Mechanically robust and personalized silk fibroin-magnesium composite scaffolds with water-responsive shape-memory for irregular bone regeneration.

The regeneration of critical-size bone defects, especially those with irregular shapes, remains a clinical challenge. Various biomaterials have been developed to enhance bone regeneration, but the limitations on the shape-adaptive capacity, the complexity of clinical operation, and the unsatisfied osteogenic bioactivity have greatly restricted their clinical application. In this work, we construct a mechanically robust, tailorable and water-responsive shape-memory silk fibroin/magnesium (SF/MgO) composite scaffold, which is able to quickly match irregular defects by simple trimming, thus leading to good interface integration. We demonstrate that the SF/MgO scaffold exhibits excellent mechanical stability and structure retention during the degradative process with the potential for supporting ability in defective areas. This scaffold further promotes the proliferation, adhesion and migration of osteoblasts and the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in vitro. With suitable MgO content, the scaffold exhibits good histocompatibility, low foreign-body reactions (FBRs), significant ectopic mineralisation and angiogenesis. Skull defect experiments on male rats demonstrate that the cell-free SF/MgO scaffold markedly enhances bone regeneration of cranial defects. Taken together, the mechanically robust, personalised and bioactive scaffold with water-responsive shape-memory may be a promising biomaterial for clinical-size and irregular bone defect regeneration.

Composited silk fibroins ensured adhesion stability and magnetic controllability of Fe3O4-nanoparticle coating on implant for biofilm treatment.

Magnetic propulsion of nano-/micro-robots is an effective way to treat implant-associated infections by physically destroying biofilm structures to enhance antibiotic killing. However, it is hard to precisely control the propulsion in vivo. Magnetic-nanoparticle coating that can be magnetically pulled off does not need precise control, but the requirement of adhesion stability on an implant surface restricts its magnetic responsiveness. Moreover, whether the coating has been fully pulled-off or not is hard to ensure in real-time in vivo. Herein, composited silk fibroins (SFMA) are optimized to stabilize Fe3O4 nanoparticles on a titanium surface in a dry environment; while in an aqueous environment, the binding force of SFMA on titanium is significantly reduced due to hydrophilic interaction, making the coating magnetically controllable by an externally-used magnet but still stable in the absence of a magnet. The maximum working distance of the magnet can be calculated using magnetomechanical simulation in which the yielding magnetic traction force is strong enough to pull Fe3O4 nanoparticles off the surface. The pulling-off removes the biofilms that formed on the coating and enhances antibiotic killing both in vitro and in a rat sub-cutaneous implant model by up to 100 fold. This work contributes to the practical knowledge of magnetic propulsion for biofilm treatment.

A Cell-Free Silk Fibroin Biomaterial Strategy Promotes In Situ Cartilage Regeneration Via Programmed Releases of Bioactive Molecules.

In situ tissue regeneration using cell-free biofunctional scaffolds has been extensively studied as a promising alternative strategy to promote cartilage repair. In this study, a cartilage-biomimetic silk fibroin (SF)-based scaffold with controlled sequential release of two bioactive molecules is developed. Transforming growth factor-ß1 (TGF-ß1) is initially loaded onto the SF scaffolds by physical absorption, which are then successively functionalized with bone marrow mesenchymal stem cells (BMSCs)-specific-affinity peptide (E7) via gradient degradation coating of Silk fibroin Methacryloyl (SilMA)/Hyaluronic acid Methacryloyl (HAMA). Such SF-based scaffolds exhibit excellent structural stability and catilage-like mechanical properties, thus providing a desirable 3D microenvironment for cartilage reconstruction. Furthermore, rapid initial release of E7 during the first few days, followed by slow and sustained release of TGF-ß1 for as long as few weeks, synergistically induced the recruitment of BMSCs and chondrogenic differentiation of them in vitro. Finally, in vivo studies indicate that the implantation of the biofunctional scaffold markedly promote in situ cartilage regeneration in a rabbit cartilage defect model. It is believed that this cartilage-biomimetic biofunctional SF-based scaffold with sequential controlled release of E7 and TGF-ß1 may have a promising potential for improved cartilage tissue engineering.

circPTP4A2-miR-330-5p-PDK2 Signaling Facilitates In Vivo Survival of HuMSCs on SF-SIS Scaffolds and Improves the Repair of Damaged Endometrium.

Background: Human umbilical cord mesenchymal stem cells- (HuMSCs-) based therapy has shown promising results in the treatment of intrauterine adhesions (IUA). In this study, we aimed to construct a HuMSCs-seeded silk fibroin small-intestinal submucosa (SF-SIS) scaffold and evaluate its ability to repair the damaged endometrium in an IUA mouse model. Methods: To identify the functional effect of HuMSCs-SF-SIS scaffolds on the repair of damaged endometrium, a mouse IUA model was established. Uterine morphology and fibrosis were evaluated by hematoxylin-eosin staining and Masson staining. CircRNA sequencing, real-time PCR, and RNA fluorescence in situ hybridization were used to screen and verify the potential circRNAs involved in the repair of damaged endometrium by HuMSCs. Real-time integrated cellular measurement of oxygen consumption rate was performed using the Seahorse XF24 Extracellular Flux Analyzer. The potential downstream miRNAs and proteins of circRNAs were analyzed by dual-luciferase reporter assay and western blot. Results: HuMSCs-SF-SIS not only increased the number of glands but also reduced the ulcer area in the IUA model. circPTP4A2 was elevated in the HuMSCs seeded on the SF-SIS scaffolds and was targeted by miR-330-5p-PDK2. It also stabilized the mitochondrial metabolism of HuMSCs. Moreover, miR-330-5p was found to inhibit PDK2 expression through the 3' UTR target region. A rescue experiment further showed that circPTP4A2-miR-330-5p-PDK2 signaling was critical to HuMSCs-SF-SIS in decreasing the fibrosis area and increasing the number of glands in the IUA model. Conclusion: We demonstrated that circPTP4A2 was elevated in HuMSCs-seeded on SF-SIS scaffolds and stabilized the mitochondrial metabolism through miR-330-5p-PDK2 signaling, which contributes to endometrial repair progression. These findings demonstrate that HuMSCs-seeded SF-SIS scaffolds have potential for the treatment of IUA.

The relationship between crosslinking structure and silk fibroin scaffold performance for soft tissue engineering.

Biologically active scaffolds with tunable mechano- and bio-performance remain desirable for soft tissue engineering. Previously, highly elastic and robust silk fibroin (SF) scaffolds were prepared via cryogelation. In order to get more insight into the role of ethylene glycol diglycidyl ether (EGDE) on the structure and properties of SF scaffolds, we investigated the fate of SF scaffolds with different usages of the crosslinking agent in vitro and in vivo. Although SF scaffolds with varied EGDE contents showed similar micro-morphology, increasing EGDE from 1 mmol/g to 5 mmol/g resulted in firstly increased and later decreased content of ß-sheet conformation, and linearly increased tensile modulus and decreased elasticity. The dual-crosslinked SF scaffolds with EGDE up to 5 mmol/g did not show in vitro cytotoxicity for NIH3T3 fibroblasts. In vivo subcutaneous implantation of SF scaffolds with <3 mmol/g EGDE displayed excellent degradation behavior and tissue ingrowth after 28 days of implantation. However, with ≥3 mmol/g EGDE, SF scaffolds exhibited obvious post-implantation foreign body reactions, probably associated with slow degradation due to excess chemical crosslinks and less mechanical compatibility. These results suggest that an appropriate dosage of crosslinking agent was critical to achieve balanced mechanical properties, degradability in vivo and immuno-properties of the SF scaffold platform for soft tissue engineering.

Influence of non-enzymatic glycation on the mechanical properties of cortical bone.

Poor bone quality induced by non-enzymatic glycation (NEG) of bone tissue in patients with type 2 diabetes mellitus (T2DM) is regarded as the major factor of bone fragility and affecting bone mechanical properties. A comprehensive and systemic mechanical investigation for evaluating the effect of NEG on bone was still lacking. In order to provide additional information for the bone quality of T2DM, the effects of NEG on mechanical properties of cortical bone were investigated in terms of elastoplasticity, fracture toughness and viscoelasticity. All samples of cortical bone, including the samples of strength test (n = 20), fracture toughness test (n = 40, quasi-static and fall-like conditions with displacement rates of 10-3 mm/s and 10 mm/s, respectively) and stress relaxation test (n = 20), were harvested from bovine tibiae. The samples of each test were equally divided into incubated-control group and ribose-incubated group. All mechanical tests were performed after incubating all samples for 15 days. Post-yield strain (p = 0.014), post-yield energy (p < 0.0001) and damage fraction (p = 0.040) of ribose-incubated group were significantly lower than those of incubated-control group, but secant modulus (p = 0.029) of ribose-incubated group was significantly higher than that of incubated-control group. In quasi-static condition, the plastic contribution Jpl of fracture toughness (p = 0.043) of ribose-incubated group was significantly lower than that of incubated-control group. In fall-like condition, there were no differences in Jpl, elastic contribution Jel and J-integral in both two groups. The quasi-static Jel (p < 0.0001, p < 0.0001) of incubated-control and ribose-incubated groups and J-integral (p = 0.007) of incubated-control group were all significantly higher than those of fall-like condition. In stress relaxation test, initial modulus E0 (p = 0.040) and equilibrium modulus (p = 0.029) of ribose-incubated group were significantly higher than those of incubated-control group. Reductions of relaxation modulus, which were the differences between two adjacent time points within 700 s-3000 s for ribose-incubated group, were significantly lower than those of incubated-control group. NEG could decrease the post-yield properties and quasi-static facture toughness of cortical bone, especially the plastic contribution of quasi-static fracture toughness. It could also decrease the viscoelasticity of cortical bone. The present study confirmed the negative effects of NEG on the mechanical properties of cortical bone in terms of elastoplasticity, fracture toughness and viscoelasticity, but NEG had no significant effect on the fracture toughness of cortical bone at fall-like loading. These results provided more evidence for increased fragility of cortical bone in patients with T2DM.

Cell membrane-biomimetic coating via click-mediated liposome fusion for mitigating the foreign-body reaction.

The foreign-body reaction (FBR) caused by the implantation of synthetic polymer scaffolds seriously affects tissue-biomaterial integration and tissue repair. To address this issue, we developed a cell membrane-biomimetic coating formed by "click"-mediated liposome immobilization and fusion on the surface of electrospun fibers to mitigate the FBR. Utilization of electrospun polystyrene microfibrous scaffold as a model matrix, we deposited azide-incorporated silk fibroin on the surface of the fibers by the layer-by-layer assembly, finally, covalently modified with clickable liposomes via copper-free SPAAC click reaction. Compared with physical adsorption, liposomes click covalently binding can quickly fuse to form lipid film and maintain fluidity, which also improved liposome stability in vitro and in vivo. Molecular dynamics simulation proved that "click" improves the binding rate and strength of liposome to silk substrate. Importantly, histological observation and in vivo fluorescent probes imaging showed that liposome-functionalized electrospun fibers had negligible characteristics of the FBR and were accompanied by many infiltrated host cells and new blood vessels. We believe that the promotion of macrophage polarization toward a pro-regenerative phenotype plays an important role in vascularization. This bioinspired strategy paves the way for utilizing cell membrane biomimetic coating to resist the FBR and promote tissue-scaffold integration.

Applications of materials for dural reconstruction in pre-clinical and clinical studies: Advantages and drawbacks, efficacy, and selections.

The dura mater provides a barrier to protect the tissue underneath and cerebrospinal fluid. However, dural defects normally cause cerebrospinal fluid leakage and other complications, such as wound infections, meningitis, etc. Therefore, the reconstruction of dura mater has important clinical significance. Current dural reconstruction materials include: homologous, acellular, natural, synthetic, and composite materials. This review comprehensively summarizes the characteristics and efficacy of these dural substitutes, especially in clinical applications, including the advantages and drawbacks of those from different sources, the host tissue response in pre-clinical studies and clinical practice, and the comparison of these materials across different surgical procedures. Furthermore, the selections of materials for different surgical procedures are highlighted. Finally, the challenges and future perspectives in the development of ideal dural repair materials are discussed.

The effects of silk layer-by-layer surface modification on the mechanical and structural retention of extracellular matrix scaffolds.

Naturally derived extracellular matrix scaffolds can effectively promote tissue repair and regeneration due to their remarkable bioactivity. However, their rapid degradation leads to the decrease of mechanical retention and the failure of physical support in vivo which limit their applications. In this paper, we modified a classic extracellular matrix scaffold - small intestinal submucosa (SIS) - by a silk fibroin (SF) layer-by-layer (LbL) assembly to replace the existing chemical crosslinking methods for improving its mechanical and structural stability. Experimental results showed that the SF LbL surface functionalized SIS scaffold had tunable mechanical properties and degradation rate by adjusting the number of layers of the SF deposited on the surface. For biological responses, in vitro NIH3T3 fibroblast culture studies demonstrated that SF surface modification did not affect the excellent biocompatibility of the SIS. In vivo subcutaneous implantation results showed that the SF modification could effectively extend the residence time of the SIS in the body, and elicit a more moderate inflammatory response compared to the traditional glutaraldehyde chemical crosslinking. Furthermore, we found that SF modification could maintain the ability of bioactive components of the SIS to regulate the transformation of M1 into M2 in macrophages in vivo. This SF LbL modification strategy offers a green process for the development of high-performance extracellular matrix-based scaffolds with tunable biodegradability.

Reforming teaching methods by integrating dental theory with clinical practice for dental students.

BACKGROUND: Transitioning from theoretical medicine to clinical practice is both an important and difficult process in dental education. Thus, there is an urgent need for teaching methods that can improve the ability of dental students to integrate dental theory with clinical practice. METHODS: First, we conducted training for problem-based learning based on real clinical cases for dental students. The students were then assigned to dentist/patient roles to rehearse and perform simulated clinical scenarios. Finally, questionnaires, clinical patient care scores, and performance assessments were utilized to evaluate and compare the effectiveness of this training with that of traditional teaching methods. RESULTS: Students' abilities to treat and communicate with patients markedly improved after using this reformed teaching method. Among the 30 enrolled students, 29 liked the method, found it time-efficient, and believed that it could help enhance their problem-solving confidence and interest in prosthodontics. They also believed that this teaching method could help them gain a good understanding of related theoretical material, generally thought that the reformed teaching method was more valuable than the traditional approach, and would like to introduce it to others. CONCLUSION: After the reformed teaching method was implemented, the students not only achieved better scholastically, but also demonstrated greater accuracy in diagnosing the conditions of patients and formulating treatment plans. They were also more frequently acknowledged by patients, indicating that this method is effective for dental students.

Controlled Cryogelation and Catalytic Cross-Linking Yields Highly Elastic and Robust Silk Fibroin Scaffolds.

Silk biomaterials with tunable mechanical properties and biological properties are of special importance for tissue engineering. Here, we fabricated silk fibroin (SF, from Bombyx mori silk) scaffolds from cryogelation under controlled temperature and catalytic cross-linking conditions. Structurally, the cryogelled scaffolds demonstrated a greater ß-sheet content but significantly smaller ß-sheet domains compared to that without chemical cross-linking and catalyst. Mechanically, the cryogelled scaffolds were softer and highly elastic under tension and compression. The 120% tensile elongation and >85% recoverable compressive strain were among the best properties reported for SF scaffolds. Cyclic compression tests proved the robustness of such scaffolds to resist fatigue. The mechanical properties, as well as the degradation rate of the scaffolds, can be fine-tuned by varying the concentrations of the catalyst and the cross-linker. For biological responses, in vitro rat bone mesenchymal stem cell (rBMSC) culture studies demonstrated that cryogelled SF scaffolds supported better cell attachment and proliferation than the routine freeze-thawed scaffolds. The in vivo subcutaneous implantation results showed excellent histocompatibility and tissue ingrowth for the cryogelled SF scaffolds. This straightforward approach of enhanced elasticity of SF scaffolds and fine-tunability in mechanical performances, suggests a promising strategy to develop novel SF biomaterials for soft tissue engineering and regenerative medicine.

Biomaterials research of China from 2013 to 2017 based on bibliometrics and visualization analysis.

OBJECTIVES: This study aims to evaluate the changes of development trends and research hotspots of biomaterials research from 2013 to 2017, which can identify the general information of papers and explore the changes of research content, thus providing perspectives for the development of biomaterials in China and other countries. METHODS: Data of the paper were retrieved from the Web of Science Core Collection, and then analyzed by the bibliometric and CiteSpace visualization analysis. RESULTS: It was found that a total of 3,839 related papers had been published from the year 2013 to 2017. The analysis of the articles showed that the annual quantity and quality of the articles in the biomaterials research have been increasing since 2013, and the Wang L / Chinese Academy of Sciences were the most productive author/institution. Meanwhile, the keywords "in vitro", "scaffold", "nanoparticle" , "mechanical property", and "biocompatibility" have the relatively higher frequency, and the keywords "apatite", "deposition", and "surface modification" have the strongest burst citation. CONCLUSIONS: After statistics and analysis, we found that biomaterials is a promising research field. The study may be helpful in understanding research trends in this field.