Scaffold-Based Poly(Vinylidene Fluoride) and Its Copolymers: Materials, Fabrication Methods, Applications, and Perspectives.

Tissue engineering involves implanting grafts into damaged tissue sites to guide and stimulate the formation of new tissue, which is an important strategy in the field of tissue defect treatment. Scaffolds prepared in vitro meet this requirement and are able to provide a biochemical microenvironment for cell growth, adhesion, and tissue formation. Scaffolds made of piezoelectric materials can apply electrical stimulation to the tissue without an external power source, speeding up the tissue repair process. Among piezoelectric polymers, poly(vinylidene fluoride) (PVDF) and its copolymers have the largest piezoelectric coefficients and are widely used in biomedical fields, including implanted sensors, drug delivery, and tissue repair. This paper provides a comprehensive overview of PVDF and its copolymers and fillers for manufacturing scaffolds as well as the roles in improving piezoelectric output, bioactivity, and mechanical properties. Then, common fabrication methods are outlined such as 3D printing, electrospinning, solvent casting, and phase separation. In addition, the applications and mechanisms of scaffold-based PVDF in tissue engineering are introduced, such as bone, nerve, muscle, skin, and blood vessel. Finally, challenges, perspectives, and strategies of scaffold-based PVDF and its copolymers in the future are discussed.

Biofabrication of biomimetic undulating microtopography at the dermal-epidermal junction and its effects on the growth and differentiation of epidermal cells.

The undulating microtopography located at the junction of the dermis and epidermis of the native skin is called rete ridges (RRs), which plays an important role in enhancing keratinocyte function, improving skin structure and stability, and providing three-dimensional (3D) microenvironment for skin cells. Despite some progress in recent years, most currently designed and manufactured tissue-engineered skin models still cannot replicate the RRs, resulting in a lack of biological signals in the manufactured skin models. In this study, a composite manufacturing method including electrospinning, 3D printing, and functional coating was developed to produce the epidermal models with RRs. Polycaprolactone (PCL) nanofibers were firstly electrospun to mimic the extracellular matrix environment and be responsible for cell attachment. PCL microfibers were then printed onto top of the PCL nanofibers layer by 3D printing to quickly prepare undulating microtopography and finally the entire structures were dip-coated with gelatin hydrogel to form a functional coating layer. The morphology, chemical composition, and structural properties of the fabricated models were studied. The results proved that the multi-process composite fabricated models were suitable for skin tissue engineering. Live and dead staining, cell counting kit-8 (CCK-8) as well as histology (haematoxylin and eosin (HE) methodology) and immunofluorescence (primary and secondary antibodies combination assay) were used to investigate the viability, metabolic activity, and differentiation of skin cells forin vitroculturing.In vitroresults showed that each model had high cell viability, good proliferation, and the expression of differentiation marker. It was worth noting that the sizes of the RRs affected the cell growth status of the epidermal models. In addition, the unique undulation characteristics of the epidermal-dermal junction can be reproduced in the developed epidermal models. Overall, thesein vitrohuman epidermal models can provide valuable reference for skin transplantation, screening and safety evaluation of drugs and cosmetics.

Evaluation of Available Energy and Standardized Ileal Digestibility of Amino Acids in Fermented Flaxseed Meal for Growing Pigs.

Flaxseed meal (FSM) is a byproduct of flaxseed oil extraction which has rich nutritional value and can be used as a high-quality new protein ingredient. However, the anti-nutrient factor (ANF) in FSM restricts its potential application in feed. The strategy of microbial fermentation is a highly effective approach to reducing ANF in FSM and enhancing its feeding value. However, evaluation of the nutritional value of fermented flaxseed meal (FFSM) in growing pigs has not yet been conducted. Thus, the purpose of this study was to investigate the nutritional value of FFSM in growing pigs and comparison of the effect of fermentation treatment on improving the nutritional value of FSM. Two experiments were conducted to determine the available energy value, apparent digestibility of nutrients, and standard ileal digestibility of amino acids of FSM and FFSM in growing pigs. The results showed as follows: (1) Fermentation treatment increased the levels of crude protein (CP), Ca and P in FSM by 2.86%, 9.54% and 4.56%, while decreasing the concentration of neutral detergent fiber (NDF) and acid detergent fiber (ADF) by 34.09% and 12.71%, respectively (p < 0.05); The degradation rate of CGs in FSM was 54.09% (p < 0.05); (2) The digestible energy (DE) and metabolic energy (ME) of FSM and FFSM were 14.54 MJ/kg, 16.68 MJ/kg and 12.85 MJ/kg, 15.24 MJ/kg, respectively; (3) Compared with FSM, dietary FFSM supplementation significantly increased the apparent digestibility of CP, NDF, ADF, Ca, and P of growing pigs (p < 0.05) and significantly increased the standard ileal digestibility of methionine (p < 0.05). These results indicate that fermentation treatment could effectively enhance the nutritional value of FSM and provide basic theoretical data for the application of FFSM in pig production.

A novel portable in situ printer for hydrogel multi-structure molding and cell printing.

Skin lesions not only disrupt appearance and barrier functionality but also lead to severe microbial infections and immune-inflammatory responses, seriously affect physical and mental health. In situ printing involves the direct deposition of bio-ink to create or repair damaged tissues or organs within a clinical setting. In this study, we designed and fabricated a novel portable in situ printer. This handheld instrument exhibits excellent printing performance, allowing hydrogels to be patterned and molded on surfaces according to specific requirements. By utilizing a dual-component hydrogels co-printing approach with high and low viscosities, we achieved in situ cell-laden printing using low-viscosity hydrogel. This demonstrates the advantages of the device in maintaining cell viability and achieving hydrogel structuring. This approach opens up the possibilities for the efficient encapsulation of active components such as drugs, proteins, and cells, enabling controlled macro- and micro-structuring of hydrogels. This breakthrough finding highlights the potential of our technical approach in dermatological treatment and wound repair, by dynamically adapting and regulating microenvironments in conjunction with hydrogel scaffolds and cell reparative impetus.

Strategies for vascularized skin models in vitro.

As the largest organ of the human body, the skin has a complex multi-layered structure. The composition of the skin includes cells, extracellular matrix (ECM), vascular networks, and other appendages. Because of the shortage of donor sites, skin substitutes are of great significance in the field of skin tissue repair. Moreover, skin models for disease research, drug screening, and cosmetic testing fall far short of the demand. Skin tissue engineering has made remarkable progress in developing skin models over the years. However, there are still several problems to be resolved. One of the crucial aspects is the lack of vascular systems for nutrient transport and waste disposal. Here, we will focus on the discussion and analysis of advanced manufacturing strategies for prevascularized skin, such as a scaffold-based method, cell coating technology, cell sheet engineering, skin-on-a-chip, and three-dimensional (3D) bioprinting. These key challenges, which restrict the prevascularized skin and provide perspectives on future directions will also be highlighted.

An Adsorption-Insertion Mechanism of Potassium in Soft Carbon.

Soft carbon (SC) has become a promising anode for potassium ion batteries (PIBs) benefiting from its structural flexibility. However, the evolution of potassium storage behavior with the microstructure (the average size of the crystallites La and the average interlayer spacing a3 ) is still unclear, which hinders the understanding of the potassium storage mechanism. Herein, a series of soft carbon with different microstructures is prepared through pyrolysis of petroleum pitch. Based on the analysis of the relationship between electrochemical behavior and microstructure, an adsorption-insertion mechanism is proposed: the capacity in the voltage range of 0.45-1.1 V is originated from the adsorption of potassium ions on edge-defect sites whereas the capacity below 0.45 V is attributed to the insertion of potassium ions into interlayers. When La equals to 10.56 Å, SCs exhibit an adsorption-controlled mechanism. However, as La increases to 120.98 Å, the insertion process is dominant. With La increasing from 21.9 to 93.02 Å, SCs have two mixed behaviors. The initial insertion coefficients do not change until a3 decreases to 3.46 Å. These findings highlight the relation of potassium storage behavior with different microstructures and the adsorption-insertion mechanism can provide insights into the design of SC anodes for PIBs.

Freestanding Surface Disordered NiCu Solid Solution as Ultrastable High Current Density Hydrogen Evolution Reaction Electrode.

The poor performance of conventional powdery catalysts under large current density and the slow kinetics of the Volmer step limit the large-scale application of alkaline hydrogen generation. Here, we report the preparation of freestanding surface disordered NiCu solid solution as an ultrastable hydrogen evolution reaction electrode. The introduction of ammonium ion could tailor the reduction/nucleation rate of metal ions during the hydrothermal process, thus contributing to its unique intertwined 3D microstructure. The catalyst exhibits superior HER activity with an overpotential of 322 mV at 1000 mA cm-2, and limited degradation after 110 h continuous operation at 1000 mA cm-2. Density functional theory calculations confirm that the substitution of Cu could accelerate the hydroxyl desorption process (OHads + e- → OH-) and thereby enhance the overall kinetics of the Volmer step. Our work demonstrates the strong efficacy of optimizing catalysts' structures and facilitating intermediate desorption for boosting industrial-scale alkaline HER performance.

New Method for Preparing Small-Caliber Artificial Blood Vessel with Controllable Microstructure on the Inner Wall Based on Additive Material Composite Molding.

The diameter of most blood vessels in cardiovascular and peripheral vascular system is less than 6 mm. Because the inner diameter of such vessels is small, a built-in stent often leads to thrombosis and other problems. It is an important goal to replace it directly with artificial vessels. This paper creatively proposed a preparation method of a small-diameter artificial vascular graft which can form a controllable microstructure on the inner wall and realize a multi-material composite. On the one hand, the inner wall of blood vessels containing direct writing structure is constructed by electrostatic direct writing and micro-imprinting technology to regulate cell behavior and promote endothelialization; on the other hand, the outer wall of blood vessels was prepared by electrospinning PCL to ensure the stability of mechanical properties of composite grafts. By optimizing the key parameters of the graft, a small-diameter artificial blood vessel with controllable microstructure on the inner wall is finally prepared. The corresponding performance characterization experimental results show that it has advantages in structure, mechanical properties, and promoting endothelialization.

3D bioprinting for fabricating artificial skin tissue.

As an organ in direct contact with the external environment, the skin is the first line of defense against external stimuli, so it is the most vulnerable to damage. In addition, there is an increasing demand for artificial skin in the fields of drug testing, disease research and cosmetic testing. Traditional skin tissue engineering has made encouraging progress after years of development. However, due to the complexity of the skin structures, there is still a big gap between existing artificial skin and natural skin in terms of function. Three-dimensional (3D) bioprinting is an advanced biological manufacturing method. It accurately deposits bioinks into pre-designed three-dimensional shapes to create complex biological tissues. This technology aims to print artificial tissues and organs with biological activities and complete physiological functions, thereby alleviating the problem of tissues and organs in short supply. Here, based on the introduction to skin structure and function, we systematically elaborate and analyze skin manufacturing methods, 3D bioprinting biomaterials and strategies, etc. Finally, the challenges and perspectives in 3D bioprinting skin field are summarized.

Uniform-sized insulin-loaded PLGA microspheres for improved early-stage peri-implant bone regeneration.

Poor initial stability at the first four weeks after surgery is becoming the major causes for metal implant failure. Previous attempts neglected the control release of insulin for the bone regeneration among nondiabetic subjects. The major reason may lie in the adverse effects, such as attenuated bone formation, hypoglycemia or hyperinsulinemia, that caused by the excessive insulin. Thus, spatiotemporal release of insulin may serve as the promising strategy. To address this, through solvent extraction (EMS), solvent evaporation (SMS) and cosolvent methods (CMS), we prepared three types of PLGA microspheres with various internal structures, but similar size distribution. The effects of the preparation methods on the properties of the microspheres, such as their release behavior, degradation of molecular weight, and structural evolution, were investigated. Human bone marrow mesenchymal stromal cells (BMSCs) and rabbit implant models were used to test the bioactivity of the microspheres in vitro and in vivo, respectively. The result demonstrated that these three preparation methods did not influence the polymer degradation but instead affected the internal structural evolution, which plays a crucial role in the release behavior, osteogenesis and peri-implant bone regeneration. Compared with EMS and CMS microspheres, SMS microspheres exhibited a relatively steady release rate in the first four weeks, which evidently stimulated the osteogenic differentiation of the stem cells and peri-implant bone regeneration. Meanwhile, SMS microspheres significantly enhanced the stability of the implant at Week 4, which is promising to reduce early failure rate of the implant without inducing adverse effects on the serum biochemical indices.

Exceptional high thermal conductivity of inter-connected annular graphite structures.

Based on the experimentally observed templating effects in CNTs containing carbon fibers, new types of inter-connected annular graphite structures are proposed and designed in order to significantly improve the cross-plane thermal conductivity of graphite. The calculations of the thermal conductivity of the newly designed structures were carried out by combining macroscopic continuous equations and microscopic molecular dynamic (MD) simulations. First, MD simulation was used to examine the influence of bending curvature on the in-plane thermal conductivity of a graphene sheet along and perpendicular to the rolling direction. Next, various types of annular graphite structures with single and inter-connected double/triple multi-layered graphite sheets were designed. Finally, finite element analysis was used to calculate the effective out of plane thermal conductivities of these structural models. The cross-plane thermal conductivity of a common graphite film is 2-3 orders of magnitude lower than its in-plane thermal conductivity, which strongly restricts its heat dissipation ability. However, the formation of annular graphite structures and the inter-connections of the outer layers lead to a dramatic improvement of effective out of plane thermal conductivity from 2.3 W m-1 K-1 to 799.8 W m-1 K-1 in this work, which is superior to common metal materials, especially considering the relatively lower density of carbon materials. These results would be valuable for designing and fabricating highly thermally conductive carbon materials for heat dissipation and temperature management.

Incorporation of Alkali Lignin in Polyacrylonitrile: Phase Separation, Coagulation, and Cyclization Kinetics.

In this study, we systematically investigated the phase separation behaviors of polyacrylonitrile (PAN)/alkali lignin (AL)/dimethyl sulfoxide (DMSO) systems and found that the addition of AL causes phase separation and the systems form sea (PAN)/island (AL) types of structures. Interestingly, the AL-rich domains are very stable even after a long time of storage up to 15 days. Additionally, how the phase separation affected the solution rheology, the coagulation process and PAN cyclization were explored. The addition of AL in PAN/DMSO solutions changes the solution viscosity and gelation behaviors. Also, the existence of AL-rich domains accelerates the coagulation rate of the PAN solution in water. Because AL degrades at a lower temperature than PAN, it reduces the PAN cyclization temperature but leads to a higher cyclization activation energy, which could be caused by their different initiation mechanisms. These results would be useful to understand how the addition of AL affects the PAN solution structures, solution rheology, solution coagulation behaviors, and PAN stabilization reactions.

Correction to: Hair follicles transcriptome profiles in Bashang long-tailed chickens with different plumage colors.

The words 'hair follicles' was replaced with 'feather follicles' in the title and the main text.

Feather follicles transcriptome profiles in Bashang long-tailed chickens with different plumage colors.

Despite the rich variety in plumage color found in nature, genetic studies on how feather follicles affect pigmentation are often limited to animals that have black and white pigment. To test how gene expression influences plumage color, transcriptomes of chicken feather follicles with white, black, hemp, reed catkins, silvery grey, and landscape plumage colors were generated using Illumina sequencing. We generated six RNA-Seq libraries with over 25 million paired-end clean reads per library with percentage of paired-end clean reads ranging from 96.73 to 96.98%. 78% of the reads mapped to the chicken genome, and approximately 70% of the reads were mapped to exons and 6% mapped to introns. Transcriptomes of feather follicles producing hemp and land plumage were similar, but these two showed moderate differences compared with gray and reed colored plumage. The black and white follicle transcriptomes were most divergent from the other colors. We identified several candidate genes, including GPNMB, PMEL, TYRP1, GPR143, OCA2, SOX10, SLC45A2, KRT75, and TYR. All of these genes are known to induce pigment formation in mice. White feathers result from the lack of pigment formation, and our results suggest that the white chickens due to the recessive insertion mutation of TYR. The formation of black area size and color depth may be due to the expression levels of GPNMB, PMEL, TYRP1, GPR143, OCA2, SOX10, SLC45A2, KRT75, and TYR. The GO analysis of the differentially expressed genes (DEGs) revealed that DEGs in our transcriptome analysis were enriched in cytoskeleton and cell structure related pathways. The black plumage transcriptome showed significant differences in melanogenesis, tyrosine metabolism, and riboflavin metabolism compared with transcriptomes of other plumage colors. The transcriptome profiles of the different chicken plumage colors provide a valuable resource to understand how gene expression influences plumage color, and will be an important resource for identifying candidate genes in breeding programs.

Regenerated cellulose I from LiCl·DMAc solution.

The regeneration of cellulose from microcrystalline cellulose/DMAc·LiCl solutions through thermal induced sol-gel transition and longtime gelation resulted in the formation of wholly cellulose I with a crystallinity as high as 84.7%.

Dynamic Self-Stiffening and Structural Evolutions of Polyacrylonitrile/Carbon Nanotube Nanocomposites.

The self-stiffening under external dynamic strain has been observed for some artificial materials, especially for nanocomposites. However, few systematic studies have been carried out on their structural evolutions, and the effect of the types of nanofillers was unclear. In this study, we used a semicrystalline polymer, polyacrylonitrile (PAN), and various types of carbon nanomaterials including C60, carbon nanotube (CNT), and graphene oxide (GO). An external uniaxial dynamic strain at small amplitude of 0.2% was applied on the prepared nanocomposite films. It was observed that PAN/CNT exhibited significant self-stiffening behavior, whereas PAN/GO showed no response. Systematic characterizations were performed to determine the structural evolutions of PAN/CNT film during dynamic strain testing, and it was found that the external dynamic strain not only induced the crystallization of PAN chains but also aligned CNT along the strain direction.

A high-yield and versatile method for the synthesis of carbon dots for bioimaging applications.

A facile and versatile molten-salt method was developed to prepare hydrosoluble carbon dots (CDs) from various precursors, in high yields and on a large scale. Citric acid-based CDs (CA-CDs) were obtained in a maximum yield of 39.6% and exhibited a high fluorescence quantum yield of 20.8% without any passivation. The CA-CDs showed little cytotoxicity even at a concentration as high as 800 µg mL-1. In addition, CA-CDs could be used as multicolour fluorescence imaging agents in vitro with blue, green, and red fluorescence emissions at excitation wavelengths of 405, 488, and 543 nm, respectively. Moreover, the CA-CDs could be chelated with gadolinium ions (Gd3+) to construct Gd-CA-CDs for dual-mode magnetic resonance and fluorescence imaging. The Gd-CA-CDs showed good water dispersibility, excellent biocompatibility, a strong fluorescence quantum yield of 13.1%, and a high magnetic resonance relaxivity of 22.45 mM-1 s-1. The molten-salt method was demonstrated to be applicable to other precursors, such as sodium lignosulphonate, sucrose, glucose, and p-phenylenediamine, and the maximum yield of the four as-prepared CDs was as high as 66.7%, which is much higher than the value reported in previous studies. This study proves that the molten-salt synthesis is a versatile method to obtain CDs in high yields, which will promote the application of CDs in the field of bioimaging.

In situ synthesis of NIR-light emitting carbon dots derived from spinach for bio-imaging applications.

Near infrared (NIR)-light emitting fluorescent probes have attracted extensive research attention in the bioimaging field due to their deep tissue penetration, minimal auto-fluorescence and lower emission light damage to bio-tissues. Herein, we designed and prepared NIR-light emitting CDs (R-CDs) from spinach by a one-step solvothermal method. The R-CDs exhibited good water solubility, a maximum fluorescence emission peak at 680 nm, a high quantum yield of 15.34%, remarkable photo-stability and resistance to metal ions in a body-simulating environment, excellent compatibility, negligible toxicity, and superior labelling capability in vitro and in vivo. These findings significantly highlight the design of NIR-light emitting CDs and exploit their bio-imaging applications.

Facile and efficient route to polyimide-TiO2 nanocomposite coating onto carbon fiber.

Polyamic acid-TiO(2) hybrid colloid emulsion with an average particle size of 200 nm was formed by dispersing nano-TiO(2) into polyamic acid colloidal emulsion. The polyimide-TiO(2) nanocomposite was coated onto carbon fiber by electrophoretic deposition. The primary properties of polyamic acid-TiO(2) hybrid colloid emulsion and polyimide-TiO(2) nanocomposite coating onto carbon fiber were characterized using laser scattering, ZetaPlus particle sizing, transmission electron microscopy, field-emission scanning electron microscope, Fourier transforms infrared spectroscopy, and X-ray Diffraction analysis. The results indicated that the small amount of nano-TiO(2) would be effectively dispersed in polyamic acid colloidal particles. The polyimide-TiO(2) hybrid nanocomposite coating carbon fiber sheet displayed an excellent photodegradation performance of methyl orange, which could be degraded more than 70 wt % after 10 cycles.