Biologically Inspired Smart Release System Based on 3D Bioprinted Perfused Scaffold for Vascularized Tissue Regeneration

Recent advances in 3D printing: vascular network for tissue and organ regeneration

Over the past years, the fabrication of adequate vascular networks has remained the main challenge in engineering tissues due to technical difficulties, while the ultimate objective of tissue engineering is to create fully functional and sustainable organs and tissues to transplant in the human body. There have been a number of studies performed to overcome this limitation, and as a result, 3D printing has become an emerging technique to serve in a variety of applications in constructing vascular networks within tissues and organs. 3D printing incorporated technical approaches allow researchers to fabricate complex and systematic architecture of vascular networks and offer various selections for fabrication materials and printing techniques. In this review, we will discuss materials and strategies for 3D printed vascular networks as well as specific applications for certain vascularized tissue and organ regeneration. We will also address the current limitations of vascular tissue engineering and make suggestions for future directions research may take.

Potent delivery of an MMP inhibitor to the tumor microenvironment with thermosensitive liposomes for the suppression of metastasis and angiogenesis

Metastasis is a major cause of chemotherapeutic failure and death. Degradation of a specific component of the extracellular matrix (ECM) by matrix metalloproteinases (MMPs) affects the physical barrier of the tumor microenvironment (TME) and induces metastasis. Here, lysolipid-containing thermosensitive liposomes (LTSLs) were prepared to deliver an MMP inhibitor, marimastat (MATT), to the TME to inhibit MMP activity and expression. LTSLs rapidly released their payloads at 42 °C. Compared with the saline control, MATT-LTSLs exhibited enhanced accumulation in the tumor and a 20-fold decrease in tumor growth in 4T1 tumor-bearing mice; moreover, MATT-LTSLs reduced MMP-2 and MMP-9 activity by 50% and 43%, respectively, and downregulated MMP-2 and MMP-9 expression in vivo by 30% and 43%, respectively. Most importantly, MATT-LTSL treatment caused a 7-fold decrease in metastatic lung nodules and a 6-fold reduction in microvessels inside the tumor. We believe this study provides an effective approach for the suppression of metastasis, and the use of a cytotoxic agent in combination with MATT is a potential strategy for metastatic cancer treatment.

Application of Micro-Scale 3D Printing in Pharmaceutics

3D printing, as one of the most rapidly-evolving fabrication technologies, has released a cascade of innovation in the last two decades. In the pharmaceutical field, the integration of 3D printing technology has offered unique advantages, especially at the micro-scale. When printed at a micro-scale, materials and devices can provide nuanced solutions to controlled release, minimally invasive delivery, high-precision targeting, biomimetic models for drug discovery and development, and future opportunities for personalized medicine. This review aims to cover the recent advances in this area. First, the 3D printing techniques are introduced with respect to the technical parameters and features that are uniquely related to each stage of pharmaceutical development. Then specific micro-sized pharmaceutical applications of 3D printing are summarized and grouped according to the provided benefits. Both advantages and challenges are discussed for each application. We believe that these technologies provide compelling future solutions for modern medicine, while challenges remain for scale-up and regulatory approval.

A Magnesium-Enriched 3D Culture System that Mimics the Bone Development Microenvironment for Vascularized Bone Regeneration

The redevelopment/regeneration pattern of amputated limbs from a blastema in salamander suggests that enhanced regeneration might be achieved by mimicking the developmental microenvironment. Inspired by the discovery that the expression of magnesium transporter-1 (MagT1), a selective magnesium (Mg) transporter, is significantly upregulated in the endochondral ossification region of mouse embryos, a Mg-enriched 3D culture system is proposed to provide an embryonic-like environment for stem cells. First, the optimum concentration of Mg ions (Mg2+) for creating the osteogenic microenvironment is screened by evaluating MagT1 expression levels, which correspond to the osteogenic differentiation capacity of stem cells. The results reveal that Mg2+ selectively activates the mitogen-activated protein kinase/extracellular regulated kinase (MAPK/ERK) pathway to stimulate osteogenic differentiation, and Mg2+ influx via MagT1 is profoundly involved in this process. Then, Mg-enriched microspheres are fabricated at the appropriate size to ensure the viability of the encapsulated cells. A series of experiments show that the Mg-enriched microenvironment not only stimulates the osteogenic differentiation of stem cells but also promotes neovascularization. Obvious vascularized bone regeneration is achieved in vivo using these Mg-enriched cell delivery vehicles. The findings suggest that biomaterials mimicking the developmental microenvironment might be promising tools to enhance tissue regeneration.

A novel near-infrared light responsive 4D printed nanoarchitecture with dynamically and remotely controllable transformation

Four-dimensional (4D) printing is an emerging and highly innovative additive manufacturing process by which to fabricate pre-designed, self-assembly structures with the ability to transform over time. However, one of the critical challenges of 4D printing is the lack of advanced 4D printing systems that not only meet all the essential requirements of shape change but also possess smart, dynamic capabilities to spatiotemporally and instantly control the shape-transformation process. Here, we present a facile 4D printing platform which incorporates nanomaterials into the conventional stimuli-responsive polymer, allowing the 4D printed object to achieve a dynamic and remote controlled, on-time and position shape transformation. A proof-of-concept 4D printed brain model was created using near-infrared light (NIR) responsive nanocomposite to evaluate the capacity for controllable 4D transformation, and the feasibility of photothermal stimulation for modulating neural stem cell behaviors. This novel 4D printing strategy can not only be used to create dynamic 3D patterned biological structures that can spatiotemporally control their shapes or behaviors of transformation under a human benign stimulus (NIR), but can also provide a potential method for building complex self-morphing objects for widespread applications.

Recent Advances in Scaffold Design and Material for Vascularized Tissue-Engineered Bone Regeneration

Bone tissue is a highly vascularized tissue and concomitant development of the vascular system and mineralized matrix requires a synergistic interaction between osteogenesis and angioblasts. Several strategies have been applied to achieve vascularized tissue-engineered bone, including the addition of cytokines as well as pre-vascularization strategies and co-culture systems. However, the scaffold is another extremely important component to consider, and development of vascularized bone scaffolds remains one of the greatest challenges for engineering clinically relevant bone substitutes. Here, this review highlights the biomaterial selection, preparation of pre-vascularized scaffolds, composition modification of the scaffold, structural design, and the comprehensive use of the above synergistic modifications of scaffold materials for vascular scaffolds in bone tissue engineering. Moreover, a strategy is proposed for the design of future scaffold structures, in which promoting the regeneration of vascularized bone by regulating the microenvironment should be the main focus. This overview can help illuminate progress in this field and identify the most recently developed scaffolds that show the greatest potential for achieving clinically vascularized bone.

Advancing Frontiers in Bone Bioprinting

Three-dimensional (3D) bioprinting of cell-laden biomaterials is used to fabricate constructs that can mimic the structure of native tissues. The main techniques used for 3D bioprinting include microextrusion, inkjet, and laser-assisted bioprinting. Bioinks used for bone bioprinting include hydrogels loaded with bioactive ceramics, cells, and growth factors. In this review, a critical overview of the recent literature on various types of bioinks used for bone bioprinting is presented. Major challenges, such as the vascularity, clinically relevant size, and mechanical properties of 3D printed structures, that need to be addressed to successfully use the technology in clinical settings, are discussed. Emerging approaches to solve these problems are reviewed, and future strategies to design customized 3D printed structures are proposed.

Tumors and Their Microenvironment Dual-Targeting Chemotherapy with Local Immune Adjuvant Therapy for Effective Antitumor Immunity against Breast Cancer

Chemotherapy turns tumor cells into "tumor vaccines" by immunogenic cell death (ICD). However, it remains a challenge to exploit chemotherapy-induced "tumor vaccines" for solid cancer immunotherapy due to the inefficient effector T cells activation and tumor microenvironment immunosuppression. Here, a matrix metalloprotease 2 responsive liposome (PEG-FA-Lip) composed of cleavable PEG chains covering the folate (FA)-modified liposome is developed to deliver ICD inducer doxorubicin. In breast cancer-bearing mice, PEG-FA-Lip targets both 4T1 breast cancer cells and M2-tumor associated macrophages (M2-TAMs) via FA-receptor mediated endocytosis, resulting in abundant "tumor vaccines" and efficient elimination of M2-TAMs. The combination of local cytosine-phosphate-guanine (CpG) therapy facilitates PEG-FA-Lip induced "tumor vaccines" to effectively arouse systematic effector T cells immune response through promoting dendritic cell maturation and immunostimulatory cytokines secretion. The simultaneous elimination of M2-TAMs ensures the activated effector T cells exert antitumor immunity within tumor via decreasing immunosuppressive cytokines secretion and tumor infiltration of Treg cells. After receiving the combined treatment, 30.1% of breast cancer-bearing mice (initial tumor volume > 100 mm3) achieves the goal of tumor eradication. Remarkably, this combination therapy greatly inhibits lung metastasis and controls the growth of already metastasized breast cancers (initial tumor volume > 100 mm3).

Bioinks and bioprinting technologies to make heterogeneous and biomimetic tissue constructs

The native tissues are complex structures consisting of different cell types, extracellular matrix materials, and biomolecules. Traditional tissue engineering strategies have not been able to fully reproduce biomimetic and heterogeneous tissue constructs because of the lack of appropriate biomaterials and technologies. However, recently developed three-dimensional bioprinting techniques can be leveraged to produce biomimetic and complex tissue structures. To achieve this, multicomponent bioinks composed of multiple biomaterials (natural, synthetic, or hybrid natural-synthetic biomaterials), different types of cells, and soluble factors have been developed. In addition, advanced bioprinting technologies have enabled us to print multimaterial bioinks with spatial and microscale resolution in a rapid and continuous manner, aiming to reproduce the complex architecture of the native tissues. This review highlights important advances in heterogeneous bioinks and bioprinting technologies to fabricate biomimetic tissue constructs. Opportunities and challenges to further accelerate this research area are also described.

Current Challenges of Bioprinted Tissues Toward Clinical Translation

IMPACT STATEMENT

This review has a broad overview of the current challenges of bioprinted tissues towards clinical translations and future directions to overcome those challenges. The development of this field has a huge impact on the situation of an insufficient number of organ donors for life-saving organ transplantations.

Bio-Based Polymers for 3D Printing of Bioscaffolds

Three-dimensional (3D) printing technologies enable not only faster bioconstructs development but also on-demand and customized manufacturing, offering patients a personalized biomedical solution. This emerging technique has a great potential for fabricating bioscaffolds with complex architectures and geometries and specifically tailored for use in regenerative medicine. The next major innovation in this area will be the development of biocompatible and histiogenic 3D printing materials with bio-based printable polymers. This review will briefly discuss 3D printing techniques and their current limitations, with a focus on novel bio-based polymers as 3D printing feedstock for clinical medicine and tissue regeneration.

4D Biofabrication: Materials, Methods, and Applications

The mission of regenerative medicine is the development of methods to regrow, repair, or replace damaged or diseased cells, organs, or tissues. 3D bioprinting techniques are one of the most promising approaches for engineering the design of artificial tissues. Current 3D bioprinting technologies possess, however, several intrinsic limitations. 4D biofabrication, a recently developed technology with the embedded ability of shape transformation upon response to intrinsic and/or external stimuli, may solve challenges of 3D bioprinting as well as more accurately mimic the dynamics of the native tissues. This article covers recent advances in 4D biofabrication. It gives a detailed picture of used materials and technologies, provides critical comparisons of methods, discusses possibilities and limitations of different 4D biofabrication technologies, and gives examples of applications.

Preparation of Polymeric and Composite Scaffolds by 3D Bioprinting

Over the recent years, the advent of 3D bioprinting technology has marked a milestone in osteochondral tissue engineering (TE) research. Nowadays, the traditional used techniques for osteochondral regeneration remain to be inefficient since they cannot mimic the complexity of joint anatomy and tissue heterogeneity of articular cartilage. These limitations seem to be solved with the use of 3D bioprinting which can reproduce the anisotropic extracellular matrix (ECM) and heterogeneity of this tissue. In this chapter, we present the most commonly used 3D bioprinting approaches and then discuss the main criteria that biomaterials must meet to be used as suitable bioinks, in terms of mechanical and biological properties. Finally, we highlight some of the challenges that this technology must overcome related to osteochondral bioprinting before its clinical implementation.

3D Bioprinting Stem Cell Derived Tissues

Stem cells offer tremendous promise for regenerative medicine as they can become a variety of cell types. They also continuously proliferate, providing a renewable source of cells. Recently, it has been found that 3D printing constructs using stem cells, can generate models representing healthy or diseased tissues, as well as substitutes for diseased and damaged tissues. Here, we review the current state of the field of 3D printing stem cell derived tissues. First, we cover 3D printing technologies and discuss the different types of stem cells used for tissue engineering applications. We then detail the properties required for the bioinks used when printing viable tissues from stem cells. We give relevant examples of such bioprinted tissues, including adipose tissue, blood vessels, bone, cardiac tissue, cartilage, heart valves, liver, muscle, neural tissue, and pancreas. Finally, we provide future directions for improving the current technologies, along with areas of focus for future work to translate these exciting technologies into clinical applications.

3D bioprinting of functional tissue models for personalized drug screening and in vitro disease modeling

3D bioprinting is emerging as a promising technology for fabricating complex tissue constructs with tailored biological components and mechanical properties. Recent advances have enabled scientists to precisely position materials and cells to build functional tissue models for in vitro drug screening and disease modeling. This review presents state-of-the-art 3D bioprinting techniques and discusses the choice of cell source and biomaterials for building functional tissue models that can be used for personalized drug screening and disease modeling. In particular, we focus on 3D-bioprinted liver models, cardiac tissues, vascularized constructs, and cancer models for their promising applications in medical research, drug discovery, toxicology, and other pre-clinical studies.

3D bioprinting for cardiovascular regeneration and pharmacology

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Compared to traditional therapeutic strategies, three-dimensional (3D) bioprinting is one of the most advanced techniques for creating complicated cardiovascular implants with biomimetic features, which are capable of recapitulating both the native physiochemical and biomechanical characteristics of the cardiovascular system. The present review provides an overview of the cardiovascular system, as well as describes the principles of, and recent advances in, 3D bioprinting cardiovascular tissues and models. Moreover, this review will focus on the applications of 3D bioprinting technology in cardiovascular repair/regeneration and pharmacological modeling, further discussing current challenges and perspectives.

3D Bioprinting Technology: Scientific Aspects and Ethical Issues

The scientific development of 3D bioprinting is rapidly advancing. This innovative technology involves many ethical and regulatory issues, including theoretical, source, transplantation and enhancement, animal welfare, economic, safety and information arguments. 3D bioprinting technology requires an adequate bioethical debate in order to develop regulations in the interest both of public health and the development of research. This paper aims to initiate and promote ethical debate. The authors examine scientific aspects of 3D bioprinting technology and explore related ethical issues, with special regard to the protection of individual rights and transparency of research. In common with all new biotechnologies, 3D bioprinting technology involves both opportunities and risks. Consequently, several scientific and ethical issues need to be addressed. A bioethical debate should be carefully increased through a multidisciplinary approach among experts and also among the public.

3D-Bioprinted Osteoblast-Laden Nanocomposite Hydrogel Constructs with Induced Microenvironments Promote Cell Viability, Differentiation, and Osteogenesis both In Vitro and In Vivo

An osteoblast-laden nanocomposite hydrogel construct, based on polyethylene glycol diacrylate (PEGDA)/laponite XLG nanoclay ([Mg5.34Li0.66Si8O20(OH)4]Na0.66, clay)/hyaluronic acid sodium salt (HA) bio-inks, is developed by a two-channel 3D bioprinting method. The novel biodegradable bio-ink A, comprised of a poly(ethylene glycol) (PEG)-clay nanocomposite crosslinked hydrogel, is used to facilitate 3D-bioprinting and enables the efficient delivery of oxygen and nutrients to growing cells. HA with encapsulated primary rat osteoblasts (ROBs) is applied as bio-ink B with a view to improving cell viability, distribution uniformity, and deposition efficiency. The cell-laden PEG-clay constructs not only encapsulated osteoblasts with more than 95% viability in the short term but also exhibited excellent osteogenic ability in the long term, due to the release of bioactive ions (magnesium ions, Mg2+ and silicon ions, Si4+), which induces the suitable microenvironment to promote the differentiation of the loaded exogenous ROBs, both in vitro and in vivo. This 3D-bioprinting method holds much promise for bone tissue regeneration in terms of cell engraftment, survival, and ultimately long-term function.

4D printing of polymeric materials for tissue and organ regeneration

Four dimensional (4D) printing is an emerging technology with great capacity for fabricating complex, stimuli-responsive 3D structures, providing great potential for tissue and organ engineering applications. Although the 4D concept was first highlighted in 2013, extensive research has rapidly developed, along with more-in-depth understanding and assertions regarding the definition of 4D. In this review, we begin by establishing the criteria of 4D printing, followed by an extensive summary of state-of-the-art technological advances in the field. Both transformation-preprogrammed 4D printing and 4D printing of shape memory polymers are intensively surveyed. Afterwards we will explore and discuss the applications of 4D printing in tissue and organ regeneration, such as developing synthetic tissues and implantable scaffolds, as well as future perspectives and conclusions.

Netrin-1 Promotes Inflammation Resolution to Achieve Endothelialization of Small-Diameter Tissue Engineering Blood Vessels by Improving Endothelial Progenitor Cells Function In Situ

The transplant of small-diameter tissue engineering blood vessels (small-diameter TEBVs) (<6 mm) in vascular replacement therapy often fails because of early onset thrombosis and long-standing chronic inflammation. The specific inflammation state involved in small-diameter TEBVs transplants remains unclear, and whether promoting inflammation resolution would be useful for small-diameter TEBVs therapy need study. The neural protuberant orientation factor 1 (Netrin-1) is found present in endothelial cells of natural blood vessels and has anti-inflammatory effects. This work generates netrin-1-modified small-diameter TEBVs by using layer-by-layer self-assembly to resolve the inflammation. The results show that netrin-1 reprograms macrophages (MΦ) to assume an anti-inflammatory phenotype and promotes the infiltration and subsequent efflux of MΦ from inflamed sites over time, which improves the local microenvironment and the function of early homing endothelial progenitor cells (EPCs). Small-diameter TEBVs modified by netrin-1 achieve endothelialization after 30 d and retain patency at 14 months. These findings suggest that promoting the resolution of inflammation in time is necessary to induce endothelialization of small-diameter TEBVs and prevent early thrombosis and problems associated with chronic inflammation. Furthermore, this work finds that the MΦ-derived exosomes can target and regulate EPCs, which may serve as a useful treatment for other inflammatory diseases.

4D Biofabrication Using Shape-Morphing Hydrogels

Despite the tremendous potential of bioprinting techniques toward the fabrication of highly complex biological structures and the flourishing progress in 3D bioprinting, the most critical challenge of the current approaches is the printing of hollow tubular structures. In this work, an advanced 4D biofabrication approach, based on printing of shape-morphing biopolymer hydrogels, is developed for the fabrication of hollow self-folding tubes with unprecedented control over their diameters and architectures at high resolution. The versatility of the approach is demonstrated by employing two different biopolymers (alginate and hyaluronic acid) and mouse bone marrow stromal cells. Harnessing the printing and postprinting parameters allows attaining average internal tube diameters as low as 20 µm, which is not yet achievable by other existing bioprinting/biofabrication approaches and is comparable to the diameters of the smallest blood vessels. The proposed 4D biofabrication process does not pose any negative effect on the viability of the printed cells, and the self-folded hydrogel-based tubes support cell survival for at least 7 d without any decrease in cell viability. Consequently, the presented 4D biofabrication strategy allows the production of dynamically reconfigurable architectures with tunable functionality and responsiveness, governed by the selection of suitable materials and cells.

αvβ3 and α5β1 integrin-specific ligands: From tumor angiogenesis inhibitors to vascularization promoters in regenerative medicine?

Integrins are cell adhesion receptors predominantly important during normal and tumor angiogenesis. A sequence present on several extracellular matrix proteins composed of Arg-Gly-Asp (RGD) has attracted attention due to its role in cell adhesion mediated by integrins. The development of ligands that can bind to integrins involved in tumor angiogenesis and brake disease progression has resulted in new investigational drug entities reaching the clinical trial phase in humans. The use of integrin-specific ligands can be useful for the vascularization of regenerative medicine constructs, which remains a major limitation for translation into clinical practice. In order to enhance vascularization, immobilization of integrin-specific RGD peptidomimetics within constructs is a recommended approach, due to their high specificity and selectivity towards certain desired integrins. This review endeavours to address the potential of peptidomimetic-coated biomaterials as vascular network promoters for regenerative medicine purposes. Clinical studies involving molecules tracking active integrins in cancer angiogenesis and reasons for their failure are also addressed.

Multifunctional Gene Carriers with Enhanced Specific Penetration and Nucleus Accumulation to Promote Neovascularization of HUVECs in Vivo

Recently, gene therapy has attracted much attention, especially for the treatment of vascular disease. However, it is still challenging to develop the gene carriers with high biocompatibility as well as highly efficient gene delivery to overcome multiple barriers. Herein, a frequently used cell-penetrating peptide PKKKRKV (TAT) was selected as a functional sequence of the gene carrier with distinctive cell-penetrating ability. REDV peptide with selectively targeting function for endothelial cells (ECs) and nuclear localization signals (NLS) were integrated with this TAT peptide to obtain a highly efficient gene delivery system with ECs specificity and nucleus accumulation capacity. Besides, the glycine sequences with different repeat numbers were inserted into the above integrated peptide. These glycine sequences acted as a flexible spacer arm to exert the targeting, cell-penetrating, and nucleus accumulation functions of each functional peptide. Three tandem peptides REDV-G_m-TAT-G_m-NLS (m = 0, 1, and 4) complexed with pZNF580 plasmid to form gene complexes. The results of hemocompatibility and cytocompatibility indicated that these peptides and gene complexes were nontoxic and biocompatible. The internalization efficiency and mechanism of these gene complexes were investigated. The internalization efficiency was improved as the introduction of targeting REDV and glycine sequence, and the REDV-G₄-TAT-G₄-NLS/pZNF580 (TP-G4/pZNF580) complexes showed the highest cellular uptake among the gene complexes. The TP-G4/pZNF580 complexes also presented significantly higher internalization efficiency (∼1.36 times) in human umbilical vein endothelial cells (HUVECs) than human umbilical artery smooth muscle cells. TP-G4/pZNF580 complexes substantially promoted the expression of pZNF580 by confocal live cell imaging, gene delivery efficiency, and HUVECs migration assay. The in vitro and in vivo revascularization ability of transfected HUVECs was further enhanced obviously. In conclusion, these multifunctional REDV-G_m-TAT-G_m-NLS peptides offer a promising and efficacious delivery option for neovascularization to treat vascular diseases.

Integrating three-dimensional printing and nanotechnology for musculoskeletal regeneration

The field of tissue engineering is advancing steadily, partly due to advancements in rapid prototyping technology. Even with increasing focus, successful complex tissue regeneration of vascularized bone, cartilage and the osteochondral interface remains largely illusive. This review examines current three-dimensional printing techniques and their application towards bone, cartilage and osteochondral regeneration. The importance of, and benefit to, nanomaterial integration is also highlighted with recent published examples. Early-stage successes and challenges of recent studies are discussed, with an outlook to future research in the related areas.

Controlled dual delivery of low doses of BMP-2 and VEGF in a silk fibroin-nanohydroxyapatite scaffold for vascularized bone regeneration

The controlled co-release of osteoinductive and angiogenic factors is an efficient approach to promote vascularized bone regeneration, and a suitable controlled release system can largely reduce the usage of these factors to avoid cost and safety problems. In this study, a cell-free vascularized bone tissue engineering system based on a silk fibroin (SF)/nanohydroxyapatite (nHAp) scaffold was developed, in which very low doses of osteoinductive and angiogenic factors, bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), were embedded and released in a controlled manner to facilitate bone formation and vascularization, respectively. BMP-2 and VEGF were adsorbed onto SF microspheres (diameter of 1.5 ± 0.3 μm) that were prepared using a co-flow capillary device, and these microspheres were subsequently incorporated within the SF/nHAp scaffolds to provide controlled release. BMP-2 and VEGF were incorporated into SF microspheres via chemical covalent bonding and physical adsorption, respectively, leading to their controlled and sustained release from the SF/nHAp scaffolds. The rapid initial release of VEGF mimicked its expression at the early bone healing stage and promoted angiogenesis, and the relatively slow and sustained release of BMP-2 facilitated osteogenic differentiation both in vitro and in vivo, and the bone completely bridged the rat calvarial defects after 12 weeks of implantation. Overall, our findings suggest that the controlled dual release of very low doses of BMP-2 (300 ng per scaffold) and VEGF (20 ng per scaffold) from SF/nHAp scaffolds results in a synergistic effect on vascularized bone regeneration; this controlled release system can largely reduce the usage of BMP-2 as compared to other systems.

Microfluidic on-chip biomimicry for 3D cell culture: a fit-for-purpose investigation from the end user standpoint

A plethora of 3D and microfluidics-based culture models have been demonstrated in the recent years with the ultimate aim to facilitate predictive in vitro models for pharmaceutical development. This article summarizes to date the progress in the microfluidics-based tissue culture models, including organ-on-a-chip and vasculature-on-a-chip. Specific focus is placed on addressing the question of what kinds of 3D culture and system complexities are deemed desirable by the biological and biomedical community. This question is addressed through analysis of a research survey to evaluate the potential use of microfluidic cell culture models among the end users. Our results showed a willingness to adopt 3D culture technology among biomedical researchers, although a significant gap still exists between the desired systems and existing 3D culture options. With these results, key challenges and future directions are highlighted.

Enhanced bone tissue regeneration using a 3D printed microstructure incorporated with a hybrid nano hydrogel

Three-dimensional (3D) functional constructs with biomimetic mechanical and chemical properties are ideal for various regenerative medicine applications. These properties of 3D fabricated constructs mainly depend on the intrinsic characteristics of the materials and fabrication method. In this respect, the current use of hydrogels for musculoskeletal tissue repair is not ideal due to the lack of suitable mechanical properties, as well as the high biomimetic requirement for success. To overcome this limitation, we developed a novel functionalized hydrogel with bioactive gold nanoparticles (GNPs), reinforcing a 3D printed microstructure via fused deposition modeling (FDM) for bone tissue regeneration. We used biodegradable thermoplastic polylactic acid (PLA) as the 3D printed microstructure in combination with photo-curable gelatin hydrogels as the encapsulation matrix for the incorporation of cyclic RGD conjugated GNPs (RGNP), and investigated their mechanical properties. In addition, human adipose-derived stem cells (ADSCs) were encapsulated within the gelatin hydrogel and examined for viability, morphology, and osteogenic differentiation in vitro. The results showed that the stiffness of the composite hydrogel on reinforcing a 3D printed microstructure can be readily modulated to simulate the stiffness of the human mandibular condyle. ADSCs encapsulated in the composite structures remained viable within the hydrogel and showed excellent spreading on the 3D printed PLA microstructure. More importantly, osteogenic differentiation with incorporated RGNPs promoted significantly higher gene expression of osteogenic specific factors. Therefore, reinforced composite hydrogels are suitable for stem cell differentiation control and bone tissue regeneration.

3D Bioprinting for Organ Regeneration

Regenerative medicine holds the promise of engineering functional tissues or organs to heal or replace abnormal and necrotic tissues/organs, offering hope for filling the gap between organ shortage and transplantation needs. Three-dimensional (3D) bioprinting is evolving into an unparalleled biomanufacturing technology due to its high-integration potential for patient-specific designs, precise and rapid manufacturing capabilities with high resolution, and unprecedented versatility. It enables precise control over multiple compositions, spatial distributions, and architectural accuracy/complexity, therefore achieving effective recapitulation of microstructure, architecture, mechanical properties, and biological functions of target tissues and organs. Here we provide an overview of recent advances in 3D bioprinting technology, as well as design concepts of bioinks suitable for the bioprinting process. We focus on the applications of this technology for engineering living organs, focusing more specifically on vasculature, neural networks, the heart and liver. We conclude with current challenges and the technical perspective for further development of 3D organ bioprinting.

Hierarchical Fabrication of Engineered Vascularized Bone Biphasic Constructs via Dual 3D Bioprinting: Integrating Regional Bioactive Factors into Architectural Design

A biphasic artificial vascularized bone construct with regional bioactive factors is presented using dual 3D bioprinting platform technique, thereby forming a large functional bone grafts with organized vascular networks. Biocompatible mussel-inspired chemistry and "thiol-ene" click reaction are used to regionally immobilize bioactive factors during construct fabrication for modulating or improving cellular events.