Living Biomaterials

Multifunctional scaffolds for bone repair following age-related biological decline: Promising prospects for smart biomaterial-driven technologies

The repair of large bone defects due to trauma, disease, and infection can be exceptionally challenging in the elderly. Despite best clinical practice, bone regeneration within contemporary, surgically implanted synthetic scaffolds is often problematic, inconsistent, and insufficient where additional osteobiological support is required to restore bone. Emergent smart multifunctional biomaterials may drive important and dynamic cellular crosstalk that directly targets, signals, stimulates, and promotes an innate bone repair response following age-related biological decline and when in the presence of disease or infection. However, their role remains largely undetermined. By highlighting their mechanism/s and mode/s of action, this review spotlights smart technologies that favorably align in their conceivable ability to directly target and enhance bone repair and thus are highly promising for future discovery for use in the elderly. The four degrees of interactive scaffold smartness are presented, with a focus on bioactive, bioresponsive, and the yet-to-be-developed autonomous scaffold activity. Further, cell- and biomolecular-assisted approaches were excluded, allowing for contemporary examination of the capabilities, demands, vision, and future requisites of next-generation biomaterial-induced technologies only. Data strongly supports that smart scaffolds hold significant promise in the promotion of bone repair in patients with a reduced osteobiological response. Importantly, many techniques have yet to be tested in preclinical models of aging. Thus, greater clarity on their proficiency to counteract the many unresolved challenges within the scope of aging bone is highly warranted and is arguably the next frontier in the field. This review demonstrates that the use of multifunctional smart synthetic scaffolds with an engineered strategy to circumvent the biological insufficiencies associated with aging bone is a viable route for achieving next-generation therapeutic success in the elderly population.

Engineered nascent living human tissues with unit programmability

Leveraging human cells as materials precursors is a promising approach for fabricating living materials with tissue-like functionalities and cellular programmability. Here we describe a set of cellular units with metabolically engineered glycoproteins that allow cells to tether together to function as macrotissue building blocks and bioeffectors. The generated human living materials, termed as Cellgels, can be rapidly assembled in a wide variety of programmable three-dimensional configurations with physiologically relevant cell densities (up to 108 cells per cm3), tunable mechanical properties and handleability. Cellgels inherit the ability of living cells to sense and respond to their environment, showing autonomous tissue-integrative behaviour, mechanical maturation, biological self-healing, biospecific adhesion and capacity to promote wound healing. These living features also enable the modular bottom-up assembly of multiscale constructs, which are reminiscent of human tissue interfaces with heterogeneous composition. This technology can potentially be extended to any human cell type, unlocking the possibility for fabricating living materials that harness the intrinsic biofunctionalities of biological systems.

Control of charge transport in electronically active systems towards integrated biomolecular circuits (IbC)

The miniaturization of traditional silicon-based electronics will soon reach its limitation as quantum tunneling and heat become serious problems at the several-nanometer scale. Crafting integrated circuits via self-assembly of electronically active molecules using a "bottom-up" paradigm provides a potential solution to these technological challenges. In particular, integrated biomolecular circuits (IbC) offer promising advantages to achieve this goal, as nature offers countless examples of functionalities entailed by self-assembly and examples of controlling charge transport at the molecular level within the self-assembled structures. To this end, the review summarizes the progress in understanding how charge transport is regulated in biosystems and the key redox-active amino acids that enable the charge transport. In addition, charge transport mechanisms at different length scales are also reviewed, offering key insights for controlling charge transport in IbC in the future.

Targeting angiogenesis in oncology, ophthalmology and beyond

Angiogenesis is an essential process in normal development and in adult physiology, but can be disrupted in numerous diseases. The concept of targeting angiogenesis for treating diseases was proposed more than 50 years ago, and the first two drugs targeting vascular endothelial growth factor (VEGF), bevacizumab and pegaptanib, were approved in 2004 for the treatment of cancer and neovascular ophthalmic diseases, respectively. Since then, nearly 20 years of clinical experience with anti-angiogenic drugs (AADs) have demonstrated the importance of this therapeutic modality for these disorders. However, there is a need to improve clinical outcomes by enhancing therapeutic efficacy, overcoming drug resistance, defining surrogate markers, combining with other drugs and developing the next generation of therapeutics. In this Review, we examine emerging new targets, the development of new drugs and challenging issues such as the mode of action of AADs and elucidating mechanisms underlying clinical benefits; we also discuss possible future directions of the field.

Light-Activated Assembly of Connexon Nanopores in Synthetic Cells

During developmental processes and wound healing, activation of living cells occurs with spatiotemporal precision and leads to rapid release of soluble molecular signals, allowing communication and coordination between neighbors. Nonliving systems capable of similar responsive release hold great promise for information transfer in materials and site-specific drug delivery. One nonliving system that offers a tunable platform for programming release is synthetic cells. Encased in a lipid bilayer structure, synthetic cells can be outfitted with molecular conduits that span the bilayer and lead to material exchange. While previous work expressing membrane pore proteins in synthetic cells demonstrated content exchange, user-defined control over release has remained elusive. In mammalian cells, connexon nanopore structures drive content release and have garnered significant interest since they can direct material exchange through intercellular contacts. Here, we focus on connexon nanopores and present activated release of material from synthetic cells in a light-sensitive fashion. To do this, we re-engineer connexon nanopores to assemble after post-translational processing by a protease. By encapsulating proteases in light-sensitive liposomes, we show that assembly of nanopores can be triggered by illumination, resulting in rapid release of molecules encapsulated within synthetic cells. Controlling connexon nanopore activity provides an opportunity for initiating communication with extracellular signals and for transferring molecular agents to the cytoplasm of living cells in a rapid, light-guided manner.

Covalent Stem Cell-Combining Injectable Materials with Enhanced Stemness and Controlled Differentiation In Vivo

Biohybrid materials, which are defined as engineered functional materials combining living components with nonliving synthetic materials, are considered promising bioactive materials for applications in in vivo tissue engineering. However, the rational design of biohybrid materials applicable to in vivo tissue engineering faces major challenges associated with techniques for combining living cells with nonliving synthetic materials and cell sources. Here, we report injectable covalent stem cell-combing biohybrid materials prepared via a bio-orthogonal click cross-linking reaction of azide-modified adipose-derived stem cells (N₃[+]ADSCs), one of the most promising cell sources utilized clinically, with alkyne-modified biocompatible alginate polymers. The mechanical properties of the covalent stem cell-combining biohybrid materials can be adapted to the mechanical properties of the surrounding environment in which they are transplanted by alternating the number of N₃[+]ADSCs, the concentration of alkyne-modified alginate, and the number of alkyne groups. Importantly, ADSCs in the covalent biohybrid materials expressed a high level of CD-105, a marker for undifferentiated mesenchymal stem cells, in the body in the absence of differentiation signals, whereas very little CD-105 was expressed in the control physical cell-loading materials, demonstrating that this covalent stem cell-combining approach results in enhanced retention of the material's "stemness" and controlled differentiation in the body. We assessed the potential utility of the covalent stem cell-combining biohybrid materials for in vivo tissue engineering using a murine severe skeletal muscle defect-healing model. Importantly, all of the tissues regenerated by the covalent biohybrid material treatment expressed MYH3, a myogenic marker protein, whereas no expression of MYH3 was detected in the tissues reconstructed by treatment with control physical stem cell-loading materials and Matrigel, indicating that this covalent stem cell-combining approach results in controlled differentiation in the body. Our data demonstrate the potential utility of covalent stem cell-combining biohybrid materials with host tissue-integrative and controlled differentiation capabilities available for in vivo tissue engineering.

Three-Dimensional Bio-Printed Cardiac Patch for Sustained Delivery of Extracellular Vesicles from the Interface

Cardiac tissue engineering has emerged as a promising strategy to treat infarcted cardiac tissues by replacing the injured region with an ex vivo fabricated functional cardiac patch. Nevertheless, integration of the transplanted patch with the host tissue is still a burden, limiting its clinical application. Here, a bi-functional, 3D bio-printed cardiac patch (CP) design is proposed, composed of a cell-laden compartment at its core and an extracellular vesicle (EV)-laden compartment at its shell for better integration of the CP with the host tissue. Alginate-based bioink solutions were developed for each compartment and characterized rheologically, examined for printability and their effect on residing cells or EVs. The resulting 3D bio-printed CP was examined for its mechanical stiffness, showing an elastic modulus between 4-5 kPa at day 1 post-printing, suitable for transplantation. Affinity binding of EVs to alginate sulfate (AlgS) was validated, exhibiting dissociation constant values similar to those of EVs with heparin. The incorporation of AlgS-EVs complexes within the shell bioink sustained EV release from the CP, with 88% cumulative release compared with 92% without AlgS by day 4. AlgS also prolonged the release profile by an additional 2 days, lasting 11 days overall. This CP design comprises great potential at promoting more efficient patch assimilation with the host.

Precise Assembly of Proteins and Carbohydrates for Next-Generation Biomaterials

The complexity and diversity of biomacromolecules make them a unique class of building blocks for generating precise assemblies. They are particularly available to a new generation of biomaterials integrated with living systems due to their intrinsic properties such as accurate recognition, self-organization, and adaptability. Therefore, many excellent approaches have been developed, leading to a variety of quite practical outcomes. Here, we review recent advances in the fabrication and application of artificially precise assemblies by employing proteins and carbohydrates as building blocks, followed by our perspectives on some of new challenges, goals, and opportunities for the future research directions in this field.

Carrageenan-Based Compounds as Wound Healing Materials

The following review is focused on carrageenan, a heteroglycan-based substance that is a very significant wound healing biomaterial. Every biomaterial has advantages and weaknesses of its own, but these drawbacks are typically outweighed by combining the material in various ways with other substances. Carrageenans' key benefits include their water solubility, which enables them to keep the wound and periwound damp and absorb the wound exudate. They have low cytotoxicity, antimicrobial and antioxidant qualities, do not stick to the wound bed, and hence do not cause pain when removed from the wounded region. When combined with other materials, they can aid in hemostasis. This review emphasizes the advantages of using carrageenan for wound healing, including the use of several mixes that improve its properties.

Modular configurations of living biomaterials incorporating nano-based artificial mediators and synthetic biology to improve bioelectrocatalytic performance: A review

Currently, the industrial application of bioelectrochemical systems (BESs) that are incubated with natural electrochemically active microbes (EABs) is limited due to inefficient extracellular electron transfer (EET) by natural EABs. Notably, recent studies have identified several novel living biomaterials comprising highly efficient electron transfer systems allowing unparalleled proficiency of energy conversion. Introduction of these biomaterials into BESs could fundamentally increase their utilization for a wide range of applications. This review provides a comprehensive assessment of recent advancements in the design of living biomaterials that can be exploited to enhance bioelectrocatalytic performance. Further, modular configurations of abiotic and biotic components promise a powerful enhancement through integration of nano-based artificial mediators and synthetic biology. Herein, recent advancements in BESs are synthesized and assessed, including heterojunctions between conductive nanomaterials and EABs, in-situ hybrid self-assembly of EABs and nano-sized semiconductors, cytoprotection in biohybrids, synthetic biological modifications of EABs and electroactive biofilms. Since living biomaterials comprise a broad range of disciplines, such as molecular biology, electrochemistry and material sciences, full integration of technological advances applied in an interdisciplinary framework will greatly enhance/advance the utility and novelty of BESs. Overall, emerging fundamental knowledge concerning living biomaterials provides a powerful opportunity to markedly boost EET efficiency and facilitate the industrial application of BESs to meet global sustainability challenges/goals.

Engineering mammalian living materials towards clinically relevant therapeutics

Engineered living materials represent a new generation of human-made biotherapeutics that are highly attractive for a myriad of medical applications. In essence, such cell-rich platforms provide encodable bioactivities with extended lifetimes and environmental multi-adaptability currently unattainable in conventional biomaterial platforms. Emerging cell bioengineering tools are herein discussed from the perspective of materializing living cells as cooperative building blocks that drive the assembly of multiscale living materials. Owing to their living character, pristine cellular units can also be imparted with additional therapeutically-relevant biofunctionalities. On this focus, the most recent advances on the engineering of mammalian living materials and their biomedical applications are herein outlined, alongside with a critical perspective on major roadblocks hindering their realistic clinical translation. All in all, transposing the concept of leveraging living materials as autologous tissue-building entities and/or self-regulated biotherapeutics opens new realms for improving precision and personalized medicine strategies in the foreseeable future.

Biomaterials and Their Biomedical Applications: From Replacement to Regeneration

The history of biomaterials dates back to the mists of time: human beings had always used exogenous materials to facilitate wound healing and try to restore damaged tissues and organs. Nowadays, a wide variety of materials are commercially available and many others are under investigation to both maintain and restore bodily functions. Emerging clinical needs forced the development of new biomaterials, and lately discovered biomaterials allowed for the performing of new clinical applications. The definition of biomaterials as materials specifically conceived for biomedical uses was raised when it was acknowledged that they have to possess a fundamental feature: biocompatibility. At first, biocompatibility was mainly associated with biologically inert substances; around the 1970s, bioactivity was first discovered and the definition of biomaterials was consequently extended. At present, it also includes biologically derived materials and biological tissues. The present work aims at walking across the history of biomaterials, looking towards the scientific literature published on this matter. Finally, some current applications of biomaterials are briefly depicted and their future exploitation is hypothesized.

Enhancing Peptide Biomaterials for Biofabrication

Biofabrication using well-matched cell/materials systems provides unprecedented opportunities for dealing with human health issues where disease or injury overtake the body’s native regenerative abilities. Such opportunities can be enhanced through the development of biomaterials with cues that appropriately influence embedded cells into forming functional tissues and organs. In this context, biomaterials’ reliance on rigid biofabrication techniques needs to support the incorporation of a hierarchical mimicry of local and bulk biological cues that mimic the key functional components of native extracellular matrix. Advances in synthetic self-assembling peptide biomaterials promise to produce reproducible mimics of tissue-specific structures and may go some way in overcoming batch inconsistency issues of naturally sourced materials. Recent work in this area has demonstrated biofabrication with self-assembling peptide biomaterials with unique biofabrication technologies to support structural fidelity upon 3D patterning. The use of synthetic self-assembling peptide biomaterials is a growing field that has demonstrated applicability in dermal, intestinal, muscle, cancer and stem cell tissue engineering.

Progress in the mechanical modulation of cell functions in tissue engineering

In mammals, mechanics at multiple stages-nucleus to cell to ECM-underlie multiple physiological and pathological functions from its development to reproduction to death. Under this inspiration, substantial research has established the role of multiple aspects of mechanics in regulating fundamental cellular processes, including spreading, migration, growth, proliferation, and differentiation. However, our understanding of how these mechanical mechanisms are orchestrated or tuned at different stages to maintain or restore the healthy environment at the tissue or organ level remains largely a mystery. Over the past few decades, research in the mechanical manipulation of the surrounding environment-known as substrate or matrix or scaffold on which, or within which, cells are seeded-has been exceptionally enriched in the field of tissue engineering and regenerative medicine. To do so, traditional tissue engineering aims at recapitulating key mechanical milestones of native ECM into a substrate for guiding the cell fate and functions towards specific tissue regeneration. Despite tremendous progress, a big puzzle that remains is how the cells compute a host of mechanical cues, such as stiffness (elasticity), viscoelasticity, plasticity, non-linear elasticity, anisotropy, mechanical forces, and mechanical memory, into many biological functions in a cooperative, controlled, and safe manner. High throughput understanding of key cellular decisions as well as associated mechanosensitive downstream signaling pathway(s) for executing these decisions in response to mechanical cues, solo or combined, is essential to address this issue. While many reports have been made towards the progress and understanding of mechanical cues-particularly, substrate bulk stiffness and viscoelasticity-in regulating the cellular responses, a complete picture of mechanical cues is lacking. This review highlights a comprehensive view on the mechanical cues that are linked to modulate many cellular functions and consequent tissue functionality. For a very basic understanding, a brief discussion of the key mechanical players of ECM and the principle of mechanotransduction process is outlined. In addition, this review gathers together the most important data on the stiffness of various cells and ECM components as well as various tissues/organs and proposes an associated link from the mechanical perspective that is not yet reported. Finally, beyond addressing the challenges involved in tuning the interplaying mechanical cues in an independent manner, emerging advances in designing biomaterials for tissue engineering are also explored.

Supramolecular gelation controlled by an iodine clock

Programming supramolecular assembly in the time domain is a fundamental aspect of the design of biomimetic materials. We achieved the time-controlled sol-gel transition of a poly(vinyl alcohol)-iodine supramolecular complex by generating iodine in situ with a clock reaction. We demonstrate that both the gelation time and the mechanical properties of the resulting hydrogel can be tuned by properly selecting the clock parameters or through competitive iodine complexation.

On the road to smart biomaterials for bone research: definitions, concepts, advances, and outlook

The demand for biomaterials that promote the repair, replacement, or restoration of hard and soft tissues continues to grow as the population ages. Traditionally, smart biomaterials have been thought as those that respond to stimuli. However, the continuous evolution of the field warrants a fresh look at the concept of smartness of biomaterials. This review presents a redefinition of the term "Smart Biomaterial" and discusses recent advances in and applications of smart biomaterials for hard tissue restoration and regeneration. To clarify the use of the term "smart biomaterials", we propose four degrees of smartness according to the level of interaction of the biomaterials with the bio-environment and the biological/cellular responses they elicit, defining these materials as inert, active, responsive, and autonomous. Then, we present an up-to-date survey of applications of smart biomaterials for hard tissues, based on the materials' responses (external and internal stimuli) and their use as immune-modulatory biomaterials. Finally, we discuss the limitations and obstacles to the translation from basic research (bench) to clinical utilization that is required for the development of clinically relevant applications of these technologies.

Surface Tension-Assisted Additive Manufacturing of Tubular, Multicomponent Biomaterials

The fabrication of functional biomaterials for organ replacement and tissue repair remains a major goal of biomedical engineering. Advances in additive manufacturing (AM) technologies and computer-aided design (CAD) are advancing the tools available for the production of these devices. Ideally, these constructs should be matched to the geometry and mechanical properties of the tissue at the needed implant site. To generate geometrically defined and structurally supported multicomponent and cell-laden biomaterials, we have developed a method to integrate hydrogels with 3D-printed lattice scaffolds leveraging surface tension-assisted AM.

Copper-enriched diamond-like carbon coatings promote regeneration at the bone-implant interface

There have been several attempts to design innovative biomaterials as surface coatings to enhance the biological performance of biomedical implants. The objective of this study was to design multifunctional Cu/a-C:H thin coating depositing on the Ti-6Al-4V alloy (TC4) via magnetron sputtering in the presence of Ar and CH4 for applications in bone implants. Moreover, the impact of Cu amount and sp2/sp3 ratio on the interior stress, corrosion behavior, mechanical properties, and tribological performance and biocompatibility of the resulting biomaterial was discussed. X-ray photoelectron spectroscopy (XPS) revealed that the sp2/sp3 portion of the coating was enhanced for samples having higher Cu contents. The intensity of the interior stress of the Cu/a-C:H thin bio-films decreased by increase of Cu content as well as the sp2/sp3 ratio. By contrast, the values of Young's modulus, the H3/E2 ratio, and hardness exhibited no significant difference with enhancing Cu content and sp2/sp3 ratio. However, there was an optimum Cu content (36.8 wt.%) and sp2/sp3 ratio (4.7) that it is feasible to get Cu/a-C:H coating with higher hardness and tribological properties. Electrochemical impedance spectroscopy test results depicted significant improvement of Ti-6Al-4V alloy corrosion resistance by deposition of Cu/a-C:H thin coating at an optimum Ar/CH4 ratio. Furthermore, Cu/a-C:H thin coating with higher Cu contents showed better antibacterial properties and higher angiogenesis and osteogenesis activities. The coated samples inhibited the growth of bacteria as compared to the uncoated sample (p < 0.05). In addition, such coating composition can stimulate angiogenesis, osteogenesis and control host response, thereby increasing the success rate of implants. Moreover, Cu/a-C:H thin films encouraged development of blood vessels on the surface of titanium alloy when the density of grown blood vessels was increased with enhancing the Cu amount of the films. It is speculated that such coating can be a promising candidate for enhancing the osseointegration features.

Additive Manufacturing of Precision Biomaterials

Biomaterials play a critical role in modern medicine as surgical guides, implants for tissue repair, and as drug delivery systems. The emerging paradigm of precision medicine exploits individual patient information to tailor clinical therapy. While the main focus of precision medicine to date is the design of improved pharmaceutical treatments based on "-omics" data, the concept extends to all forms of customized medical care. This includes the design of precision biomaterials that are tailored to meet specific patient needs. Additive manufacturing (AM) enables free-form manufacturing and mass customization, and is a critical enabling technology for the clinical implementation of precision biomaterials. Materials scientists and engineers can contribute to the realization of precision biomaterials by developing new AM technologies, synthesizing advanced (bio)materials for AM, and improving medical-image-based digital design. As the field matures, AM is poised to provide patient-specific tissue and organ substitutes, reproducible microtissues for drug screening and disease modeling, personalized drug delivery systems, as well as customized medical devices.

Inducing Endogenous Cardiac Regeneration: Can Biomaterials Connect the Dots?

Heart failure (HF) after myocardial infarction (MI) due to blockage of coronary arteries is a major public health issue. MI results in massive loss of cardiac muscle due to ischemia. Unfortunately, the adult mammalian myocardium presents a low regenerative potential, leading to two main responses to injury: fibrotic scar formation and hypertrophic remodeling. To date, complete heart transplantation remains the only clinical option to restore heart function. In the last two decades, tissue engineering has emerged as a promising approach to promote cardiac regeneration. Tissue engineering aims to target processes associated with MI, including cardiomyogenesis, modulation of extracellular matrix (ECM) remodeling, and fibrosis. Tissue engineering dogmas suggest the utilization and combination of two key components: bioactive molecules and biomaterials. This chapter will present current therapeutic applications of biomaterials in cardiac regeneration and the challenges still faced ahead. The following biomaterial-based approaches will be discussed: Nano-carriers for cardiac regeneration-inducing biomolecules; corresponding matrices for their controlled release; injectable hydrogels for cell delivery and cardiac patches. The concept of combining cardiac patches with controlled release matrices will be introduced, presenting a promising strategy to promote endogenous cardiac regeneration.

Outlooks on Three-Dimensional Printing for Ocular Biomaterials Research

Given its potential for high-resolution, customizable, and waste-free fabrication of medical devices and in vitro biological models, 3-dimensional (3D) bioprinting has broad utility within the biomaterials field. Indeed, 3D bioprinting has to date been successfully used for the development of drug delivery systems, the recapitulation of hard biological tissues, and the fabrication of cellularized organ and tissue-mimics, among other applications. In this study, we highlight convergent efforts within engineering, cell biology, soft matter, and chemistry in an overview of the 3D bioprinting field, and we then conclude our work with outlooks toward the application of 3D bioprinting for ocular research in vitro and in vivo.

Recent advances in gelatin-based therapeutics

INTRODUCTION

Biomaterials have provided a wide range of exciting opportunities in tissue engineering and regenerative medicine. Gelatin, a collagen-derived natural biopolymer, has been extensively used in regenerative medicine applications over the years, due to its cell-responsive properties and the capacity to deliver a wide range of biomolecules.

AREAS COVERED

The most relevant properties of gelatin as biomaterial are presented together with its main therapeutic applications. The latter includes drug delivery systems, tissue engineering approaches, potential uses as ink for 3D/4D Bioprinting, and its relevance in organ-on-a-chip platforms.

EXPERT OPINION

Advances in polymer chemistry, mechanobiology, imaging technologies, and 3D biofabrication techniques have expanded the application of gelatin in multiple biomedical research applications ranging from bone and cartilage tissue engineering, to wound healing and anti-cancer therapy. Here, we highlight the latest advances in gelatin-based approaches within the fields of biomaterial-based drug delivery and tissue engineering together with some of the most relevant challenges and limitations.

Double-headed nanosystems for oral drug delivery

We demonstrate a novel strategy to engineer double-headed nanosystems by chemical modification of the carboxyl terminal polyester with a linker that offers tripodal arrangement of ligands on the particle surfaces. The in vivo results suggest that the bioavailability of encapsulated curcumin is proportional to the ligand density rendered by double-headed nanosystems.

Effects of Extrusion on Mechanical and Corrosion Resistance Properties of Biomedical Mg-Zn-Nd-xCa Alloys

Magnesium alloys act as ideal biomedical materials with good biocompatibility. In this paper, the extruded biomedical Mg-6Zn-0.5Nd-0.5/0.8Ca alloys were prepared and their microstructure, mechanical properties and corrosion properties were investigated. The results showed that the surfaces of Mg-6Zn-0.5Nd-0.5/0.8Ca alloys extruded at medium temperature were smooth and compact without cracks. The tensile strength and elongation of Mg-6Zn-0.5Nd-0.5/0.8Ca alloys were 222.5 MPa and 20.2%, and 287.2 MPa and 18.4%, respectively. A large number of dislocations were generated in the grains and on grain boundaries after the extrusion. The alloy was immersed in simulating body fluid (SBF) for the weightlessness corrosion, and the corrosion products were analyzed by FTIR, SEM equipped with EDS. It was found that the corrosion rate of Mg-6Zn-0.5Nd-0.5Ca and Mg-6Zn-0.5Nd-0.8Ca alloy were 0.82 and 2.98 mm/a, respectively. Furthermore, the compact layer was formed on the surface of the alloy, which can effectively hinder the permeation of Cl⁻ and significantly improve the corrosion resistance of magnesium alloys.

AuBr3 -Catalyzed Chemoselective Annulation of Isocyanates with 2H-Azirine

The chemoselective cyclization of isocyanates with 2H-azirine was achieved with AuBr₃ as catalyst. This transfer sets the stage for the synthesis of aromatic oxazole-ureas in a tandem process. The addition of a catalytic amount of phosphite enhances the process enormously. The reaction can also be performed in a one-pot process using benzoyl azide instead of isocyanate under the same conditions. A detailed study on the role of the phosphite that was applied as an additive revealed that only non-coordinated phosphite can reduce gold(III) and that gold(I) coordinated phosphite is not oxidized. Accompanied by the reduction of gold, HBr is generated in situ, which turned out to be the actual promotor in combination with the remaining AuBr₃ . The positive effect of acid can be explained by a strong N-Au coordination, which tends to break more easily in the presence of small amount of protic acid in the reaction solution.

Light-Induced Hypoxia-Triggered Living Nanocarriers for Synergistic Cancer Therapy

Living drug delivery system has been proposed as new concept materials because it is able to communicate with biological system, sense subtle changes in body microenvironment caused by disease, and then make rapid response to cure in the early stage of disease. Herein, taking full advantage of the tumor hypoxia physiology and successive effects of photodynamic therapy (PDT), we designed a new living delivery system via combining the PDT and hypoxia-responsive chemotherapy, abbreviated as Ce6-PEG-Azo-PCL. Then, according to the fact that oxygen can be converted into reactive oxygen species during irradiation of the photosensitizer, tumor cells could be killed after the poly(ethylene glycol) (PEG) conjugated photosensitizer chlorine e6 was irradiated at the tumor site. What is more, the continuous consumption of oxygen could further amplify the hypoxia condition of tumor and trigger the disassembly of hypoxia-responsive azobenzene bridges at the tumor site to release loaded chemotherapeutics drugs doxorubicin. The ongoing collaboration with PDT and hypoxia-responsive chemotherapy provided an integrated therapeutic effect in vitro and in vivo to suppress tumor growth.

The Synergy of Scaffold-Based and Scaffold-Free Tissue Engineering Strategies

Tissue engineering (TE) is a highly interdisciplinary research field driven by the goal to restore, replace, or regenerate defective tissues. Throughout more than two decades of intense research, different technological approaches, which can be principally categorized into scaffold-based and scaffold-free strategies, have been developed. In this opinion article, we discuss the emergence of a third strategy in TE. This synergetic strategy integrates the advantages of both of these traditional approaches, while being clearly distinct from them. Its characteristic attributes, numerous practical benefits, and recent literature reports supporting our opinion, are discussed in detail.

Engineering precision biomaterials for personalized medicine

As the demand for precision medicine continues to rise, the "one-size-fits-all" approach to designing medical devices and therapies is becoming increasingly outdated. Biomaterials have considerable potential for transforming precision medicine, but individual patient complexity often necessitates integrating multiple functions into a single device to successfully tailor personalized therapies. Here, we introduce an engineering strategy based on unit operations to provide a unified vocabulary and contextual framework to aid the design of biomaterial-based devices and accelerate their translation.

Fabrication of multi-stimuli responsive supramolecular hydrogels based on host–guest inclusion complexation of a tadpole-shaped cyclodextrin derivative with the azobenzene dimer

Multi-responsive supramolecular hydrogels, based on host–guest complexation of tadpole-shaped cyclodextrin with the azobenzene dimer, possess reversible sol–gel transition behaviors and better biocompatibility.