Current progress in hepatic tissue regeneration by tissue engineering

Small Molecule-Mediated Stage-Specific Reprogramming of MSCs to Hepatocyte-Like Cells and Hepatic Tissue for Liver Injury Treatment

BACKGROUND

Derivation of hepatocytes from stem cells has been established through various protocols involving growth factor (GF) and small molecule (SM) agents, among others. However, mesenchymal stem cell-based derivation of hepatocytes still remains expensive due to the use of a cocktail of growth factors, and a long duration of differentiation is needed, thus limiting its potential clinical application.

METHODS

In this study, we developed a chemically defined differentiation strategy that is exclusively based on SM and takes 14 days, while the GF-based protocol requires 23-28 days.

RESULTS

We optimized a stage-specific differentiation protocol for the differentiation of rat bone marrow-derived mesenchymal stem cells (MSCs) into functional hepatocyte-like cells (dHeps) that involved four stages, i.e., definitive endoderm (DE), hepatic competence (HC), hepatic specification (HS) and hepatic differentiation and growth. We further generated hepatic tissue using human decellularized liver extracellular matrix and compared it with hepatic tissue derived from the growth factor-based protocol at the transcriptional level. dHep, upon transplantation in a rat model of acute liver injury (ALI), was capable of ameliorating liver injury in rats and improving liver function and tissue damage compared to those in the ALI model.

CONCLUSIONS

In summary, this is the first study in which hepatocytes and hepatic tissue were derived from MSCs utilizing a stage-specific strategy by exclusively using SM as a differentiation factor.

Advancing the understanding of diabetic encephalopathy through unravelling pathogenesis and exploring future treatment perspectives

Diabetic encephalopathy (DE), a significant micro-complication of diabetes, manifests as neurochemical, structural, behavioral, and cognitive alterations. This condition is especially dangerous for the elderly because aging raises the risk of neurodegenerative disorders and cognitive impairment, both of which can be made worse by diabetes. Despite its severity, diagnosis of this disease is challenging, and there is a paucity of information on its pathogenesis. The pivotal roles of various cellular pathways, activated or influenced by hyperglycemia, insulin sensitivity, amyloid accumulation, tau hyperphosphorylation, brain vasculopathy, neuroinflammation, and oxidative stress, are widely recognized for contributing to the potential causes of diabetic encephalopathy. We also reviewed current pharmacological strategies for DE encompassing a comprehensive approach targeting metabolic dysregulations and neurological manifestations. Antioxidant-based therapies hold promise in mitigating oxidative stress-induced neuronal damage, while anti-diabetic drugs offer neuroprotective effects through diverse mechanisms, including modulation of insulin signaling pathways and neuroinflammation. Additionally, tissue engineering and nanomedicine-based approaches present innovative strategies for targeted drug delivery and regenerative therapies for DE. Despite significant progress, challenges remain in translating these therapeutic interventions into clinical practice, including long-term safety, scalability, and regulatory approval. Further research is warranted to optimize these approaches and address remaining gaps in the management of DE and associated neurodegenerative disorders.

Multimaterial 3D and 4D Bioprinting of Heterogenous Constructs for Tissue Engineering

Additive manufacturing (AM), which is based on the principle of layer-by-layer shaping and stacking of discrete materials, has shown significant benefits in the fabrication of complicated implants for tissue engineering (TE). However, many native tissues exhibit anisotropic heterogenous constructs with diverse components and functions. Consequently, the replication of complicated biomimetic constructs using conventional AM processes based on a single material is challenging. Multimaterial 3D and 4D bioprinting (with time as the fourth dimension) has emerged as a promising solution for constructing multifunctional implants with heterogenous constructs that can mimic the host microenvironment better than single-material alternatives. Notably, 4D-printed multimaterial implants with biomimetic heterogenous architectures can provide a time-dependent programmable dynamic microenvironment that can promote cell activity and tissue regeneration in response to external stimuli. This paper first presents the typical design strategies of biomimetic heterogenous constructs in TE applications. Subsequently, the latest processes in the multimaterial 3D and 4D bioprinting of heterogenous tissue constructs are discussed, along with their advantages and challenges. In particular, the potential of multimaterial 4D bioprinting of smart multifunctional tissue constructs is highlighted. Furthermore, this review provides insights into how multimaterial 3D and 4D bioprinting can facilitate the realization of next-generation TE applications.

The impact of matrix stiffness on hepatic cell function, liver fibrosis, and hepatocellular carcinoma-Based on quantitative data

Over the past few decades, extensive research has explored the development of supportive scaffold materials for in vitro hepatic cell culture, to effectively mimic in vivo microenvironments. It is crucial for hepatic disease modeling, drug screening, and therapeutic evaluations, considering the ethical concerns and practical challenges associated with in vivo experiments. This review offers a comprehensive perspective on hepatic cell culture using bioscaffolds by encompassing all stages of hepatic diseases-from a healthy liver to fibrosis and hepatocellular carcinoma (HCC)-with a specific focus on matrix stiffness. This review begins by providing physiological and functional overviews of the liver. Subsequently, it explores hepatic cellular behaviors dependent on matrix stiffness from previous reports. For hepatic cell activities, softer matrices showed significant advantages over stiffer ones in terms of cell proliferation, migration, and hepatic functions. Conversely, stiffer matrices induced myofibroblastic activation of hepatic stellate cells, contributing to the further progression of fibrosis. Elevated matrix stiffness also correlates with HCC by increasing proliferation, epithelial-mesenchymal transition, metastasis, and drug resistance of HCC cells. In addition, we provide quantitative information on available data to offer valuable perspectives for refining the preparation and development of matrices for hepatic tissue engineering. We also suggest directions for further research on this topic.

Wheat germ meal replaces cottonseed meal at different levels in diets of Ossimi lambs: Impact on growth performance, feed utilization and economic efficiency

This experiment aimed to evaluate the replacement of cottonseed meal (CSM) with wheat germ meal (WGM) in diets of growing lambs on feed utilization and growth performance. Twenty-eight Ossimi male lambs (38 ± 0.8 kg weight), and 180 ± 5 days were divided randomly into four experimental groups in a complete randomized design for 105 days. Cottonseed meal was replaced with WGM at 0 (WGM0 treatment), 50 (WGM50 treatment), 75 (WGM75 treatment) and 100% (WGM100 treatment). The chemical analysis of the total essential and non-essential amino acids showed an increase at the WGM diet compared to CSM. The replacement of CSM with WGM linearly and quadratically improved (p ˂ 0.05) lambs' growth performance and feed conversion. The WGM50 and WGM100 treatments lowered (p ˂ 0.05) feed intake, without affecting nutrient digestibility or diets' nutritive. Feeding WGM increased (p ˂ 0.05) total protein, albumin, and urea-N concentrations in blood of lambs. The WGM100 treatment showed the highest relative percentage of net revenue compared to the other treatments. It is concluded that the complete replacement of CSM with WGM showed positive effects on lambs' performance and economic efficiency.

Mechanical properties of human hepatic tissues to develop liver-mimicking phantoms for medical applications

Using liver phantoms for mimicking human tissue in clinical training, disease diagnosis, and treatment planning is a common practice. The fabrication material of the liver phantom should exhibit mechanical properties similar to those of the real liver organ in the human body. This tissue-equivalent material is essential for qualitative and quantitative investigation of the liver mechanisms in producing nutrients, excretion of waste metabolites, and tissue deformity at mechanical stimulus. This paper reviews the mechanical properties of human hepatic tissues to develop liver-mimicking phantoms. These properties include viscosity, elasticity, acoustic impedance, sound speed, and attenuation. The advantages and disadvantages of the most common fabrication materials for developing liver tissue-mimicking phantoms are also highlighted. Such phantoms will give a better insight into the real tissue damage during the disease progression and preservation for transplantation. The liver tissue-mimicking phantom will raise the quality assurance of patient diagnostic and treatment precision and offer a definitive clinical trial data collection.

Advances in 3D bioprinting for regenerative medicine applications

Biofabrication techniques allow for the construction of biocompatible and biofunctional structures composed from biomaterials, cells and biomolecules. Bioprinting is an emerging 3D printing method which utilizes biomaterial-based mixtures with cells and other biological constituents into printable suspensions known as bioinks. Coupled with automated design protocols and based on different modes for droplet deposition, 3D bioprinters are able to fabricate hydrogel-based objects with specific architecture and geometrical properties, providing the necessary environment that promotes cell growth and directs cell differentiation towards application-related lineages. For the preparation of such bioinks, various water-soluble biomaterials have been employed, including natural and synthetic biopolymers, and inorganic materials. Bioprinted constructs are considered to be one of the most promising avenues in regenerative medicine due to their native organ biomimicry. For a successful application, the bioprinted constructs should meet particular criteria such as optimal biological response, mechanical properties similar to the target tissue, high levels of reproducibility and printing fidelity, but also increased upscaling capability. In this review, we highlight the most recent advances in bioprinting, focusing on the regeneration of various tissues including bone, cartilage, cardiovascular, neural, skin and other organs such as liver, kidney, pancreas and lungs. We discuss the rapidly developing co-culture bioprinting systems used to resemble the complexity of tissues and organs and the crosstalk between various cell populations towards regeneration. Moreover, we report on the basic physical principles governing 3D bioprinting, and the ideal bioink properties based on the biomaterials' regenerative potential. We examine and critically discuss the present status of 3D bioprinting regarding its applicability and current limitations that need to be overcome to establish it at the forefront of artificial organ production and transplantation.

A review on the application of chitosan-based polymers in liver tissue engineering

Chitosan-based polymers have enormous structural tendencies to build bioactive materials with novel characteristics, functions, and various applications, mainly in liver tissue engineering (LTE). The specific physicochemical, biological, mechanical, and biodegradation properties give the effective ways to blend these biopolymers with synthetic and natural polymers to fabricate scaffolds matrixes, sponges, and complexes. A variety of natural and synthetic biomaterials, including chitosan (CS), alginate (Alg), collagen (CN), gelatin (GL), hyaluronic acid (HA), hydroxyapatite (HAp), polyethylene glycol (PEG), polycaprolactone (PCL), poly(lactic-co-glycolic) acid (PGLA), polylactic acid (PLA), and silk fibroin gained considerable attention due to their structure-properties relationship. The incorporation of CS within the polymer matrix results in increased mechanical strength and also imparts biological behavior to the designed PU formulations. The significant and growing interest in the LTE sector, this review aims to be a detailed exploration of CS-based polymers biomaterials for LTE. A brief explanation of the sources and extraction, properties, structure, and scope of CS is described in the introduction. After that, a full overview of the liver, its anatomy, issues, hepatocyte transplantation, LTE, and CS LTE applications are discussed.

Scaffold-mediated liver regeneration: A comprehensive exploration of current advances

The liver coordinates over 500 biochemical processes crucial for maintaining homeostasis, detoxification, and metabolism. Its specialized cells, arranged in hexagonal lobules, enable it to function as a highly efficient metabolic engine. However, diseases such as cirrhosis, fatty liver disease, and hepatitis present significant global health challenges. Traditional drug development is expensive and often ineffective at predicting human responses, driving interest in advanced in vitro liver models utilizing 3D bioprinting and microfluidics. These models strive to mimic the liver's complex microenvironment, improving drug screening and disease research. Despite its resilience, the liver is vulnerable to chronic illnesses, injuries, and cancers, leading to millions of deaths annually. Organ shortages hinder liver transplantation, highlighting the need for alternative treatments. Tissue engineering, employing polymer-based scaffolds and 3D bioprinting, shows promise. This review examines these innovative strategies, including liver organoids and liver tissue-on-chip technologies, to address the challenges of liver diseases.

Combination of melt-electrospun poly-ε-caprolactone scaffolds and hepatocyte-like cells from footprint-free hiPSCs to create 3D biohybrid constructs for liver tissue engineering

The liver is a vital organ with numerous functions, including metabolic functions, detoxification, and the synthesis of secretory proteins. The increasing prevalence of liver diseases requires the development of effective treatments, models, and regenerative approaches. The field of liver tissue engineering represents a significant advance in overcoming these challenges. In this study, 3D biohybrid constructs were created by combining hepatocyte-like cells (HLCs) derived from patient-specific footprint-free human induced pluripotent stem cells (hiPSCs) and 3D melt-electrospun poly-ε-caprolactone (PCL) scaffolds. First, a differentiation procedure was established to obtain autologous HCLs from hiPSCs reprogrammed from renal epithelial cells using self-replicating mRNA. The obtained cells expressed hepatocyte-specific markers and exhibited important hepatocyte functions, such as albumin synthesis, cytochrome P450 activity, glycogen storage, and indocyanine green metabolism. Biocompatible PCL scaffolds were fabricated by melt-electrospinning and seeded with pre-differentiated hepatoblasts, which uniformly attached to the fibers of the scaffolds and successfully matured into HLCs. The use of patient-specific, footprint-free hiPSC-derived HLCs represents a promising cell source for personalized liver regeneration strategies. In combination with biocompatible 3D scaffolds, this innovative approach has a broader range of applications spanning liver tissue engineering, drug testing and discovery, and disease modeling.

Study of laser fluorescence spectroscopy in livers of rats with hypothermic ischemia

PURPOSE

After partial hepatectomy (PH), the remaining liver (RL) undergoes regenerative response proportional to the host. Limited literature exists on hepatic viability after tissue injury during hypothermic preservation. Spectroscopy measures cellular fluorescence and is explored for tissue characterization and parameter investigation. This study aimed to assess fluorescence analysis (spectroscopy) in evaluating liver viability and its relationship with hepatic tissue regeneration 24 hours after PH. Additionally, we analyzed liver regeneration in RL after 70% partial hepatectomy under hypothermic conditions with laser irradiation.

METHODS

Fifty-six Wistar rats were divided into four groups: total non-perfused liver (control), total perfused liver, partial hepatectomy "in situ", and partial hepatectomy "ex situ". Tissue analysis was performed at 0 and 24 hours using spectroscopy with laser devices emitting at 532 (green) and 405 nm (violet).

RESULTS

Spectroscopy identified tissue viability based on consistent results with Ki67 staining. The fluorescence spectra and Ki67 analysis displayed similar patterns, linking proliferative activity and absorption intensity.

CONCLUSIONS

Fluorescence spectroscopy proves to be promising for real-time analysis of cellular activity and viability. Metabolic activity was observed in groups of live animals and hypothermically preserved samples, indicating cellular function even under blood deprivation and hypothermic conditions.

Decellularization Techniques for Tissue Engineering: Towards Replicating Native Extracellular Matrix Architecture in Liver Regeneration

The process of tissue regeneration requires the utilization of a scaffold, which serves as a structural framework facilitating cellular adhesion, proliferation, and migration within a physical environment. The primary aim of scaffolds in tissue engineering is to mimic the structural and functional properties of the extracellular matrix (ECM) in the target tissue. The construction of scaffolds that accurately mimic the architecture of the extracellular matrix (ECM) is a challenging task, primarily due to the intricate structural nature and complex composition of the ECM. The technique of decellularization has gained significant attention in the field of tissue regeneration because of its ability to produce natural scaffolds by removing cellular and genetic components from the extracellular matrix (ECM) while preserving its structural integrity. The present study aims to investigate the various decellularization techniques employed for the purpose of isolating the extracellular matrix (ECM) from its native tissue. Additionally, a comprehensive comparison of these methods will be presented, highlighting their respective advantages and disadvantages. The primary objective of this study is to gain a comprehensive understanding of the anatomical and functional features of the native liver, as well as the prevalence and impact of liver diseases. Additionally, this study aims to identify the limitations and difficulties associated with existing therapeutic methods for liver diseases. Furthermore, the study explores the potential of tissue engineering techniques in addressing these challenges and enhancing liver performance. By investigating these aspects, this research field aims to contribute to the advancement of liver disease treatment and management.

Gelatin-Based Hybrid Hydrogel Scaffolds: Toward Physicochemical Liver Mimicry

There exists a clear need to develop novel materials that could serve liver tissue engineering purposes. Those materials need to be researched for the development of bioengineered liver tissue as an alternative to donor livers, as well as for materials that could be applied for scaffolds to develop an in vitro model for drug-induced liver injury (DILI) detection . In this paper, the hydrogels oxidized dextran-gelatin (Dexox-Gel) and norbornene-modified dextran-thiolated gelatin (DexNB-GelSH) were developed, and their feasibility toward processing via indirect 3D-printing was investigated with the aim to develop hydrogel scaffolds that physicochemically mimic native liver tissue. Furthermore, their in vitro biocompatibility was assessed using preliminary biological tests using HepG2 cells. Both materials were thoroughly physicochemically characterized and benchmarked to the methacrylated gelatin (GelMA) reference material. Due to inferior properties, Dexox-gel was not further processed into 3D-hydrogel scaffolds. This research revealed that DexNB-GelSH exhibited physicochemical properties that were in excellent agreement with the properties of natural liver tissue in contrast to GelMA. In combination with an equally good biological evaluation of DexNB-GelSH in comparison with GelMA based on an MTS proliferation assay and an albumin quantification assay, DexNB-GelSH can be considered promising in the field of liver tissue engineering.

Whole Liver Derived Acellular Extracellular Matrix for Bioengineering of Liver Constructs: An Updated Review

Biomaterial templates play a critical role in establishing and bioinstructing three-dimensional cellular growth, proliferation and spatial morphogenetic processes that culminate in the development of physiologically relevant in vitro liver models. Various natural and synthetic polymeric biomaterials are currently available to construct biomimetic cell culture environments to investigate hepatic cell-matrix interactions, drug response assessment, toxicity, and disease mechanisms. One specific class of natural biomaterials consists of the decellularized liver extracellular matrix (dECM) derived from xenogeneic or allogeneic sources, which is rich in bioconstituents essential for the ultrastructural stability, function, repair, and regeneration of tissues/organs. Considering the significance of the key design blueprints of organ-specific acellular substrates for physiologically active graft reconstruction, herein we showcased the latest updates in the field of liver decellularization-recellularization technologies. Overall, this review highlights the potential of acellular matrix as a promising biomaterial in light of recent advances in the preparation of liver-specific whole organ scaffolds. The review concludes with a discussion of the challenges and future prospects of liver-specific decellularized materials in the direction of translational research.

Advantages and Prospective Implications of Smart Materials in Tissue Engineering: Piezoelectric, Shape Memory, and Hydrogels

Conventional biomaterial is frequently used in the biomedical sector for various therapies, imaging, treatment, and theranostic functions. However, their properties are fixed to meet certain applications. Smart materials respond in a controllable and reversible way, modifying some of their properties because of external stimuli. However, protein-based smart materials allow modular protein domains with different functionalities and responsive behaviours to be easily combined. Wherein, these "smart" behaviours can be tuned by amino acid identity and sequence. This review aims to give an insight into the design of smart materials, mainly protein-based piezoelectric materials, shape-memory materials, and hydrogels, as well as highlight the current progress and challenges of protein-based smart materials in tissue engineering. These materials have demonstrated outstanding regeneration of neural, skin, cartilage, bone, and cardiac tissues with great stimuli-responsive properties, biocompatibility, biodegradability, and biofunctionality.

Review on Additives in Hydrogels for 3D Bioprinting of Regenerative Medicine: From Mechanism to Methodology

The regeneration of biological tissues in medicine is challenging, and 3D bioprinting offers an innovative way to create functional multicellular tissues. One common way in bioprinting is bioink, which is one type of the cell-loaded hydrogel. For clinical application, however, the bioprinting still suffers from satisfactory performance, e.g., in vascularization, effective antibacterial, immunomodulation, and regulation of collagen deposition. Many studies incorporated different bioactive materials into the 3D-printed scaffolds to optimize the bioprinting. Here, we reviewed a variety of additives added to the 3D bioprinting hydrogel. The underlying mechanisms and methodology for biological regeneration are important and will provide a useful basis for future research.

Interfacial Polyelectrolyte Complexation-Inspired Bioprinting of Vascular Constructs

Bioprinting is a precise layer-by-layer manufacturing technology utilizing biomaterials, cells, and sometimes growth factors for the fabrication of customized three-dimensional (3D) biological constructs. In recent years, it has gained considerable interest in various biomedical studies. However, the translational application of bioprinting is currently impeded by the lack in efficient techniques for blood vessel fabrications. In this report, by systematically studying the previously reported phenomenon, interfacial polyelectrolyte complexation, an efficient blood vessel bioprinting technique based on the phenomenon, was proposed and subsequently investigated. In this technique, anionic hyaluronate and cationic lysine-based peptide amphiphiles were placed concentrically to bioprint with human umbilical endothelial cells for the fabrication of biological tubular constructs. These constructs demonstrated clear vascular features, which made them highly resemble blood vessels. In addition, to optimize the bioactivity of the printed constructs, this report also, for the first time, studied peptide sequencing's effect on the biocompatibility of the polyelectrolyte-peptide amphiphile complex. All these studies conducted in the report are highly relevant and interesting for research in vascular structure fabrication, which will eventually be beneficial for translational application development of bioprinting.

Engineering orthotopic tumor spheroids with organ-specific vasculatures for local chemoembolization evaluation

Developing a three-dimensional (3D) in vitro tumor model with vasculature systems suitable for testing endovascular interventional therapies remains a challenge. Here we develop an orthotopic liver tumor spheroid model that captures the organ-level complexity of vasculature systems and the extracellular matrix to evaluate transcatheter arterial chemoembolization (TACE) treatment. The orthotopic tumor spheroids are derived by seeding HepG2 cell colonies with controlled size and location surrounding the portal triads in a decellularized rat liver matrix and are treated by clinically relevant drug-eluting beads embolized in a portal vein vasculature while maintaining dynamic physiological conditions with nutrient and oxygen supplies through the hepatic vein vasculature. The orthotopic tumor model exhibits strong drug retention inside the spheroids and embolization location-dependent cellular apoptosis responses in an analogous manner to in vivo conditions. Such a tumor spheroid model built in a decellularized scaffold containing organ-specific vasculatures, which closely resembles the unique tumor microenvironment, holds the promise to efficiently assess various diagnostic and therapeutic strategies for endovascular therapies.

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

The native liver as inspiration to create superior in vitro hepatic models

Drug induced liver injury (DILI) is one of the major reasons of drug withdrawal during the different phases of drug development. The later in the drug development a drug is discovered to be toxic, the higher the economical as well as the ethical impact will be. In vitro models for early detection of drug liver toxicity are under constant development, however to date a superior model of the liver is still lacking. Ideally, a highly reliable model should be established to maintain the different hepatic cell functionalities to the greatest extent possible, during a period of time long enough to allow for tracking of the toxicity of compounds. In the case of DILI, toxicity can appear even after months of exposure. To reach this goal, an in vitro model should be developed that mimics the in vivo liver environment, function and response to external stimuli. The different approaches for the development of liver models currently used in the field of tissue engineering will be described in this review. Combining different technologies, leading to optimal materials, cells and 3D-constructs will ultimately lead to an ideal superior model that fully recapitulates the liver.

Efficient Neural Differentiation of Mouse Embryonic Stem Cells by Mastic Gum

Purpose: Promoting neurogenesis is a promising strategy to treat neurodegenerative disorders. In the present study, we aimed to evaluate the effect of mastic gum resin from the Pistacia lentiscus var. Chia (Anacardiaceae family) in proliferation capacity and differentiation of embryonic mesenchymal stem cells into a neural lineage. Methods: For this purpose, mastic gum was applied as a neural inducer for stem cell differentiation into the neuronal lineage. Following treatment of embryonic stem cells (ESCs) with mastic gum, verification differentiation of the ESCs into the neuronal lineage, gene expression analysis, and immunocytochemistry staining approach were performed. Results: Gene expression analysis demonstrated that mastic gum increased the expression level of neuron markers in the ESCs-derived neuron-like cells. Moreover, our immunocytochemistry staining results of two important neural stem cell markers, including Nestin and microtubule-associated protein-2 (Map2) expression confirmed that mastic gum has the potential to promote neuronal differentiation in ESCs. Conclusion: In summary, the use of mastic gum to stimulate the differentiation of ESCs into a neural lineage can be considered as a good candidate in stem cell therapy.

Effects of Different Perfusing Routes through The Portal Vein, Hepatic Vein, and Biliary Duct on Whole Rat Liver Decellularization

OBJECTIVE

Organ transplantation is the last therapeutic choice for end-stage liver failure, which is limited by the lack of sufficient donors. Decellularized liver can be used as a suitable matrix for liver tissue engineering with clinical application potential. Optimizing the decellularization procedure would obtain a biological matrix with completely removed cellular components and preserved 3-dimensional structure. This study aimed to evaluate the decellularization efficacy through three anatomical routes.

MATERIALS AND METHODS

In this experimental study, rat liver decellularization was performed through biliary duct (BD), portal vein (PV), and hepatic vein (HV); using chemical detergents and enzymes. The decellularization efficacy was evaluated by measurement of DNA content, extracellular matrix (ECM) total proteins, and glycosaminoglycans (GAGs). ECM preservation was examined by histological and immunohistochemical (IHC) staining and scanning electron microscopy (SEM). Scaffold biocompatibility was tested by the MTT assay for HepG2 and HUVEC cell lines.

RESULTS

Decellularization through HV and PV resulted in a transparent scaffold by complete cell removal, while the BD route produced an opaque scaffold with incomplete decellularization. H and E staining confirmed these results. Maximum DNA loss was obtained using 1% and 0.5% sodium dodecyl sulfate (SDS) in the PV and HV groups and the DNA content decreased faster in the HV group. At the final stages, the proteins excreted in the HV and PV groups were significantly less than the BD group. The GAGs level was diminished after decellularization, especially in the PV and HV groups. In the HV and PV groups the collagen amount was significantly more than the BD group. The IHC and SEM images showed that the ECM structure was preserved and cellular components were entirely removed. MTT assay showed the biocompatibility of the decellularized scaffold.

CONCLUSION

The results revealed that the HV is a more suitable route for liver decellularization than the PV and BD.

Rat liver extracellular matrix and perfusion bioreactor culture promote human amnion epithelial cell differentiation towards hepatocyte-like cells

Congenital and chronic liver diseases have a substantial health burden worldwide. The most effective treatment available for these patients is whole organ transplantation; however, due to the severely limited supply of donor livers and the side effects associated with the immunosuppressive regimen required to accept allograft, the mortality rate in patients with end-stage liver disease is annually rising. Stem cell-based therapy aims to provide alternative treatments by either cell transplantation or bioengineered construct transplantation. Human amnion epithelial cells (AEC) are a widely available, ethically neutral source of cells with the plasticity and potential of multipotent stem cells and immunomodulatory properties of perinatal cells. AEC have been proven to be able to achieve functional improvement towards hepatocyte-like cells, capable of rescuing animals with metabolic disorders; however, they showed limited metabolic activities in vitro. Decellularised extracellular matrix (ECM) scaffolds have gained recognition as adjunct biological support. Decellularised scaffolds maintain native ECM components and the 3D architecture instrumental of the organ, necessary to support cells' maturation and function. We combined ECM-scaffold technology with primary human AEC, which we demonstrated being equipped with essential ECM-adhesion proteins, and evaluated the effects on AEC differentiation into functional hepatocyte-like cells (HLC). This novel approach included the use of a custom 4D bioreactor to provide constant oxygenation and media perfusion to cells in 3D cultures over time. We successfully generated HLC positive for hepatic markers such as ALB, CYP3A4 and CK18. AEC-derived HLC displayed early signs of hepatocyte phenotype, secreted albumin and urea, and expressed Phase-1 and -2 enzymes. The combination of liver-specific ECM and bioreactor provides a system able to aid differentiation into HLC, indicating that the innovative perfusion ECM-scaffold technology may support the functional improvement of multipotent and pluripotent stem cells, with important repercussions in the bioengineering of constructs for transplantation.

Horizon of exosome-mediated bone tissue regeneration: The all-rounder role in biomaterial engineering

Bone injury repair has always been a tricky problem in clinic, the recent emergence of bone tissue engineering provides a new direction for the repair of bone injury. However, some bone tissue processes fail to achieve satisfactory results mainly due to insufficient vascularization or cellular immune rejection. Exosomes with the ability of vesicle-mediated intercellular signal transmission have gained worldwide attention and can achieve cell-free therapy. Exosomes are small vesicles that are secreted by cells, which contain genetic material, lipids, proteins and other substances. It has been found to play the function of material exchange between cells. It is widely used in bone tissue engineering to achieve cell-free therapy because it not only does not produce some immune rejection like cells, but also can play a cell-like function. Exosomes from different sources can bind to scaffolds in various ways and affect osteoblast, angioblast, and macrophage polarization in vivo to promote bone regeneration. This article reviews the recent research progress of exosome-loaded tissue engineering, focusing on the mechanism of exosomes from different sources and the application of exosome-loaded scaffolds in promoting bone regeneration. Finally, the existing deficiencies and challenges, future development directions and prospects are summarized.

Analysis of decellularized mouse liver fragment and its recellularization with human endometrial mesenchymal cells as a candidate for clinical usage

Decellularized tissue has been used as a natural extracellular matrix (ECM) or bioactive biomaterial for tissue engineering. The present study aims to compare and analyze different decellularization protocols for mouse liver fragments and cell seeding and attachment in the created scaffold using human endometrial mesenchymal cells (hEMCs).After collecting and dissecting the mouse liver into small fragments, they were decellularized by Triton X-100 and six concentrations of sodium dodecyl sulfate (SDS; 0.025, 0.05, 0.1, 0.25, 0.5, and 1%) at different exposure times. The morphology and DNA content of decellularized tissues were studied, and the group with better morphology and lower DNA content was selected for additional assessments. Masson's tri-chrome and periodic acid Schiff staining were performed to evaluate ECM materials. Raman confocal spectroscopy analysis was used to quantify the amount of collagen type I, III and IV, glycosaminoglycans and elastin. Scanning electron microscopy and MTT assay were applied to assess the ultrastructure and porosity and cytotoxicity of decellularized scaffolds, respectively. In the final step, hEMCs were seeded on the decellularized scaffold and cultured for one week, and finally the cell attachment and homing were studied morphologically.The treated group with 0.1% SDS for 24 h showed a well preserved ECM morphology similar to native control and showing the minimum level of DNA. Raman spectroscopy results demonstrated that the amount of collagen type I and IV was not significantly changed in this group compared to the control, but a significant reduction in collagen III and elastin protein levels was seen (P < 0.001). The micrographs showed a porous ECM in decellularized sample similar to the native control with the range of 2.25 µm to 7.86 µm. After cell seeding, the infiltration and migration of cells in different areas of the scaffold were seen. In conclusion, this combined protocol for mouse liver decellularization is effective and its recellularization with hEMCs could be suitable for clinical applications in the future.

Mir-122 upregulation and let-7f downregulation combination: The effects on hepatic differentiation of hiPSCs on the PCL-Gel-HA nanofibrous scaffold

Cell therapy and tissue engineering as promising candidates for the liver transplantation dilemma are of special interest. Induced pluripotent stem cells (iPSCs) are one of the best sources in this field, but their differentiation methods to hepatocytes have remained challenging. We transduced human iPSCs (hiPSCs) with miR-122 and off-let-7f (hiPSCs^{miR-122 + off-let-7f} ) to evaluate how they can differentiate hiPSCs to hepatocyte-like cells (HLCs) without any extrinsic growth factor. Additionally, we studied the effect of Poly ɛ-caprolactone-gelatin-hyaluronic acid (PCL-Gel-HA) nanofibrous scaffold as an extracellular matrix (ECM) simulator on differentiation improvement. Definitive endoderm markers (FOXA2 and SOX17), as well as hepatic markers (AFP, Albumin, CK18, HNF4α) expression, were significantly higher in hiPSCs^{miR-122 + off-let-7f} derived HLCs (hiPSCs-HLCs) compared to the control group (miR-scramble transduced hiPSCs: hiPSCs^scramble ). hiPSCs-HLCs indicated hepatocyte morphological characteristics and positive immunostaining for AFP, Albumin and HNF4α. Albumin and urea secretion were significantly higher in hiPSCs-HLCs than hiPSCs^scramble . Comparing these markers in the PCL-Gel-HA group with the tissue culture plate (TCP) group revealed that PCL-Gel-HA could improve differentiation towards HLCs significantly. Regarding our results, these microRNAs can be used to differentiate hiPSCs to the functional hepatocytes for disease modelling, drug screening and cell-based therapy in future studies.

Core-shell bioprinting of vascularized in vitro liver sinusoid models

In vitro liver models allow the investigation of the cell behavior in disease conditions or in response to changes in the microenvironment. A major challenge in liver tissue engineering is to mimic the tissue-level complexity: Besides the selection of suitable biomaterial(s) replacing the extracellular matrix (ECM) and cell sources, the three-dimensional (3D) microarchitecture defined by the fabrication method is a critical factor to achieve functional constructs. In this study, coaxial extrusion-based 3D bioprinting has been applied to develop a liver sinusoid-like model that consists of a core compartment containing pre-vascular structures and a shell compartment containing hepatocytes. The shell ink was composed of alginate and methylcellulose (algMC), dissolved in human fresh frozen plasma. The algMC blend conferred high printing fidelity and stability to the core-shell constructs and the plasma as biologically active component enhanced viability and supported cluster formation and biomarker expression of HepG2 embedded in the shell. For the core, a natural ECM-like ink based on angiogenesis-supporting collagen-fibrin (CF) matrices was developed; the addition of gelatin (G) enabled 3D printing in combination with the plasma-algMC shell ink. Human endothelial cells (HUVEC), laden in the CFG core ink together with human fibroblasts as supportive cells, formed a pre-vascular network in the core in the absence and presence of HepG2 in the shell. The cellular interactions occurring in the triple culture model enhanced the albumin secretion. In conclusion, core-shell bioprinting was shown to be a valuable tool to study cell-cell-interactions and to develop complex tissue-like models.

Chemically Modified Dipeptide Based Hydrogel Supports Three-Dimensional Growth and Functions of Primary Hepatocytes

A huge shortage of organ donors, particularly in the case of liver, has necessitated the development of alternative therapeutic strategies. Primary hepatocytes (pHCs) transplantation has made a considerable transition from bench to bedside, but the short-term viability and functionality of pHCs in in vitro limit their use for clinical applications. Different cell culture strategies are required to maintain the proliferation of pHCs for extended periods. Here, we described the formation of a hybrid scaffold based on a modified dipeptide for the culture of pHCs. First, the dipeptide (Dp), isoleucine-α,β-dehydrophenylalanine (IΔF) was synthesized, purified, and fully characterized. IΔF readily formed a highly stable hydrogel, which was also characterized by CD, TEM, and thioflavin T assay. The addition of soluble liver extracellular matrix (sLEM) to the dipeptide readily formed a hybrid scaffold that was characterized by TEM, and its mechanical strength was determined by rheology experiments. The hybrid scaffold was translucent, biocompatible, and proteolytically stable and, with its mechanical strength, closely mimicked that of the native liver. LEM1-Dp matrix exhibited high biocompatibility in the readily available adherent liver cell line Huh7 and primary rat hepatocyte cells (pHCs). pHCs cultured on LEM1-Dp matrix also maintained significantly higher cell viability and an escalated expression of markers related to the hepatocytes such as albumin as compared to that observed in cells cultured on collagen type I (Col I)-coated substrate plate (col-TCTP). Z-stacking of confocal laser microscopy's volume view clearly indicated pHCs seeded on top of the hydrogel matrix migrated toward the Z direction showing 3D growth. Our results indicated that low molecular weight dipeptide hydrogel along with sLEM can resemble biomimetic 3D-like microenvironments for improved pHCs proliferation, differentiation, and function. This hybrid scaffold is also easy to scale up, which makes it suitable for several downstream applications of hepatocytes, including drug development, pHCs transplantation, and liver regeneration.

Recombinant Spidroin Microgel as the Base of Cell-Engineered Constructs Mediates Liver Regeneration in Rats

Aim: In this study, we seek to check if recombinant spidroin rS1/9 is applicable for cell-engineering construct development. Novel technologies of cell and tissue engineering are relevant for chronic liver failure management. Liver regeneration may represent one of the possible treatment options if a cell-engineered construct (CEC) is used. Nowadays, one can see the continuous study of various matrices to create an appropriate CEC. Materials and Methods: We have adhered allogenic liver cells and multipotent mesenchymal bone marrow stem cells (MMSC BM) to a microgel with recombinant spidroin rS1/9. Then we have studied the developed implantable CEC in a rat model (n = 80) of chronic liver failure achieved by prolonged poisoning with carbon tetrachloride. Results: Our results demonstrate that the CECs change the values of biochemical tests and morphological parameters in chronic liver failure in rats. Conclusion: We consider there to be a positive effect from the microgel-based CECs with recombinant spidroin rS1/9 in the treatment of chronic liver failure.

3D Bioprinting of Multi-Material Decellularized Liver Matrix Hydrogel at Physiological Temperatures

Bioprinting is an acclaimed technique that allows the scaling of 3D architectures in an organized pattern but suffers from a scarcity of appropriate bioinks. Decellularized extracellular matrix (dECM) from xenogeneic species has garnered support as a biomaterial to promote tissue-specific regeneration and repair. The prospect of developing dECM-based 3D artificial tissue is impeded by its inherent low mechanical properties. In recent years, 3D bioprinting of dECM-based bioinks modified with additional scaffolds has advanced the development of load-bearing constructs. However, previous attempts using dECM were limited to low-temperature bioprinting, which is not favorable for a longer print duration with cells. Here, we report the development of a multi-material decellularized liver matrix (dLM) bioink reinforced with gelatin and polyethylene glycol to improve rheology, extrudability, and mechanical stability. This shear-thinning bioink facilitated extrusion-based bioprinting at 37 °C with HepG2 cells into a 3D grid structure with a further enhancement for long-term applications by enzymatic crosslinking with mushroom tyrosinase. The heavily crosslinked structure showed a 16-fold increase in viscosity (2.73 Pa s⁻¹) and a 32-fold increase in storage modulus from the non-crosslinked dLM while retaining high cell viability (85–93%) and liver-specific functions. Our results show that the cytocompatible crosslinking of dLM bioink at physiological temperatures has promising applications for extended 3D-printing procedures.

Differentiation of the mesenchymal stem cells to pancreatic β-like cells in alginate/trimethyl chitosan/alginate microcapsules

Cell therapy is one of the proposed treatments for diabetes. Cell encapsulation and differentiation inside the biodegradable polymers overcome the limitations such as islet deficiency and the host immune responses. This study was set to encapsulate the mesenchymal stem cells (MSCs) and differentiate them into insulin-producing cells (IPCs). Human bone marrow-mesenchymal stem cells (hBM-MSCs) were encapsulated in alginate/trimethyl chitosan/alginate (Alg/TMC/Alg) coating. At first, morphology and swelling properties of the cell-free microcapsules were investigated. Next, a three-step protocol was used in the presence of exendin-4 and nicotinamide to differentiate hBM-MSCs into IPCs. Viability of the encapsulated cells was investigated using MTT assay. The differentiated cells were analyzed using a real-time RT-PCR to investigate Glut-2, Insulin, Pdx-1, Ngn-3, nestin, and Isl-1 gene expression. The results revealed that differentiation of the encapsulated cells was higher than non-encapsulated cells. Also, dithizone staining in  two-dimensional (2D) environment showed the differentiated cell clusters. In summary, here, hBM-MSCs after encapsulation in Alg/TMC/Alg microcapsules, as a new design, were differentiated properly in the presence of exendin-4 and nicotinamide as main inducers. A three-dimensional (3D) matrix is more similar to the native ECM in the body and prepares higher cell-cell contacts.

Fabrication of a Tailored, Hybrid Extracellular Matrix Composite

The extracellular matrix (ECM) is a network of connective fibers that supports cells living in their surroundings. Native ECM, generated by the secretory products of each tissue's resident cells, has a unique architecture with different protein composition depending on the tissue. Therefore, it is very difficult to artificially design in vivo architecture in tissue engineering. In this study, we fabricated a hybrid ECM scaffold from the basic structure of fibroblast-derived cellular ECMs by adding major ECM components of fibronectin (FN) and collagen (COL I) externally. It was confirmed that while maintaining the basic structure of the native ECM, major protein components can be regulated. Then, decellularization was performed to prepare hybrid ECM scaffolds with various protein compositions and we demonstrated that a liver-mimicking fibronectin (FN)-rich hybrid ECM promoted successful settling of H4IIE rat hepatoma cells. We believe that our method holds promise for the fabrication of scaffolds that provide a tailored cellular microenvironment for specific organs and serve as novel pathways for the replacement or regeneration of specific organ tissues. This article is protected by copyright. All rights reserved.

Liver organ-on-chip models for toxicity studies and risk assessment

The liver is a key organ that plays a pivotal role in metabolism and ensures a variety of functions in the body, including homeostasis, synthesis of essential components, nutrient storage, and detoxification. As the centre of metabolism for exogenous molecules, the liver is continuously exposed to a wide range of compounds, such as drugs, pesticides, and environmental pollutants. Most of these compounds can cause hepatotoxicity and lead to severe and irreversible liver damage. To study the effects of chemicals and drugs on the liver, most commonly, animal models or in vitro 2D cell cultures are used. However, data obtained from animal models lose their relevance when extrapolated to the human metabolic situation and pose ethical concerns, while 2D static cultures are poorly predictive of human in vivo metabolism and toxicity. As a result, there is a widespread need to develop relevant in vitro liver models for toxicology studies. In recent years, progress in tissue engineering, biomaterials, microfabrication, and cell biology has created opportunities for more relevant in vitro models for toxicology studies. Of these models, the liver organ-on-chip (OoC) has shown promising results by reproducing the in vivo behaviour of the cell/organ or a group of organs, the controlled physiological micro-environment, and in vivo cellular metabolic responses. In this review, we discuss the development of liver organ-on-chip technology and its use in toxicity studies. First, we introduce the physiology of the liver and summarize the traditional experimental models for toxicity studies. We then present liver OoC technology, including the general concept, materials used, cell sources, and different approaches. We review the prominent liver OoC and multi-OoC integrating the liver for drug and chemical toxicity studies. Finally, we conclude with the future challenges and directions for developing or improving liver OoC models.

Biomaterials to enhance stem cell transplantation

The successful transplantation of stem cells has the potential to transform regenerative medicine approaches and open promising avenues to repair, replace, and regenerate diseased, damaged, or aged tissues. However, pre-/post-transplantation issues of poor cell survival, retention, cell fate regulation, and insufficient integration with host tissues constitute significant challenges. The success of stem cell transplantation depends upon the coordinated sequence of stem cell renewal, specific lineage differentiation, assembly, and maintenance of long-term function. Advances in biomaterials can improve pre-/post-transplantation outcomes by integrating biophysiochemical cues and emulating tissue microenvironments. This review highlights leading biomaterials-based approaches for enhancing stem cell transplantation.

Decellularized liver ECM-based 3D scaffolds: Compositional, physical, chemical, rheological, thermal, mechanical, and in vitro biological evaluations

The extracellular matrix (ECM) is involved in many critical cellular interactions through its biological macromolecules. In this study, a macroporous 3D scaffold originating from decellularized bovine liver ECM (dL-ECM), with defined compositional, physical, chemical, rheological, thermal, mechanical, and in vitro biological properties was developed. First, protocols were determined that effectively remove cells and DNA while ECM retains biological macromolecules collagen, elastin, sGAGs in tissue. Rheological analysis revealed the elastic properties of pepsin-digested dL-ECM. Then, dL-ECM hydrogel was neutralized, molded, formed into macroporous (~100-200 μm) scaffolds in aqueous medium at 37 °C, and lyophilized. The scaffolds had water retention ability, and were mechanically stable for at least 14 days in the culture medium. The findings also showed that increasing the dL-ECM concentration from 10 mg/mL to 20 mg/mL resulted in a significant increase in the mechanical strength of the scaffolds. The hemolysis test revealed high in vitro hemocompatibility of the dL-ECM scaffolds. Studies investigating the viability and proliferation status of human adipose stem cells seeded over a 2-week culture period have demonstrated the suitability of dL-ECM scaffolds as a cell substrate. Prospective studies may reveal the extent to which 3D dL-ECM sponges have the potential to create a biomimetic environment for cells.

Artificial Kidney Engineering: The Development of Dialysis Membranes for Blood Purification

The artificial kidney, one of the greatest medical inventions in the 20th century, has saved innumerable lives with end stage renal disease. Designs of artificial kidney evolved dramatically in decades of development. A hollow-fibered membrane with well controlled blood and dialysate flow became the major design of the modern artificial kidney. Although they have been well established to prolong patients’ lives, the modern blood purification system is still imperfect. Patient’s quality of life, complications, and lack of metabolic functions are shortcomings of current blood purification treatment. The direction of future artificial kidneys is toward miniaturization, better biocompatibility, and providing metabolic functions. Studies and trials of silicon nanopore membranes, tissue engineering for renal cell bioreactors, and dialysate regeneration are all under development to overcome the shortcomings of current artificial kidneys. With all these advancements, wearable or implantable artificial kidneys will be achievable.

Liver scaffolds obtained by decellularization: A transplant perspective in liver bioengineering

Liver transplantation is the only definitive treatment for many diseases that affect this organ, however, its quantity and viability are reduced. The study of liver scaffolds based on an extracellular matrix is a tissue bioengineering strategy with great application in regenerative medicine. Collectively, recent studies suggest that liver scaffold transplantation may assist in reestablishing hepatic function in preclinical diseased animals, which represents a great potential for application as a treatment for patients with liver disease in the future. This review focuses on useful strategies to promote liver scaffold transplantation and the main open questions about this context. We outline the current knowledge about ex vivo bioengineered liver transplantation, including the surgical techniques, recipient survival time, scaffold preparation before transplantation, and liver disease models. We also highlight the current limitations and future directions regarding in vivo bioengineering techniques.

Molecular targets regulating endoplasmic reticulum-mitochondria crosstalk for NAFLD treatment

Non-alcoholic fatty liver disease (NAFLD) as the most common chronic liver disease poses a significant impact on public healthcare and economic risk worldwide. As a multifactorial disease, NAFLD is usually associated with many comorbidities such as obesity, insulin resistance, hypertension, hyperlipidemia, diabetes, and cardiovascular disease. Without effectively preventive intervention, the advanced stage of NAFLD, non-alcoholic steatohepatitis (NASH), can progress to cirrhosis and hepatocellular carcinoma (HCC). However, there is no approved therapeutic treatment. Excessive fat accumulation in the liver is the hallmark of NAFLD, which can lead to mitochondrial dysfunction and endoplasmic reticulum (ER) stress. Dysfunction of two organelles also induces the upregulation of reactive oxygen species (ROS), activation of the unfolded protein response (UPR), and disruption of calcium transport, which promote NAFLD progression. Herein, this review summarized the current understanding of the roles of mitochondrial dysfunction and ER stress in the pathogenesis of NAFLD. Specifically, this review focused on the key molecules associated with the ER-mitochondria communication and different treatment options by targeting ER stress and mitochondrial dysfunction to treat NAFLD or NASH. Clinical trials to evaluate the therapeutic efficacy of representative agents, such as natural products, metabolites, and modulators of stress, have been reviewed and analyzed. Overall, recent findings suggest that targeting ER stress and mitochondrial dysfunction holds a promise for NAFLD treatment.

Temporally Controlled Photouncaged Epidermal Growth Factor Influences Cell Fate in Hydrogels

Hydrogels are powerful materials that more accurately mimic the cellular microenvironment over static two-dimensional culture. Photochemical strategies enable dynamic complexity to be achieved within hydrogels to better mimic the extracellular matrix; however, many photochemical systems to pattern proteins within hydrogels are complicated by long reaction times to immobilize these proteins wherein the protein can lose activity. As proof-of-concept, we demonstrate an elegant method where photocaged proteins are immobilized in hydrogels and then directly photoactivated. Specifically, we immobilized streptavidin-ortho-nitrobenzyl-modified epidermal growth factor (EGF) to cross-linked hyaluronan hydrogels and cultured two EGF-responsive cancer cells of breast and lung therein. We used light to temporally uncage and control EGF activation, thereby inducing cell death in breast cancer cells and proliferation in lung cancer cells. These results show how temporal, photochemical, protein activation influences cellular response and lays the foundation for further advances in manipulating the in vitro environment to control cell fate.

Alginate-Based Smart Materials and Their Application: Recent Advances and Perspectives

Nature produces materials using available molecular building blocks following a bottom-up approach. These materials are formed with great precision and flexibility in a controlled manner. This approach offers the inspiration for manufacturing new artificial materials and devices. Synthetic artificial materials can find many important applications ranging from personalized therapeutics to solutions for environmental problems. Among these materials, responsive synthetic materials are capable of changing their structure and/or properties in response to external stimuli, and hence are termed "smart" materials. Herein, this review focuses on alginate-based smart materials and their stimuli-responsive preparation, fragmentation, and applications in diverse fields from drug delivery and tissue engineering to water purification and environmental remediation. In the first part of this report, we review stimuli-induced preparation of alginate-based materials. Stimuli-triggered decomposition of alginate materials in a controlled fashion is documented in the second part, followed by the application of smart alginate materials in diverse fields. Because of their biocompatibility, easy accessibility, and simple techniques of material formation, alginates can provide solutions for several present and future problems of humankind. However, new research is needed for novel alginate-based materials with new functionalities and well-defined properties for targeted applications.

A small molecule modulating monounsaturated fatty acids and Wnt signaling confers maintenance to induced pluripotent stem cells against endodermal differentiation

Background

Stearoyl-coenzyme A desaturase 1 (SCD1) is required for de novo synthesis of fatty acids. Through the fatty acid acylation process, this enzyme orchestrates post-translational modifications to proteins involved in cell development and differentiation. In this study, we used biochemical methods, immunostaining, and covalent labeling to evaluate whether a small molecule modulating unsaturated fatty acids can influence the early endodermal differentiation of human-induced pluripotent stem cells (iPSCs).

Methods

The hiPSCs were cultured in an endoderm-inducing medium containing activin A and defined fetal bovine serum in the presence of an SCD1 inhibitor at different time points. The cell cycles and the yields of the three germ layers (endoderm, mesoderm, and ectoderm) were assessed using flow cytometry. The expression of endoderm and pluripotency markers and the expressions of Wnt signaling pathway proteins were assessed using western blotting and RT-PCR. Total protein acylation was evaluated using a click chemistry reaction.

Results

When SCD1 was inhibited on the first day, the population of cells with endodermal features decreased at the end of differentiation. Moreover, early SCD1 inhibition preserved the properties of hiPSCs, preventing their shift toward mesodermal or ectodermal lineage. Also, first-day-only treatment of cells with the SCD1 inhibitor decreased β-catenin gene expression and the intensity of fluorescent emission in the click chemistry assay. The cells were effectively rescued from these effects by cotreatment with oleate. Late treatment with the inhibitor in the two subsequent days of endoderm induction did not have any significant effects on endoderm-specific markers or fluorescent intensity. Reproducible results were also obtained with human embryonic stem cells.

Conclusion

The small molecule SCD1 inhibitor attenuates the Wnt/β-catenin signaling pathway, conferring the maintenance of hiPSCs by opposing the initiation of endoderm differentiation. The immediate requirement for SCD1 activity in the endoderm commitment of pluripotent stem cells may be of importance in disorders of endoderm-derived organs and dysregulated metabolism.

The schematic representation of the study design and main results. Activin A induces endoderm features through Smad2/3/4 and increases the expression of SCD1. SCD1 can produce MUFAs and subsequently modify the Wnt molecules. MUFA acylated/activated Wnts are secreted to interact with corresponding receptors on the target cells. β-catenin accumulates in the cytoplasm and is translocated into the nucleus after the interaction of Wnt with the receptor. Then, β-catenin increases the expression of the endoderm markers Sox17 and CXCR4.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02617-x.

Aspects of In Vitro Biodegradation of Hybrid Fibrin-Collagen Scaffolds

The success of the regenerative process resulting from the implantation of a scaffold or a tissue-engineered structure into damaged tissues depends on a series of factors, including, crucially, the biodegradability of the implanted materials. The selection of a scaffold with appropriate biodegradation characteristics allows for synchronization of the degradation of the construct with the processes involved in new tissue formation. Thus, it is extremely important to characterize the biodegradation properties of potential scaffold materials at the stage of in vitro studies. We have analyzed the biodegradation of hybrid fibrin–collagen scaffolds in both PBS solution and in trypsin solution and this has enabled us to describe the processes of both their passive and enzymatic degradation. It was found that the specific origin of the collagen used to form part of the hybrid scaffolds could have a significant effect on the nature of the biodegradation process. It was also established, during comparative studies of acellular scaffolds and scaffolds containing stem cells, that the cells, too, make a significant contribution to changes in the biodegradation and structural properties of such scaffolds. The study results also provided evidence indicating the dependency between the pre-cultivation period for the cellular scaffolds and the speed and extent of their subsequent biodegradation. Our discussion of results includes an attempt to explain the mechanisms of the changes found. We hope that the said results will make a significant contribution to the understanding of the processes affecting the differences in the biodegradation properties of hybrid, biopolymer, and hydrogel scaffolds.

MicroRNAs: Crucial Players in the Differentiation of Human Pluripotent and Multipotent Stem Cells into Functional Hepatocyte-Like Cells

Hepatic disease negatively impacts liver function and metabolism. Primary human hepatocytes are the gold standard for the prediction and successful treatment of liver disease. However, the sources of hepatocytes for drug toxicity testing and disease modeling are limited. To overcome this issue, pluripotent stem cells (PSCs) have emerged as an alternative strategy for liver disease therapy. Human PSCs, including embryonic stem cells (ESC) and induced pluripotent stem cells (iPSC) can self-renew and give rise to all cells of the body. Human PSCs are attractive cell sources for regenerative medicine, tissue engineering, drug discovery, and developmental studies. Several recent studies have shown that mesenchymal stem cells (MSCs) can also differentiate (or trans-differentiate) into hepatocytes. Differentiation of human PSCs and MSCs into functional hepatocyte-like cells (HLCs) opens new strategies to study genetic diseases, hepatotoxicity, infection of hepatotropic viruses, and analyze hepatic biology. Numerous in vitro and in vivo differentiation protocols have been established to obtain human PSCs/MSCs-derived HLCs and mimic their characteristics. It was recently discovered that microRNAs (miRNAs) play a critical role in controlling the ectopic expression of transcription factors and governing the hepatocyte differentiation of human PSCs and MSCs. In this review, we focused on the role of miRNAs in the differentiation of human PSCs and MSCs into hepatocytes.

Sex and Regeneration

Regeneration is usually regarded as a unique plant or some animal species process. In reality, regeneration is a ubiquitous process in all multicellular organisms. It ranges from response to wounding by healing the wounded tissue to whole body neoforming (remaking of the new body). In a larger context, regeneration is one facet of two reproduction schemes that dominate the evolution of life. Multicellular organisms can propagate their genes asexually or sexually. Here I present the view that the ability to regenerate tissue or whole-body regeneration is also determined by the sexual state of the multicellular organisms (from simple animals such as hydra and planaria to plants and complex animals). The above idea is manifested here by showing evidence that many organisms, organs, or tissues show inhibited or diminished regeneration capacity when in reproductive status compared to organs or tissues in nonreproductive conditions or by exposure to sex hormones.

Bioengineered Liver Models for Investigating Disease Pathogenesis and Regenerative Medicine

Owing to species-specific differences in liver pathways, in vitro human liver models are utilized for elucidating mechanisms underlying disease pathogenesis, drug development, and regenerative medicine. To mitigate limitations with de-differentiated cultures, bioengineers have developed advanced techniques/platforms, including micropatterned cocultures, spheroids/organoids, bioprinting, and microfluidic devices, for perfusing cell cultures and liver slices. Such techniques improve mature functions and culture lifetime of primary and stem-cell human liver cells. Furthermore, bioengineered liver models display several features of liver diseases including infections with pathogens (e.g., malaria, hepatitis C/B viruses, Zika, dengue, yellow fever), alcoholic/nonalcoholic fatty liver disease, and cancer. Here, we discuss features of bioengineered human liver models, their uses for modeling aforementioned diseases, and how such models are being augmented/adapted for fabricating implantable human liver tissues for clinical therapy. Ultimately, continued advances in bioengineered human liver models have the potential to aid the development of novel, safe, and efficacious therapies for liver disease.

Upgrading Hepatic Differentiation and Functions on 3D Printed Silk-Decellularized Liver Hybrid Scaffolds

We developed hybrid liver-specific three-dimensional (3D) printed scaffolds using a solubilized native decellularized liver (DCL) matrix and silk fibroin (SF) and investigated their ability to support functional cultures of hepatic cells. Rat livers were decellularized by perfusing detergents via the portal vein, solubilized using pepsin to form DCL, and characterized. SF blended with gelatin (8% w/v) was optimized with varying percentages of DCL to obtain silk gelatin-DCL bioink (SG-DCL). Different compositions of SG-DCL were studied by rheology for optimum versatility and print fidelity. 3D printed six-layered scaffolds were fabricated using a sophisticated direct-write 3D bioprinter. Huh7 cells were cultured on the 3D printed scaffolds for 3 weeks. 3D printed SG scaffolds without DCL along with 2D films (SG and SG-DCL) and 2D culture on tissue culture Petri dish control were used for comparative studies. The DCL matrix showed the absence of cells in histology and SEM. The combined SG-DCL ink at all of the studied DCL percentages (1-10%) revealed shear-thinning behavior in the printable range. The storage modulus value for the SG-DCL ink at all DCL percentages was higher than the loss modulus. In comparison to 2D controls, hepatic cells cultured on 3D SG-DCL revealed increased proliferation until 2 weeks and an upregulated expression of hepatocyte markers, including asialoglycoprotein receptor 1 (ASGR1). The Wnt pathway gene β-catenin was upregulated by more than 4-fold in 3D SG-DCL on day 3, while it showed a decline on day 7 as compared to 3D SG and also 2D controls. The expression of the epithelial cell adhesion molecule (EpCAM) was however lower in both 2D SG-DCL (2-fold) and 3D SG-DCL (2.5-fold) as compared to that in 2D controls. Immunofluorescence studies validated the protein expression of ASGR1 in 3D SG-DCL. Albumin (ALB) was not identified on SG scaffolds but prominently expressed in 3D SG-DCL constructs. In comparison to 2D SG, both ALB (1.8-fold) and urea (5-fold) were enhanced in cells cultured on 3D SG-DCL on day 7 of culture. Hence, the SG-DCL 3D printed scaffolds provide a conducive microenvironment for elevating differentiation and functions of hepatic cells possibly through an involvement of the Wnt/β-catenin signaling pathway.

Tissue engineered artificial liver model based on viscoelastic hyaluronan-collagen hydrogel and the effect of EGCG intervention on ALD

In alcoholic liver disease (ALD) research, animal models, as one of the most popular methods to explore pathology and therapeutic drug screening, show the limitations of expensive cost and ethic, as well as long modeling time. To minimize the use of animal models in ALD research, an artificial liver model has been developed by incorporating HepG2 cells into hydrogel matrix based on difunctional hyaluronan and collagen. And on this basis an alcohol-induced ALD model in vitro by adding alcohol in the engineering process has been established. Results showed that the construct exhibited a simulated synthetic and metabolic liver function thanks to the bionic fibrillar and viscoelastic characteristics of hydrogels. And the in vitro alcohol-induced ALD model was also proved to be successfully established, even presenting equal results with ALD mice. Furthermore, epigallocatechin gallate (EGCG) as an intervention on ALD was confirmed in both in vitro and in vivo model. The findings indicate our simple artificial liver model is not only highly predictive but also easy to apply to drug screening and implantation studies, suggesting a promising alternative to animal models. Moreover, as the main active ingredient of tea, EGCG's effective intervention and reversal effect on fatty liver provides support for the theory that green tea could prevent alcoholic fatty liver.

3D Printing in Breast Reconstruction: From Bench to Bed

Surgical management of breast cancer often results in the absence of the breast. However, existing breast reconstruction methods may not meet the need for a replacement tissue. Tissue engineering with the use of emerging materials offers the promise of generating appropriate replacements. Three-dimensional (3D) printing technology has seen a significantly increased interest and application in medically-related fields in the recent years. This has been especially true in complex medical situations particularly when abnormal or complicated anatomical surgical considerations or precise reconstructive procedures are contemplated. In addition, 3D bio-printing which combines cells with bio-material scaffolds offers an exciting technology with significant applications in the field of tissue engineering. The purpose of this manuscript was to review a number of studies in which 3D printing technology has been used in breast reconstructive surgical procedures, and future directions and applications of 3D bio-printing.