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Mild‐heat photothermal antibacterial therapy avoids heat‐induced damage to normal tissues but causes bacterial tolerance. The use of photothermal therapy in synergy with chemodynamic therapy is expected to address this issue. Herein, two pseudo‐conjugated polymers PM123 with photothermal units and PFc with ferrocene (Fc) units are designed to co‐assemble with DSPE‐mPEG2000 into nanoparticle NPM123/Fc. NPM123/Fc under 1064 nm laser irradiation (NPM123/Fc+NIR‐II) generates mild heat and additionally more toxic ∙OH from endogenous H2O2, displaying a strong synergistic photothermal and chemodynamic effect. NPM123/Fc+NIR‐II gives >90% inhibition rates against MDR ESKAPE pathogens in vitro. Metabolomics analysis unveils that NPM123/Fc+NIR‐II induces bacterial metabolic dysregulation including inhibited nucleic acid synthesis, disordered energy metabolism, enhanced oxidative stress, and elevated DNA damage. Further, NPM123/Fc+NIR‐II possesses >90% bacteriostatic rates at infected wounds in mice, resulting in almost full recovery of infected wounds. Immunodetection and transcriptomics assays disclose that the therapeutic effect is mainly dependent on the inhibition of inflammatory reactions and the promotion of wound healing. What is more, thioketal bonds in NPM123/Fc are susceptible to ROS, making it degradable with highly favorable biosafety in vitro and in vivo. NPM123/Fc+NIR‐II with a unique synergistic antibacterial strategy would be much less prone to select bacterial resistance and represent a promising antibiotics‐alternative anti‐infective measure. [ABSTRACT FROM AUTHOR]

Neural machine translation (NMT) typically relies on a substantial number of bilingual parallel corpora for effective training. Mongolian, as a low-resource language, has relatively few parallel corpora, resulting in poor translation performance. Data augmentation (DA) is a practical and promising method to solve problems related to data sparsity and single semantic structure by expanding the size and structure of available data. In order to address the issues of data sparsity and semantic inconsistency in Mongolian–Chinese NMT processes, this paper proposes a new semantic-context DA method. This method adds an additional semantic encoder based on the original translation model, which utilizes both source and target sentences to generate different semantic vectors to enhance each training instance. The results show that this method significantly improves the quality of Mongolian–Chinese NMT tasks, with an increase of approximately 2.5 BLEU values compared to the basic Transformer model. Compared to the basic model, this method can achieve the same translation results with about half of the data, greatly improving translation efficiency. [ABSTRACT FROM AUTHOR]

Finding an ideal scaffold is always an important issue in the field of cartilage tissue engineering. Both decellularized extracellular matrix and silk fibroin have been used as natural biomaterials for tissue regeneration. In this study, a secondary crosslinking method of γ irradiation and ethanol induction was used to prepare decellularized cartilage extracellular matrix and silk fibroin (dECM-SF) hydrogels with biological activity. Furthermore, the dECM-SF hydrogels were cast in custom-designed molds to produce a three-dimensional multi-channeled structure to improve internal connectivity. The adipose-derived stromal cells (ADSC) were seeded on the scaffolds, cultured in vitro for 2 weeks, and implanted in vivo for another 4 and 12 weeks. The double crosslinked dECM-SF hydrogels exhibited an excellent pore structure after lyophilization. The multi-channeled hydrogel scaffold presents higher water absorption ability, surface wettability, and no cytotoxicity. The addition of dECM and a channeled structure could promote chondrogenic differentiation of ADSC and engineered cartilage formation, confirmed by H&E, safranin O staining, type II collagen immunostaining, and qPCR assay. In conclusion, the hydrogel scaffold fabricated by the secondary crosslinking method has good plasticity and can be used as a scaffold for cartilage tissue engineering. The multi-channeled dECM-SF hydrogel scaffolds possess a chondrogenic induction activity that promotes engineered cartilage regeneration of ADSC in vivo. [ABSTRACT FROM AUTHOR]

The emergence of multi‐drug resistant (MDR) bacteria poses a serious threat to human health. It has become imperative to develop efficient antimicrobial strategies. Here, a manganese‐doped dopamine‐derived hollow carbon sphere (MnOx/HNCS) is developed as a nanozyme and photothermal agent for the synergistic treatment of MDR bacterial infections. MnOx/HNCS possesses oxidase, superoxide dismutase, and peroxidase like activities and implements self‐cascading enzymatic catalysis to produce superoxide anion (O2•−), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). Importantly, near‐infrared light facilitates the electron transport of MnOx/HNCS, allowing it to exhibit stable photothermal effects and photo‐enhanced enzymatic activity. Thereby MnOx/HNCS displays a broad‐spectrum synergistic antibacterial efficiency in vitro against six MDR pathogens based on the above photo‐regulated properties. In vivo experiments further demonstrate the excellent antibacterial efficiency of MnOx/HNCS in the MDR bacteria‐infected wound model. Notably, MnOx/HNCS not only has excellent disinfection capacity, but also can accelerate wound healing by stimulating the deposition of the extracellular matrix and reepithelialization. This study proposes a promising antibiotics‐alternative broad‐spectrum antibacterial strategy and paves a new avenue for the establishment of multifunctional photo‐responsive synergistic therapeutic platform. [ABSTRACT FROM AUTHOR]

Clinical therapy of multidrug resistant (MDR) bacteria‐induced deep‐tissue infections such as pneumonia is highly challenging. Ultrasound (US)‐induced sonodynamic therapy (SDT) is a promising strategy for treatment of deep‐tissue diseases given the strong tissue penetration of US. Here, ZIF‐8‐derived carbon@TiO2 nanoparticles (ZTNs) are developed as inhalable sonosensitizers for bacterial pneumonia. ZTNs upon US irradiation exhibit an excellent efficacy to produce reactive oxygen species (ROS) and thereby to kill Gram‐negative MDR bacteria in vitro. Taking advantage of aerosolized intratracheal inoculation, ZTNs can be precisely delivered to lung infection sites, and display an effective SDT‐based elimination of Gram‐negative MDR bacteria in the lung infection models of immunocompetent or immunodeficient mice. Particularly, ZTNs upon US irradiation give a 100% survival rate in the severely immunodeficient NOD/SCID mice with a lethal bacterial pneumonia. In addition, ZTNs have no obvious toxicity at both cellular and animal levels. Metal–organic‐framework‐derived nanoparticles as safe and efficient inhalable sonosensitizer have a great potential to be used for the clinical antibiotics‐alternative treatment of MDR bacterial pneumonia. This study presents a new paradigm for SDT‐based treatment of deep‐tissue bacterial infections, and will expand the nanomedicine application of inorganic sonosensitizers. [ABSTRACT FROM AUTHOR]

Photothermal therapy based on conjugated polymers represents a promising antibacterial strategy but still possesses notable limitations. Herein, degradable pseudo conjugated polymers (PCPs) containing photothermal molecular backbones and reactive oxygen species (ROS)‐sensitive thioketal bonds are designed. Triphenylphosphine (PPh3) is introduced into PCPs to generate phosphonium‐based PCPs (pPCPs), which further assembled with hyaluronic acid into pPCP nanoparticles (pPCP‐NPs). pPCP‐NPs with quaternary phosphonium cations selectively anchor on and destroy bacterial cell membranes through electrostatic action. Under 1064 nm laser irradiation, pPCP‐NPs (pPCP‐NPs/+L) produce near‐infrared‐II (NIR‐II) photothermal antibacterial effect, thereby killing bacteria in a sustained manner. pPCP‐NPs are readily degraded upon ROS abundant at infection sites, therefore exhibiting enough biosafety. pPCP‐NPs/+L display an almost 100% bacterial inhibition rate in vitro and resultin a nearly complete recovery of bacteria‐induced mouse wounds. A further metabolomics analysis denotes that pPCP‐NPs/+L work in a concerted way to induce bacterial DNA damage, inhibit bacterial carbon/nitrogen utilization and amino acid/nucleotide synthesis. Taken together, degradable pPCP‐NPs with both NIR‐II photothermal effect and cationic phosphonium structural bacteriostasis provide a new avenue for antibiotics‐alternative anti‐infection therapy. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the effects of six common commercial lactic acid bacteria (LAB) additives [A1, Lactobacillus plantarum , L. buchneri , and Enterococcus faecalis ; A2, L. plantarum and L. casei ; A3, L. plantarum and L. buchneri ; A4, L. plantarum , L. buchneri , L. casei , and Pediococcus acidilactici ; A5, L. plantarum (producing feruloyl esterase); and A6, L. buchneri , P. acidilactici , β-glucanase, and xylanase] on the bacterial community and fermentation quality of alfalfa silage. Alfalfa was harvested at the squaring stage, wilted in the field for 24 h, and ensiled without any additives (Control) or with A1, A2, A3, A4, A5, or A6. Microbial counts, bacterial community, fermentation parameters, and nutritional composition were determined after ensiling for 90 days. The total abundance of LAB genera on alfalfa pre-ensiling was 0.38% in bacterial community. The abundances of Lactobacillus , Enterococcus , and Pediococcus in the Control silage were 42.18, 40.18, and 8.09% of abundance, respectively. The abundances of Lactobacillus in A1-, A2-, A3-, A4-, and A5-treatments were 89.32, 92.93, 92.87, 81.12, and 80.44%, respectively. The abundances of Pediococcus and Lactobacillus in A6-treatment were 70.14 and 24.86%, respectively. Compared with Control silage, LAB-treated silage had lower pH and less ammonia nitrogen and water-soluble carbohydrates concentrations (p < 0.05). Further, the A5- and A6-treatments contained lower neutral detergent fiber, acid detergent fiber, and hemicellulose than other treatments (p < 0.05). Overall, LAB genera were presented as minor taxa in alfalfa pre-ensiling and as dominant taxa in alfalfa silage. Adding LAB additives improved the fermentation quality and altered the bacterial community of alfalfa silage. The main bacterial genera in Control silage were Lactobacillus , Enterococcus , and Pediococcus. Lactobacillus dominated the bacterial communities of A1-, A2-, A3-, A4-, and A5-treatments, while Pediococcus and Lactobacillus were dominant bacterial genera in A6-treatment. Inoculating A5 and A6 degraded the fiber in alfalfa silage. It is necessary to ensile alfalfa with LAB inoculants. [ABSTRACT FROM AUTHOR]

The Escherichia coli YfiF protein is functionally unknown, being predicted as a transfer RNA/ribosomal RNA (tRNA/rRNA) methyltransferase. We find that absence of the yfiF gene delays initiation of chromosome replication and the delay is reversed by ectopic expression of YfiF, whereas excess YfiF causes an early initiation. A slight decrease in both cell size and number of origin per mass is observed in ΔyfiF cells. YfiF does not genetically interact with replication proteins such as DnaA, DnaB, and DnaC. Interestingly, YfiF is associated with ribosome modulation factor (RMF), hibernation promotion factor (HPF), and the tRNA methyltransferase TrmL. Defects in replication initiation of Δrmf, Δhpf, and ΔtrmL can be rescued by overexpression of YfiF, indicating that YfiF is functionally identical to RMF, HPF, and TrmL in terms of replication initiation. Also, YfiF interacts with the rRNA methyltransferase RsmC. Moreover, the total amount of proteins and DnaA content per cell decreases or increases in the absence of YfiF or the presence of excess YfiF. These facts suggest that YfiF is a ribosomal dormancy‐like factor, affecting ribosome function. Thus, we propose that YfiF is involved in the correct timing of chromosome replication by changing the DnaA content per cell as a result of affecting ribosome function. [ABSTRACT FROM AUTHOR]

With the development of natural language processing and neural machine translation, the neural machine translation method of end-to-end (E2E) neural network model has gradually become the focus of research because of its high translation accuracy and strong semantics of translation. However, there are still problems such as limited vocabulary and low translation loyalty, etc. In this paper, the discriminant method and the Conditional Random Field (CRF) model were used to segment and label the stem and affixes of Mongolian in the preprocessing stage of Mongolian-Chinese bilingual corpus. Aiming at the low translation loyalty problem, a decoding model combining Convolution Neural Network (CNN) and Gated Recurrent Unit (GRU) was constructed. The target language decoding was performed by using the GRU. A global attention model was used to obtain the bilingual word alignment information in the process of bilingual word alignment processing. Finally, the quality of the translation was evaluated by Bilingual Evaluation Understudy (BLEU) values and Perplexity (PPL) values. The improved model yields a BLEU value of 25.13 and a PPL value of − 3 8. 1. The experimental results show that the E2E Mongolian-Chinese neural machine translation model was improved in terms of translation quality and semantic confusion compared with traditional statistical methods and machine translation models based on Recurrent Neural Networks (RNN). [ABSTRACT FROM AUTHOR]

Providencia as an opportunistic pathogen can cause serious infection, and moreover the emergence of multi-drug-resistant Providencia strains poses a potentially life-threatening risk to public health. However, a comprehensive genomic study to reveal the population structure and dissemination of Providencia is still lacking. In this study, we conducted a genomic epidemiology analysis on the 580 global sequenced Providencia isolates, including 257 ones sequenced in this study (42 ones were fully sequenced). We established a genome sequence-based species classification scheme for Providencia , redefining the conventional 11 Providencia species into seven genocomplexes that were further divided into 18 genospecies, providing an extensively updated reference for Providencia species discrimination based on the largest Providencia genome dataset to date. We then dissected the profile of antimicrobial resistance genes and the prevalence of multi-drug-resistant Providencia strains among these genocomplexes/genospecies, disclosing the presence of diverse and abundant antimicrobial resistance genes and high resistance ratios against multiple classes of drugs in Providencia . We further dissected the genetic basis for the spread of bla NDM-1 in Providencia . bla NDM-1 genes were mainly carried by five incompatible (Inc) groups of plasmids: IncC, IncW, Inc pPROV114-NR , Inc pCHS4.1-3 , and Inc pPrY2001 , and the last three were newly designated in this study. By tracking the spread of bla NDM-1 -carrying plasmids, IncC, Inc pPROV114-NR , Inc pCHS4.1-3 , and Inc pPrY2001 plasmids were found to be highly involved in parallel horizontal transfer or vertical clonal expansion of bla NDM-1 among Providencia . Overall, our study provided a comprehensive genomic view of species differentiation, antimicrobial resistance prevalence, and plasmid-mediated bla NDM-1 dissemination in Providencia .

To investigate community synergy of lactic acid bacteria (LAB) and cleaner fermentation of oat silage, oat silages were prepared with or without (control) commercial LAB inoculants LI1 (containing Lactiplantibacillus plantarum, Lentilactobacillus buchneri, Lacticaseibacillus paracasei, and Pediococcus acidilactici) and LI2 (containing Lactiplantibacillus plantarum and Lentilactobacillus buchneri). The microbial community, LAB synergy, and cleaner fermentation were analyzed at 1, 3, 6, 15, 35, and 90 days of ensiling. The LAB inoculant improved fermentation quality, with significantly ( P <  0.05) lower pH, ammonia nitrogen content, and gas production and higher lactic acid and acetic acid contents than those of the control. Enterobacteriaceae was the main bacterial community in early stage of fermentation, which utilizes sugar to produce CO 2 gas, causing dry matter (DM) and energy loss. As fermentation progressed, the microbial diversity decreased, and the microbial community shifted from Gram-negative to Gram-positive bacteria. The inoculation of multispecies LAB displayed community synergy; Pediococcus acidilactici formed a dominant community in the early stage of fermentation, which produced an acid and anaerobic environment for the subsequent growth of Lentilactobacillus and Lacticaseibacillus species, thus forming a LAB-dominated microbial community. The predicted functional profile indicated that the silage inoculated with LI1 enhanced the carbohydrate metabolism pathway but inhibited the amino acid metabolism pathway, which played a role in promoting faster lactic acid production, reducing the decomposition of protein to ammonia nitrogen, and improving the fermentation quality of silage. Therefore, oat silage can be processed to high-quality and cleaner fermented feed by using an LAB inoculant, and LI1 showed better efficiency than LI2. IMPORTANCE Oat natural silage is rich in Enterobacteriaceae , increasing gas production and fermentation loss. Lactic acid bacteria interact synergistically to form a dominant community during ensiling. Pediococci grow vigorously in the early stage of fermentation and create an anaerobic environment. Lactobacilli inhibit the harmful microorganisms and result in cleaner fermentation of oat silage., Competing Interests: The authors declare no conflict of interest.

Sweet sorghum is an important forage in arid and semi-arid climatic regions. This study aimed to reveal the fermentation weight loss (FWL), fermentation quality, and bacterial community of ensiling of sweet sorghum with lactic acid bacteria LAB; ( Lactiplantibacillus plantarum and Lentilactobacillus buchneri ) at different silo densities. For this study, sweet sorghum was harvested at the first spikelet of inflorescence stage and ensiled without or with LAB (CK or L) in polyethylene laboratory-scale silos (diameter, 20 cm; height, 30 cm) at densities of 650 (CK&#95;650 and L&#95;650), 700 (CK&#95;700 and L&#95;700), and 750 kg/m 3 (CK&#95;750 and L&#95;750), respectively. The FWL, fermentation quality, microbial counts, and bacterial community of the silage were assessed after 100 days of ensiling. L&#95;750 had a lower FWL than CK&#95;650, &#95;700, and &#95;750 after 100 days of ensiling ( P < 0.005), and the FWL was affected by silo density and inoculating LAB ( P < 0.005). All silages had low pH (<4.0) and ammonia nitrogen content (<50 g/kg total nitrogen) and did not contain propionic and butyric acids; moreover, inoculating LAB increased lactic and acetic acids ( P < 0.005). Bacterial communities in inoculated and uninoculated silages were clustered together, respectively, and clearly separated from each other. The total abundance of Lactiplantibacillus and Lentilactobacillus in fresh forage was <1%. Lactiplantibacillus had the highest abundance in all silages (from 71.39 to 93.27%), followed by Lentilactobacillus (from 3.59 to 27.63%). Inoculating LAB increased the abundance of Lentilactobacillus in each silo density ( P < 0.005) and decreased Lactiplantibacillus in the silage in densities of 700 and 750 kg/m 3 ( P < 0.005); moreover, increasing silo density decreased Lactiplantibacillus abundance and increased Lentilactobacillus abundance in inoculated silages ( P < 0.005). Overall, sweet sorghum silage showed satisfactory fermentation quality, with a density of no <650 kg/m 3 , and inoculating LAB improved fermentation quality and reduced FWL. Lactiplantibacillus and Lentilactobacillus presented as minor taxa in fresh sweet sorghum and dominated the bacterial community of all silages. Inoculating LAB was the main factor affecting the bacterial community of sweet sorghum silage. Moreover, inoculating LAB and increasing silo density can contribute to the decreasing Lactiplantibacillus abundance and increasing Lentilactobacillus abundance., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Xu, Wu, Na, Sun, Zhao, Ding, Fang, Wang, Xue and Zhong.)

Leymus chinensis is a major forage resource for herbivores on typical steppe and meadow steppes in Northern China. This study aimed to reveal the fermentation quality, bacterial community, and aerobic stability of L. chinensis silage treated with lactic acid bacteria or/and water after long-term storage. Leymus chinensis was harvested at the heading stage and ensiled with lactic acid bacteria [LAB, 2.00 ml/kg fresh weight (FW) of LAB, L], water (100 ml/kg FW of distilled water, W), or a combination of both [2.00 ml/kg fresh weight (FW) of LAB and 100 ml/kg FW of distilled water, LW] in polyethylene laboratory-scale silos (diameter, 20 cm; height, 30 cm) at a density of 650 kg/m 3 . As a control silage (CK), untreated L. chinensis silage was also assessed. The samples were taken at 0 day of opening after 300 days of ensiling (CK&#95;0d, L&#95;0d, W&#95;0d, and LW&#95;0d) and at 10 days of opening (CK&#95;10d, L&#95;10d, W&#95;10d, and LW&#95;10d). The fermentation quality, microbial counts, bacterial community, and aerobic stability of the silage were assessed. The CK&#95;0d contained higher pH and aerobic bacteria count, and lower LA and BC concentrations than L&#95;0d, W&#95;0d, and LW&#95;0d ( p < 0.05), and the LAB and yeasts were only detected in CK at 0 day of opening. Lactobacillus had the most abundance among bacterial genera in all silages at 0 day of opening. Just CK had 2°C above the ambient temperature during aerobic exposure (at 224 h). During aerobic exposure, the pH and microbial counts in CK increased ( p < 0.05), and Lactobacillus in L and LW had decreasing abundance ( p < 0.05). The CK&#95;10d had higher pH and microbial counts, and lower lactic acid and buffering capacity than L&#95;10d, W&#95;10d, and LW&#95;10d ( p < 0.05). At 10 days of opening, the coliforms and yeasts were just detected in CK, and Lactobacillus also had the most abundance among bacterial genera in all silages at 10 days of opening. Overall, inoculating LAB and adding water improved the fermentation quality and the aerobic exposure of L. chinensis silage after long-term storage. The activities of coliforms and yeasts during aerobic exposure contributed to the aerobic deterioration of L. chinensis silage without any treating. Lactobacillus dominated the bacterial communities of all silage at 0 and 10 days of opening. During aerobic exposure, the abundance of Lactobacillus reduced in L. chinensis silage treated with LAB or water., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Xu, Xue, Na, Wu, Zhao, Sun, Qili, Wang and Zhong.)

Antibiotic resistance genes (ARGs) are recognized as contaminants due to their potential risk for human and environment. The aim of the present study is to investigate the effects of pyroligneous acid (PA), a waste of biochar production, on fermentation characteristics, diversity, and dynamics of ARGs during ensiling of alfalfa using metagenomic analysis. The results indicated that PA decreased ( P  < 0.05) dry matter loss, pH value, gas production, coliform bacteria count, protease activity, and nonprotein-N, ammonia-N, and butyric acid contents and increased ( P  < 0.05) lactic acid content during ensiling. During fermentation, Bacteria , Firmicutes , and Lactobacillus were the most abundant at kingdom, phylum, and genus levels, respectively. Pyroligneous acid reduced the relative abundance of Bacteria and Firmicutes and increased that of Lactobacillus . The detected ARGs belonged to 36 drug classes, including mainly macrolides, tetracycline, lincosamides, and phenicol. These types of ARGs decreased during fermentation and were further reduced by PA. These types of ARGs were positively correlated ( P  < 0.05) with fermentation parameters like pH value and ammonia-N content and with bacterial communities. At the genus level, the top several drug classes, including macrolide, tetracycline, lincosamide, phenicol, oxazolidinone, streptogramin, pleuromutilin, and glycopeptide, were positively correlated with Staphylococcus , Streptococcus , Listeria , Bacillus , Klebsiella , Clostridium , and Enterobacter , the potential hosts of ARGs. Overall, ARGs in alfalfa silage were abundant and were influenced by the fermentation parameters and microbial community composition. Ensiling could be a feasible way to mitigate ARGs in forages. The addition of PA could not only improve fermentation quality but also reduce ARG pollution of alfalfa silage. IMPORTANCE Antibiotic resistance genes (ARGs) are considered environmental pollutants posing a potential human health risk. Silage is an important and traditional feed, mainly for ruminants. ARGs in silages might influence the diversity and distribution of ARGs in animal intestinal and feces and then the manure and the manured soil. However, the diversity and dynamics of ARGs in silage during fermentation are still unknown. We ensiled alfalfa, one of the most widely used forages, with or without pyroligneous acid (PA), which was proved to have the ability to reduce ARGs in soils. The results showed that ARGs in alfalfa silage were abundant and were influenced by the fermentation parameters and microbial community. The majority of ARGs in alfalfa silage reduced during fermentation. The addition of PA could improve silage quality and reduce ARG pollution in alfalfa silage. This study can provide useful information for understanding and controlling ARG pollution in animal production.

Although advances in protein assembly preparation have provided a new platform for drug delivery during tissue engineering, achieving long-term controlled exosome delivery remains a significant challenge. Diffusion-dominated exosome release using protein hydrogels results in burst release of exosomes. Here, a fibroin-based cryo-sponge was developed to provide controlled exosome release. Fibroin chains can self-assemble into silk I structures under ice-cold conditions when annealed above the glass transition temperature. Exosome release is enzyme-responsive, with rates primarily determined by enzymatic degradation of the scaffolds. In vivo experiments have demonstrated that exosomes remain in undigested sponge material for two months, superior to their retention in fibrin glue, a commonly used biomaterial in clinical practice. Fibroin cryo-sponges were implanted subcutaneously in nude mice. The exosome-containing sponge group exhibited better neovascularization and tissue ingrowth effects, demonstrating the efficacy of this exosome-encapsulating strategy by realizing sustained release and maintaining exosome bioactivity. These silk fibroin cryo-sponges containing exosomes provide a new platform for future studies of exosome therapy., (© 2021 The Authors.)

The development of 3D printing techniques has provided a promising platform to study tissue engineering and mechanobiology; however, the pursuit of printability limits the possibility of tailoring scaffolds' mechanical properties. The brittleness of those scaffolds also hinders potential clinical application. To overcome these drawbacks, a double-network ink composed of only natural biomaterials is developed. A shear-thinning hydrogel made of silk fibroin (SF) and methacrylated hyaluronic acid (MAHA) presents a high mechanical modulus with a low concentration of macromers. The physical cross-linking due to protein folding further increases the strength of the scaffolds. The proposed SF/MAHA scaffold exhibits a storage modulus 10 times greater than that of methacrylated gelatin scaffold, along with better flexibility and biodegradation. The synergistic effect between fibroin and hyaluronic allows us to tailor the mechanical strength of scaffolds without compromising their printability. The hierarchy porous structure of the SF/MAHA scaffolds offers a better spatial microenvironment for the migration and proliferation of cells compared to gelatin scaffolds. For the first time, this strategy achieves 3D printing of natural biomaterials with controlled mechanical characteristics by manipulating the cross-linking of peptide chains. The design of such ductile scaffolds with hydrolysis resistance provides a new platform for the mechanobiology research. It also shows promise in the tissue engineering of musculoskeletal system where structural strength is needed.

Meniscus deficiency, the most common and refractory disease in human knee joints, often progresses to osteoarthritis (OA) due to abnormal biomechanical distribution and articular cartilage abrasion. However, due to its anisotropic spatial architecture, complex biomechanical microenvironment, and limited vascularity, meniscus repair remains a challenge for clinicians and researchers worldwide. In this study, we developed a 3D printing-based biomimetic and composite tissue-engineered meniscus scaffold consisting of polycaprolactone (PCL)/silk fibroin (SF) with extraordinary biomechanical properties and biocompatibility. We hypothesized that the meticulously tailored composite scaffold could enhance meniscus regeneration and cartilage protection. Methods : The physical property of the scaffold was characterized by scanning electron microscopy (SEM) observation, degradation test, frictional force of interface assessment, biomechanical testing, and fourier transform infrared (FTIR) spectroscopy analysis. To verify the biocompatibility of the scaffold, the viability, morphology, proliferation, differentiation, and extracellular matrix (ECM) production of synovium-derived mesenchymal stem cell (SMSC) on the scaffolds were assessed by LIVE/DEAD staining, alamarBlue assay, ELISA analysis, and qRT-PCR. The recruitment ability of SMSC was tested by dual labeling with CD29 and CD90 by confocal microscope at 1 week after implantation. The functionalized hybrid scaffold was then implanted into the meniscus defects on rabbit knee joint for meniscus regeneration, comparing with the Blank group (no scaffold) and PS group. The regenerated meniscus tissue was evaluated by histological and immunohistochemistry staining, and biomechanical test. Macroscopic and histological scoring was performed to assess the outcome of meniscus regeneration and cartilage protection in vivo . Results : The combination of SF and PCL could greatly balance the biomechanical properties and degradation rate to match the native meniscus. SF sponge, characterized by fine elasticity and low interfacial shear force, enhanced energy absorption capacity of the meniscus and improved chondroprotection. The SMSC-specific affinity peptide (LTHPRWP; L7) was conjugated to the scaffold to further increase the recruitment and retention of endogenous SMSCs. This meticulously tailored scaffold displayed superior biomechanics, structure, and function, creating a favorable microenvironment for SMSC proliferation, differentiation, and extracellular matrix (ECM) production. After 24 weeks of implantation, the histological assessment, biochemical contents, and biomechanical properties demonstrated that the polycaprolactone/silk fibroin-L7 (PS-L7) group was close to the native meniscus group, showing significantly better cartilage protection than the PS group. Conclusion : This tissue engineering scaffold could greatly strengthen meniscus regeneration and chondroprotection. Compared with traditional cell-based therapies, the meniscus tissue engineering approach with advantages of one-step operation and reduced cost has a promising potential for future clinical and translational studies., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

Silk fibroin (SF) is a natural polymer with low immunogenicity and good biocompatibility. However, most silk-based hydrogels formed through chemical or physical cross-linking are brittle, the preparation of which also inevitably introduces cytotoxic cross-linking agents. Herein, a simple strategy is presented for synthesizing SF hydrogels with tunable mechanical properties by combining γ-ray radiation with ethanol treatment. Neither toxic initiators nor chemical agents are utilized during the whole preparation procedure. For "soft" hydrogels, the compressive moduli are less than 29 kPa (SF-S hydrogels), while for "tough" hydrogels, the compressive moduli are between 1.21 and 2.41 MPa (SF-D hydrogels). Specifically, γ-ray radiation makes SF form uniform and stable chemical cross-linking sites within and between molecular chains, resulting in "soft" and highly elastic SF hydrogels. The physical cross-linking via ethanol treatment leads to the self-assembly of fibroin chains, transforming those soft hydrogels to tough hydrogels. These double cross-linked SF hydrogels (SF-D hydrogels) exhibit excellent mechanical strength. Effects of various cross-linking conditions on the secondary structure, pore structure, mechanical properties, gelation degree, swelling, and in vitro degradation properties are explored. A series of cell experiments demonstrate that the SF hydrogels with different mechanical strength can stimulate the expression of specific genes of rat bone marrow mesenchymal stem cells (BMSCs) in various differentiation directions. These results also show the application prospects in tissue engineering by customizing hydrogels for the mechanical strength of different tissues.

The human body has difficulty repairing damaged dental enamel, an acellular hard tissue. Researchers have sought feasible biomimicry strategies to repair enamel defects; however, few have been successfully translated to clinical applications. In this study, we propose a new method for achieving rapid enamel mineralization under a near-physiological environment. Through treatment with a laser and chelating agents, 15 μm crystals could be grown compactly on an enamel substrate in less than 20 min. The compact crystal layer had similar structure as native enamel prisms and high elastic modulus. This layer also had the potential for further remineralization in saliva. The benefit of using laser can not only speed up the mineralization, but also control the crystal growth precisely where in need. A mechanism for how laser and chelating agents synergistically function is also proposed. This strategy offers a possibility for enamel-biomimicking repair in dental clinics.