Intelligent Vascularized 3D/4D/5D/6D-Printed Tissue Scaffolds

Three-step crosslinking dependent self-bending transformation of a nano-spherical mineralized collagen laden 4D printed sodium alginate scaffold for bone regeneration

Although 3D printed scaffolds are widely used in irregularly shaped bone defects, additional steps often need to be introduced when fabricating structures with curvature. In contrast, 4D printing has a unique advantage in the fabrication of scaffolding with a curved structure. Bone defects such as skull is generally curved, so a self-bending scaffold would be more appropriate for the cranial defect site. This paper presents a novel self-bending SAGMA hydrogel was loaded with nano-spherical mineralized collagen, then fabricated by a 4D printing method, which achieves adjustable self-bending through three-step crosslinking. When subjected to UV light irradiation, variations in gradient of photo-crosslinking are induced within the scaffold. This gradient of photo-crosslinking serves as the foundation for the scaffold's self-bending. The scaffold exhibited self-bending after crosslinking with calcium ions and chitosan, respectively, with curvature ranging from 0.05 mm-1 to 0.446 mm-1. In vivo experiments demonstrated the efficacy of the scaffold in enhancing the repair of cranial bone defects and promoting new bone formation in rats, as evidenced by microcomputed tomography and histochemical analysis. Therefore, this self-bending scaffold provides a potentially effective method for the clinical treatment of skull defects with curvature.

An insightful overview on osteogenic potential of nano hydroxyapatite for bone regeneration

The orthopaedic surgeries were greatly aided by bone grafting with the use of nanomaterials which provide new strategies for bone regeneration, despite the significant drawbacks of traditional treatments. Hydroxyapatite is one of the bioactive ceramics that has gained substantial research attention due to its biocompatibility, bioactivity and osteointegration ability for the manufacturing of nano bone grafts. The organized complex and porous structures of the human bone tissue is a nanocomposite which consists of both organic and inorganic matrix including hydroxyapatite naturally. Conventional hydroxyapatite was known to provide good adhesion and proliferation of host cells but very low mechanical strength. Hence biomaterial made of hydroxyapatite with various polymers and cross linking agents were used to enhance the mechanical strength of the material. Out of 293 articles obtained from the literature search, only 90 articles met the inclusion criteria about bone regeneration using nano hydroxyapatite materials. The present review addresses the potential capping agents with plant extracts for the synthesis of hydroxyapatite nanomaterials with multi-functional applications include drug delivery for targeting the desired therapeutic effect for bone regeneration with osteoprotective ability and tumour therapy.

3D printing in musculoskeletal interface engineering: Current progress and future directions

The musculoskeletal system relies on critical tissue interfaces for its function; however, these interfaces are often compromised by injuries and diseases. Restoration of these interfaces is complex by nature which renders traditional treatments inadequate. An emerging solution is three-dimensional printing, which allows for precise fabrication of biomimetic scaffolds to enhance tissue regeneration. This review summarizes the utility of 3D printing in creating scaffolds for musculoskeletal interfaces, mainly focusing on advanced techniques such as multi-material printing, bioprinting, and 4D printing. We emphasize the significance of mimicking natural tissue gradients and the selection of appropriate biomaterials to ensure scaffold success. The review outlines state-of-the-art 3D printing technologies, varying from extrusion, inkjet and laser-assisted bioprinting, which are crucial for producing scaffolds with tailored mechanical and biological properties. Applications in cartilage-bone, intervertebral disc, tendon/ligament-bone, and muscle-tendon junction engineering are discussed, highlighting the potential for improved integration and functionality. Furthermore, we address challenges in material development, printing resolution, and the in vivo performance of scaffolds, as well as the prospects for clinical translation. The review concludes by underscoring the transformative potential of 3D printing to advance orthopedic medicine, offering a roadmap for future research at the intersection of biomaterials, drug delivery, and tissue engineering.

Versatile hydrogels prepared by microfluidics technology for bone tissue engineering applications

Bone defects are a prevalent issue resulting from various factors, such as trauma, degenerative diseases, congenital disabilities, and the surgical removal of tumors. Current methods for bone regeneration have limitations. In this context, the fusion of tissue engineering and microfluidics has emerged as a promising strategy in the field of bone regeneration. This study describes the classification of microfluidic devices based on the nature of flow and channel type, as well as the materials and techniques required. An overview of microfluidic methods used to prepare hydrogels and the advantages of using these hydrogels in bone tissue engineering (BTE) combining several basic elements of BTE to highlight its advantages is provided. Furthermore, this work emphasizes the benefits of using hydrogels prepared via microfluidics over conventional hydrogels in BTE because of their controlled release of cargo, they can be used for in situ injection, simplify the steps of single-cell encapsulation and have the advantages of high-throughput and precise preparation. Additionally, organ-on-a-chip models fabricated via microfluidics offer a platform for studying cell and tissue behaviors in an authentic and dynamic environment. Moreover, microfluidic devices can be utilized for noninvasive diagnosis and therapy. Finally, this paper summarizes the preclinical and clinical applications of hydrogels prepared via microfluidics for bone regeneration by focusing on their current developmental status, limitations associated with their application, and future challenges, which underscore their potential impacts on advancing regenerative medicine practices.

Periosteum-bone inspired hierarchical scaffold with endogenous piezoelectricity for neuro-vascularized bone regeneration

The development of scaffolds for repairing critical-sized bone defects heavily relies on establishing a neuro-vascularized network for proper penetration of nerves and blood vessels. Despite significant advancements in using artificial bone-like scaffolds infused with various agents, challenges remain. Natural bone tissue consists of a porous bone matrix surrounded by a neuro-vascularized periosteum, with unique piezoelectric properties essential for bone growth. Drawing inspiration from this assembly, we developed a periosteum-bone-mimicking bilayer scaffold with piezoelectric properties for regeneration of critical-sized bone defects. The periosteum-like layer of this scaffold features a double network hydrogel composed of chelated alginate, gelatin methacrylate, and sintered whitlockite nanoparticles, emulating the viscoelastic and piezoelectric properties of the natural periosteum. The bone-like layer is composed of a porous structure of chitosan and bioactive hydroxyapatite created through a biomineralization process. Unlike conventional bone-like scaffolds, this bioinspired bilayer scaffold significantly enhances osteogenesis, angiogenesis, and neurogenesis combined with low-intensity pulsed ultrasound-assisted piezoelectric stimulation. Such a scheme enhances neuro-vascularized bone regeneration in vivo. The results suggest that the bilayer scaffold could serve as an effective self-powered electrical stimulator to expedite bone regeneration under dynamic physical stimulation.

4D printing: innovative solutions and technological advances in orthopedic repair and reconstruction, personalized treatment and drug delivery

With precise control of smart materials deformation in time dimension, doctors can customize orthopedic implants. This review focuses on the advances of 4D printing technology in orthopedics, including its applications in bone repair and reconstruction, personalized treatment, and drug delivery. 4D printing enables the creation of bionic scaffolds and fixation devices for bone repair, customized implants matching patients' conditions for personalized treatment, and specific carriers for accurate drug release and delivery, which together contribute to accelerating bone healing, providing exclusive treatments, enhancing therapeutic effects and reducing side effects, thus helping improve orthopedic medicine. It offers comprehensive reference materials for relevant medical personnel.

Black Phosphorus Tagged Responsive Strontium Hydrogel Particles for Bone Defect Repair

Hydrogel-derived implants have proven value in bone tissue regeneration, and current efforts have concentrated on devising strategies for producing functional implants with desired structures and functions to improve therapeutic outcomes. Herein, a novel black phosphorus (BP) tagged responsive strontium (Sr) hydrogel particles are presented for bone defect repair. By applying microfluidic technology, Sr and carboxymethyl chitosan, and BP are integrated into poly(N-isopropyl acrylamide) (pNIPAM) hydrogel matrix to generate such microparticles called pNBCSMs. Upon exposure to near-infrared irradiation, the pNBCSMs experience volume shrinkage and provoke the extrusion of the incorporated Sr, ascribed to the photothermal conversion ability of BP and the thermosensitivity of pNIPAM. In vitro and in vivo experimental results reveal that pNBCSMs subjected to near-infrared light display superior anti-inflammatory, anti-apoptotic, bacterial inhibitory, as well as osteogenesis-promoting effects, thereby effectively improving defective cranial bone repair. These features suggest that the proposed pNBCSMs can be promising candidates for bone repair.

Implantable Multifunctional Micro-Oxygen Reservoir System for Promoting Vascular-Osteogenesis via Remodeling Regenerative Microenvironment

Hypoxia and reactive oxygen species (ROS) overaccumulation cause persistent oxidative stress and impair intrinsic regenerative potential upon tissue injury. For local tissue injury with hypoxia, such as bone fracture and defects, a localized-sufficient oxygen supply is highly desirable but remains challenging. Therefore, to explore a strategy and its intrinsic mechanism for supplying oxygen locally and remodeling the regenerative microenvironment, an innovative oxygenating hydrogel microsphere system with sustained oxygenation and antioxidant properties is introduced by loading CaO2@SiO2@PDA (CSP) nanoparticles. Specifically, the CSP nanoparticles exhibited broad-spectrum free radicals scavenging ability, along with prolonged controlled-release of oxygen once integrated into the gelatin methacrylate anhydride (GelMA) microspheres (CSP-GM). The CSP-GM with extra cellular matrix (ECM)-mimicking structures reconstructed living niches, promoting the adhesion and proliferation of bone marrow stromal cells (BMSCs). As a multifaceted microenvironment regulator, CSP-GM remodeled the regenerative microenvironment by synergistically producing oxygen and scavenging ROS, recovering mitochondrial homeostasis and antioxidant defenses of BMSCs, promoting angiogenesis and osteogenesis under hypoxia conditions via precisely modulating the Nrf2/HO-1 signaling pathway. The multiple pro-regenerative effects of the implantable functionalized micro-oxygen reservoir on bone repair are further corroborated by the enhanced vascularized bone formation in rat femoral defects, presenting a comprehensive and promising strategy for tissue repair.

Photoactivated Hydrogel Therapeutic System with MXene-Based Nanoarchitectonics Potentiates Endogenous Bone Repair Through Reshaping the Osteo-Vascularization Network

The repair and reconstruction of large-scale bone defects face enormous challenges because of the failure to reconstruct the osteo-vascularization network. Herein, a near-infrared (NIR) light-responsive hydrogel system is reported to achieve programmed tissue repair and regeneration through the synergetic effects of on-demand drug delivery and mild heat stimulation. The spatiotemporal hydrogel system (HG/MPa) composed of polydopamine-coated Ti3C2Tx MXene (MP) nanosheets decorated with acidic fibroblast growth factor (aFGF, a potent angiogenic drug) and hydroxypropyl chitosan/gelatin (HG) hydrogel is developed to orchestrate the reconstruction of the osteo-vascularization network and boost bone regeneration. Upon exposure to NIR light irradiation, the engineered HG/MPa hydrogel can achieve the initial complete release of aFGF to induce rapid angiogenesis and provide sufficient blood supply, maximizing its biofunction in the defect area. This integrated hydrogel system demonstrated good therapeutic efficacy in promoting cell adhesion, proliferation, migration, angiogenesis, and osteogenic differentiation through periodic NIR irradiation. In vivo, animal experiments further revealed that the spatiotemporalized hydrogel platform synergized with mild photothermal treatment significantly accelerated critical-sized bone defect healing by increasing the osteo-vascularization network density, recruiting endogenous stem cells, and facilitating the production of osteogenesis/angiogenesis-related factors. Overall, smart-responsive hydrogel could enhance the reconstruction of the osteo-vascularization network in bone regeneration.

Commercially available bioinks and state-of-the-art lab-made formulations for bone tissue engineering: A comprehensive review

Bioprinting and bioinks are two of the game changers in bone tissue engineering. This review presents different bioprinting technologies including extrusion-based, inkjet-based, laser-assisted, light-based, and hybrid technologies with their own strengths and weaknesses. This review will aid researchers in the selection and assessment of the bioink; the discussion ranges from commercially available bioinks to custom lab-made formulations mainly based on natural polymers, such as agarose, alginate, gelatin, collagen, and chitosan, designed for bone tissue engineering. The review is centered on technological advancements and increasing clinical demand within the rapidly growing bioprinting market. From this point of view, 4D, 5D, and 6D printing technologies promise a future where unprecedented levels of innovation will be involved in fabrication processes leading to more dynamic multifunctionalities of bioprinted constructs. Further advances in bioprinting technology, such as hybrid bioprinting methods are covered, with the promise to meet personalized medicine goals while advancing patient outcomes for bone tissues engineering applications.

Unleashing the Potential of Electroactive Hybrid Biomaterials and Self-Powered Systems for Bone Therapeutics

The incidence of large bone defects caused by traumatic injury is increasing worldwide, and the tissue regeneration process requires a long recovery time due to limited self-healing capability. Endogenous bioelectrical phenomena have been well recognized as critical biophysical factors in bone remodeling and regeneration. Inspired by bioelectricity, electrical stimulation has been widely considered an external intervention to induce the osteogenic lineage of cells and enhance the synthesis of the extracellular matrix, thereby accelerating bone regeneration. With ongoing advances in biomaterials and energy-harvesting techniques, electroactive biomaterials and self-powered systems have been considered biomimetic approaches to ensure functional recovery by recapitulating the natural electrophysiological microenvironment of healthy bone tissue. In this review, we first introduce the role of bioelectricity and the endogenous electric field in bone tissue and summarize different techniques to electrically stimulate cells and tissue. Next, we highlight the latest progress in exploring electroactive hybrid biomaterials as well as self-powered systems such as triboelectric and piezoelectric-based nanogenerators and photovoltaic cell-based devices and their implementation in bone tissue engineering. Finally, we emphasize the significance of simulating the target tissue's electrophysiological microenvironment and propose the opportunities and challenges faced by electroactive hybrid biomaterials and self-powered bioelectronics for bone repair strategies.

Microorganism microneedle micro-engine depth drug delivery

As a transdermal drug delivery method, microneedles offer minimal invasiveness, painlessness, and precise in-situ treatment. However, current microneedles rely on passive diffusion, leading to uncontrollable drug penetration. To overcome this, we developed a pneumatic microneedle patch that uses live Enterobacter aerogenes as microengines to actively control drug delivery. These microbes generate gas, driving drugs into deeper tissues, with adjustable glucose concentration allowing precise control over the process. Our results showed that this microorganism-powered system increases drug delivery depth by over 200%, reaching up to 1000 μm below the skin. In a psoriasis animal model, the technology effectively delivered calcitriol into subcutaneous tissues, offering rapid symptom relief. This innovation addresses the limitations of conventional microneedles, enhancing drug efficiency, transdermal permeability, and introducing a creative paradigm for on-demand controlled drug delivery.

Injectable Photothermal PDA/Chitosan/β-Glycerophosphate Thermosensitive Hydrogels for Antibacterial and Wound Healing Promotion

Controlling infections while reducing the use of antibiotics is what doctors as well as researchers are looking for. As innovative smart materials, photothermal materials can achieve localized heating under light excitation for broad-spectrum bacterial inhibition. A polydopamine/chitosan/β-glycerophosphate temperature-sensitive hydrogel with excellent antibacterial ability is synthesized here. Initially, the hydrogel has good biocompatibility. In vitro experiments reveal its noncytotoxic property when cocultured with gingival fibroblasts and nonhemolytic capability. Concurrently, the in vivo biocompatibility is confirmed through liver and kidney blood markers and staining of key organs. Crucially, the hydrogel has excellent photothermal conversion performance, which can realize the photothermal conversion of hydrogel up to 3 mm thickness. When excited by near-infrared light, localized heating is attainable, resulting in clear inhibition impacts on both Staphylococcus aureus and Escherichia coli, with the inhibition rates of 91.22% and 96.69%, respectively. During studies on mice's infected wounds, it is observed that the hydrogel can decrease S. aureus' presence in the affected area when exposed to near-infrared light, and also lessen initial inflammation and apoptosis, hastening tissue healing. These findings provide valuable insights into the design of antibiotic-free novel biomaterials with good potential for clinical applications.

3D Printing of Tough Hydrogel Scaffolds with Functional Surface Structures for Tissue Regeneration

Hydrogel scaffolds have numerous potential applications in the tissue engineering field. However, tough hydrogel scaffolds implanted in vivo are seldom reported because it is difficult to balance biocompatibility and high mechanical properties. Inspired by Chinese ramen, we propose a universal fabricating method (printing-P, training-T, cross-linking-C, PTC & PCT) for tough hydrogel scaffolds to fill this gap. First, 3D printing fabricates a hydrogel scaffold with desired structures (P). Then, the scaffold could have extraordinarily high mechanical properties and functional surface structure by cycle mechanical training with salting-out assistance (T). Finally, the training results are fixed by photo-cross-linking processing (C). The tough gelatin hydrogel scaffolds exhibit excellent tensile strength of 6.66 MPa (622-fold untreated) and have excellent biocompatibility. Furthermore, this scaffold possesses functional surface structures from nanometer to micron to millimeter, which can efficiently induce directional cell growth. Interestingly, this strategy can produce bionic human tissue with mechanical properties of 10 kPa-10 MPa by changing the type of salt, and many hydrogels, such as gelatin and silk, could be improved with PTC or PCT strategies. Animal experiments show that this scaffold can effectively promote the new generation of muscle fibers, blood vessels, and nerves within 4 weeks, prompting the rapid regeneration of large-volume muscle loss injuries.

From the microspheres to scaffolds: advances in polymer microsphere scaffolds for bone regeneration applications

The treatment and repair of bone tissue damage and loss due to infection, tumours, and trauma are major challenges in clinical practice. Artificial bone scaffolds offer a safer, simpler, and more feasible alternative to bone transplantation, serving to fill bone defects and promote bone tissue regeneration. Ideally, these scaffolds should possess osteoconductive, osteoinductive, and osseointegrative properties. However, the current first-generation implants, represented by titanium alloys, have shown poor bone-implant integration performance and cannot meet the requirements for bone tissue repair. This has led to increased research on second and third generation artificial bone scaffolds, which focus on loading bioactive molecules and cells. Polymer microspheres, known for their high specific surface areas at the micro- and nanoscale, exhibit excellent cell and drug delivery behaviours. Additionally, with their unique rigid structure, microsphere scaffolds can be constructed using methods such as thermal sintering, injection, and microsphere encapsulation. These scaffolds not only ensure the excellent cell drug loading performance of microspheres but also exhibit spatial modulation behaviour, aiding in bone repair within a three-dimensional network structure. This article provides a summary and discussion of the use of polymer microsphere scaffolds for bone repair, focusing on the mechanisms of bone tissue repair and the current status of clinical bone grafts, aimed at advancing research in bone repair.

A Biomimetic Optical Cardiac Fibrosis-on-a-Chip for High-Throughput Anti-Fibrotic Drug Screening

Cardiac fibrosis has emerged as the primary cause of morbidity, disability, and even mortality in numerous nations. In light of the advancements in precision medicine strategies, substantial attention has been directed toward the development of a practical and precise drug screening platform customized for individual patients. In this study, we introduce a biomimetic cardiac fibrosis-on-a-chip incorporating structural color hydrogels (SCHs) to enable optical high-throughput drug screening. By cocultivating a substantial proportion of cardiac fibroblasts (CFBs) with cardiomyocytes on the SCH, this biomimetic fibrotic microtissue successfully replicates the structural components and biomechanical properties associated with cardiac fibrosis. More importantly, the structural color shift observed in the SCH can be indicative of cardiac contraction and relaxation, making it a valuable tool for evaluating fibrosis progression. By incorporating such fibrotic microtissue into a microfluidic gradient chip, we develop a biomimetic optical cardiac fibrosis-on-a-chip platform that accurately and efficiently screens potential anti-fibrotic drugs. These characteristics suggest that this microphysiological platform possesses the capability to establish a preclinical framework for screening cardiac drugs, and may even contribute to the advancement of precision medicine.

Assessment of artificial bone materials with different structural pore sizes obtained from 3D printed polycaprolactone/β-tricalcium phosphate (3D PCL/β-TCP)

Artificial bone is the alternative candidate for the bone defect treatment under the circumstance that there exits enormous challenge to remedy the bone defect caused by attributes like trauma and tumors. However, the impact of pore size discrepancy for regulating new bone generation is still ambiguous. Using direct 3D printing technology, customized 3D polycaprolactone/β-tricalcium phosphate (PCL/β-TCP) artificial bones with different structural pore sizes (1.8, 2.0, 2.3, 2.5, and 2.8 mm) were successfully prepared, abbreviated as the 3D PCL/β-TCP. 3D PCL/β-TCP exhibited a 3D porous structure morphology similar to natural bone and possessed outstanding mechanical properties. Computational fluid dynamics analysis indicated that as the structural pore size increased from 1.8 to 2.8 mm, both velocity difference (from 4.64 × 10-5to 7.23 × 10-6m s-1) and depressurization (from 7.17 × 10-2to 2.25 × 10-2Pa) decreased as the medium passed through.In vitrobiomimetic mineralization experiments confirmed that 3D PCL/β-TCP artificial bones could induce calcium-phosphate complex generation within 4 weeks. Moreover, CCK-8 and Calcein AM live cell staining experiments demonstrated that 3D PCL/β-TCP artificial bones with different structural pore sizes exhibited advantageous cell compatibility, promoting MC3T3-E1 cell proliferation and adhesion.In vivoexperiments in rats further indicated that 3D PCL/β-TCP artificial bones with different structural pore sizes promoted new bone formation, with the 2.5 mm group showing the most significant effect. In conclusion, 3D PCL/β-TCP artificial bone with different structural pore sizes could promote new bone formation and 2.5 mm group was the recommended for the bone defect repair.

Injectable dual drug-loaded thermosensitive liposome-hydrogel composite scaffold for vascularised and innervated bone regeneration

Adequate blood supply and thorough innervation are essential to the survival of tissue-engineered bones. Though great progress has been created in the application of bone tissue engineering technology to bone defect repair, many challenges remain, such as insufficient vascularisation and deficient innervation in newly regenerated bone. In the present study, we addressed these challenges by manipulating the bone regeneration microenvironment in terms of vascularisation and innervation. We used a novel injectable thermosensitive liposome-hydrogel composite scaffold as a sustained-release carrier for basic fibroblast growth factor (bFGF, which promotes angiogenesis and neurogenic differentiation) and dexamethasone (Dex, which promotes osteogenic differentiation). In vitro biological assessment demonstrated that the composite scaffold had sufficient cell compatibility; it enhanced the capacity for angiogenesis in human umbilical vein endothelial cells, and the capacity for neurogenic/osteogenic differentiation in human bone marrow mesenchymal stem cells. Moreover, the introduction of bFGF/Dex liposome-hydrogel composite scaffold to bone defect sites significantly improved vascularisation and innervated bone regeneration properties in a rabbit cranial defect model. Based on our findings, the regeneration of sufficiently vascularised and innervated bone tissue through a sustained-release scaffold with excellent injectability and body temperature sensitivity represents a promising tactic towards bone defect repair.

Jellyfish-Inspired Artificial Spider Silk for Luminous Surgical Sutures

The development of functional surgical sutures with excellent mechanical properties, good fluorescence, and high cytocompatibility is highly required in the field of medical surgeries. Achieving fibers that simultaneously exhibit high mechanical robustness, good spinnability, and durable fluorescence emission has remained challenging up to now. Taking inspiration from the spinning process of spider silk and the luminescence mechanism of jellyfish, this work reports a luminous artificial spider silk prepared with the aim of balancing the fiber spinnability and mechanical robustness. This is realized by employing highly hydrated segments with aggregation-induced luminescence for enhancing the fiber spinnability and polyhydroxyl segments for increasing the fiber mechanical robustness. Twist insertion during fiber spinning improves the fiber strength, toughness, and fluorescence emission. Furthermore, coating the fiber with an additional polymer layer results in a "sheath-core" architecture with improved mechanical properties and capacity to withstand water. This work provides a new design strategy for performing luminescent and robust surgical sutures.

The Role of Fibroblasts in Skin Homeostasis and Repair

Fibroblasts are typical mesenchymal cells widely distributed throughout the human body where they (1) synthesise and maintain the extracellular matrix, ensuring the structural role of soft connective tissues; (2) secrete cytokines and growth factors; (3) communicate with each other and with other cell types, acting as signalling source for stem cell niches; and (4) are involved in tissue remodelling, wound healing, fibrosis, and cancer. This review focuses on the developmental heterogeneity of dermal fibroblasts, on their ability to sense changes in biomechanical properties of the surrounding extracellular matrix, and on their role in aging, in skin repair, in pathologic conditions and in tumour development. Moreover, we describe the use of fibroblasts in different models (e.g., in vivo animal models and in vitro systems from 2D to 6D cultures) for tissue bioengineering and the informative potential of high-throughput assays for the study of fibroblasts under different disease contexts for personalized healthcare and regenerative medicine applications.

4D bioprinting of programmed dynamic tissues

Setting time as the fourth dimension, 4D printing allows us to construct dynamic structures that can change their shape, property, or functionality over time under stimuli, leading to a wave of innovations in various fields. Recently, 4D printing of smart biomaterials, biological components, and living cells into dynamic living 3D constructs with 4D effects has led to an exciting field of 4D bioprinting. 4D bioprinting has gained increasing attention and is being applied to create programmed and dynamic cell-laden constructs such as bone, cartilage, and vasculature. This review presents an overview on 4D bioprinting for engineering dynamic tissues and organs, followed by a discussion on the approaches, bioprinting technologies, smart biomaterials and smart design, bioink requirements, and applications. While much progress has been achieved, 4D bioprinting as a complex process is facing challenges that need to be addressed by transdisciplinary strategies to unleash the full potential of this advanced biofabrication technology. Finally, we present future perspectives on the rapidly evolving field of 4D bioprinting, in view of its potential, increasingly important roles in the development of advanced dynamic tissues for basic research, pharmaceutics, and regenerative medicine.

A scientometric and visualization analysis of 3D printing scaffolds for vascularized bone tissue engineering over the last decade

The introduction of three-dimensional (3D) printing scaffolds has emerged as an effective approach to achieving satisfactory revascularization for bone tissue engineering (BTE). However, there is a notable absence of analytical and descriptive investigations concerning the trajectory, essential research directions, current research scenario, pivotal investigative focuses, and forthcoming perspectives. Hence, the objective of this research is to offer a thorough overview of the advancements achieved in 3D printing structures for vascularized BTE within the last 10 years. Information extracted from the Web of Science repository spans from January 1, 2014, to April 1, 2024. Utilizing advanced analytical instruments, we conducted comprehensive scientometric and visual analyses. The findings underscore the predominant influence of China, representing 59.62 % of the overall publications and playing a pivotal role in shaping research within this field. Notable productivity was evident at various institutions, including Shanghai Jiao Tong University, Chinese Academy of Sciences, and Sichuan University. Wang Jinwu and Wu Chengtie stand out as the most prolific contributors in this domain. The highest number of publications in this area was contributed by the journal Advanced Healthcare Materials. In this study, osteogenesis imperfecta, osteosarcoma, fractures, osteonecrosis, and cartilage diseases were identified as the most significant disorders investigated in this research area. By providing a comprehensive scientometric assessment, this study benefits both experienced researchers and newcomers alike, offering prompt access to essential information and fostering the extraction of innovative concepts within this specific field.

Application of 3D, 4D, 5D, and 6D bioprinting in cancer research: what does the future look like?

The application of three- and four-dimensional (3D/4D) printing in cancer research represents a significant advancement in understanding and addressing the complexities of cancer biology. 3D/4D materials provide more physiologically relevant environments compared to traditional two-dimensional models, allowing for a more accurate representation of the tumor microenvironment that enables researchers to study tumor progression, drug responses, and interactions with surrounding tissues under conditions similar to in vivo conditions. The dynamic nature of 4D materials introduces the element of time, allowing for the observation of temporal changes in cancer behavior and response to therapeutic interventions. The use of 3D/4D printing in cancer research holds great promise for advancing our understanding of the disease and improving the translation of preclinical findings to clinical applications. Accordingly, this review aims to briefly discuss 3D and 4D printing and their advantages and limitations in the field of cancer. Moreover, new techniques such as 5D/6D printing and artificial intelligence (AI) are also introduced as methods that could be used to overcome the limitations of 3D/4D printing and opened promising ways for the fast and precise diagnosis and treatment of cancer.

Degradable biomedical elastomers: paving the future of tissue repair and regenerative medicine

Degradable biomedical elastomers (DBE), characterized by controlled biodegradability, excellent biocompatibility, tailored elasticity, and favorable network design and processability, have become indispensable in tissue repair. This review critically examines the recent advances of biodegradable elastomers for tissue repair, focusing mainly on degradation mechanisms and evaluation, synthesis and crosslinking methods, microstructure design, processing techniques, and tissue repair applications. The review explores the material composition and cross-linking methods of elastomers used in tissue repair, addressing chemistry-related challenges and structural design considerations. In addition, this review focuses on the processing methods of two- and three-dimensional structures of elastomers, and systematically discusses the contribution of processing methods such as solvent casting, electrostatic spinning, and three-/four-dimensional printing of DBE. Furthermore, we describe recent advances in tissue repair using DBE, and include advances achieved in regenerating different tissues, including nerves, tendons, muscle, cardiac, and bone, highlighting their efficacy and versatility. The review concludes by discussing the current challenges in material selection, biodegradation, bioactivation, and manufacturing in tissue repair, and suggests future research directions. This concise yet comprehensive analysis aims to provide valuable insights and technical guidance for advances in DBE for tissue engineering.

Electrospun fiber-based immune engineering in regenerative medicine

Immune engineering, a burgeoning field within regenerative medicine, involves a spectrum of strategies to optimize the intricate interplay between tissue regenerative biomaterials and the host tissue. These strategies are applied across different types of biomaterials and various disease models, which encompasses finely modulating the immune response at the levels of immune cells and factors, aiming to mitigate adverse effects like fibrosis and persistent inflammation that may arise at the injury site and consequently promote tissue regeneration. With the continuous progress in electrospinning technology, the immunoregulatory capabilities of electrospun fibers have gained substantial attention over the years. Electrospun fibers, with their extracellular matrix-like characteristics, high surface-area-to-volume ratio, and reliable pharmaceutical compound capacity, have emerged as key players among tissue engineering materials. This review specifically focuses on the role of electrospun fiber-based immune engineering, emphasizing their unique design strategies. Notably, electrospinning actively engages in immune engineering by modulating immune responses through four essential strategies: (i) surface modification, (ii) drug loading, (iii) physicochemical parameters, and (iv) biological grafting. This review presents a comprehensive overview of the intricate mechanisms of the immune system in injured tissues while unveiling the key strategies adopted by electrospun fibers to orchestrate immune regulation. Furthermore, the review explores the current developmental trends and limitations concerning the immunoregulatory function of electrospun fibers, aiming to drive the advancements in electrospun fiber-based immune engineering to its full potential.