Nano LIFE

Biomanufacturing of cell-laden scaffolds with biomimetic cell-scaffold organizations resembling the structures and anatomy of human body tissues and organs holds great promise in tissue engineering and regenerative medicine. In human body tissues and organs, specific types of cells are supported by nanofibrous extracellular matrix (ECM) in well-defined three-dimensional (3D) manners. Electrospinning is a facile and effective technique for producing nanofibrous scaffolds, which exhibit high similarities in the structure compared to ECM that offers structural and mechanical supports to cells in the human body. The incorporation within the electrospun nanofibrous scaffolds has therefore been considered as a promising approach for biomanufacturing of cell-laden scaffolds with tissue-mimicking structures. However, limited by low controllability of conventional cell seeding strategies and small sizes of interconnected pores of normal electrospun scaffolds, it is highly difficult to incorporate living cells within electrospun scaffolds on demand and results in cell-laden scaffolds with desirable 3D cell-scaffold organization. With recent advances in electrospinning and electrospraying with cells, it is visible to directly incorporate living cells within scaffolds via cell microencapsulation approaches and therefore offer promising alternatives for biomanufacturing of cell-laden scaffolds with tissue-mimicking structures. In this review, we will summarize the applications and challenges of cell seeding strategies and cell microencapsulation technologies for incorporating cells within electrospun scaffolds. Some techniques with high potentials to be integrated with electrospinning for forming the cell-laden scaffolds in continuous and noncontact manners, including aerodynamic-assisted cell microencapsulation, hydrodynamic-assisted cell microencapsulation and electrohydrodynamic-assisted cell microencapsulation (i.e., cell electrospinning and cell electrospraying), are highlighted. In particular, the cell microencapsulation and the subsequent formation of cell-laden scaffolds directly by electrospinning and electrospraying with living cells are overviewed in a detailed manner. Finally, the perspective and challenges of electrospinning and electrospraying with cells for biomanufacturing of cell-laden scaffolds with tissue-mimicking structures are discussed.

Electrospun fibrous scaffolds attract great attention in tissue engineering owing to their high similarity in architecture to the extracellular matrix (ECM) that support cell attachment and growth in human bodies. Although they have shown superiority in promoting cell attachment and proliferation on their surfaces and hence, hold great promise for the regeneration of body tissues, the research still faces a great challenge of three-dimensional (3D) cell incorporation in electrospun scaffolds to form thick and cell-dense constructs because deep cell infiltration is hard to achieve in conventional electrospun scaffolds that normally have very small diameters of interconnected pores. Such hindrance has severely limited the clinical application of electrospun fibrous scaffolds to repair/regenerate various body tissues, particularly those with complex anatomies. To address this challenge, we have developed a concurrent cell electrospinning and emulsion electrospinning technique for fabricating bioactive bio-hybrid scaffolds with 3D and high-density cell incorporation. Through concurrent electrospinning, cell-encapsulated hydrogel fibers (“cell fibers”) and growth factor-containing ultrafine fibers are simultaneously deposited to form two-component scaffolds (i.e., scaffolds composed of two types of fibers) according to the design. With the breakup of cell fibers, live cells with well-preserved cell viability are released in situ inside the scaffolds, resulting in the creation of cell-incorporated bioactive scaffolds with ECM-mimicking fibrous architectures and 3D and high-density incorporation of cells. The growth and functions of incorporated cells in the scaffolds can be enhanced by the released growth factor from the emulsion electrospun fibrous component. The bioactive bio-hybrid scaffolds fabricated via concurrent electrospinning mimic the cell-matrix organization of body tissues and therefore have great potential for regenerating body tissues such as tendon and ligament.

The demand for treating degenerative osteoarthritis is dramatically growing during the past decade due to the increasing aging population. Compared to arthroscopic debridement and injection of lubricating hydrogels, implantation of a cartilage tissue engineering scaffold with a customized architecture and excellent stem cell delivery ability has been deemed as a superior alternative to regenerate defected cartilage tissues. However, relatively low mechanical strength of cell-laden hydrogel limits its potential in treating diseased/defected cartilage or tissues with an anisotropic structure. In this study, a composite cell-laden scaffold composed of three-dimensional (3D) fibrous patterns which was made through near-field electrospinning direct write (NEDW) and mesenchymal stem cell (MSC)-laden collagen I (COL I) hydrogel was fabricated. The hydrogel acted as a favorable microenvironment to load cells and growth factors to facilitate chondrogenic differentiation while the 3D fibrous patterns made of poly(caprolactone)-reinforced hydrogels and provided the composite scaffolds with a precisely designed micro-architecture. Compared to hydrogel scaffold alone, the fabricated composite scaffold had significantly higher mechanical properties. The composite scaffolds were biocompatible and can accelerate the chondrogenic differentiation of MSCs by up-regulating the expression of SOX9, collagen II (COL II) and aggrecan (ACAN), when transforming growth factor (TGF)-$\beta$1 was loaded in COL I hydrogel. However, the morphology of differentiated cells was not identical to that of the natural chondrocytes, suggesting that the modulation of initial MSC morphology is needed to pursue the target phenotype after the chondrogenic differentiation.

The aim of skeletal muscle tissue engineering is to replace or repair skeletal muscle functions that have been injured or lost part of their functions. Skeletal muscle tissue engineering is an important strategy for muscle injury repair. The previous review on skeletal muscle tissue engineering was limited to the discussion of seed cells, biological materials and growth factors. In recent years, research results in this field have continued to emerge. This paper first briefly introduces the anatomy of skeletal muscle, and then combines the latest domestic and foreign study, from the basic problems of tissue engineering skeletal muscle construction to its vascularization, neuralization, etc., to review the current research status of skeletal muscle tissue engineering using three-dimensional (3D) printing, and look forward to its research prospects.

In recent years, 4D printing has gained increasing attention in the tissue engineering field since this advanced manufacturing platform can create stimulus-responsive structures, which can change their shapes, functions, and/or properties when appropriate external stimulus/stimuli is/are applied. A number of hydrogels with swellable/shrinkable abilities have been explored for 4D printing to fabricate different shape-morphing structures for tissue engineering. Among them, gelatin methacryloyl (GelMA) has been 4D printed, which can self-fold into microtubular structures. Currently, the self-folding ability of 4D printed GelMA hydrogels is mainly based on the different cross-linking degrees (which control and govern the swelling degrees) across the thickness of hydrogels. However, this strategy alone can only form self-folding GelMA tubes with diameters at the micrometer level and cannot create self-folding GelMA tubes with diameters at the millimeter level, which is mainly due to the insufficient internal force generated in 4D printed GelMA hydrogels when they are exposed to water. To overcome this limitation, this study has investigated a new strategy to fabricate self-folding GelMA tubes with large diameters at the millimeter level for tissue engineering applications. The new strategy introduced a cross-linking degree gradient across the GelMA plane in addition to its thickness by printing a second layer of strips on the first 4D printed GelMA film. In the aqueous environment, under the current fabrication condition, such bilayer GelMA hydrogels could self-fold into tubes of larger diameters up to 6mm. The in vitro release behavior of heparin incorporated into the 4D printed GelMA was also studied. It was shown that heparin release could be controlled by the GelMA concentration and heparin content in 4D printed GelMA. The 4D printed GelMA hydrogels with the improved self-folding ability and controlled release of a drug are promising for targeted tissue engineering applications.

Cancer threatens the life and well-being of human beings. Millions of newly diagnosed cancer cases and a large number of deaths caused by cancer are reported each year in the world. Early detection and effective treatment are key to reduce cancer mortality, which can be potentially realized by using “theranostics”. Theranostics are a group of hybrid nanoparticles that perform in cancer patients to provide both diagnostic and therapeutic functions through a single nano-sized structure. In particular, core-shell structured theranostics have shown unique physicochemical properties, allowing them to facilitate molecular/cell targeting, bio-imaging, and drug delivery functions. This review, therefore, aims to present and discuss the recent development of research on core-shell structured theranostics. Specifically, it focuses on core-shell structured theranostics made of metals, silica and polymers. Different aspects, such as synthesis and structure, of core-shell structured theranostics are discussed in this review. This review helps readers to have a good understanding of the design and fabrication of core-shell structured theranostics.

Nanozyme is a kind of nanomaterial with simulated enzyme activity. Due to its high catalytic efficiency, better stability and modifiability, the role of nanozymes in medicine, especially in the diagnosis and treatment of tumors, is receiving more and more attention. Nanozymes usually contain metals and are often used in combination with drugs or antigens/antibodies to become multifunctional materials for the diagnosis and treatment of tumors. At present, the detailed synthesis, classification and function of nanozymes need to be supplemented. In our review, we introduce the research status, synthesis and classification of nanozymes roundly. Then we summarized and introduced some characteristic nanozymes according to their functions, mainly including tumor diagnosis, tumor therapy, tumor surgical adjuvant therapy and multifunctional complexes. We believe that many breakthroughs have been made in the research of nanozymes, and more and more multifunctional nanozymes have been studied. However, there are still some shortcomings in the current research on nanozymes such as the lack of solutions to some of the insufficient properties of nanoparticles, like spontaneous aggregation, nonspecific phagocytosis, etc. At the same time, the catalytic reaction is relatively simple, which limits the further application of nanozyme. In our review, we made our own comments and prospects on the diagnostic, therapeutic and application of nanozymes. In the future, nanozymes will play an increasingly important role in the diagnosis and treatment of tumors due to their potential modifiability and versatility as well as their increasingly perfect physicochemical properties.