Customizing biomimetic surface attributes of dendritic lipopeptide nanoplatforms for extended circulation.

The pressing demand for innovative approaches to create delivery systems with heightened drug loading and prolonged circulation has spurred numerous efforts, yielding some successes but accompanied by constraints. Our study proposes employing dendritic lipopeptide with precisely balanced opposing charges to extend blood residency for biomimetic nanoplatforms. Neutrally mixed-charged zwitterionic nanoparticles (NNPs) achieved a notable 19 % simvastatin loading content and kept stable even after one-month storage at 4 °C. These nanoplatforms demonstrated low cytotoxicity in NIH-3T3 and L02 cells and negligible hemolysis (<5 %). NNPs inhibited protein adhesion (>95 %) from positively and negatively charged sources through surface hydration. In comparison to positively charged CNPs, NNPs demonstrated an 86 % decrease in phagocytic rate by BMDMs, highlighting their efficacy. Importantly, NNPs showed prolonged circulation compared to CNPs and free simvastatin. These findings highlight the potential of this biomimetic nanoplatform for future therapeutic applications with enhanced drug loading and circulation traits.

Investigating the Biodegradation Mechanism of Poly(trimethylene carbonate): Macrophage-Mediated Erosion by Secreting Lipase.

Poly(trimethylene carbonate) (PTMC), as one of the representatives of biodegradable aliphatic polycarbonates, has been found to degrade in vivo via surface erosion. This unique degradation behavior and the resulting nonacidic products make it more competitive with aliphatic polyesters (e.g., polylactide) in clinical practice. However, this surface degradation mechanism is complicated and not fully understood to date despite the findings that several reactive oxygen species and enzymes can specifically degrade PTMC in vitro. Herein, the biodegradation mechanism of PTMC was investigated by using possible degradation factors, distinct cell lines, and the inhibitors of these factors. The results demonstrate that PTMC undergoes a specific macrophage-mediated erosion. Macrophages tend to fuse into giant cells and elicit a typical inflammatory response by releasing proinflammatory cytokines. In addition, macrophages are suggested to primarily secrete enzymes (lipase specifically) to erode the PTMC bulk extracellularly as inhibiting their activity effectively prevented this eroding process. The clarification of the biodegradation mechanism in this work suggests that the degradation of PTMC highly depends on the foreign body response. Thus, it reminds the researchers to consider the effect of the microenvironment on the degradation and drug release of PTMC-based implantation devices and localized drug delivery systems.

Congenital coagulation factor V deficiency with intracranial hemorrhage.

BACKGROUND: Congenital coagulation factor V (FV) deficiency is a very rare hemorrhagic disease with an incidence of approximately one in a million. The common clinical manifestations of FV deficiency include ecchymosis and mucosal bleeding. Life-threatening intracranial bleeding is rare. It has been reported in several cases. However, the molecular basis has been established in only a few cases. METHODS: We reported a 2-month-old girl with congenital FV deficiency and intracranial hemorrhage. Coagulation screening combined with clinical manifestations was performed to diagnose congenital FV deficiency. Genetic testing was performed to identify the pathogenic genes. A literature review was included to emphasize the clinical manifestation, diagnosis, and treatment for congenital FV deficiency with intracranial bleeding. RESULTS: The coagulation tests revealed a significantly prolonged prothrombin time (PT) of 51 s and an activated partial thromboplastin time (APTT) of 73.7 s. The patient had a plasma FV activity of 0.9%. Genetic testing showed compound heterozygous mutations of the patient's FV gene. A literature review showed that patients with homozygous or compound heterozygous variants of the FV gene were often associated with a severe bleeding phenotype. CONCLUSION: Our study provides a direction for the rapid and accurate diagnosis and treatment for FV deficiency to avoid life-threatening bleeding. Infants with spontaneous cranial hematoma and intracranial hemorrhage should be investigated for underlying hemostatic defects. Congenital coagulation factor deficiency should be considered. Once congenital FV deficiency is diagnosed, fresh frozen plasma (FFP) should be given on a regular basis. Liver transplantation may be performed in severe cases.

VDAC1 promotes cardiomyocyte autophagy in anoxia/reoxygenation injury via the PINK1/Parkin pathway.

Ischemia/reperfusion (I/R) is a well-known injury to the myocardium, but the mechanism involved remains elusive. In addition to the well-accepted apoptosis theory, autophagy was recently found to be involved in the process, exerting a dual role as protection in ischemia and detriment in reperfusion. Activation of autophagy is mediated by mitochondrial permeability transition pore (MPTP) opening during reperfusion. In our previous study, we showed that MPTP opening is regulated by VDAC1, a channel protein located in the outer membrane of mitochondria. Thus, upregulation of VDAC1 expression is a possible trigger to cardiomyocyte autophagy via an unclear pathway. Here, we established an anoxia/reoxygenation (A/R) model in vitro to simulate the I/R process in vivo. At the end of A/R treatment, VDAC1, Beclin 1, and LC3-II/I were upregulated, and autophagic vacuoles were increased in cardiomyocytes, which showed a connection of VDAC1 and autophagy development. These variations also led to ROS burst, mitochondrial dysfunction, and aggravated apoptosis. Knockdown of VDAC1 by RNAi could alleviate the above-mentioned cellular damages. Additionally, the expression of PINK1 and Parkin was enhanced after A/R injury. Furthermore, Parkin was recruited to mitochondria from the cytosol, which suggested that the PINK1/Parkin autophagic pathway was activated during A/R. Nevertheless, the PINK1/Parkin pathway was effectively inhibited when VDAC1 was knocked-down. Taken together, the A/R-induced cardiomyocyte injury was mediated by VDAC1 upregulation, which led to cell autophagy via the PINK1/Parkin pathway, and finally aggravated apoptosis.

Facile fabrication of multi-pocket nanoparticles with stepwise size transition for promoting deep penetration and tumor targeting.

BACKGROUND: Nanocarriers-derived antitumor therapeutics are often associated with issues of limited tumor penetration and dissatisfactory antitumor efficacies. Some multistage delivery systems have been constructed to address these issues, but they are often accompanied with complicated manufacture processes and undesirable biocompatibility, which hinder their further application in clinical practices. Herein, a novel dual-responsive multi-pocket nanoparticle was conveniently constructed through self-assembly and cross-linking of amphiphilic methoxypolyethylene glycol-lipoic acid (mPEG-LA) conjugates to enhance tumor penetration and antitumor efficacy. RESULTS: The multi-pocket nanoparticles (MPNs) had a relatively large size of ~ 170 nm at physiological pH which results in prolonged blood circulation and enhanced accumulation at the tumor site. But once extravasated into acidic tumor interstices, the increased solubility of PEG led to breakage of the supramolecular nanostructure and dissolution of MPNs to small-sized (< 20 nm) nanoparticles, promoting deep penetration and distribution in tumor tissues. Furthermore, MPNs exhibited not only an excellent stable nanostructure for antitumor doxorubicin (DOX) loading, but rapid dissociation of the nanostructure under an intracellular reductive environment. With the capacity of long blood circulation, deep tumor penetration and fast intracellular drug release, the DOX-loaded multi-pocket nanoparticles demonstrated superior antitumor activities against large 4T1 tumor (~ 250 mm3) bearing mice with reduced side effect. CONCLUSIONS: Our facile fabrication of multi-pocket nanoparticles provided a promising way in improving solid tumor penetration and achieving a great therapeutic efficacy.

Cellular uptake of single-walled carbon nanotubes in 3D extracellular matrix-mimetic composite collagen hydrogels.

Carbon nanotubes (CNTs) exhibit intrinsic unique physical and chemical properties that make them attractive candidates for biological and biomedicine applications. An efficient cellular uptake of CNTs is vital for many of these applications. However, most of the cellular uptake studies have been performed with a two-dimensional cell culture system. In this study, cellular uptake of single-walled carbon nanotubes (SWCNTs) was investigated by using a three-dimensional cell culture system. Bovine articular chondrocytes cultured in SWCNTs/collagen composite hydrogels maintained their proliferation capacity when compared to the culture in collagen hydrogels. Ultraviolet-visible-near-infrared spectroscopy analysis revealed a high amount of SWCNTs were internalized by cells. Confocal Raman imaging showed that most of the internalized SWCNTs were distributed in the perinuclear region. The results indicated that SWCNTs could be internalized by chondrocytes when SWCNTs were incorporated in the three-dimensional biomimetic collagen hydrogels.

Effect of single-wall carbon nanotubes on mechanical property of chondrocytes.

It is important to elucidate the effects of carbon nanotubes on cell functions for their biomedical applications. In this study, the effect of single-walled carbon nanotubes (SWCNTs) on the mechanical property of chondrocytes was investigated by atomic force microscopy. Chondrocytes were cultured in medium containing SWCNTs and showed an increase uptake of SWCNTs with culture time. The mechanical property of chondrocytes cultured with or without SWCNTs was measured at an indentation depth of 200 nm and 500 nm. The chondrocytes cultured with SWCNTs showed higher Young's modulus than that of cells cultured without SWCNTs at both indentation depths. The increase became significant after culture for more than 3 hours. Indentation at 500 nm depth magnified the change of Young's modulus compared to that monitored at 200 nm indentation depth. The results indicated uptake of SWCNTs increased the Young's modulus of chondrocytes.

Magnetically anisotropic hydrogels for tissue engineering.

Many soft tissues of the human body possess hierarchically anisotropic structures, exhibiting orientation-specific mechanical properties and biological functionality. Hydrogels have been proposed as promising scaffold materials for tissue engineering applications due to their water-rich composition, excellent biocompatibility, and tunable physico-chemical properties. However, conventional hydrogels with homogeneous structures often exhibit isotropic properties that differ from those of biological tissues, limiting their further application. Recently, magnetically anisotropic hydrogels containing long-range ordered magneto-structures have attracted widespread interest owing to their highly controllable assembly strategy, rapid magnetic responsiveness and remote spatiotemporal regulation. In this review, we summarize the latest progress of magnetically anisotropic hydrogels for tissue engineering. The fabrication strategy of magnetically anisotropic hydrogels from magnetic nanofillers with different dimensions is systemically introduced. Then, the effects of magnetically anisotropic cues on the physicochemical properties of hydrogels and the cellular biological behavior are discussed. And the applications of magnetically anisotropic hydrogels in the engineering of different tissues are emphasized. Finally, the current challenges and the future perspectives for magnetically anisotropic hydrogels are presented.

Peptide-dendrimer-reinforced bioinks for 3D bioprinting of heterogeneous and biomimetic in vitro models.

Despite 3D bioprinting having emerged as an advanced method for fabricating complex in vitro models, developing suitable bioinks that fulfill the opposing requirements for the biofabrication window still remains challenging. Although naturally derived hydrogels can better mimic the extracellular matrix (ECM) of numerous tissues, their weak mechanical properties usually result in architecturally simple shapes and patchy functions of in vitro models. Here, this limitation is addressed by a peptide-dendrimer-reinforced bioink (HC-PDN) which contained the peptide-dendrimer branched PEG with end-grafted norbornene (PDN) and the cysteamine-modified HA (HC). The extensive introduction of ethylene end-groups facilitates the grafting of sufficient moieties and enhances thiol-ene-induced crosslinking, making HC-PDN exhibits improved mechanical and rheological properties, as well as a significant reduction in reactive oxygen species (ROS) accumulation than that of methacrylated hyaluronic acid (HAMA). In addition, HC-PDN can be applied for the bioprinting of numerous complex structures with superior shape fidelity and soft matrix microenvironment. A heterogeneous and biomimetic hepatic tissue is concretely constructed in this work. The HepG2-C3As, LX-2s, and EA.hy.926s utilized with HC-PDN and assisted GelMA bioinks closely resemble the parenchymal and non-parenchymal counterparts of the native liver. The bioprinted models show the endothelium barrier function, hepatic functions, as well as increased activity of drug-metabolizing enzymes, which are essential functions of liver tissue in vivo. All these properties make HC-PDN a promising bioink to open numerous opportunities for in vitro model biofabrication. STATEMENT OF SIGNIFICANCE: In this manuscript, we introduced a peptide dendrimer system, which belongs to the family of hyperbranched 3D nanosized macromolecules that exhibit high molecular structure regularity and various biological advantages. Specifically, norbornene-modified peptide dendrimer was grafted onto PEG, and hyaluronic acid (HA) was selected as a base material for bioink formulation because it is a component of the ECM. Peptide dendrimers confer the following advantages to bioinks: (a) Geometric symmetry can facilitate construction of bioinks with homogeneous networks; (b) abundant surface functional groups allow for abundant crosslinking points; (c) the biological origin can promote biocompatibility. This study shows conceptualization to application of a peptide-dendrimer bioink to extend the Biofabrication Window of natural bioinks and will expand use of 3D bioprinting of in vitro models.

Effects of Chemical Composition on the Shape Memory Property of Poly(dl-lactide-co-trimethylene carbonate) as Self-Morphing Small-Diameter Vascular Scaffolds.

Smart materials have great potential in many biomedical applications, in which biodegradable shape memory polymers (SMPs) can be used as surgical sutures, implants, and stents. Poly(dl-lactide-co-trimethylene carbonate) (PDLLTC) represents one of the promising SMPs and is widely used in biomedical applications. However, the relationship between its shape memory property and chemical structure has not been fully studied and needs further elaboration. In this work, PDLLTC copolymers in different compositions have been synthesized, and their shape memory properties have been investigated. It has been found that the shape memory property is related to the chemical composition and polymeric chain segments. The copolymer with a DLLA/TMC ratio of 75:25 (PDLLTC7525) has been demonstrated with great shape fixation and recovery ratio at human body temperature. Furthermore, PDLLTC7525-based self-morphing small-diameter vascular scaffolds adhered with inner electrospun aligned gelatin/hyaluronic acid (Gel/HA) nanofibers have been constructed, as a merit of its shape memory property. The scaffolds have been demonstrated to facilitate the proliferation and adhesion of endothelial cells on the inner layer. Therefore, PDLLTC with tailorable shape memory properties represents a promising candidate for the development of SMPs, as well as for small-diameter vascular scaffolds construction.

Stepwise Multi-Cross-Linking Bioink for 3D Embedded Bioprinting to Promote Full-Thickness Wound Healing.

The emergence and innovation of three-dimensional (3D) bioprinting provide new development opportunities for tissue engineering and regenerative medicine. However, how to obtain bioinks with both biomimicry and manufacturability remains a great issue in 3D bioprinting. Developing intelligent responsive biomaterials is conducive to break through the current dilemma. Herein, a stepwise multi-cross-linking strategy concerning thermosensitive thiolated Pluronic F127 (PF127-SH) and hyaluronic acid methacrylate (HAMA) is proposed to achieve temperature-controlled 3D embedded bioprinting, specifically pre-cross-linking (Michael addition reaction) at low temperatures (4-20 °C) and subsequently self-assembly (hydrophobic interaction) in a high-temperature (30-37 °C) suspension bath as well as final photo-cross-linking (mainly thiol-ene "click" reaction). The unique stepwise cross-linking mechanism promises the thermosensitive bioink appropriate viscosity at different printing stages, making it possible to print complex structures with excellent shape fidelity and simultaneously maintain the biological activity of cells. In vitro studies reveal that 3D-printed hydrogels are beneficial for enhancing cell viability. Further, in vivo experiments demonstrate that cell-laden printed hydrogels significantly promote wound healing and re-epithelialization by modulating inflammation and accelerating collagen deposition and angiogenesis. Therefore, the proposed stepwise multi-cross-linking strategy is expected to accelerate the development of novel bioinks and promote the clinical applications of 3D bioprinting.

Engineered Hierarchical Microdevices Enable Pre-Programmed Controlled Release for Postsurgical and Unresectable Cancer Treatment.

Drug treatment is required for both resectable and unresectable cancers to strive for any meaningful improvement in patient outcomes. However, the clinical benefit of receiving conventional systemic administrations is often less than satisfactory. Drug delivery systems are preferable substitutes but still fail to meet diverse clinical demands due to the difficulty in programming drug release profiles. Herein, a microfabrication concept, termed "Hierarchical Multiple Polymers Immobilization" (HMPI), is introduced and biodegradable-polymer-based hierarchical microdevices (HMDs) that can pre-program any desired controlled release profiles are engineered. Based on the first-line medication of pancreatic and breast cancer, controlled release of single gemcitabine and the doxorubicin/paclitaxel combination in situ for multiple courses is implemented, respectively. Preclinical models of postsurgical pancreatic, postsurgical breast, and unresectable breast cancer are established, and the designed HMDs are demonstrated as well-tolerable and effective treatments for inhibiting tumor growth, recurrence, and metastasis. The proposed HMPI strategy allows the creation of tailorable and high-resolution hierarchical microstructures for pre-programming controlled release according to clinical medication schedules, which may provide promising alternative treatments for postsurgical and unresectable tumor control.

Photo-crosslinkable hyaluronic acid microgels with reactive oxygen species scavenging capacity for mesenchymal stem cell encapsulation.

Mesenchymal stem cells (MSCs) have gained increasing attention in various biomedical applications. However, conventional therapeutic approaches, such as direct intravenous injection, are associated with low cell survival due to the shear force during injection and the oxidative stress microenvironments in the lesion area. Herein, a photo-crosslinkable antioxidant hydrogel based on tyramine- and dopamine-modified hyaluronic acid (HA-Tyr/HA-DA) was developed. Meanwhile, human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) were encapsulated in HA-Tyr/HA-DA hydrogel using a microfluidic system to create size-controllable microgels (hUC-MSCs@microgels). The HA-Tyr/HA-DA hydrogel was demonstrated to have good rheology, biocompatibility, and antioxidant properties for cell microencapsulation. The hUC-MSCs encapsulated in microgels showed a high viability and a significantly improved the survival rate under oxidative stress conditions. Therefore, the presented work provides a promising platform for MSCs microencapsulation, which may further improve the stem cell-based biomedical applications.

A facile bioorthogonal chemistry-based reversible to irreversible strategy to surmount the dilemma between injectability and stability of hyaluronic acid hydrogels.

Injectable and stable hydrogels have great promise for clinical applications. Fine-tuning the injectability and the stability of the hydrogels at different stages has been challenging due to the limited number of coupling reactions. A distinct "reversible to irreversible" concept using a thiazolidine-based bioorthogonal reaction between 1,2-aminothiols and aldehydes in physiological conditions to surmount the dilemma between injectability and stability is presented for the first time. Upon mixing aqueous solutions of aldehyde-functionalized hyaluronic acid (SA-HA) and cysteine-capped ethylenediamine (DI-Cys), SA-HA/DI-Cys hydrogels formed through reversible hemithioacetal crosslinking within 2 min. The reversible kinetic intermediate facilitated thiol-triggered gel-to-sol transition, shear-thinning and injectability of the SA-HA/DI-Cys hydrogel but then converted to the irreversible thermodynamic network after injection, thereby permitting the resulting gel with improved stability. As compared to the Schiff base hydrogels, the hydrogels generated from this simple, yet effective concept awarded improved protection to the embedded mesenchymal stem cells and fibroblast during injection, retained the cells homogeneously within the gel, and allowed them further proliferation in vitro and in vivo. There is potential for the proposed approach of "reversible to irreversible" based on thiazolidine chemistry to be applied as a general coupling technique for developing injectable and stable hydrogels for biomedical applications.

Functionalized gelatin-alginate based bioink with enhanced manufacturability and biomimicry for accelerating wound healing.

Three-dimensional (3D) bioprinting is a promising technique to construct heterogeneous architectures that mimic cell microenvironment. However, the current bioinks for 3D bioprinting usually show some limitations, such as low printing accuracy, unsatisfactory mechanical properties and compromised cytocompatibility. Herein, a novel bioink comprising hydroxyphenyl propionic acid-conjugated gelatin and tyramine-modified alginate is developed for printing 3D constructs. The bioink takes advantage of an ionic/covalent intertwined network that combines covalent bonds formed by photo-mediated redox reaction and ionic bonds formed by chelate effect. Benefiting from the thermosensitivity of gelatin and the double-crosslinking mechanism, the developed bioink shows controllable rheological behaviors, enhanced mechanical behavior, improved printing accuracy and structure stability. Moreover, the printed cell-laden hydrogels exhibit a homogeneous cell distribution and considerable cell survival because the pre-crosslinking of the bioink prevents cellular sedimentation and the visible light crosslinking mechanism preserves cell viability. Further in vivo studies demonstrate that resulting cell-laden hydrogels are beneficial for the reduction of inflammation response and the promotion of collagen deposition and angiogenesis, thereby improving the quality of skin wound healing. This convenient and effective strategy is of great significance for accelerating the development of multifunctional bioinks and broadening the biomedical applications of 3D bioprinting.

Ultra-stretchable and conductive polyacrylamide/carboxymethyl chitosan composite hydrogels with low modulus and fast self-recoverability as flexible strain sensors.

There is a great demand for the fabrication of soft electronics using hydrogels due to their biomimetic structures and good flexibility. However, conventional hydrogels have poor mechanical properties, which restricts their applications as stretchable sensors. Herein, a facile one-step strategy is proposed to fabricate tough and conductive hydrogels by making use of the graftability of carboxymethyl chitosan without extra conductive matter and crosslinking agent. The obtained polyacrylamide/carboxymethyl chitosan composite hydrogels possess outstanding transmittance and excellent mechanical performances, with tensile breaking stress of 630 kPa, breaking strain of 4560 %, toughness of 8490 kJ/m3. These hydrogels have low modulus of 5-20 kPa, fast recoverability after unloading, high conductivity of ∼0.85 S/m without the addition of other conductive substances and good biocompatibility. The ionic conductivity of the gels originates from the counterions of carboxymethyl chitosan, affording the hydrogels as resistive-type sensors. The resultant hydrogel sensors demonstrate a broad strain window (0.12-1500 %), excellent linear response, high sensitivity with the gauge factor reaching 11.72, and great durability, capable of monitoring diverse human motions. This work provides a new strategy to develop stretchable conductive hydrogels with promising applications in the fields of artificial intelligence and flexible electronics.

Design of a Haversian system-like gradient porous scaffold based on triply periodic minimal surfaces for promoting bone regeneration.

INTRODUCTION: The bone ingrowth depth in the porous scaffolds is greatly affected by the structural design, notably the pore size, pore geometry, and the pore distribution. To enhance the bone regeneration capability of scaffolds, the bionic design can be regarded as a potential solution. OBJECTIVES: We proposed a Haversian system-like gradient structure based on the triply periodic minimal surface architectures with pore size varying from the edge to the center. And its effects in promoting bone regeneration were evaluated in the study. METHODS: The gradient scaffold was designed using the triply periodic minimal surface architectures. The mechanical properties were analyzed by the finite element simulation and confirmed using the universal machine. The fluid characteristics were calculated by the computational fluid dynamics analysis. The bone regeneration process was simulated using a in silico computational model containing the main biological, physical, and chemical variation during the bone growth process. Finally, the in vitro and in vivo studies were carried out to verify the actual osteogenic effect. RESULTS: Compared to the uniform scaffold, the biomimetic gradient scaffold demonstrated better performance in stress conduction and reduced stress shielding effects. The fluid features were appropriate for cell migration and flow diffusion, and the permeability was in the same order of magnitude with the natural bone. The bone ingrowth simulation exhibited improved angiogenesis and bone regeneration. Higher expression of the osteogenesis-related genes, higher alkaline phosphatase activity, and increased mineralization could be observed on the gradient scaffold in the in vitro study. The 12-week in vivo study proved that the gradient scaffold had deeper bone inserting depth and a more stable bone-scaffold interface. CONCLUSION: The Haversian system-like gradient structure can effectively promote the bone regeneration. This structural design can be used as a new solution for the clinical application of prosthesis design.

Bioactive hydrogels based on polysaccharides and peptides for soft tissue wound management.

Due to their inherent and tunable biomechanical and biochemical performances, bioactive hydrogels based on polysaccharides and peptides have shown attractive potential for wound management. In this review, the recent progress of bioactive hydrogels prepared by polysaccharides and peptides for soft tissue wound management is overviewed. Meanwhile, we focus on the elaboration of the relationship between chemical structures and inherent bioactive functions of polysaccharides and peptides, as well as the strategies that are taken for achieving multiple wound repairing effects including hemostasis, adhesion, wound contraction and closure, anti-bacteria, anti-oxidation, immunomodulation, molecule delivery, etc. Some innovative and important works are well introduced as well. In the end, current study limitations, clinical unmet needs, and future directions are discussed.

Photoclick polysaccharide-based bioinks with an extended biofabrication window for 3D embedded bioprinting.

Although significant breakthroughs have been achieved in constructing complex tissue/organ models in vitro, the progress of 3D bioprinting has long been subjected to trade-offs between the printability and biocompatibility of bioinks. Methacrylated hyaluronic acid (HAMA) has been widely adopted for 3D bioprinting due to its limited immunogenicity and simple synthetic method. However, the challenges arising from HAMA are its limited mechanical properties, low printing resolution, inhomogeneity networks, and the accumulation of reactive oxygen species (ROS) during polymerization. Here, these limitations are addressed by developing a thiol-norbornene photoclick polysaccharide-based bioink (HC-HN), which is prepared through the modification of hyaluronic acid with norbornene functional groups (Nor) and cysteamine hydrochloride (Cys). Compared with traditional HAMA, the HC-HN bioink via a step-growth polymerization mechanism can realize increased viscoelastic properties, reduced ROS accumulation, and superior shape fidelity in a range of complex structures by 3D embedded bioprinting. To further confirm its potential in 3D bioprinting applications, the HC-HN bioink is employed to print a liver model in vitro, which shows higher albumin secretion and urea production. Furthermore, a markedly increased sensitivity to drug-induced hepatotoxicity is observed in the bioprinted liver model compared to the 2D culture. Therefore, the proposed photoclick HC-HN bioink expands the palette of available polysaccharide-based bioinks and greatly extends the biofabrication window to broaden the application opportunities of 3D bioprinting.

Hydrogels for 3D embedded bioprinting: a focused review on bioinks and support baths.

Three-dimensional (3D) bioprinting has played an increasingly crucial role in the manufacturing of organized complex tissues and organs, which has shown tremendous potential in the field of tissue engineering. Extrusion-based bioprinting takes advantage of its competitive pricing and flexibility to print various biomaterials, and it has now developed into one of the most used printing techniques. However, extruding soft hydrogels, also known as bioinks, often leads to poor fidelity when printed in air. As an emerging printing approach, 3D embedded bioprinting deposits bioinks not on a platform but into a support bath, preventing constructs from settling and collapsing. This review discusses the challenges faced in the traditional 3D bioprinting of soft or low-viscosity bioinks and the changes brought by embedded bioprinting as an emerging solution. Particular focus is given to the progress of hydrogels used as bioinks and support baths. Finally, we highlight the challenges involved in this process and look forward to the prospects of this technology.