Jianguang Zhang

Electrospun fibers, with proven ability to promote tissue regeneration, are widely being explored for rotator cuff repairing. However, without post treatment, the microstructure of the electrospun scaffold is vastly different from that of natural extracellular matrix (ECM). Moreover, during mechanical loading, the nanofibers slip that hampers the proliferation and differentiation of migrating stem cells. Here, electrospun nanofiber scaffolds, with crimped nanofibers and welded joints to biomimic the intricate natural microstructure of tendon-to-bone insertion, were prepared using poly(ester-urethane)urea and gelatin via electrospinning and double crosslinking by a multi-bonding network densification strategy. The crimped nanofiber scaffold (CNS) features bionic tensile stress and induces chondrogenic differentiation, laying credible basis for in vivo experimentation. After repairing a rabbit massive rotator cuff tear using a CNS for 3 months, the continuous translational tendon-to-bone interface was fully regenerated, and fatty infiltration was simultaneously inhibited. Instead of micro-CT, μCT was employed to visualize the integrity and intricateness of the three-dimensional microstructure of the CNS-induced-healed tendon-to-bone interface at an ultra-high resolution of less than 1 μm. This study sheds light on the correlation between nanofiber post treatment and massive rotator cuff repair and provides a general strategy for crimped nanofiber preparation and tendon-to-bone interface imaging characterization.

Keeping the stemness of human mesenchymal stem cells (hMSCs) and their adipocyte differentiation potential is critical for clinical use. However, these features are lost on traditional substrates. hMSCs have often been studied on stiff materials whereas culturing hMSCs in their native niche increases their potential. Herein, a patterned hydrogel nanocomposite with the stiffness of liver tissues is obtained without any molding process. To investigate hMSCs' mechanoresponse to the material, the RGD spacing units and the stiffness of the hydrogels are dually tuned via the linker length. This work suggests that hMSCs' locomotion is influenced by the nature of the hydrogel layer (bulk or thin film). Contrary to on bulk surfaces, cell traction occurs during cell spreading on thin films. In addition, hMSCs' spreading behavior varies from shorter to longer linker‐based hydrogels, where on both surfaces hMSCs maintains their stemness as well as their adipogenic differentiation potential with a higher number of adipocytes for nanocomposites with a longer polymer linker. Overall, this work addresses the need for a new alternative for hMSCs culture allowing the cells to differentiate exclusively into adipocytes. This material represents a cell‐responsive platform with a tissue‐mimicking architecture given by the mechanical and morphological properties of the hydrogel.

Although mechanisms of how physical forces convert into biochemical signals are increasingly understood, it is still unknown how soft cues guide cell behavior. Herein, it is shown that the commitment and differentiation of encapsulating human mesenchymal stem cell (hMSC) spheroids in thermosensitive 3D hydrogels are simply altered by interpenetrating poly(N‐isopropylacrylamide‐co‐2‐hydroxyethyl methacrylate) (NIPAM‐HEMA) nanogel to a gelatin methacryloyl (GelMA) network. This cell‐laden hydrogel provides dynamic mechanics with covalent crosslinking coordinated reversible physical networks, which can regulate hMSCs in situ by reversibly stiffening soft niches via multicyclic temperature changes from 25 to 37 °C. The spreading of hMSC spheroids in the hydrogel is strongly dependent on myosin‐dependent traction stress with dynamic mechanical stimuli through focal adhesion kinase (FAK) signaling. Notably, the dynamic microenvironment gradually influences the expression and distribution from the basal to apical side of nuclear lamin A/C and increases the Yes‐associated protein (YAP) nuclear localization with cycles, which ultimately favors hMSCs undergoing osteogenesis (but not adipogenesis) in the soft microniche. Moreover, it is demonstrated that the viscoelastic behavior of the soft microniche can be guided by temperature through a nonlinear model. These findings highlight the central roles of the dynamic relationship between the biomechanical signals and mechanosensitive transcriptional regulators in cellular mechanosensing.

The role of mechanical forces is crucial for stem cell adhesion, viability, proliferation, self‐renewal, and differentiation. The relationship between the natural extracellular matrix mechanics and cell behavior is dynamic, such as compressive stress from skeletal muscle contraction. Thus, relatively little is known about how stem cells respond to reversibly dynamic mechanical stimulation (RD‐MS) in a 3D fiber network. Here, thermosensitive electrospun microfibrous cross‐linked hydrogels are investigated from variants of polycaprolactone and poly(N‐isopropylacrylamide) in which the mechanosensing can be in situ thermo‐induced switched from stiff (37 °C) to soft (25 °C) for multiple cycles. It is found that human mesenchymal stem cells seeded in bioengineered fibrillar microenvironments with multicyclic RD‐MS result in an increased cell spreading area and polarization. This 3D cell shape deformation can ultimately alter the intracellular signaling related to the differentiation. Combining with mechanosensing computer simulations, a positive correlation between the elongated morphology and the cycles of RD‐MS is predicted, suggesting that the cell polarization is proportional to dynamic changes of local stiffness and geometric fiber density of the fiber network. This study reveals RD‐MS as a key design parameter for biomaterial scaffolds as well to control cell behavior in tissue engineering applications.

Endothelialization of the polymer substrate is limited by unspecific cell adhesion. Herein, a biodegradable microfibrous scaffold with a reversibly thermoswitchable property was developed to dynamically regulate endothelial progenitor cell adhesion by exposing or concealing cRGD motif to the surface with a thermosensitive moiety (cRGD-PNIPAM) and antifouling moiety linear polyglycerol (LPG). Owing to a reversible α_vβ₃ integrin–cRGD interaction and ligand presentation, the accelerated endothelial cell adhesion and spreading were achieved. Under the static and dynamic conditions, prestained endothelial cells were quickly attached to the surface at 25 °C via the integrin–cRGD interaction, and the cRGD was the headgroup of the stretched PNIPAM below the LCST of PNIPAM. With the increase of the temperature to 37 °C, a quick detachment of cells from the surface was observed due to the cRGD moiety being shielded by the antifouling LPG layer. As compared to current strategies for endothelialization, for example, loaded drugs or growth factors, such a tunable dynamic system based on “switchable surfaces” may unlock new application in in situ targeted cell recruitment and might become useful in regenerative medicine.

The capabilities of conductive nanomaterials to be produced in liquid form with well‐defined chemical, physical, and biological properties are highly important for the construction of next‐generation flexible bioelectronic devices. Although functional graphene nanomaterials can serve as attractive liquid nanoink platforms for the fabrication of bioelectronics, scalable synthesis of graphene nanoink with an integration of high colloidal stability, water processability, electrochemical activity, and especially bioactivity remains a major challenge. Here, a facile and scalable synthesis of supramolecular‐functionalized multivalent graphene nanoink (mGN‐ink) via [2+1] nitrene cycloaddition is reported. The mGN‐ink unambiguously displays a well‐defined and flat 2D morphology and shows good water processability and bioactivity. The uniquely chemical, physical, and biological properties of mGN‐ink endow the constructed bioelectronic films and nanofibers with high flexibility and durability, suitable conductivity and electrochemical activity, and most importantly, good cellular compatibility and a highly efficient control of stem‐cell spreading and orientation. Overall, for the first time, a water‐processable and bioactive mGN‐ink is developed for the design of flexible and electrochemically active bioelectronic composites and devices, which not only presents manifold possibilities for electronic‐cellular applications but also establishes a new pathway for adapting macroscopic usages of graphene nanomaterials in bionic, biomedical, electronic, and even energy fields.

Currently, electroactive biomaterials have often been fabricated as tissue engineering scaffolds to provide electrical stimulation for neural tissue engineering. The goal of this work was to study the synergistic effect of electrical stimulation and nerve growth factor (NGF) on neuron growth. The composite meshes of polyaniline (PANi) and well-blended poly(L-lactic acid-co-ε-caprolactone)/silk fibroin (PS) incorporated with nerve growth factor (NGF) were prepared by coaxial electrospinning. The results showed that the increased concentration of PANi had a large effect on the fiber diameter, which was significantly reduced from 683 ± 138 nm to 411 ± 98 nm and then increased to 498 ± 100 nm. The contact angles and Young's modulus decreased to 28.3° ± 5.4° and 7.2 ± 1.2 MPa, respectively, and the conductance increased to 30.5 ± 3.1 mS cm⁻¹. The results of the viability and morphology of mouse Schwann cells on the nanofibrous meshes showed that PS-PANi-1 loaded with NGF exhibited the highest cell number after 5 days culture and the aligned nanofibers could guide cell orientation. The synergistic effects of electrical stimulation and NGF were also investigated via the growth and differentiation of rat pheochromocytoma 12 (PC12) cells. The scaffolds loaded with NGF under electrical stimulation could effectively support PC12 neurite outgrowth and increase the percentage of neurite-bearing cells as well as the median neurite length. More importantly, the NGF release from the conductive core–shell structure nanofiber could be increased by electrical stimulation. These promising results demonstrated that there was a potential use of this functional scaffold for nerve tissue regeneration.