionally, the rheology studies showed that the mechanical properties of the gel only deteriorated under high strain, demonstrating the robustness of the gel upon injection. The results of a cell cytotoxicity test and a preliminary cell encapsulation study were promising, showing good cell compatibility and thus suggesting that the hydrogels could potentially be used for cell delivery.