Mechanically reinforced cell-laden scaffolds formed using alginate-based bioink printed onto the surface of a PCL/alginate mesh structure for regeneration of hard tissue

The Dual Angiogenesis Effects via Nrf2/HO-1 Signaling Pathway of Melatonin Nanocomposite Scaffold on Promoting Diabetic Bone Defect Repair

Purpose

Given the escalating prevalence of diabetes, the demand for specific bone graft materials is increasing, owing to the greater tendency towards bone defects and more difficult defect repair resulting from diabetic bone disease (DBD). Melatonin (MT), which is known for its potent antioxidant properties, has been shown to stimulate both osteogenesis and angiogenesis.

Methods

MT was formulated into MT@PLGA nanoparticles (NPs), mixed with sodium alginate (SA) hydrogel, and contained within a 3D printing polycaprolactone/β-Tricalcium phosphate (PCL/β-TCP) scaffold. The osteogenic capacity of the MT nanocomposite scaffold under diabetic conditions was demonstrated via in vitro and in vivo studies and the underlying mechanisms were investigated.

Results

Physicochemical characterization experiments confirmed the successful fabrication of the MT nanocomposite scaffold, which can achieve long-lasting sustained release of MT. The in vitro and in vivo studies demonstrated that the MT nanocomposite scaffold exhibited enhanced osteogenic capacity, which was elucidated by the dual angiogenesis effects activated through the NF-E2-related factor 2/Heme oxygenase 1 (Nrf2/HO-1) signaling pathway, including the enhancement of antioxidant enzyme activity to reduce the oxidative stress damage of vascular endothelial cells (VECs) and directly stimulating vascular endothelial growth factor (VEGF) production, which reversed the angiogenesis-osteogenesis uncoupling and promoted osteogenesis under diabetic conditions.

Conclusion

This study demonstrated the research prospective and clinical implications of the MT nanocomposite scaffold as a novel bone graft for treating bone defect and enhancing bone fusion in diabetic individuals.

Is it possible to 3D bioprint load-bearing bone implants? A critical review

Rehabilitative capabilities of any tissue engineered scaffold rely primarily on the triad of (i) biomechanical properties such as mechanical properties and architecture, (ii) chemical behavior such as regulation of cytokine expression, and (iii) cellular response modulation (including their recruitment and differentiation). The closer the implant can mimic the native tissue, the better it can rehabilitate the damage therein. Among the available fabrication techniques, only 3D bioprinting (3DBP) can satisfactorily replicate the inherent heterogeneity of the host tissue. However, 3DBP scaffolds typically suffer from poor mechanical properties, thereby, driving the increased research interest in development of load-bearing 3DBP orthopedic scaffolds in recent years. Typically, these scaffolds involve multi-material 3D printing, comprising of at-least one bioink and a load-bearing ink; such that mechanical and biological requirements of the biomaterials are decoupled. Ensuring high cellular survivability and good mechanical properties are of key concerns in all these studies. 3DBP of such scaffolds is in early developmental stages, and research data from only a handful of preliminary animal studies are available, owing to limitations in print-capabilities and restrictive materials library. This article presents a topically focused review of the state-of-the-art, while highlighting aspects like available 3DBP techniques; biomaterials' printability; mechanical and degradation behavior; and their overall bone-tissue rehabilitative efficacy. This collection amalgamates and critically analyses the research aimed at 3DBP of load-bearing scaffolds for fulfilling demands of personalized-medicine. We highlight the recent-advances in 3DBP techniques employing thermoplastics and phosphate-cements for load-bearing applications. Finally, we provide an outlook for possible future perspectives of 3DBP for load-bearing orthopedic applications. Overall, the article creates ample foundation for future research, as it gathers the latest and ongoing research that scientists could utilize.

Advances in additive manufacturing of polycaprolactone based scaffolds for bone regeneration

Critical sized bone defects are difficult to manage and currently available clinical/surgical strategies for treatment are not completely successful. Polycaprolactone (PCL) which is a biodegradable and biocompatible thermoplastic can be 3D printed using medical images into patient specific bone implants. The excellent mechanical properties and low immunogenicity of PCL makes it an ideal biomaterial candidate for 3D printing of bone implants. Though PCL suffers from the limitation of being bio-inert. Here we describe the use of PCL as a biomaterial for 3D printing for bone regeneration, and advances made in the field. The specific focus is on the different 3D printing techniques used for this purpose and various modification that can enhance bone regeneration following the development pathways. We further describe the effect of various scaffold characteristics on bone regeneration both in vitro and the translational assessment of these 3D printed PCL scaffolds in animal studies. The generated knowledge will help understand cell-material interactions of 3D printed PCL scaffolds, to further improve scaffold chemistry and design that can replicate bone developmental processes and can be translated clinically.

A Roadmap to Fabricate Geometrically Accurate Three-Dimensional Scaffolds CO-Printed by Natural and Synthetic Polymers

Three-dimensional bioprinting is a promising field in regenerating patient-specific tissues and organs due to its inherent capability of releasing biocompatible materials encapsulating living cells in a predefined location. Due to the diverse characteristics of tissues and organs in terms of microstructures and cell types, a multinozzle extrusion-based 3D bioprinting system has gained popularity. The investigations on interactions between various biomaterials and cell-to-material can provide relevant information about the scaffold geometry, cell viability, and proliferation. Natural hydrogels are frequently used in bioprinting materials because of their high-water content and biocompatibility. However, the dominancy of liquid characteristics of only-hydrogel materials makes the printing process challenging. Polycaprolactone (PCL) is the most frequently used synthetic biopolymer. It can provide mechanical integrity to achieve dimensionally accurate fabricated scaffolds, especially for hard tissues such as bone and cartilage scaffolds. In this paper, we explored various multimaterial bioprinting strategies with our recently proposed bio-inks and PCL intending to achieve dimensional accuracy and mechanical aspects. Various strategies were followed to coprint natural and synthetic biopolymers and interactions were analyzed between them. Printability of pure PCL with various molecular weights was optimized with respect to different process parameters such as nozzle temperature, printing pressure, printing speed, porosity, and bed temperature to coprint with natural hydrogels. The relationship between the rheological properties and shape fidelity of natural polymers was investigated with a set of printing strategies during coprinting with PCL. The successful application of this research can help achieve dimensionally accurate scaffolds.

3D Bioprinted Scaffolds for Bone Tissue Engineering: State-Of-The-Art and Emerging Technologies

Treating large bone defects, known as critical-sized defects (CSDs), is challenging because they are not spontaneously healed by the patient’s body. Due to the limitations associated with conventional bone grafts, bone tissue engineering (BTE), based on three-dimensional (3D) bioprinted scaffolds, has emerged as a promising approach for bone reconstitution and treatment. Bioprinting technology allows for incorporation of living cells and/or growth factors into scaffolds aiming to mimic the structure and properties of the native bone. To date, a wide range of biomaterials (either natural or synthetic polymers), as well as various cells and growth factors, have been explored for use in scaffold bioprinting. However, a key challenge that remains is the fabrication of scaffolds that meet structure, mechanical, and osteoconductive requirements of native bone and support vascularization. In this review, we briefly present the latest developments and discoveries of CSD treatment by means of bioprinted scaffolds, with a focus on the biomaterials, cells, and growth factors for formulating bioinks and their bioprinting techniques. Promising state-of-the-art pathways or strategies recently developed for bioprinting bone scaffolds are highlighted, including the incorporation of bioactive ceramics to create composite scaffolds, the use of advanced bioprinting technologies (e.g., core/shell bioprinting) to form hybrid scaffolds or systems, as well as the rigorous design of scaffolds by taking into account of the influence of such parameters as scaffold pore geometry and porosity. We also review in-vitro assays and in-vivo models to track bone regeneration, followed by a discussion of current limitations associated with 3D bioprinting technologies for BTE. We conclude this review with emerging approaches in this field, including the development of gradient scaffolds, four-dimensional (4D) printing technology via smart materials, organoids, and cell aggregates/spheroids along with future avenues for related BTE.

Advances of Hydrogel-Based Bioprinting for Cartilage Tissue Engineering

Bioprinting has gained immense attention and achieved the revolutionized progress for application in the multifunctional tissue regeneration. On account of the precise structural fabrication and mimicking complexity, hydrogel-based bio-inks are widely adopted for cartilage tissue engineering. Although more and more researchers have reported a number of literatures in this field, many challenges that should be addressed for the development of three-dimensional (3D) bioprinting constructs still exist. Herein, this review is mainly focused on the introduction of various natural polymers and synthetic polymers in hydrogel-based bioprinted scaffolds, which are systematically discussed via emphasizing on the fabrication condition, mechanical property, biocompatibility, biodegradability, and biological performance for cartilage tissue repair. Further, this review describes the opportunities and challenges of this 3D bioprinting technique to construct complex bio-inks with adjustable mechanical and biological integrity, and meanwhile, the current possible solutions are also conducted for providing some suggestive ideas on developing more advanced bioprinting products from the bench to the clinic.

The Application of Polycaprolactone in Three-Dimensional Printing Scaffolds for Bone Tissue Engineering

Bone tissue engineering commonly encompasses the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the propagation of cells to regenerate damaged tissues or organs. 3D printing technology has been extensively applied to allow direct 3D scaffolds manufacturing. Polycaprolactone (PCL) has been widely used in the fabrication of 3D scaffolds in the field of bone tissue engineering due to its advantages such as good biocompatibility, slow degradation rate, the less acidic breakdown products in comparison to other polyesters, and the potential for loadbearing applications. PCL can be blended with a variety of polymers and hydrogels to improve its properties or to introduce new PCL-based composites. This paper describes the PCL used in developing state of the art of scaffolds for bone tissue engineering. In this review, we provide an overview of the 3D printing techniques for the fabrication of PCL-based composite scaffolds and recent studies on applications in different clinical situations. For instance, PCL-based composite scaffolds were used as an implant surgical guide in dental treatment. Furthermore, future trend and potential clinical translations will be discussed.

Electrospun chitosan oligosaccharide/polycaprolactone nanofibers loaded with wound-healing compounds of Rutin and Quercetin as antibacterial dressings

Burn injury has posed devastating burdens on the public health due to its inevitable damage to the skin structure resulting in the increased risk of infection. Therefore, it is highly demanding to develop efficacious antibacterial wound-healing dressing. Despite the favourable wound-healing activities, the curative efficacy of phytochemical compounds of quercetin (Qe) and its derivatives is limited by their poor water solubility. Here, we have fabricated a novel electrospun nanofiber membrane (ENM) consisting of polycaprolactone (PCL), chitosan oligosaccharides (COS), and Qe/Rutin (Ru) as the potential bioactive dressing for wound healing. The incorporation of chitosan oligosaccharides (COSs) in the PCL scaffold at the optimized molar ratio not only contributed to the improved hydrophilicity and water absorption performance of the ENM but effectively increased the specific surface area of the formed nanofibers. In particular, the antioxidant and antibacterial activities of the Qe/rutin-loaded nanofiber membranes were tested, which revealed that the PCL-COS-Qe membrane exhibited superior performance among all nanofiber membranes. Therefore, the developed PCL-COS-Qe/Ru nanofiber membranes hold enormous potential as healthcare products, such as wound dressings for burn injuries.

Recent trends in natural polysaccharide based bioinks for multiscale 3D printing in tissue regeneration: A review

Biofabrication by three-dimensional (3D) printing has been an attractive technology in harnessing the possibility to print anatomical shaped native tissues with controlled architecture and resolution. 3D printing offers the possibility to reproduce complex microarchitecture of native tissues by printing live cells in a layer by layer deposition to provide a biomimetic structural environment for tissue formation and host tissue integration. Plant based biomaterials derived from green and sustainable sources have represented to emulate native physicochemical and biological cues in order to direct specific cellular response and formation of new tissues through biomolecular recognition patterns. This comprehensive review aims to analyze and identify the most commonly used plant based bioinks for 3D printing applications. An overview on the role of different plant based biomaterial of terrestrial origin (Starch, Nanocellulose and Pectin) and marine origin (Ulvan, Alginate, Fucoidan, Agarose and Carrageenan) used for 3D printing applications are discussed elaborately. Furthermore, this review will also emphasis in the functional aspects of different 3D printers, appropriate printing material, merits and demerits of numerous plant based bioinks in developing 3D printed tissue-like constructs. Additionally, the underlying potential benefits, limitations and future perspectives of plant based bioinks for tissue engineering (TE) applications are also discussed.

3D Bioprinting of Human Tissues: Biofabrication, Bioinks, and Bioreactors

The field of tissue engineering has progressed tremendously over the past few decades in its ability to fabricate functional tissue substitutes for regenerative medicine and pharmaceutical research. Conventional scaffold-based approaches are limited in their capacity to produce constructs with the functionality and complexity of native tissue. Three-dimensional (3D) bioprinting offers exciting prospects for scaffolds fabrication, as it allows precise placement of cells, biochemical factors, and biomaterials in a layer-by-layer process. Compared with traditional scaffold fabrication approaches, 3D bioprinting is better to mimic the complex microstructures of biological tissues and accurately control the distribution of cells. Here, we describe recent technological advances in bio-fabrication focusing on 3D bioprinting processes for tissue engineering from data processing to bioprinting, mainly inkjet, laser, and extrusion-based technique. We then review the associated bioink formulation for 3D bioprinting of human tissues, including biomaterials, cells, and growth factors selection. The key bioink properties for successful bioprinting of human tissue were summarized. After bioprinting, the cells are generally devoid of any exposure to fluid mechanical cues, such as fluid shear stress, tension, and compression, which are crucial for tissue development and function in health and disease. The bioreactor can serve as a simulator to aid in the development of engineering human tissues from in vitro maturation of 3D cell-laden scaffolds. We then describe some of the most common bioreactors found in the engineering of several functional tissues, such as bone, cartilage, and cardiovascular applications. In the end, we conclude with a brief insight into present limitations and future developments on the application of 3D bioprinting and bioreactor systems for engineering human tissue.

Three dimensional bioprinting technology: Applications in pharmaceutical and biomedical area

3D bioprinting is a technology based on the principle of three-dimensional printing of designed biological materials, which has been widely used recently. The production of biological materials, such as tissues, organs, cells and blood vessels with this technology is alternative and promising approach for organ and tissue transplantation. Apart from tissue and organ printing, it has a wide range of usage, such as in vitro/in vivo modeling, production of drug delivery systems and, drug screening. However, there are various restrictions on the use of this technology. In this review, the process steps, classification, advantages, limitations, usage and application areas of 3D bioprinting technology, materials and auxiliary materials used in this technology are discussed.

Co-Immobilization of Ce6 Sono/Photosensitizer and Protonated Graphitic Carbon Nitride on PCL/Gelation Fibrous Scaffolds for Combined Sono-Photodynamic Cancer Therapy

Aiming at developing a moderate and efficient sono-photodynamic therapy for breast cancer, tissue engineering scaffolds may provide an easy and efficient strategy to eliminate serious side effects in conventional surgery or chemotherapy, and thus, they are highly desired. However, the development of ideal sono-photodynamic therapeutic scaffolds is always hindered by the poor stability and incompatibility between the different biomaterial components. Herein, the Food and Drug Administration (FDA)-approved sono/photosensitizer Chlorin e6 (Ce6) was successfully and tightly incorporated into electrospun polycaprolactone/gelatin (PG) scaffolds via positively charged protonated g-C₃N₄ nanosheets (pCN). The PG fibers were precoated with graphene oxide (GO) to enable the assembly of pCN on the surface through electrostatic interactions. The Ce6@pCN-GO-PG composite scaffolds exhibited good cytocompatibility and excellent sono-photodynamic activity, leading to distinctly boosted reactive oxygen species (ROS) generation and a 95.8% inactivation rate of breast cancer cells through a synergistic sono-photodynamic process triggered by an 808 nm laser and 1 MHz ultrasound (US) excitation, within the clinical therapeutic dose. The as-developed scaffolds with unique ultrasound cavitation therapeutic effects can be used not only for complete eradication of tumor cells after surgery but also as a cell behavior observation platform of sono-photodynamic cancer therapy.

Bioprintable tough hydrogels for tissue engineering applications

Bioprinting is an advanced fabrication approach to engineer complex living structures as the conventional fabrication methods are incapable of integrating structural and biological complexities. It offers the versatility of printing different cell incorporated hydrogels (bioink) layer by layer; offering control over spatial resolution and cell distribution to mimic native tissue architectures. However, the bioprinting of tough hydrogels involve additional complexities, such as employing complex crosslinking or reinforcing mechanisms during printing and pre/post printing cellular activities. Solving this complexity requires attention from engineering, material science and cell biology perspectives. In this review, we discuss different types of bioprinting techniques with focus on current state-of-the-art in bioink formulations and pivotal characteristics of bioinks for tough hydrogel printing. We discuss the scope of transition from 3D to 4D bioprinting and some of the advanced characterization techniques for in-depth understanding of the 3D printing process from the microstructural perspective, along with few specific applications and conclude with the future perspectives in biofabrication of hydrogels for tissue engineering applications.

Micro- and Macrobioprinting: Current Trends in Tissue Modeling and Organ Fabrication

The recapitulation of human anatomy and physiology is critical for organ regeneration. Due to this fundamental requirement, bioprinting holds great promise in tissue engineering and regenerative medicine due to the possibility of fabricating complex scaffolds that host cells and biochemical cues in a physiologically relevant fashion. The ever-growing research in this field has been proceeding along two different, yet complementary, routes: on the one hand, the development of bioprinting to fabricate large tissue surrogates for transplantation purposes in vivo (macrobioprinting), and on the other the spread of bioprinting-based miniaturized systems to model the tissue microenvironment in vitro (microbioprinting). The latest advances in both macro- and microbioprinting are reviewed, emphasizing their impact on specific areas of tissue engineering. Additionally, a critical comparison of macro- versus microbioprinting is presented together with advantages and limitations of each approach. Ultimately, findings obtained both at the macro-and microscale are expected to provide a deeper insight in tissue biology and offer clinically relevant solutions for organ regeneration.

3D bioprinting for biomedical devices and tissue engineering: A review of recent trends and advances

3D printing, an additive manufacturing based technology for precise 3D construction, is currently widely employed to enhance applicability and function of cell laden scaffolds. Research on novel compatible biomaterials for bioprinting exhibiting fast crosslinking properties is an essential prerequisite toward advancing 3D printing applications in tissue engineering. Printability to improve fabrication process and cell encapsulation are two of the main factors to be considered in development of 3D bioprinting. Other important factors include but are not limited to printing fidelity, stability, crosslinking time, biocompatibility, cell encapsulation and proliferation, shear-thinning properties, and mechanical properties such as mechanical strength and elasticity. In this review, we recite recent promising advances in bioink development as well as bioprinting methods. Also, an effort has been made to include studies with diverse types of crosslinking methods such as photo, chemical and ultraviolet (UV). We also propose the challenges and future outlook of 3D bioprinting application in medical sciences and discuss the high performance bioinks.

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The most recent promising advances in three-dimensional bioprinting are reviewed.

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Extrusion, inkjet, stereolithography, and laser bioprinting studies are cited.

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Challenges toward successful employment of bioprinting are discussed.

Assessing bioink shape fidelity to aid material development in 3D bioprinting

During extrusion-based bioprinting, the deposited bioink filaments are subjected to deformations, such as collapse of overhanging filaments, which compromises the ability to stack several layers of bioink, and fusion between adjacent filaments, which compromises the resolution and maintenance of a desired pore structure. When developing new bioinks, approaches to assess their shape fidelity after printing would be beneficial to evaluate the degree of deformation of the deposited filament and to estimate how similar the final printed construct would be to the design. However, shape fidelity has been prevalently assessed qualitatively through visual inspection after printing, hampering the direct comparison of the printability of different bioinks. In this technical note, we propose a quantitative evaluation for shape fidelity of bioinks based on testing the filament collapse on overhanging structures and the filament fusion of parallel printed strands. Both tests were applied on a hydrogel platform based on poloxamer 407 and poly(ethylene glycol) blends, providing a library of hydrogels with different yield stresses. The presented approach is an easy way to assess bioink shape fidelity, applicable to any filament-based bioprinting system and able to quantitatively evaluate this aspect of printability, based on the degree of deformation of the printed filament. In addition, we built a simple theoretical model that relates filament collapse with bioink yield stress. The results of both shape fidelity tests underline the role of yield stress as one of the parameters influencing the printability of a bioink. The presented quantitative evaluation will allow for reproducible comparisons between different bioink platforms.

Bioinks for bioprinting functional meniscus and articular cartilage

3D bioprinting can potentially enable the engineering of biological constructs mimicking the complex geometry, composition, architecture and mechanical properties of different tissues and organs. Integral to the successful bioprinting of functional articular cartilage and meniscus is the identification of suitable bioinks and cell sources to support chondrogenesis or fibrochondrogenesis, respectively. Such bioinks must also possess the appropriate rheological properties to be printable and support the generation of complex geometries. This review will outline the parameters required to develop bioinks for such applications and the current recent advances in 3D bioprinting of functional meniscus and articular cartilage. The paper will conclude by discussing key scientific and technical hurdles in this field and by defining future research directions for cartilage and meniscus bioprinting.

Advances in three-dimensional bioprinting for hard tissue engineering

The need for organ and tissue regeneration in patients continues to increase because of a scarcity of donors, as well as biocompatibility issues in transplant immune rejection. To address this, scientists have investigated artificial tissues as an alternative to transplantation. Three-dimensional (3D) bioprinting technology is an additive manufacturing method that can be used for the fabrication of 3D functional tissues or organs. This technology promises to replicate the complex architecture of structures in natural tissue. To date, 3D bioprinting strategies have confirmed their potential practice in regenerative medicine to fabricate the transplantable hard tissues, including cartilage and bone. However, 3D bioprinting approaches still have unsolved challenges to realize 3D hard tissues. In this manuscript, the current technical development, challenges, and future prospects of 3D bioprinting for engineering hard tissues are reviewed.

Hydrogel Layers on the Surface of Polyester-Based Materials for Improvement of Their Biointeractions and Controlled Release of Proteins

The modification of bioresorbable polyester surfaces in order to alter their biointeractions presents an important problem in biomedical polymer science. In this study, the covalent modification of the surface of poly(lactic acid)-based (PLA-based) films with poly(acryl amide) and sodium alginate hydrogels was performed to change the non-specific polyester interaction with proteins and cells, as well as to make possible the covalent attachment of low-molecular weight ligands and to control protein release. The effect of such modification on the film surface properties was studied. Parameters such as swelling, water contact angle, surface area, and binding capacity of low-molecular weight substances were evaluated and compared. The comparative study of adsorption of model protein (BSA) on the surface of non-modified and modified films was investigated and the protein release was evaluated. Cell viability on the surface of hydrogel-coated films was also tested. The developed approach could be applied for the modification of PLA-based scaffolds for tissue engineering and will be further studied for molecular-imprinting of biomolecules on the surface of polyester-based materials for control of biointeractions.

Combining a micro/nano-hierarchical scaffold with cell-printing of myoblasts induces cell alignment and differentiation favorable to skeletal muscle tissue regeneration

Biomedical scaffolds must be used in tissue engineering to provide physical stability and topological/biochemical properties that directly affect tissue regeneration. In this study, a new cell-laden scaffold was developed that supplies micro/nano-topological cues and promotes efficient release of cells. The hierarchical structure consisted of poly(ε-caprolactone) macrosized struts for sustaining a three-dimensional structural shape, aligned nanofibers obtained with optimized electrospinning, and cell-printed myoblasts. Importantly, the printed myoblasts were fully safe and were efficiently released from the cell-laden struts to neighboring nanofiber networks. The incorporation of micro/nanofibers in the hierarchical scaffold significantly affected myoblast proliferation, alignment, and even facilitated the formation of myotubes. We observed that myosin heavy chain expression and the expression levels of various myogenic genes (MyoD, myogenin, and troponin T) were significantly affected by the fiber alignment achieved in our hierarchical cell-laden structure. We believe that the combination of cell-printing and a hierarchical scaffold that encourages fiber alignment is a highly promising technique for skeletal muscle tissue engineering.