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3D bioprinting techniques have been attracting attention for tissue scaffold fabrication in nerve tissue engineering applications. However, due to the inherent complexity of nerve tissues, bioprinting scaffolds that can appropriately promote the regeneration of damaged tissues is still challenging. This paper presents our study on bioprinting Schwann cell-laden scaffolds from low-viscosity hydrogel compositions including RGD modified alginate, hyaluronic acid and fibrin, with a focus on investigating the printability of hydrogel compositions and characterizing the functions of printed scaffolds for potential use in nerve tissue regeneration. We assessed the rheological properties of hydrogel precursors via temperature, time and shear rate sweeps, and then designed/determined the bioprinting process parameters including printing pressure and needle type/size. Bioprinting with a submerged crosslinking method was applied for scaffold fabrication, where the key was to rigorously regulate the bioprinting speed and the crosslinking conditions. Optical imaging techniques and advanced synchrotron imaging-based techniques were utilized to characterize the printed scaffolds; specifically factors including strand diameter, scaffold stability and scaffold pore size were measured and used to characterize the hydrogel printability. Schwann cells laden in the scaffolds were assessed in vitro, with results revealing that the elongation of Schwann cells and thus the aligned DRG neurite outgrowth could be well-regulated through the control of the bioprinting process. Taken together, this study shows that scaffolds can be bioprinted from low-viscosity hydrogel compositions for potential use in tissue regeneration.

Embryonic microenvironments can reverse the metastatic phenotype of aggressive tumors by inhibiting the Nodal signaling pathway. Here, we hypothesize that embryonic microenvironments can be transplanted for the purpose of oncotherapy. We report the development of an injectable bioactive hydrogel system containing the key antagonists of Nodal signaling—Cripto-1 receptor antibodies (2B11)—for the creation of embryonic microenvironments and the examination of their effect on tumor reversion treatment using a mouse model. Our in vitro results show that the hydrogel system can reduce the mitochondrial membrane potential of MDA-MB-231 and MCF-7, promote cell apoptosis, and reduce the invasive ability of cells. Our in vivo results illustrate that the hydrogel system can significantly inhibit tumor growth in both breast cancer and melanoma tumor-bearing mouse models, as well as transform the cell morphology of melanoma B16 cells to melanin-like cells. Furthermore, the results of the up-regulation of tumor suppressor genes and the down-regulation of oncogenes by high-throughput sequencing confirm that the developed system can also selectively turn on some tumor suppressor genes and turn off certain oncogenes so as to prompt the benign reversion of the tumor phenotype. Taken together, our results demonstrate the injectable biomaterial system is able to create an effective microenvironment for melanoma and breast tumor therapy.

When a biomaterial solution containing living cells is subject to bioprinting, the cells experience process-induced stresses, including shear and extensional stresses. These process-induced stresses breach cell membranes and can lead to cell damage, thus reducing cell viability and functioning within the printed constructs. Studies have been conducted to determine the influence of shear stress on cell damage; however, the effect of extensional stress has been typically ignored in the literature until the recently collected evidence of its importance. This paper presents a novel method to characterize and quantify the cell damage caused by both shear and extensional stresses in bioprinting. In this method, cell damage law is first established to relate cell damage to shear stress based on the experiments with a rheometer; the process-induced shear stress experienced by cells in bioprinting is represented, and the established cell damage model is applied to calculate the degree of cell damage caused by shear stress in bioprinting; then cell damage caused by extensional stress is inferred from the difference between the total cell damage and the amount of cell damage attributed to shear stress. With the obtained magnitude of extensional stress from fluidic simulation, the model that relates extensional stress to cell damage is established; the bioprinting process-induced cell damage attributed to both shear and extensional stresses is therefore presented. Schwann cells and myoblasts were used as examples to validate the models. Comparison between experimental and simulation results shows the effectiveness of the models presented in this paper. Moreover, the viability and proliferative ability of cells in the first 72 h after bioprinting is investigated, with the results illustrating that the process-induced forces affect not only cell viability but also their proliferative ability after bioprinting.

Three dimensional (3D) bioplotting requires appropriate crosslinkers to crosslink the hydrogel precursor while simultaneously maintaining the viability of embedded cells. However, the evaluation and comparison of various types of crosslinkers in bioplotting remains underexplored to date. This paper presents our study of the influence of three ionic crosslinkers—calcium chloride (CaCl2), barium chloride (BaCl2), and zinc chloride (ZnCl2)—on the mechanical and biological properties of 3D bioplotted alginate scaffolds. The scaffold mechanical properties characterized included the elastic modulus, swelling, and degradation while the biological properties considered included Schwann cell viability and surface morphology. The mechanical and biological properties of the bioplotted scaffolds were both dependent on the crosslinkers used for fabrication; specifically, crosslinking ions resulted in the elastic modulus of the hydrogels decreasing in the order BaCl2>CaCl2>ZnCl2 over 42 days while Schwann cell ...

Biofabrication of cell supportive cardiac patches that can be directly implanted on myocardial infarct is a potential solution for myocardial infarction repair. Ideally, cardiac patches should be able to mimic myocardium extracellular matrix for rapid integration with the host tissue, raising the need to develop cardiac constructs with complex features. In particular, cardiac patches should be electrically conductive, mechanically robust and elastic, biologically active and prevascularized. In this study, we aim to biofabricate a nanoreinforced hybrid cardiac patch laden with human coronary artery endothelial cells (HCAECs) with improved electrical, mechanical, and biological behavior. A safe ultraviolet (UV) exposure time with insignificant effect on cell viability was identified for methacrylated collagen (MeCol) micropatterning. The effects of carboxyl functionalized carbon nanotubes (CNTs) on MeCol and alginate matrix morphology, mechanical properties, electrical behavior, and cellular response were investigated at different CNT mass ratios. A UV-integrated 3D-bioprinting technique was implemented to create hybrid hydrogel constructs consisting of CNT-incorporated alginate framework and cell-laden MeCol. The compressive modulus, impedance, and swelling degree of hybrid constructs were assessed over 20 days of incubation in culture medium at 37°C for different CNT mass ratios. The HCAEC viability, proliferation, and differentiation in the context of the bioprinted hybrid constructs were assessed over 10 days in vitro. The functionalized CNTs provided a highly interconnected nanofibrous meshwork that significantly improved viscoelastic behavior and electrical conductivity of photo-cross-linked MeCol. Alginate-coated CNTs provided a nanofilamentous network with fiber size of ∼25-500 nm, improving not only electrical and mechanical properties but also HCAEC attachment and elongation compared to pristine alginate. The CNT-reinforced 3D-printed hybrid constructs presented significantly higher stiffness and electrical conductivity particularly in the physiologically relevant frequency range (∼5 Hz). The CNT-reinforced hybrid implants maintained a significantly higher swelling degree over 20 days of culturing compared to CNT-free hybrid constructs. For a selected CNT mass ratio, HCAECs presented significant cellular proliferation, migration, and differentiation (lumen-like formation) over 10 days of incubation in vitro. Findings from this study deliver essential steps toward developing conductive, robust, and potentially prevascularized hybrid cardiac patches.

Respiratory tissue engineering aims to provide improved treatment options for respiratory diseases and injuries, as well as improved modelling of respiratory diseases and therapeutic-host tissue interactions. To this end, fabrication of constructs to mimic native respiratory tissues with the appropriate biological, mechanical and architectural properties is an essential, yet challenging, task. Bioprinting, an emerging three-dimensional (3D) printing technology, is uniquely situated for such construct development as it allows for the incorporation of cells and other biologically-active molecules into printed constructs in a highly precise and repeatable manner. This review provides an overview of the development of 3D bioprinted constructs for respiratory tissue engineering, highlighting the tissue structure, components, and properties of native lung, as well as the reported studies of bioprinting in both regenerative and modelling applications of respiratory tissues. Challenges faced in the development and application of bioprinted constructs in respiratory tissue engineering are identified and discussed, along with suggested future research directions of this field.

Background: The influence of pulmonary vein (PV) anatomy on cryo kinetics during cryoballoon (CB) ablation is unclear. Objective: To investigate the relationship between PV anatomy and cryo kinetics during CB ablation for atrial fibrillation (AF). Methods: Sixty consecutive patients were enrolled. PV anatomy, including ostial diameters (long, short and corrected), ratio between short and long diameters, ostium shape (round, oval, triangular, and narrow), and drainage pattern (typical, with common trunk, common antrum, ostial branch and supernumerary PV) were evaluated on multi-detector computed tomography (MDCT) images pre-procedure. Cryo kinetics parameters [balloon freeze time from 0 to -30ºC (BFT), balloon nadir temperature (BNT) and balloon warming time from -30 to +15ºC (BWT)] were recorded during procedure. All p values are two-sided, with values of p < 0.05 considered to be statistically significant. Results: 606 times of freezing cycle were accomplished. Moderate negative correlation was documented between BNT and corrected PV diameter (r = -0.51, p < 0.001) when using 23-mm CBs, and mild negative correlation (r = - 0.32, p = 0.001) was found when using 28-mm CBs. Multivariate logistic regression analysis revealed that PV corrected ostial diameter (OR, 1.4; p = 0.004) predicted a BNT < -51ºC when using 23-mm CBs, while PV ostium oval shape (OR, 0.3; p = 0.033) and PV locations (left inferior PV: OR, 0.04; p = 0.005; right superior PV: OR, 4.3; p = 0.025) predicted BNT < -51ºC when using 28-mm CBs. Conclusions: MDCT can provide PV anatomy accurate evaluation prior CB ablation. PV anatomy is associated with cryo kinetics during ablation.

The nano-silica can be incorporated into polymers for improved mechanical properties. Notably, the interaction between nano-silica and polymer is of a microscopic phenomenon and thus, hard to observe and study by using experimental methods. Based on molecular dynamics, this paper presents a study on the properties and the interaction mechanism of nano-silica in the polyvinyl alcohol (PVA)/polyacrylamide (PAM) blends at an atomic level. Specifically, six blends of PVA/PAM with varying concentrations of nano-silica (0-13wt%) and two interfacial interaction models of polymers on the silica surface were designed and analyzed at an atomic level in terms of concentration profile, mechanical properties, fractional free volume (FFV), dynamic properties of polymers and X-ray diffraction patterns. The concentration profile results and micromorphologies of equilibrium models suggest PAM molecular chains are easier to be adsorbed on the silica surface than PVA molecular chains in blends. The incorporation of nano-silica into the PVA/PAM blends can increase the blend mechanical properties, densities, and semicrystalline character. Meanwhile, the FFV and the mobility of polymer chain decrease with the silica concentration, which agrees with the results of mechanical properties, densities, and semicrystalline character. Our results also illustrate that an analysis of binding energies and pair correlation functions (PCF) allows for the discovery of the interaction mechanism of nano-silica in PVA/PAM blends; and that hydrogen bond interactions between polar functional groups of polymer molecular chains and the hydroxyl groups of the silica surface are involved in adsorption of the polymers on the silica surface, thus affecting the interaction mechanism of nano-silica in PVA/PAM blend systems.

Binder properties are a key factor affecting the quality of bone scaffolds produced using 3D powder printing. In this research, molecular dynamics simulation (MD) and experimental methods were applied to study the cohesive energy density, mechanical properties, bonding behavior, and surface morphology of three polymer binders (PVP, PAM, PVA) employed in the 3D fabrication of hydroxyapatite (HA) bone scaffolds. The bonding mechanisms of the three polymer binders were revealed by analyzing the interaction between the binders and the HA surface. The binding energies between the binders and HA are associated with the cohesive energy density and viscosity of each of the binders, which are attributed to functional groups in the binders. The mechanical properties determined experimentally for the bone scaffolds produced using each of the three polymer binders were in a different relative order than the engineering modulus of the binders and the interaction between the binders and HA calculated in simulations. This is a reflection of the mechanical properties of bone scaffolds being a comprehensive reflection of the basic materials and their bonding effect. Finally, SEM imaging indicated additional factors affecting the mechanical properties and degradation rate of the scaffolds. Conclusions from this work can be used to forecast the properties of three commonly used polymer binders and provide a theoretical basis for the choice of binders in the production of 3DP-fabricated bone scaffolds.

Idiopathic pulmonary fibrosis (IPF) is a progressive disease that causes unremitting deposition of extracellular matrix proteins, thus resulting in distortion of the pulmonary architecture and impaired gas exchange. Associated with high morbidity and mortality, IPF is generally refractory to current pharmacological therapies. Lefty A, a potent inhibitor of transforming growth factor-β signaling, has been shown to have promising antifibrotic ability in vitro for the treatment of renal fibrosis and other potential organ fibroses. Here, we determined whether Lefty A can attenuate bleomycin (BLM)-induced pulmonary fibrosis in vivo based on a novel therapeutic strategy where human embryonic kidney 293 (HEK293) cells are genetically engineered with the Lefty A-associated GFP gene. The engineered HEK293 cells were encapsulated in alginate microcapsules and then subcutaneously implanted in ICR mice that had 1 wk earlier been intratracheally administered BLM to induce pulmonary fibrosis. The severity of fibrosis in lung tissue was assessed using pathological morphology and collagen expression to examine the effect of Lefty A released from the microencapsulated cells. The engineered HEK293 cells with Lefty A significantly reduced the expression of connective tissue growth factor and collagen type I mRNA, lessened the morphological fibrotic effects induced by BLM, and increased the expression of matrix metalloproteinase-9. This illustrates that engineered HEK293 cells with Lefty A can attenuate pulmonary fibrosis in vivo, thus providing a novel method to treat human pulmonary fibrotic disease and other organ fibroses.

Hyaluronan (HA), a polymer with various molecular weights (MW) found in tumor microenvironments, is associated with malignant progression of breast cancer. Reducing the amount of high-MW HA in the microenvironment by hyaluronidase is a promising approach for breast cancer treatment. However, whether the generation of HA fragments negatively affects breast cancer cells remains to be determined. Furthermore, HA forms three-dimensional (3D) networks by cross-linking with other extracellular molecules to function. Therefore, a model mimicking the cross-linked HA network is required to determine the effect of HA fragments on breast cancer cells. To clarify the differential roles of low (HA35) versus high (HA117) MW HA on cancer cell phenotype, a 3D culture system was set up by covalently cross-linking HA with alginate and investigating the behavior of 4T-1 and SKBR3 breast cancer cells alongside a two-dimensional (2D) control. The results show the invasion and migration abilities of 4T-1 and SKBR3 cells are significantly enhanced by the presence of HA35 but inhibited by HA117 in both 2D monolayers and 3D spheroids. The differential effects of HA35 and HA117 on cancer cell epithelial-mesenchymal transition (EMT) phenotype were further confirmed in terms of differential regulation of E-cadherin and vimentin as important EMT markers at both the cellular and mRNA levels. Additional experiments show the CD44-Twist signaling pathway might be involved in the differential effects of HA35 and HA117. These results have important implications with respect to understanding the role of HA in breast cancer development and for the design of therapeutic approaches based on the eradication of HA with hyaluronidase.

Three-dimensional (3D)-printed constructs made of polycaprolactone and chondrocyte-impregnated alginate hydrogel (hybrid cartilage constructs) can mimic the biphasic nature of articular cartilage, thus offering promise for cartilage tissue engineering applications. Notably, the regulatory pathway for medical device development requires validation of such constructs through in vitro bench tests and in vivo preclinical examinations for premarket approval. For this, noninvasive imaging techniques are required for effective evaluation of the progress of these cartilage constructs, especially when implanted in animal models or human subjects. However, characterization of the individual components of the hybrid cartilage constructs and their associated time-dependent structural changes by currently available noninvasive techniques is challenging as these constructs contain a combination of hydrophobic and hydrophilic biomaterials with different refractive indices. In this study, we report the use of a novel synchrotron radiation inline phase contrast imaging computed tomography (SR-inline-PCI-CT) approach for noninvasive (in situ) characterization of 3D-printed hybrid cartilage constructs that has been implanted subcutaneously in mice over a 21-day period. In parallel, traditional invasive assays were used to evaluate the in vivo performance of the implanted hybrid cartilage constructs with respect to their cell viability and secretion of cartilage-specific extracellular matrix over the 21-day period postimplantation in mice. SR-inline-PCI-CT allowed striking visualization of the individual components within the 3D-printed hybrid cartilage constructs, as well as characterization of the time-dependent structural changes after implantation. In addition, the relationship between the implanted constructs and the surrounding tissues was delineated. Furthermore, traditional assays showed that cell viability within the cartilage constructs was at least 70% at all three time points, and secretion of alcian blue- and collagen type 2-positive matrices increased progressively over the 21-day period postimplantation. Overall, these results demonstrate that the 3D-printed hybrid cartilage constructs have good in vivo performance and validate their potential for regeneration of articular cartilage in vivo. In addition, SR-inline-PCI-CT has demonstrated potential for longitudinal and noninvasive monitoring of the functionality of 3D-printed hybrid cartilage constructs in a way that is translatable to other soft tissue engineering applications.

The blood clotting protein fibrin contains cell-binding domains, providing potential advantage for the fabrication of tissue repair scaffolds and for live cell encapsulation. However, fabrication of fibrin scaffolds with encapsulated cells using three dimensional (3D) printing has proven challenging due to the mechanical difficulties of fabricating protein hydrogel scaffolds with defined microstructure. For example, extrusion based 3D printing of fibrin is generally unfeasible because of the low viscosity of precursor fibrinogen solution. Here we describe a novel technique for bioprinting of fibrin scaffolds by extruding fibrinogen solution into thrombin solution, utilizing hyaluronic acid (HA) and polyvinyl alcohol (PVA) to increase the viscosities of the fibrinogen and thrombin solutions, respectively. Clotting factor XIII was also included to enhance fibrin crosslinking. This technique produced 3D fibrin-factor XIII-HA hydrogel scaffolds without the use of support structures. Living Schwann cells encapsulated within these scaffolds during fabrication were viable and proliferated in culture. Moreover, extrusion based bioprinting induced longitudinal alignment of fine fibrin fibers, which apparently provided haptotactic cues directing alignment of encapsulated Schwann cells and elongation of dorsal root ganglion neurites along the 3D printed strands. These aligned fibrin-factor XIII-HA scaffolds mimic the natural fibrin clot that forms between injured nerve ends, and the aligned, encapsulated Schwann cells may provide natural guidance of neurite growth. Bioprinted fibrin-factor XIII-HA scaffolds also have the potential to be applied towards regeneration of other aligned tissues.

Biodegradable Mg alloys have appeared as the most appealing metals for biomedical applications, particularly as temporary bone implants. However, issues regarding high corrosion rate and biocompatibility restrict their application. Hence, in the present work, nanostructured clinoenstatite (CLT, MgSiO3)/tantalum nitride (TaN) was deposited on the Mg-Ca-Zn alloy via electrophoretic deposition (EPD) along with physical vapor deposition (PVD) to improve the corrosion and biological characteristics of the Mg-Ca-Zn alloy. The TaN intermediate layer with bubble like morphology possessed a compact and homogenous structure with a thickness of about 950 nm while the thick CLT over-layer (~15 μm) displayed a less compact structure containing nano-porosities as well as nanoparticles with spherical morphology. The electrochemical tests demonstrated that the as prepared CLT/TaN film is able to substantially increase the anticorrosion property of Mg-Ca-Zn bare alloy. Cytocompatibility outcomes indicated that formation of CLT and TaN on the Mg bare alloy surface enhanced cell viability, proliferation and growth, implying excellent biocompatibility. Taken together, the CLT/TaN coating exhibits appropriate characteristic including anticorrosion property and biocompatibility in order to employ in biomedical files.

Materials and scaffolds with antimicrobial properties are of great importance in wound dressing and other tissue engineering applications. The objective of the present work was to fabricate scaffolds made from nanocomposites of polycaprolactone (PCL) and quaternary ammonium salt-modified montmorillonite (MMT) by the electrospinning technique, and then characterize their antimicrobial and other properties for wound dressing applications. The effect of MMT on the structure, morphology, and thermal behavior of the electrospun wound dressings was assessed by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM); the swelling capacity, antibacterial activity, and cytotoxicity were also evaluated. The results of XRD and SEM analyses showed MMT was successfully incorporated into the PCL polymeric matrix and its inclusion reduced the size and thickness of the electrospun fibers compared to pure PCL fibers. The TGA results illustrated an increase in the thermal stability of nanocomposites upon incorporation of nanoclay into the PCL matrix. The swelling capacity of the wound dressings was reduced by increasing the amount of MMT in the PCL matrix due to the increased hydrophobicity of the original MMT resulting from its modification with quaternary ammonium salt. The

Oral squamous cell carcinoma (OSCC), which encompasses the oral cavity-derived malignancies, is a devastating disease causing substantial morbidity and mortality in both men and women. It is the most common subtype of the head and neck squamous cell carcinoma (HNSCC), which is ranked the sixth most common malignancy worldwide. Despite promising advancements in the conventional therapeutic approaches currently available for patients with oral cancer, many drawbacks are still to be addressed; surgical resection leads to permanent disfigurement, altered sense of self and debilitating physiological consequences, while chemo- and radio-therapies result in significant toxicities, all affecting patient wellbeing and quality of life. Thus, the development of novel therapeutic approaches or modifications of current strategies is paramount to improve individual health outcomes and survival, while early tumour detection remains a priority and significant challenge. In recent years, drug delivery systems and chronotherapy have been developed as alternative methods aiming to enhance the benefits of the current anticancer therapies, while minimizing their undesirable toxic effects on the healthy non-cancerous cells. Targeted drug delivery systems have the potential to increase drug bioavailability and bio-distribution at the site of the primary tumour. This review confers current knowledge on the diverse drug delivery methods, potential carriers (e.g., polymeric, inorganic, and combinational nanoparticles; nanolipids; hydrogels; exosomes) and anticancer targeted approaches for oral squamous cell carcinoma treatment, with an emphasis on their clinical relevance in the era of precision medicine, circadian chronobiology and patient-centred health care.

Nanofibrous-based pH sensors have shown promise in a wide range of industrial and medical applications due to their fast response time and good mechanical properties. In the present study, we fabricated pH-sensitive sensors of nanofibrous membranes by electrospinning polyurethane (PU)/poly 2-acrylamido-2-methylpropanesulfonic acid (PAMPS)/graphene oxide (GO) with indicator dyes. The morphology of the electrospun nanofibers was examined using scanning electron microscopy (SEM). The effect of hydrophilic polymer ratio and concentration of GO on the sensing response time was investigated. The sensitivity of the membranes was studied over a wide pH range (1&ndash, 8) in solution tests, with color change measured by calculating total color difference using UV-vis spectroscopy. The membranes were also subjected to vapor tests at three different pH values (1, 4, 8). SEM results show the successful fabrication of bimodal fiber diameter distributions of PU (mean fiber diameter 519 nm) and PAMPS (mean fiber diameter 78 nm). Sensing response time decreased dramatically with increasing concentrations of PAMPS and GO. The hybrid hydrophobic/hydrophilic/GO nanofibrous membranes are capable of instantly responding to changes in solution pH as well as detecting pH changes in chemical vapor solution in as little as 7 s.

Three-dimensional (3D) cell cultures developed with living cells and scaffolds have demonstrated outstanding potential for tissue engineering and regenerative medicine applications. However, no suitable tools are available to monitor dynamically variable cell behavior in such a complex microenvironment. In particular, simultaneously assessing cell behavior, cell secretion, and the general state of a 3D culture system is of a really challenging task. This paper presents our development of a dual-transduction-integrated biosensing system that assesses electrical impedance in conjunction with imaging techniques to simultaneously investigate the 3D cell-culture for bone regeneration. First, we created models to mimic the dynamic deposition of the extracellular matrix (ECM) in 3D culture, which underwent osteogenesis by incorporating different amounts of bone-ECM components (collagen, hydroxyapatite [HAp], and hyaluronic acid [HA]) into alginate-based hydrogels. The formed models were investigated by means of electrical impedance spectroscopy (EIS), with the results showing that the impedances increased linearly with collagen and hyaluronan, but changed in a more complex manner with HAp. Thereafter, we created two models that consisted of primary osteoblast cells (OBs), which expressed the enhanced green fluorescent protein (EGFP), and 4T1 cells, which secreted the EGFP-HA, in the alginate hydrogel. We found the capacitance (associated with impedance and measured by EIS) increased with the increases in initial embedded OBs, and also confirmed the cell proliferation over 3 days with the EGFP signal as monitored by the fluorescent imaging component in our system. Interestingly, the change in capacitance is found to be associated with OB migration following stimulation. Also, we show higher capacitance in 4T1 cells that secret HA when compared to control 4T1 cells after a 3-day culture. Taken together, we demonstrate that our biosensing system is able to investigate the dynamic process of 3D culture in a non-invasive and real-time manner.

Low-concentration hydrogels have favorable properties for many cell functions in tissue engineering but are considerably limited from a scaffold fabrication point of view due to poor three-dimensional (3D) printability. Here, we developed an indirect-bioprinting process for alginate scaffolds and characterized the potential of these scaffolds for nerve tissue engineering applications. The indirect-bioprinting process involves (1) printing a sacrificial framework from gelatin, (2) impregnating the framework with low-concentration alginate, and (3) removing the gelatin framework by an incubation process, thus forming low-concentration alginate scaffolds. The scaffolds were characterized by compression testing, swelling, degradation, and morphological and biological assessment of incorporated or seeded Schwann cells. For comparison, varying concentrations of alginate scaffolds (from 0.5% to 3%) were fabricated and sterilized using either ultraviolet light or ethanol. Results indicated that scaffolds can be fabricated using the indirect-bioprinting process, wherein the scaffold properties are affected by the concentration of alginate and sterilization technique used. These factors provide effective means of regulating the properties of scaffolds fabricated using the indirect-bioprinting process. Cell-incorporated scaffolds demonstrated better cell viability than bulk gels. In addition, scaffolds showed better cell functionality when fabricated with a lower concentration of alginate compared to a higher concentration. The indirect-bioprinting process that we implemented could be extended to other types of low-concentration hydrogels to address the tradeoffs between printability and properties for favorable cell functions.

It is known that discrete events causing extreme societal and economic pressures as well as technological opportunity are major driving factors of innovation. Due to the presence of both of these factors during the COVID-19 pandemic it was hypothesized that there would be significant on-going innovation throughout society during the pandemic, with many of the innovations having the ability to have long-term societal impact. Analysis of literature and patent databases determined sectors of accelerated innovation to include manufacturing, personal protective equipment and digital technologies. The ability of flexible and advanced manufacturing technologies to provide more adaptable production capabilities that are less susceptible to disruption, make it likely that these technologies will be incorporated further, changing the way many manufacturing firms operate. Collaboration has increased, demonstrating increases in problem-solving efficiency; however, concerns around intellectual property is likely to reduce the long-term impact of these procedural changes. Advancements in personal protective equipment and disinfection technologies may have the long-term impact of reducing waste production and triggering changes in cleaning protocols throughout society. Digital technologies such as telemedicine, data collection, artificial intelligence and communication technologies were found to have undergone significant innovation, with possible impacts such as large-scale systemic shifts, and changes in how governments, corporations, the scientific community and the public interact.

Scaffolds in tissue engineering can be created or printed nowadays with various structures that consist of a number of three-dimensional (3D) units stacked together periodically. The performance or properties of such scaffolds can be affected by the unit configurations and parameters, which, however, has not been well investigated and elucidated. This paper presents our study on the influence of unit configuration and parameters on the scaffolds performance by taking triply periodic minimal surfaces (TPMS) as the basic unit. The normalized values of elastic modulus, shear modulus and permeability were used to characterize the scaffold performance and analyzed by means of finite element analysis and CFD simulation, with focus on identifying the influence of unit configurations and parameters on the scaffold mechanical and permeable properties. Furthermore, by selective laser melting (SLM) printing technique, the cubic Primitive and IWP scaffolds with an oversize of 12 mm (2 × 2 × 2 units) were created and subjected to compressive tests. Both simulation and experiment results are in agreement to illustrate that unit configuration and parameters have significant influence on the mechanical and permeable properties of TPMS units. The methods and findings in the present work would serve as the base or rationales to regulate the unit configurations and parameters with trade-off solutions for given tissue engineering application.

Tissue scaffolds with living cells fabricated by three-dimensional bioprinting/plotting techniques are becoming more prevalent in tissue repair and regeneration. In the bioprinting process, cells are subject to process-induced forces (such as shear force) that can result in cell damage and loss of cell function. The flow behavior of the biomaterial solutions that encapsulate living cells in this process plays an important role. This study used a rheometer to examine the flow behavior of alginate solution and alginate-Schwann cell (RSC96), alginate-fibroblast cell (NIH-3T3), and alginate-skeletal muscle cell (L8) suspensions during shearing with respect to effects on cell viability and proliferation. The flow behavior of all the alginate-cell suspensions varied with alginate concentration and cell density and had a significant influence on the viability and proliferation of the cells once sheared as well as on the recovery of the sheared cells. These findings provide a mean to preserve cell viability and/or retain cell proliferation function in the bioprinting process by regulating the flow behavior of cell-biomaterial suspensions and process parameters.

Hydrogels are particularly attractive as scaffolding materials for cartilage tissue engineering because their high water content closely mimics the native extracellular matrix (ECM). Hydrogels can also provide a three-dimensional (3D) microenvironment for homogeneously suspended cells that retains their rounded morphology and thus facilitates chondrogenesis in cartilage tissue engineering. However, fabricating hydrogel scaffolds or cell-laden hydrogel constructs with a predesigned external shape and internal structure that does not collapse remains challenging because of the low viscosity and high water content of hydrogel precursors. Here, we present a study on the fabrication of (cell-laden) alginate hydrogel constructs using a 3D bioplotting system supplemented with a submerged cross-linking process. Swelling, mechanical properties and protein release profiles were examined and tuned by controlling the initial cross-linking density. Porous cell-laden alginate hydrogel constructs were also fabricated and cell viability, cell proliferation, and cartilaginous ECM deposition were investigated. The fabrication technique and the hydrogel scaffolds obtained supported high cell viability and the deposition of cartilaginous ECM, demonstrating their potential for applications in the field of cartilage tissue engineering.

Synchrotron radiation inline phase-contrast imaging combined with computed tomography (SR-inline-PCI-CT) offers great potential for non-invasive characterization and three-dimensional visualization of fine features in weakly absorbing materials and tissues. For cartilage tissue engineering, the biomaterials and any associated cartilage extracellular matrix (ECM) that is secreted over time are difficult to image using conventional absorption-based imaging techniques. For example, three-dimensional printed polycaprolactone (PCL)/alginate/cell hybrid constructs have low, but different, refractive indices and thicknesses. This paper presents a study on the optimization and utilization of inline-PCI-CT for visualizing the components of three-dimensional printed PCL/alginate/cell hybrid constructs for cartilage tissue engineering. First, histological analysis using Alcian blue staining and immunofluorescent staining assessed the secretion of sulfated glycosaminoglycan (GAGs) and collagen type II (Col2) in the cell-laden hybrid constructs over time. Second, optimization of inline PCI-CT was performed by investigating three sample-to-detector distances (SDD): 0.25, 1 and 3 m. Then, the optimal SDD was utilized to visualize structural changes in the constructs over a 42-day culture period. The results showed that there was progressive secretion of cartilage-specific ECM by ATDC5 cells in the hybrid constructs over time. An SDD of 3 m provided edge-enhancement fringes that enabled simultaneous visualization of all components of hybrid constructs in aqueous solution. Structural changes that might reflect formation of ECM also were evident in SR-inline-PCI-CT images. Summarily, SR-inline-PCI-CT images captured at the optimized SDD enables visualization of the different components in hybrid cartilage constructs over a 42-day culture period.

In tissue engineering, non-invasive imaging of biomaterial scaffolds and tissues in living systems is essential to longitudinal animal studies for assessments without interrupting the repair process. Conventional X-ray imaging is inadequate for use in soft tissue engineering due to the limited absorption difference between the soft tissue and biomaterial scaffolds. X-ray phase-based imaging techniques that derive contrast from refraction or phase effects rather than absorption can provide the necessary contrast to see low-density biomaterial scaffolds and tissues in large living systems. This paper explores and compares three synchrotron phase-based X-ray imaging techniques-computed tomography (CT)-diffraction enhanced imaging (DEI), -analyzer based imaging (ABI), and -phase contrast imaging (PCI)-for visualization and characterization of low-density biomaterial scaffolds and tissues in situ for non-invasive soft tissue engineering assessments. Intact pig joints implanted with polycaprolactone scaffolds were used as the model to assess and compare the imaging techniques in terms of different qualitative and quantitative criteria. For long-term in vivo live animal imaging, different strategies for reducing the imaging radiation dose and scan time-reduced number of CT projections, region of interest, and low resolution imaging-were examined with the presented phase-based imaging techniques. The results demonstrated promising capabilities of the phase-based techniques for visualization of biomaterial scaffolds and soft tissues in situ. The low-dose imaging strategies were illustrated effective for reducing the radiation dose to levels appropriate for live animal imaging. The comparison among the imaging techniques suggested that CT-DEI has the highest efficiency in retaining image contrast at considerably low radiation doses.

Three-dimensional (3D) bioprinting of hybrid constructs is a promising biofabrication method for cartilage tissue engineering because a synthetic polymer framework and cell-impregnated hydrogel provide structural and biological features of cartilage, respectively. During bioprinting, impregnated cells may be subjected to high temperatures (caused by the adjacent melted polymer) and process-induced mechanical forces, potentially compromising cell function. This study addresses these biofabrication issues, evaluating the heat distribution of printed polycaprolactone (PCL) strands and the rheological property and structural stability of alginate hydrogels at various temperatures and concentrations. The biocompatibility of parameters from these studies was tested by culturing 3D hybrid constructs bioprinted with primary cells from embryonic chick cartilage. During initial two-dimensional culture expansion of these primary cells, two morphologically and molecularly distinct cell populations ("rounded" and "fibroblastic") were isolated. The biological performance of each population was evaluated in 3D hybrid constructs separately. The cell viability, proliferation, and cartilage differentiation were observed at high levels in hybrid constructs of both cell populations, confirming the validity of these 3D bioprinting parameters for effective cartilage tissue engineering. Statistically significant performance variations were observed, however, between the rounded and fibroblastic cell populations. Molecular and morphological data support the notion that such performance differences may be attributed to the relative differentiation state of rounded versus fibroblastic cells (i.e., differentiated chondrocytes vs. chondroprogenitors, respectively), which is a relevant issue for cell-based tissue engineering strategies. Taken together, our study demonstrates that bioprinting 3D hybrid constructs of PCL and cell-impregnated alginate hydrogel is a promising approach for cartilage tissue engineering.

This article presents the data of using three phase-based X-ray imaging techniques to characterize biomaterial scaffold and soft tissues in situ, as reported in our study “Low-dose phase-based X-ray imaging techniques for in situ soft tissue engineering assessments” [1]. The examined parameters include the radiation dose, scan time, and image quality, which are all critical to longitudinal in situ live animal assessments. The data presented were obtained from three dimensional imaging of scaffolds in situ cartilage by means of synchrotron-based computed tomography-diffraction enhanced imaging (CT-DEI), analyzer based imaging (CT-ABI), and in-line phase contrast imaging (CT-PCI) at standard and low dose imaging modalities.

Wound dressing made from biomaterials has been illustrated promising to treat subcutaneous injuries. The paper presents a novel method for the in situ synthesis of silver nanoparticle on cotton fabric with reducing agent and in vitro characterization of tragacanth/polyvinyl alcohol (PVA) wound dressing with curcumin. For synthesizing the wound dressings, nanosilver was used as the carrier for controlled release of curcumin and then coated, along with tragacanth/PVA hydrogels, on the cotton fabric that was used to provide mechanical support to the dressing. For characterizing the wound dressings, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), contact angle measurement were performed. Also, these wound dressings were evaluated in vitro for drug release, cell culture and MTT analysis. Our results showed that the addition of curcumin could decrease the cell cytotoxicity, thus improving cell viability of the wound dressings. The measurements of contact angle indicated that with the addition of the PVA and tragacanth, the hydrophobicity of the wound dressing could be improved, while the SEM results illustrate the presence of the in situ synthesized coated nanosilver in the dressings. The loading efficiency on the fabric was around 85% and the in-vitro release profile of curcumin showed 42% burst release. Taken together, this study illustrates that fabricated wound dressing composite have the appropriate swelling capacity, mechanical and biological properties for wound healing.

Infectious diseases have the ability to impact health on a global scale, as is being demonstrated by the current coronavirus disease 2019 (COVID-19) pandemic. The strenuous circumstances related to this global health crisis have been highlighting the challenges faced by the biomedical field in combating infectious diseases. Notably, printing technologies have advanced rapidly over the last decades, allowing for the incorporation of living cells in the printing process (or bioprinting) to create constructs that are able to serve as in vitro tissue or virus-disease models in combating infectious diseases. This paper describes applications of bioprinting in addressing the challenges faced in combating infectious diseases, with a specific focus on in vitro modelling and on development of therapeutic agents and vaccines. Integration of these technologies may allow for a more efficient and effective response to current and future pandemics.

Magnesium (Mg) alloys present great potential for the development of orthopedic implants, whereas, their high degradation rate and poor antibacterial performance have restricted orthopedic applications. In this work, PLLA/GO-AgNP (poly-L-lactic acid/graphene oxide- silver nanoparticle) with different concentration of GO-AgNPs were deposited on Mg alloy via electrospinning method for enhancement of corrosion resistance and antibacterial performance. The result revealed that incorporation of GO into PLLA fibrous considerably slowed down the degradation rate of Mg alloy substrate and reduced the H2 release rate from the substrate. Also, co-incorporation of GO and AgNPs into PLLA fibrous resulted in substantial escalate in compressive strength after immersion in simulated body fluid (SBF). Antibacterial activity test exhibited that Mg alloy and neat PLLA fibrous presented minimal inhibition area toward Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). In contrast, using PLLA/GO-AgNPs fibrous improved antibacterial performance against both bacteria. Cytocompatibility results indicated that PLLA/GO-AgNPs fibrous with a low amount of GO-AgNPs enhanced cell proliferation and growth while high co-incorporation of GO-AgNPs showed a negative effect on cell proliferation. Taken together, PLLA/1GO-AgNPs fibrous coating shows suitable corrosion resistance, cytocompatibility, and antibacterial function for use in orthopedic applications.

Over the past decades, tissue regeneration with scaffolds has achieved significant progress that would eventually be able to solve the worldwide crisis of tissue and organ regeneration. While the recent advancement in additive manufacturing technique has facilitated the biofabrication of scaffolds mimicking the host tissue, thick tissue regeneration remains challenging to date due to the growing complexity of interconnected, stable, and functional vascular network within the scaffold. Since the biological performance of scaffolds affects the blood vessel regeneration process, perfect selection and manipulation of biological factors (i.e., biopolymers, cells, growth factors, and gene delivery) are required to grow capillary and macro blood vessels. Therefore, in this study, a brief review has been presented regarding the recent progress in vasculature formation using single, dual, or multiple biological factors. Besides, a number of ways have been presented to incorporate these factors into scaffolds. The merits and shortcomings associated with the application of each factor have been highlighted, and future research direction has been suggested.

Bone injury, especially bone damages due to the removal of bone tumors, is one of the most important issues in the field of therapeutic research in tissue engineering applications. In this context, ceramic-based composites have attracted widespread attention since they have mechanical properties close to the natural bone, hence providing similar conditions for the extracellular matrix (ECM). Thus, in this study, hardystonite and diopside (HT-Di) scaffolds containing various diopside amounts from 5 to 25 wt% were prepared by the space holder method. The results revealed that the fabricated scaffolds contain 70%-75% porosity with a pore size of 300-500 μm and a compressive strength of about 0.54 to 1.71 MPa which is perfectly in the range of the compressive strength of the sponge bone. Noticeably, great apatite formation ability was observed in the scaffold with diopside, although the scaffold without diopside showed poor bioactivity. The MTT assay depicted that the inclusion of diopside into hardystonite scaffold resulted in dramatic enhancement in the MG-63 cell viability. Moreover, the scaffold with diopside offered greater cell attachment and spreading than the scaffold without diopside. Therefore, the synergistic effects of the scaffold with 12.5 wt% of diopside, including great mechanical characteristic, excellent bioactivity, and appealing biocompatibility enable it to be an appealing choice for bone tissue engineering applications.

During the bioprinting processes that employ either pneumatic or screw-driven mechanisms, living cells are subject to process-induced forces, which may cause cell injury or damage. However, the similarities and differences between these two mechanisms have not been discovered and documented in terms of process-induced forces and cell damage. In this paper, we examined the process-induced forces, including hydrostatic pressure, shear stress, extensional stress, and tensile/compressive forces that the cells experienced during the bioprinting processes by means of these two mechanisms; we also experimentally investigated the process-induced cell damage (featured by the rupture of the cell membrane) under various printing conditions or factors, including the volumetric flow rates, cell types, bioink solutions, needle types and sizes, and printing head-movement speeds. On this basis, we correlated the percent of cell damage to the process-induced forces, which were considered mainly responsible for the rupture of the cell membrane. Our results illustrate that compared to the pneumatic bioprinting process, the screw-driven bioprinting process generally induces more cell damage, varying with the printing conditions. This study, for the first time, discovers the similarities and differences between the pneumatic and screw-driven bioprinting processes and further demonstrates their merits and demerits for bioprinting in terms of printing-process control, process-induced forces, and cell damage.

Wound dressings based on nanofiber polymer scaffolds with good antimicrobial performance and skin reconstruction ability are promising options to thwart wound infection and accelerate wound healing. This paper reports on the synthesis via electrospinning of chitosan-alginate (CS-Alg) nanofiber dressings with various amounts of gentamicin (Gn; 0–10 wt%) as a drug delivery system. Smooth and continuous nanofibers with no obvious beads were created, with increases in the amount of Gn resulting in reduced fiber diameter. Antimicrobial tests showed the Gn-loaded nanofibers had good antibacterial performance as indicated by the inhibition of bacterial growth. CS-Alg nanofibers loaded with higher Gn concentrations exhibited greater antibacterial performance than those with lower Gn concentrations. In vitro cell culture studies demonstrated that CS-Alg wound dressings with 1–3% Gn improved L929 cell attachment and proliferation more than wound dressings with higher Gn concentrations. In vivo experiments revealed that Cs-Alg nanofibers loaded with 3% Gn significantly enhanced skin regeneration in a Balb/C mice model by stimulating the formation of a thicker dermis, increasing collagen deposition, and increasing the formation of new blood vessels and hair follicles. Collectively, Gn-loaded CS-Alg wound dressings can be considered a good candidate for drug delivery systems and skin regeneration applications.

Calcified cartilage regeneration plays an important role in successful osteochondral repair, since it provides a biological and mechanical transition from the unmineralized cartilage at the articulating surface to the underlying mineralized bone. To biomimic native calcified cartilage in engineered constructs, here we test the hypothesis that hydroxyapatite (HAP) stimulates chondrocytes to secrete the characteristic matrix of calcified cartilage. Sodium citrate (SC) was added as a dispersant of HAP within alginate (ALG), and homogeneous dispersal of HAP within ALG hydrogel was confirmed using sedimentation tests, electron microscopy, and energy dispersive spectroscopy. To examine the biological performance of ALG/HAP composites, chondrocyte survival and proliferation, extracellular matrix production, and mineralization potential were evaluated in the presence or absence of the HAP phase. Chondrocytes in ALG/HAP constructs survived well and proliferated, but also expressed higher levels of calcified cartilage markers compared to controls, including Collagen type X secretion, alkaline phosphatase (ALP) activity, and mineral deposition. Compared to controls, ALG/HAP constructs also showed an elevated level of mineralized matrix in vivo when implanted subcutaneously in mice. The printability of ALG/HAP composite hydrogel precursors was verified by 3D printing of ALG/HAP hydrogel scaffolds with a porous structure. In summary, these results confirm the hypothesis that HAP in ALG hydrogel stimulates chondrocytes to secrete calcified matrix in vitro and in vivo and reveal that ALG/HAP composites have the potential for 3D bioprinting and osteochondral regeneration.

Bone being a hierarchical composite material has a structure varying from macro- to nanoscale. The arrangement of the components of bone material and the bonding between fibers and matrix gives rise to its unique material properties. In this study, the micromechanisms of cortical bone failure were examined under different loading conditions using scanning electron microscopy. The experimental tests were conducted in longitudinal and transverse directions of bone diaphysis under tensile as well as compressive loading. The results show that bone material has maximum stiffness under longitudinal tensile loading, while the strength is higher under transverse compressive loading. A reverse trend of compressive mechanical properties of bone is observed for longitudinal and transverse loading as compared to trends reported in the previous studies. Therefore, micromechanisms of cortical bone failure were analyzed for different loading conditions to reveal such type of behavior of cortical bone and to correlate bone microstructure with mechanical response of bone.

Due to the superior performances of nanosilica particles, this research has been designed to study their effects on the mechanical and trigological properties of a PVA/PAM polymer composite by a molecular dynamics simulation method. To realize the research objectives mentioned above, the molecular models of amorphous cells and sandwiched friction models for pure polyvinyl alcohol (PVA)/polyacrylamide (PAM) (component weight ratio is 1:1) and PVA/PAM/nanosilica (component weight ratio is 5.75:5.75:1) polymer composites were constructed and simulated, respectively. The simulation results of the mechanical properties show increases about 31.6% in the bulk modulus, 53.1% in the shear modulus, and 50.1% in the Young&rsquo, s modulus by incorporating a nanosilica particle into a pure PVA/PAM polymer composite. Meanwhile, the changes in Cauchy pressure, B/G ratio, and Poisson&rsquo, s ratio values indicate that incorporating a nanosilica particle into pure PVA/PAM weakened the ductility of the composite. Incorporating a nanosilica particle into a pure PVA/PAM composite also showed a decrease about 28.2% in the abrasion rates and relative concentration distributions of polymer molecules in the final friction models. Additionally, the binding energy and the pair correlation functions between a nanosilica particle and the polymer chains in a cubic cell demonstrate that incorporating nanosilica into PVA/PAM polymer composites improves the internal binding strength between different components through the forming hydrogen bonds. As a result, the mechanical and tribological properties of PVA/PAM polymer composites can be enhanced by incorporating nanosilica particles.

The naked mole rat (nmr) is cancer resistant due to the abundant production of extremely high-molecular-weight hyaluronan (EHMW-HA). However, whether EHMW-HA has similar anti-cancer effects in mice and humans remains to be determined. The present study used breast cancer cells to clarify the effect of EHMW-HA on breast cancer. First, the overexpression of nmrHas2 in 4T1 and BT549 cell lines in both two-dimensional (2D) and three-dimensional (3D) models to mimic tumor microenvironment was established. The 4T1/BT549-nmrHas2 cells could secrete EHMW-HA (with a molecular weight of up to 6 MDa), which was similar to that found in the naked mole rat. Second, EHMW-HA altering tumor microenvironment in both 2D monolayers and 3D spheroids significantly enhanced apoptosis, inhibiting the proliferation of 4T1 and BT549 cells. The prominent anticancer effects of EHMW-HA on the cancer-cell apoptosis phenotype were further confirmed by inhibiting tumor formation in nude mice. Finally, EHMW-HA significantly induced higher p53 protein expression, which enhanced pro-apoptotic proteins p21 and Bax in breast cancer cells; this is in contrast with the triggering of hypersensitivity of the naked mole rat cells to early contact inhibition (ECI). These results have important implications for the design of therapeutic approaches based on the application of EHMW-HA.

Three-dimensional bioprinting of biomaterials shows great potential for producing cell-encapsulated scaffolds to repair nerves after injury or disease. For this, preparation of biomaterials and bioprinting itself are critical to create scaffolds with both biological and mechanical properties appropriate for nerve regeneration, yet remain unachievable. This paper presents our study on bioprinting Schwann cell-encapsulated scaffolds using composite hydrogels of alginate, fibrin, hyaluronic acid, and/or RGD peptide, for nerve tissue engineering applications. For the preparation of composite hydrogels, suitable hydrogel combinations were identified and prepared by adjusting the concentration of fibrin based on the morphological spreading of Schwann cells. In bioprinting, the effects of various printing process parameters (including the air pressure for dispensing, dispensing head movement speed, and crosslinking conditions) on printed structures were investigated and, by regulating these parameters, mechanically-stable scaffolds with fully interconnected pores were printed. The performance of Schwann cells within the printed scaffolds were examined in terms of viability, proliferation, orientation, and ability to produce laminin. Our results show that the printed scaffolds can promote the alignment of Schwann cells inside scaffolds and thus provide haptotactic cues to direct the extension of dorsal root ganglion neurites along the printed strands, demonstrating their great potential for applications in the field of nerve tissue engineering.

Indirect Tool Condition Monitoring (TCM) methods have shown significant potential to automatically detect worn tools without intervention in the machining process. This paper presents the development of a non-intrusive and online TCM system for large diameter indexable insert drills. The TCM system developed used two cutting force-related signals of a horizontal boring machine, namely the spindle motor current and the axial feed motor current, and features extracted from these signals were taken as the inputs to a series of models to predict the tool wear state and the hole diameter. A tool replacement strategy based on applying limits to the predicted hole diameter was also developed. Adjusting these limits allows the strategy to be tuned for either hole accuracy or tool life depending on the requirements of a specific application. Experiments of drilling of 39.0-mm-diameter holes in 2205 Duplex stainless steel in an industrial field were designed and performed with the results to illustrate the effectiveness of developed TCM and strategies. Specifically, the TCM system ensured that none of over tolerance holes would have been drilled, which is critically important since any over-tolerance hole can result in the failure of an entire finished product of tubesheet; the replacement strategy for tool life resulted in a 44 % increase in tool life and a non-trivial reduction in machine down time due to fewer tool changes while holding a hole diameter tolerance of ±0.1 mm.

Poly(lactic-co-glycolic acid) (PLGA) microspheres and PLGA/alginate composite microspheres were prepared by a novel double emulsion and solvent evaporation technique and loaded with bovine serum albumin (BSA) or rabbit anti-laminin antibody protein. The addition of alginate and the use of a surfactant during microsphere preparation increased the encapsulation efficiency and reduced the initial burst release of hydrophilic BSA. Confocal laser scanning microcopy (CLSM) of BSA-loaded PLGA/alginate composite microspheres showed that PLGA, alginate, and BSA were distributed throughout the depths of microspheres; no core/shell structure was observed. Scanning electron microscopy revealed that PLGA microspheres erode and degrade more quickly than PLGA/alginate composite microspheres. When loaded with anti-laminin antibody, the function of released antibody was well preserved in both PLGA and PLGA/alginate composite microspheres. The biocompatibility of PLGA and PLGA/alginate microspheres were examined using four types of cultured cell lines, representing different tissue types. Cell survival was variably affected by the inclusion of alginate in composite microspheres, possibly due to the sensitivity of different cell types to excess calcium that may be released from the calcium cross-linked alginate.

The in vitro chondrocyte cell culture for cartilage tissue regeneration in a perfusion bioreactor is a complex process. Mathematical modeling and computational simulation can provide important insights into the culture process, which would be helpful for selecting culture conditions to improve the quality of the developed tissue constructs. However, simulation of the cell culture process is a challenging task due to the complicated interaction between the cells and local fluid flow and nutrient transport inside the complex porous scaffolds. In this study, a mathematical model and computational framework has been developed to simulate the three-dimensional (3D) cell growth in a porous scaffold placed inside a bi-directional flow perfusion bioreactor. The model was developed by taking into account the two-way coupling between the cell growth and local flow field and associated glucose concentration, and then used to perform a resolved-scale simulation based on the lattice Boltzmann method (LBM). The simulation predicts the local shear stress, glucose concentration, and 3D cell growth inside the porous scaffold for a period of 30 days of cell culture. The predicted cell growth rate was in good overall agreement with the experimental results available in the literature. This study demonstrates that the bi-directional flow perfusion culture system can enhance the homogeneity of the cell growth inside the scaffold. The model and computational framework developed is capable of providing significant insight into the culture process, thus providing a powerful tool for the design and optimization of the cell culture process.

Tissue engineering opens up a new area to restore the function of damaged tissue or replace a defective organ. Common strategies in tissue engineering to repair and form new tissue containing a functional vascular network include the use of cells, growth factors, extracellular matrix proteins, and biophysical stimuli. Yet, formation of well-distributed, interconnected, and stable vascular network still remains challenging. In addition, anastomoses with host vasculature upon implantation and long-time survival of the new blood vessel in vivo are other critical issues to be addressed. This paper presents a brief review of recent advances in vascularization in vitro as well as in vivo for tissue engineering, along with suggestions for future research.

In this paper, large eddy simulation (LES) of a three-dimensional turbulent lid-driven cavity (LDC) flow at Re = 10,000 has been performed using the multiple relaxation time lattice Boltzmann method. A Smagorinsky eddy viscosity model was used to represent the sub-grid scale stresses with appropriate wall damping. The prediction for the flow field was first validated by comparing the velocity profiles with previous experimental and LES studies, and then subsequently used to investigate the large-scale three-dimensional vortical structures in the LDC flow. The instantaneous three-dimensional coherent structures inside the cavity were visualised using the second invariant (Q), Δ criterion, λ2 criterion, swirling strength (λci) and streamwise vorticity. The vortex structures obtained using the different criteria in general agree well with each other. However, a cleaner visualisation of the large vortex structures was achieved with the λci criterion and also when the visualisation is based on the vortex ident...

The in vitro chondrocyte cell culture process in a perfusion bioreactor provides enhanced nutrient supply as well as the flow-induced shear stress that may have a positive influence on the cell growth. Mathematical and computational modelling of such a culture process, by solving the coupled flow, mass transfer and cell growth equations simultaneously, can provide important insight into the biomechanical environment of a bioreactor and the related cell growth process. To do this, a two-way coupling between the local flow field and cell growth is required. Notably, most of the computational and mathematical models to date have not taken into account the influence of the cell growth on the local flow field and nutrient concentration. The present research aimed at developing a mathematical model and performing a numerical simulation using the lattice Boltzmann method to predict the chondrocyte cell growth without a scaffold on a flat plate placed inside a perfusion bioreactor. The model considers the two-way coupling between the cell growth and local flow field, and the simulation has been performed for 174 culture days. To incorporate the cell growth into the model, a control-volume-based surface growth modelling approach has been adopted. The simulation results show the variation of local fluid velocity, shear stress and concentration distribution during the culture period due to the growth of the cell phase and also illustrate that the shear stress can increase the cell volume fraction to a certain extent.

Graphical abstract, Mathematical and numerical modelling of the tissue culture process in a perfusion bioreactor is able to provide insight into the fluid flow, nutrients and wastes transport, dynamics of the pH value, and the cell growth rate. Knowing the complicated interdependence of these processes is essential for optimizing the culture process for cell growth. This paper presents a resolved scale numerical simulation, which allows one not only to characterize the supply of glucose inside a porous tissue scaffold in a perfusion bioreactor, but also to assess the overall culture condition and predict the cell growth rate. The simulation uses a simplified scaffold that consists of a repeatable unit composed of multiple strands. The simulation results explore some problematic regions inside the simplified scaffold where the concentration of glucose becomes lower than the critical value for the chondrocyte cell viability and the cell growth rate becomes significantly reduced.

Knowledge of the fluid flow and mass transfer over circular strands is fundamental to the cell culture of tissue scaffolds in bio-reactors. This paper presents a study on the simulation of fluid flow and mass transfer over the circular strands of a tissue scaffold by using the multiple relaxation time lattice Boltzmann method for the low Reynolds number regime, with Re D = 0.01 and 0.1, respectively. The mass transfer problem approximates the transport of a scalar nutrient from the bulk fluid to the strand surface, such as is encountered in the flow through tissue scaffolds placed in bio-reactors. The circular geometry of the scaffold strand is treated and implemented by means of the interpolated bounce-back boundary condition formulation. Our simulation illustrates that the flow accelerates around the strand, resulting in the maximum shear stress at the shoulder of the strand and that diffusion mass transfer plays the dominant role in the scalar transport. The local Sherwood number varies significantly over the surface of the strand, with a peak value located on the upstream surface. Increasing the Schmidt number of the scalar and decreasing the blockage ratio results in higher mass transfer rates on the surface of the stand. Overall, the simulation results provide one with the insight into the fluid flow and mass transfer over the circular strands of a tissue scaffold in a bio-reactor, which would be impractical to obtain by experiments.

Three dimensional (3D) bioplotting requires appropriate crosslinkers to crosslink the hydrogel precursor while simultaneously maintaining the viability of embedded cells. However, the evaluation and comparison of various types of crosslinkers in bioplotting remains underexplored to date. This paper presents our study of the influence of three ionic crosslinkers-calcium chloride (CaCl

Tissue engineering scaffolds combined with bioreactors are used to cultivate cells with the aim of reproducing tissues and organs. The cultivating process is critical due to the delicate in-vitro environment in which the cells should reproduce. The distribu- tion of nutrients within the engineered construct depend on the scaffold morphology and the analysis of the fluid flow and transport phenomena under mechanical loading when the scaffold is coupled with a bioreactor is crucial for this scope. Unfortunately, due to the complicated microstructure of the scaffold, it is not possible to perform this analysis with experiments and numerical simulation can help in this sense. In this study we have computed the fluid flow and the mass transport of a parametrized scaffold in perfusion bioreactors analyzing the influence of the microstructure of the scaffold using the fluid-structure interaction approach. The latter allows considering the porous construct as compliant yet determining important structural parameters such as stresses and strains that could be sensed by the cells. The presented model considered flow perfusion that provided nutrients and mechanical compression. In particular, we have studied the effect of controllable parameters such as the diam- eter of the scaffold strand and the porosity on the mechanical stresses and strains, shear stress and mass transport. The results of this work will help to shed light on the necessary microenvironment surrounding the cultivated cells improving culturing scaffold fabrication. The authors acknowledge the financial supports to this project from the Spanish Ministry of Education, Culture and Sport via the National Program“Salvador de Madariaga”(PRX17/00335) and the Saskatchewan Health Research Foundation via the Health Research Group Program (SHRF Reference #2784). Also, the authors thank the CIBER-BBN financed by the Instituto de Salud Carlos III and the Spanish Ministry of Education, Industry and Competitiveness via the research project (DP12017-83259-R).