Biomimetic Lamellar Chitosan Scaffold for Soft Gingival Tissue Regeneration

Mucogingival surgery has become a common procedure for soft gingival tissue reparation in dental clinical practice, which mainly relies on autograft or commercial collagen membranes (CM). However, the autograft faces grand challenges in source availability and long-term post-surgery pain management, and the CM is restricted by its poor mechanical properties in an aqueous environment. Here, it is reported that a bio-inspired lamellar chitosan scaffold (LCS) with long range ordered porous structure, manufactured through a bidirectional freezing method, can serve as a promising gingival tissue engineering material. The LCS not only exhibits excellent mechanical properties in the hydrated state but also accelerates vessel formation and soft tissue regeneration in vivo. Most interestingly, the LCS is found to be capable of inducing macrophage differentiation to M2 macrophages, which is thought to play an important role in tissue regeneration. These advantages combined with its easy and low-cost preparation process make the LCS a promising candidate for dental clinical applications.     

Electrospun Extracellular Matrix: Paving the Way to Tailor‐Made Natural Scaffolds for Cardiac Tissue Regeneration

Biomimetic scaffolds generally aim at structurally and compositionally imitating native tissue, thus providing a supportive microenvironment to the transplanted or recruited cells in the tissue. Native decellularized porcine extracellular matrix (ECM) is becoming the ultimate bioactive material for the regeneration of different organs. Particularly for cardiac regeneration, ECM is studied as a patch and injectable scaffolds, which improve cardiac function, yet lack reproducibility and are difficult to control or fine‐tune for the desired properties, like most natural materials. Seeking to harness the natural advantages of ECM in a reproducible, scalable, and controllable scaffold, for the first time, a matrix that is produced from whole decellularized porcine cardiac ECM using electrospinning technology, is developed. This unique electrospun cardiac ECM mat preserves the composition of ECM, self‐assembles into the same microstructure of cardiac ECM ,and ,above all, preserves key cardiac mechanical properties. It supports cell growth and function, and demonstrates biocompatibility in vitro and in vivo. Importantly, this work reveals the great potential of electrospun ECM‐based platforms for a wide span of biomedical applications, thus offering the possibility to produce complex natural materials as tailor‐made, well‐defined structures.     

Electrospun Fibrous Architectures for Drug Delivery,Tissue Engineering and Cancer Therapy

The versatile electrospinning technique is recognized as an efficient strategy to deliver active pharmaceutical ingredients and has gained tremendous progress in drug delivery, tissue engineering, cancer therapy, and disease diagnosis. Numerous drug delivery systems fabricated through electrospinning regarding the carrier compositions, drug incorporation techniques, release kinetics, and the subsequent therapeutic efficacy are presented herein. Targeting for distinct applications, the composition of drug carriers vary from natural/synthetic polymers/blends, inorganic materials, and even hybrids. Various drug incorporation approaches through electrospinning are thoroughly discussed with respect to the principles, benefits, and limitations. To meet the various requirements in actual sophisticated in vivo environments and to overcome the limitations of a single carrier system, feasible combinations of multiple drug‐inclusion processes via electrospinning could be employed to achieve programmed, multi‐staged, or stimuli‐triggered release of multiple drugs. The therapeutic efficacy of the designed electrospun drug‐eluting systems is further verified in multiple biomedical applications and is comprehensively overviewed, demonstrating promising potential to address a variety of clinical challenges.     

Silk Hydrogels as Soft Substrates for Neural Tissue Engineering

There is great need for soft biomaterials that match the stiffness of human tissues for tissue engineering and regeneration. Hydrogels are frequently employed for extracellular matrix functionalization and to provide appropriate mechanical cues. It is challenging, however, to achieve structural integrity and retain bioactive molecules in hydrogels for complex tissue formation that may take months to develop. This work aims to investigate mechanical and biochemical characteristics of silk hydrogels for soft tissue engineering, specifically for the nervous system. The stiffness of 1 to 8% silk hydrogels, measured by atomic force microscopy, is 4 to 33 kPa. The structural integrity of silk gels is maintained throughout embryonic chick dorsal root ganglion (cDRG) explant culture over 4 days whereas fibrin and collagen gels decrease in mass over time. Neurite extension of cDRGs cultured on 2 and 4% silk hydrogels exhibit greater growth than softer or stiffer gels. Silk hydrogels release <5% of neurotrophin‐3 (NT‐3) over 2 weeks and 11‐day old gels show maintenance of growth factor bioactivity. Finally, fibronectin‐ and NT‐3‐functionalized silk gels elicit increased axonal bundling suggesting their use in bridging nerve injuries. These results support silk hydrogels as soft and sustainable biomaterials for neural tissue engineering.     

A Single Component Conducting Polymer Hydrogel as a Scaffold for Tissue Engineering

Conducting polymers (CPs) have exciting potential as scaffolds for tissue engineering, typically applied in regenerative medicine applications. In particular, the electrical properties of CPs has been shown to enhance nerve and muscle cell growth and regeneration. Hydrogels are particularly suitable candidates as scaffolds for tissue engineering because of their hydrated nature, their biocompatibility, and their tissue‐like mechanical properties. This study reports the development of the first single component CP hydrogel that is shown to combine both electro‐properties and hydrogel characteristics. Poly(3‐thiopheneacetic acid) hydrogels were fabricated by covalently crosslinking the polymer with 1,1′‐carbonyldiimidazole (CDI). Their swelling behavior was assessed and shown to display remarkable swelling capabilities (swelling ratios up to 850%). The mechanical properties of the networks were characterized as a function of the crosslinking density and were found to be comparable to those of muscle tissue. Hydrogels were found to be electroactive and conductive at physiological pH. Fibroblast and myoblast cells cultured on the hydrogel substrates were shown to adhere and proliferate. This is the first time that the potential of a single component CP hydrogel has been demonstrated for cell growth, opening the way for the development of new tissue engineering scaffolds.     

In Situ Crosslinkable Gelatin Hydrogels for Vasculogenic Induction and Delivery of Mesenchymal Stem Cells

Clinical trials utilizing mesenchymal stem cells (MSCs) for severe vascular diseases have highlighted the need to effectively engraft cells and promote pro‐angiogenic activity. A functional material accomplishing these two goals is an ideal solution as spatiotemporal and batch‐to‐batch variability in classical therapeutic delivery can be minimized, and tissue regeneration would begin rapidly at the implantation site. Gelatin may serve as a promising biomaterial due to its excellent biocompatibility, biodegradability, and non‐immuno/antigenicity. However, the dissolution of gelatin at body temperature and quick enzymatic degradation in vivo have limited its use thus far. To overcome these challenges, an injectable, in situ crosslinkable gelatin was developed by conjugating enzymatically crosslinkable hydroxyphenyl propionic acid (GHPA). When MSCs are cultured in 3D in vitro or injected in vivo in GHPA, spontaneous endothelial differentiation occurs, as evidenced by marked increases in endothlelial cell marker expressions (Flk1, Tie2, ANGPT1, vWF) in addition to forming an extensive perfusable vascular network after 2‐week subcutaneous implantation. Additionally, favorable host macrophage response is achieved with GHPA as shown by decreased iNOS and increased MRC1 expression. These results indicate GHPA as a promising soluble factor‐free cell delivery template which induces endothelial differentiation of MSCs with robust neovasculature formation and favorable host response.     

Scalable High‐Throughput Production of Modular Microgels for In Situ Assembly of Microporous Tissue Scaffolds

Hydrogel scaffolds that template the regeneration of tissue structures are widely explored; however, there is often a trade‐off between material properties, such as stiffness and interconnected pore size, that may be equally important in supporting tissue growth. Microporous annealed particle scaffolds are introduced to address this trade‐off while maintaining a flowable precursor; however, manufacturing throughput, reproducibility, and flexibility of hydrogel microparticle building blocks are limited, hindering widespread adoption. The scalable high‐throughput production of bioactive microgels for the formation of microporous tissue scaffolds in situ is presented. Using a parallelized step emulsification device, scalable high‐throughput generation of monodisperse microgels is achieved. Crosslinking is initiated downstream of droplet generation using pH modulation via proton acceptors dissolved in the oil phase. This approach enables continuous production of microgels for over 12 h while ensuring highly uniform physicochemical properties. Using this platform, the effects of local matrix stiffness on cell growth orthogonal to scaffold porosity are studied. Formation of injectable cell‐laden mechanically heterogeneous microporous scaffolds is also demonstrated. This approach is particularly suited for the formation of modular, multimaterial scaffolds in situ, which could be applied to 3D bioprinting or to form more complex scaffolds to enhance regeneration of irregular wounds.     

Nanobiology Dependent Therapeutic Convergence between Biocompatibility and Bioeffectiveness of Graphene Oxide Quantum Dot Scaffold for Immuno-Inductive Angiogenesis and Nerve Regeneration

The understanding of nanomaterial biology determines material selection and scaffold fabrication in regenerative medicine. The translational application of advanced functional nanomaterials, like graphene and derivatives, requires an in-depth investigation on the sophisticated material-cell action network. To achieve the therapeutic convergence between biocompatibility and bioeffectiveness, herein, series of graphene derivatives are screened and the superiority of graphene oxide quantum dots (GOQDs) is confirmed. Thereby, a GOQD functionalized nerve scaffold is fabricated for peripheral nerve repair with electrospinning and freeze-drying technology. The behavioral, electrophysiological, and pathological analysis confirms that GOQDs promote nerve structural reconstruction and attenuate denervation-induced myopathy. Macrophages perceive the implanted materials and initiate a variety of biological processes. GOQDs activate the macrophage ERK/CERB/VEGF pathway in vitro and in vivo, thereby contributing to intraneural vascularization. In addition, an enzyme-activated degradation route of GOQDs is explored and the implanted scaffolds trigger negligible scar formation and blood toxicity. These findings demonstrate the ability of the GOQD, a biocompatible graphene derivative, to facilitate intraneural vascularization and regeneration of injured peripheral nerves through a macrophage intracellular signaling-mediated mechanism. This enlightens the authors to continuously explore the mechanisms behind the material nanobiology-dependent therapeutic convergence between biocompatibility and bioeffectiveness for clinical translation.     

Surface-Triggered In Situ Gelation for Tunable Conformal Hydrogel Coating of Therapeutic Cells and Biomedical Devices

Hydrogel coatings have been proposed as a promising strategy to improve the biocompatibility of therapeutic cells and biomedical devices. However, developed coating methods are only applicable for simple geometries, typical sizes, and limited substrates. In addition, its applications in therapeutic cell encapsulation are hampered by inadequate construction of the hydrogel capsules such as off-center encapsulation, immense volume, and lack of control over the thickness of capsules. Here, a method called surface-triggered in situ gelation (STIG) for universal hydrogel coating of multiscale objects ranging from single cells to mini-organs to biomedical devices with arbitrary shapes and heterogeneous components is reported. By covering cells or devices with calcium carbonate particles, progressive propagation of alginate hydrogel from their surface under the stimulation of GDL is achieved. The thickness of the hydrogel layers can be easily controlled from several micrometers to hundreds of micrometers by adjusting the gelation time and the release rate of calcium ions. Importantly, STIG facilitates accurate, complete, and individual cell encapsulation, which potentially overcomes the pitfalls of conventional strategies. It is further proven that the low-cost and facile method can potentially lead to advances in different fields by rendering precisely controlled microscale alginate layers on a wide variety of biomedical substrates.     

Smart Design of Stable Extracellular Matrix Mimetic Hydrogel: Synthesis,Characterization, and In Vitro and In Vivo Evaluation for Tissue Engineering

The simplicity and versatility of hydrazone crosslinking has made it a strategy of choice for the conjugation of bioactive molecules. However, the labile nature of hydrazone linkages and reversibility of this coupling reaction restricts its full potential. Based on the fundamental understanding of hydrazone stability, this problem is circumvented by resonance‐stabilization of a developing N² positive charge in a hydrazone bond. A novel chemistry is presented to develop a resilient hydrazone bond that is stable and non‐ reversible under physiological conditions. A carbodihydrazide (CDH) type hydrazide derivative of the biomolecule forms intrinsically stabilized hydrazone‐linkages that are nearly 15‐fold more stable at pH 5 than conventional hydrazone. This chemoselective coupling reaction is catalyst‐free, instantaneous, and virtually non‐cleavable under physiological conditions, therefore can serve as a catalyst‐free alternative to click chemistry. This novel crosslinking reaction is used to tailor a hyaluronan hydrogel, which delivered exceptional hydrolytic stability, mechanical properties, low swelling, and controlled enzymatic degradation. These desired characteristics are achieved without increasing the chemical crosslinking. The in vivo evaluation of this hydrogel revealed neo‐bone with highly ordered collagen matrix mimicking natural bone regeneration. The proximity ligation assay or PLA is used to detect blood vessels, which highlighted the quality of engineered tissue.     

Evaluation of the Biocompatibility of PLACL/Collagen Nanostructured Matrices with Cardiomyocytes as a Model for the Regeneration of Infarcted Myocardium

Pioneering research suggests various modes of cellular therapeutics and biomaterial strategies for myocardial tissue engineering. Despite several advantages, such as safety and improved function, the dynamic myocardial microenvironment prevents peripherally or locally administered therapeutic cells from homing and integrating of biomaterial constructs with the infarcted heart. The myocardial microenvironment is highly sensitive due to the nanoscale cues that it exerts to control bioactivities, such as cell migration, proliferation, differentiation, and angiogenesis. Nanoscale control of cardiac function has not been extensively analyzed in the field of myocardial tissue engineering. Inspired by microscopic analysis of the ventricular organization in native tissue, a scalable in‐vitro model of nanoscale poly(L ‐lactic acid)‐co ‐poly(? ‐caprolactone)/collagen biocomposite scaffold is fabricated, with nanofibers in the order of 594 ± 56 nm to mimic the native myocardial environment for freshly isolated cardiomyocytes from rabbit heart, and the specifically underlying extracellular matrix architecture: this is done to address the specificity of the underlying matrix in overcoming challenges faced by cellular therapeutics. Guided by nanoscale mechanical cues provided by the underlying random nanofibrous scaffold, the tissue constructs display anisotropic rearrangement of cells, characteristic of the native cardiac tissue. Surprisingly, cell morphology, growth, and expression of an interactive healthy cardiac cell population are exquisitely sensitive to differences in the composition of nanoscale scaffolds. It is shown that suitable cell–material interactions on the nanoscale can stipulate organization on the tissue level and yield novel insights into cell therapeutic science, while providing materials for tissue regeneration.     

Linear Dendritic Block Copolymers as Promising Biomaterials for the Manufacturing of Soft Tissue Adhesive Patches Using Visible Light Initiated Thiol–Ene Coupling Chemistry

A library of dendritic–linear–dendritic (DLD) materials comprising linear poly(ethylene glycol) and hyperbranched dendritic blocks based on 2,2‐bis(hydroxymethyl) propionic acid is successfully synthesized and postfunctionalized with peripheral allyl groups. Reactive DLDs with pseudo‐generations of 3 to 6 (G3‐G6) are isolated in large scale allowing their thorough evaluation as important components for the development of biomedical adhesives. Due to their branched nature and inherent degradable ester‐bonds, promising biomaterial resins are accomplished with suitable viscosity, eliminating the excessive use of co‐solvents. By utilizing benign high‐energy visible light initiated thiol–ene coupling chemistry, DLDs together with tris[2‐(3‐mercaptopropionyloxy)ethyl] isocyanurate and surgical mesh enable the fabrication of soft tissue adhesive patches (STAPs) within a total irradiation time of 30 s. The STAPs display the ability to create good adhesion to wet soft tissue and encouraging results in cytotoxicity tests. All crosslinked materials are also found to degrade after being stored in human blood plasma and phosphate buffered saline. The proposed benign methodology coupled with the promising features of the crosslinked materials is herein envisioned as a soft tissue adhesive with properties that do not exist in currently available tissue adhesives.