Stereolithographic bone scaffold design parameters: osteogenic differentiation and signal expression

Microstructural, Fluid Dynamic, and Mechanical Characterization of Zinc Oxide and Magnesium Chloride-Modified Hydrogel Scaffolds

Scaffolds for the filling and regeneration of osteochondral defects are a current challenge in the biomaterials field, and solutions with greater functionality are still being sought. The novel approach of this work was to obtain scaffolds with biologically active additives possessing microstructural, permeability, and mechanical properties, mimicking the complexity of natural cartilage. Four types of scaffolds with a gelatin/alginate matrix modified with hydroxyapatite were obtained, and the relationship between the modifiers and substrate properties was evaluated. They differed in the type of second modifier used, which was hydrated MgCl2 in two proportions, ZnO, and nanohydroxyapatite. The samples were obtained by freeze-drying by using two-stage freezing. Based on microstructural observations combined with X-ray microanalysis, the microstructure of the samples and the elemental content were assessed. Permeability and mechanical tests were also performed. The scaffolds exhibited a network of interconnected pores and complex microarchitecture, with lower porosity at the surface (15 ± 7 to 29 ± 6%) and higher porosity at the center (67 ± 8 to 75 ± 8%). The additives had varying effects on the pore sizes and permeabilities of the samples. ZnO yielded the most permeable scaffolds (5.92 × 10-11 m2), whereas nanohydroxyapatite yielded the scaffold with the lowest permeability (1.18 × 10-11 m2), values within the range reported for trabecular bone. The magnesium content had no statistically significant effect on the permeability. The best mechanical parameters were obtained for ZnO samples and those containing hydrated MgCl2. The scaffold's properties meet the criteria for filling osteochondral defects. The developed scaffolds follow a biomimetic approach in terms of hierarchical microarchitecture and mechanical parameters as well as chemical composition. The obtained composite materials have the potential as biomimetic scaffolds for the regeneration of osteochondral defects.

Leveraging the Recent Advancements in GelMA Scaffolds for Bone Tissue Engineering: An Assessment of Challenges and Opportunities

The field of bone tissue engineering has seen significant advancements in recent years. Each year, over two million bone transplants are performed globally, and conventional treatments, such as bone grafts and metallic implants, have their limitations. Tissue engineering offers a new level of treatment, allowing for the creation of living tissue within a biomaterial framework. Recent advances in biomaterials have provided innovative approaches to rebuilding bone tissue function after damage. Among them, gelatin methacryloyl (GelMA) hydrogel is emerging as a promising biomaterial for supporting cell proliferation and tissue regeneration, and GelMA has exhibited exceptional physicochemical and biological properties, making it a viable option for clinical translation. Various methods and classes of additives have been used in the application of GelMA for bone regeneration, with the incorporation of nanofillers or other polymers enhancing its resilience and functional performance. Despite promising results, the fabrication of complex structures that mimic the bone architecture and the provision of balanced physical properties for both cell and vasculature growth and proper stiffness for load bearing remain as challenges. In terms of utilizing osteogenic additives, the priority should be on versatile components that promote angiogenesis and osteogenesis while reinforcing the structure for bone tissue engineering applications. This review focuses on recent efforts and advantages of GelMA-based composite biomaterials for bone tissue engineering, covering the literature from the last five years.

Biomaterial engineering for cell transplantation

The current paradigm of medicine is mostly designed to block or prevent pathological events. Once the disease-led tissue damage occurs, the limited endogenous regeneration may lead to depletion or loss of function for cells in the tissues. Cell therapy is rapidly evolving and influencing the field of medicine, where in some instances attempts to address cell loss in the body. Due to their biological function, engineerability, and their responsiveness to stimuli, cells are ideal candidates for therapeutic applications in many cases. Such promise is yet to be fully obtained as delivery of cells that functionally integrate with the desired tissues upon transplantation is still a topic of scientific research and development. Main known impediments for cell therapy include mechanical insults, cell viability, host's immune response, and lack of required nutrients for the transplanted cells. These challenges could be divided into three different steps: 1) Prior to, 2) during the and 3) after the transplantation procedure. In this review, we attempt to briefly summarize published approaches employing biomaterials to mitigate the above technical challenges. Biomaterials are offering an engineerable platform that could be tuned for different classes of cell transplantation to potentially enhance and lengthen the pharmacodynamics of cell therapies.

An Overview on the Big Players in Bone Tissue Engineering: Biomaterials, Scaffolds and Cells

Presently, millions worldwide suffer from degenerative and inflammatory bone and joint issues, comprising roughly half of chronic ailments in those over 50, leading to prolonged discomfort and physical limitations. These conditions become more prevalent with age and lifestyle factors, escalating due to the growing elderly populace. Addressing these challenges often entails surgical interventions utilizing implants or bone grafts, though these treatments may entail complications such as pain and tissue death at donor sites for grafts, along with immune rejection. To surmount these challenges, tissue engineering has emerged as a promising avenue for bone injury repair and reconstruction. It involves the use of different biomaterials and the development of three-dimensional porous matrices and scaffolds, alongside osteoprogenitor cells and growth factors to stimulate natural tissue regeneration. This review compiles methodologies that can be used to develop biomaterials that are important in bone tissue replacement and regeneration. Biomaterials for orthopedic implants, several scaffold types and production methods, as well as techniques to assess biomaterials' suitability for human use-both in laboratory settings and within living organisms-are discussed. Even though researchers have had some success, there is still room for improvements in their processing techniques, especially the ones that make scaffolds mechanically stronger without weakening their biological characteristics. Bone tissue engineering is therefore a promising area due to the rise in bone-related injuries.

Application of additively manufactured bone scaffold: a systematic review

The application of additive manufacturing (AM) technology plays a significant role in various fields, incorporating a wide range of cutting-edge technologies such as aerospace, medical treatment, electronic information, and materials. It is currently widely adopted for medical services, national defense, and industrial manufacturing. In recent years, AM has also been extensively employed to produce bone scaffolds and implant materials. Through AM, products can be manufactured without being constrained by complex internal structures. AM is particularly advantageous in the production of macroscopically irregular and microscopically porous biomimetic bone scaffolds, with short production cycles required. In this paper, AM commonly used to produce bone scaffolds and orthopedic implants is overviewed to analyze the different materials and structures adopted for AM. The applications of antibacterial bone scaffolds and bone scaffolds in biologically relevant animal models are discussed. Also, the influence on the comprehensive performance of product mechanics, mass transfer, and biology is explored. By identifying the reasons for the limited application of existing AM in the biomedical field, the solutions are proposed. This study provides an important reference for the future development of AM in the field of orthopedic healthcare. In conclusion, various AM technologies, the requirements of bone scaffolds and the important role of AM in building bridges between biomaterials, additives, and bone tissue engineering scaffolds are described and highlighted. Nevertheless, more caution should be exercised when designing bone scaffolds and conducting in vivo trials, due to the lack of standardized processes, which prevents the accuracy of results and reduces the reliability of information.

Recent Advances in 3D Printing of Polymers for Application in Prosthodontics

Contemporary mass media frequently depict 3D printing as a technology with widespread utilization in the creation of dental prosthetics. This paper endeavors to provide an evidence-based assessment of the current scope of 3D printing's integration within dental laboratories and practices. Its primary objective is to offer a systematic evaluation of the existing applications of 3D-printing technology within the realm of dental prosthetic restorations. Furthermore, this article delves into potential prospects, while also critically examining the sustained relevance of conventional dental laboratory services and manufacturing procedures. The central focus of this article is to expound upon the extent to which 3D printing is presently harnessed for crafting dental prosthetic appliances. By presenting verifiable data and factual insights, this article aspires to elucidate the actual implementation of 3D printing in prosthetic dentistry and its seamless integration into dental practices. The aim of this narrative review is twofold: firstly, to provide an informed and unbiased evaluation of the role that 3D printing currently plays within dental laboratories and practices; and secondly, to instigate contemplation on the transformative potential of this technology, both in terms of its contemporary impact and its future implications, while maintaining a balanced consideration of traditional dental approaches.

Additive Manufacturing of Bioactive Glass and Its Polymer Composites as Bone Tissue Engineering Scaffolds: A Review

Bioactive glass (BG) and its polymer composites have demonstrated great potential as scaffolds for bone defect healing. Nonetheless, processing these materials into complex geometry to achieve either anatomy-fitting designs or the desired degradation behavior remains challenging. Additive manufacturing (AM) enables the fabrication of BG and BG/polymer objects with well-defined shapes and intricate porous structures. This work reviewed the recent advancements made in the AM of BG and BG/polymer composite scaffolds intended for bone tissue engineering. A literature search was performed using the Scopus database to include publications relevant to this topic. The properties of BG based on different inorganic glass formers, as well as BG/polymer composites, are first introduced. Melt extrusion, direct ink writing, powder bed fusion, and vat photopolymerization are AM technologies that are compatible with BG or BG/polymer processing and were reviewed in terms of their recent advances. The value of AM in the fabrication of BG or BG/polymer composites lies in its ability to produce scaffolds with patient-specific designs and the on-demand spatial distribution of biomaterials, both contributing to effective bone defect healing, as demonstrated by in vivo studies. Based on the relationships among structure, physiochemical properties, and biological function, AM-fabricated BG or BG/polymer composite scaffolds are valuable for achieving safer and more efficient bone defect healing in the future.

A Review on the Role of Wollastonite Biomaterial in Bone Tissue Engineering

Millions of people around the world have bone-tissue defects. Autologous and allogeneic bone grafting are frequent therapeutic techniques; however, none has produced the best therapeutic results. This has inspired researchers to investigate novel bone-regeneration technologies. In recent years, the development of bone tissue engineering (BTE) scaffolds has been at the forefront of this discipline. Due to their limitless supply and lack of disease transmission, engineered bone tissue has been advanced for the repair and reconstruction of bone deformities. Bone tissue is a highly vascularized, dynamic tissue that constantly remodels during an individual's lifetime. Bone tissue engineering is aimed at stimulating the creation of new, functional bone by combining biomaterials, cells, and factor treatment synergistically. This article provides a review of wollastonite's biomaterial application in bone tissue engineering. This work includes an explanation of wollastonite minerals including mining, raw materials for the synthesis of artificial wollastonite with various methods, its biocompatibility, and biomedical applications. Future perspectives are also addressed, along with topics like bone tissue engineering, the qualities optimal bone scaffolds must have, and the way a scaffold is designed can have a big impact on how the body reacts.

A Review on Stimuli-Actuated 3D Micro/Nanostructures for Tissue Engineering and the Potential of Laser-Direct Writing via Two-Photon Polymerization for Structure Fabrication

In this review, we present the most recent and relevant research that has been done regarding the fabrication of 3D micro/nanostructures for tissue engineering applications. First, we make an overview of 3D micro/nanostructures that act as backbone constructs where the seeded cells can attach, proliferate and differentiate towards the formation of new tissue. Then, we describe the fabrication of 3D micro/nanostructures that are able to control the cellular processes leading to faster tissue regeneration, by actuation using topographical, mechanical, chemical, electric or magnetic stimuli. An in-depth analysis of the actuation of the 3D micro/nanostructures using each of the above-mentioned stimuli for controlling the behavior of the seeded cells is provided. For each type of stimulus, a particular recent application is presented and discussed, such as controlling the cell proliferation and avoiding the formation of a necrotic core (topographic stimulation), controlling the cell adhesion (nanostructuring), supporting the cell differentiation via nuclei deformation (mechanical stimulation), improving the osteogenesis (chemical and magnetic stimulation), controlled drug-delivery systems (electric stimulation) and fastening tissue formation (magnetic stimulation). The existing techniques used for the fabrication of such stimuli-actuated 3D micro/nanostructures, are briefly summarized. Special attention is dedicated to structures' fabrication using laser-assisted technologies. The performances of stimuli-actuated 3D micro/nanostructures fabricated by laser-direct writing via two-photon polymerization are particularly emphasized.

Craniomaxillofacial derived bone marrow mesenchymal stem/stromal cells (BMSCs) for craniomaxillofacial bone tissue engineering: A literature review

Craniomaxillofacial bone defects seriously affect the appearance, function, and psychological status of patients. Traditional autologous bone grafting is very challenging due to the limited sources of bone tissue, excessive surgical trauma, and high incidence of related complications. Craniomaxillofacial bone tissue engineering (BTE) strategies based on bone marrow mesenchymal stem cells (BMSCs) are emerging as an alternative. Craniomaxillofacial BMSCs (C-BMSCs) are homologous to craniomaxillofacial bones, which develop from the mesoderm and neural crest. This article aims to compare the differences in osteogenesis, angiogenesis, and immune regulation of C-BMSCs and other sources of BMSCs, and propose ideas and strategies such as 3D printing and mechanotherapy to completely harness the characteristics of C-BMSCs. In conclusion, C-BSMCs are a promising source of stem cells for the repair and reconstruction of craniomaxillofacial bone defects, and more attention should be paid to accelerating their basic research and clinical practices.

Additive Manufactured Polymers in Dentistry, Current State-of-the-Art and Future Perspectives-A Review

3D-printing application in dentistry not only enables the manufacture of patient-specific devices and tissue constructs, but also allows mass customization, as well as digital workflow, with predictable lower cost and rapid turnaround times. 4D printing also shows a good impact in dentistry, as it can produce dynamic and adaptable materials, which have proven effective in the oral environment, under its continuously changing thermal and humidity conditions. It is expected to further boost the research into producing a whole tooth, capable to harmoniously integrate with the surrounding periodontium, which represents the ultimate goal of tissue engineering in dentistry. Because of their high versatility associated with the wide variety of available materials, additive manufacturing in dentistry predominantly targets the production of polymeric constructs. The aim of this narrative review is to catch a glimpse of the current state-of-the-art of additive manufacturing in dentistry, and the future perspectives of this modern technology, focusing on the specific polymeric materials.

Advances in Translational 3D Printing for Cartilage, Bone, and Osteochondral Tissue Engineering

The regeneration of 3D tissue constructs with clinically relevant sizes, structures, and hierarchical organizations for translational tissue engineering remains challenging. 3D printing, an additive manufacturing technique, has revolutionized the field of tissue engineering by fabricating biomimetic tissue constructs with precisely controlled composition, spatial distribution, and architecture that can replicate both biological and functional native tissues. Therefore, 3D printing is gaining increasing attention as a viable option to advance personalized therapy for various diseases by regenerating the desired tissues. This review outlines the recently developed 3D printing techniques for clinical translation and specifically summarizes the applications of these approaches for the regeneration of cartilage, bone, and osteochondral tissues. The current challenges and future perspectives of 3D printing technology are also discussed.

3D printing of inorganic-biopolymer composites for bone regeneration

In most cases, bone injuries heal without complications, however, there is an increasing number of instances where bone healing needs major clinical intervention. Available treatment options have severe drawbacks, such as donor site morbidity and limited availability for autografting. Bone graft substitutes containing growth factors would be a viable alternative, however they have been associated with dose-related safety concerns and lack control over spatial architecture to anatomically match bone defect sites. 3D printing offers a solution to produce patient specific bone graft substitutes that are customized to the patient bone defect with temporal control over the incorporated therapeutics to maximize their efficacy. Inspired by the natural constitution of bone tissue, composites made of inorganic phases, such as nanosilicate particles, calcium phosphate, and bioactive glasses, combined with biopolymer matrices have been investigated as building blocks for the biofabrication of bone constructs. Besides capturing elements of the bone physiological structure, these inorganic/organic composites can be designed for specific cohesivity, rheological and mechanical properties, while both inorganic and organic constituents contribute to the composite bioactivity. This review provides an overview of 3D printed composite biomaterial-inks for bone tissue engineering. Furthermore, key aspects in biomaterial-ink design, 3D printing techniques, and the building blocks for composite biomaterial-inks are summarized.

Self-Crosslinkable Oxidized Alginate-Carboxymethyl Chitosan Hydrogels as an Injectable Cell Carrier for In Vitro Dental Enamel Regeneration

Injectable hydrogels, as carriers, offer great potential to incorporate cells or growth factors for dental tissue regeneration. Notably, the development of injectable hydrogels with appropriate structures and properties has been a challenging task, leaving much to be desired in terms of cytocompatibility, antibacterial and self-healing properties, as well as the ability to support dental stem cell functions. This paper presents our study on the development of a novel self-cross-linkable hydrogel composed of oxidized alginate and carboxymethyl chitosan and its characterization as a cell carrier for dental enamel regeneration in vitro. Oxidized alginate was synthesized with 60% theoretical oxidation degree using periodate oxidation and characterized by Fourier Transform Infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and Ultraviolet-visible absorption spectroscopy. Then, hydrogels were prepared at three varying weight ratios of oxidized alginate to carboxymethyl chitosan (4:1, 3:1, and 2:1) through Schiff base reactions, which was confirmed by Fourier Transform Infrared spectroscopy. The hydrogels were characterized in terms of gelation time, swelling ratio, structure, injectability, self-healing, antibacterial properties, and in vitro characterization for enamel regeneration. The results demonstrated that, among the three hydrogels examined, the one with the highest ratio of oxidized alginate (i.e., 4:1) had the fastest gelation time and the lowest swelling ability, and that all hydrogels were formed with highly porous structures and were able to be injected through a 20-gauge needle without clogging. The injected hydrogels could be rapidly reformed with the self-healing property. The hydrogels also showed antibacterial properties against two cariogenic bacteria: Streptococcus mutans and Streptococcus sobrinus. For in vitro enamel regeneration, a dental epithelial cell line, HAT-7, was examined, demonstrating a high cell viability in the hydrogels during injection. Furthermore, HAT-7 cells encapsulated in the hydrogels showed alkaline phosphatase production and mineral deposition, as well as maintaining their round morphology, after 14 days of in vitro culture. Taken together, this study has provided evidence that the oxidized alginate-carboxymethyl chitosan hydrogels could be used as an injectable cell carrier for dental enamel tissue engineering applications.

An in silico model predicts the impact of scaffold design in large bone defect regeneration

Large bone defects represent a clinical challenge for which the implantation of scaffolds appears as a promising strategy. However, their use in clinical routine is limited, in part due to a lack of understanding of how scaffolds should be designed to support regeneration. Here, we use the power of computer modeling to investigate mechano-biological principles behind scaffold-guided bone regeneration and the influence of scaffold design on the regeneration process. Computer model predictions are compared to experimental data of large bone defect regeneration in sheep. We identified two main key players in scaffold-guided regeneration: (1) the scaffold surface guidance of cellular migration and tissue formation processes and (2) the stimulation of progenitor cell activity by the scaffold material composition. In addition, lower scaffold surface-area-to-volume ratio was found to be beneficial for bone regeneration due to enhanced cellular migration. To a lesser extent, a reduced scaffold Young's modulus favored bone formation. STATEMENT OF SIGNIFICANCE: 3D-printed scaffolds offer promising treatment strategies for large bone defects but their broader clinical use requires a more thorough understanding of their interaction with the bone regeneration process. The predictions of our in silico model compared to two experimental set-ups highlighted the importance of (1) the scaffold surface guidance of cellular migration and tissue formation processes and (2) the scaffold material stimulation of progenitor cell activity. In addition, the model was used to investigate the effect on the bone regeneration process of (1) the scaffold surface-area-to-volume ratio, with lower ratios favoring more bone growth, and (2) the scaffold material properties, with stiffer scaffold materials yielding a lower bone growth.

Advancing bone tissue engineering one layer at a time: a layer-by-layer assembly approach to 3D bone scaffold materials

The layer-by-layer (LbL) assembly technique has shown excellent potential in tissue engineering applications. The technique is mainly based on electrostatic attraction and involves the sequential adsorption of oppositely charged electrolyte complexes onto a substrate, resulting in uniform single layers that can be rapidly deposited to form nanolayer films. LbL has attracted significant attention as a coating technique due to it being a convenient and affordable fabrication method capable of achieving a wide range of biomaterial coatings while keeping the main biofunctionality of the substrate materials. One promising application is the use of nanolayer films fabricated by LbL assembly in the development of 3-dimensional (3D) bone scaffolds for bone repair and regeneration. Due to their versatility, nanoscale films offer an exciting opportunity for tailoring surface and bulk property modification of implants for osseous defect therapies. This review article discusses the state of the art of the LbL assembly technique, and the properties and functions of LbL-assembled films for engineered bone scaffold application, combination of multilayers for multifunctional coatings and recent advancements in the application of LbL assembly in bone tissue engineering. The recent decade has seen tremendous advances in the promising developments of LbL film systems and their impact on cell interaction and tissue repair. A deep understanding of the cell behaviour and biomaterial interaction for the further development of new generations of LbL films for tissue engineering are the most important targets for biomaterial research in the field. While there is still much to learn about the biological and physicochemical interactions at the interface of nano-surface coated scaffolds and biological systems, we provide a conceptual review to further progress in the LbL approach to 3D bone scaffold materials and inform the future of LbL development in bone tissue engineering.

3D-Printed Hydroxyapatite and Tricalcium Phosphates-Based Scaffolds for Alveolar Bone Regeneration in Animal Models: A Scoping Review

Three-dimensional-printed scaffolds have received greater attention as an attractive option compared to the conventional bone grafts for regeneration of alveolar bone defects. Hydroxyapatite and tricalcium phosphates have been used as biomaterials in the fabrication of 3D-printed scaffolds. This scoping review aimed to evaluate the potential of 3D-printed HA and calcium phosphates-based scaffolds on alveolar bone regeneration in animal models. The systematic search was conducted across four electronic databases: Ovid, Web of Science, PubMed and EBSCOHOST, based on PRISMA-ScR guidelines until November 2021. The inclusion criteria were: (i) animal models undergoing alveolar bone regenerative surgery, (ii) the intervention to regenerate or augment bone using 3D-printed hydroxyapatite or other calcium phosphate scaffolds and (iii) histological and microcomputed tomographic analyses of new bone formation and biological properties of 3D-printed hydroxyapatite or calcium phosphates. A total of ten studies were included in the review. All the studies showed promising results on new bone formation without any inflammatory reactions, regardless of the animal species. In conclusion, hydroxyapatite and tricalcium phosphates are feasible materials for 3D-printed scaffolds for alveolar bone regeneration and demonstrated bone regenerative potential in the oral cavity. However, further research is warranted to determine the scaffold material which mimics the gold standard of care for bone regeneration in the load-bearing areas, including the masticatory load of the oral cavity.

(Bio)manufactured Solutions for Treatment of Bone Defects with Emphasis on US-FDA Regulatory Science Perspective

Bone defects, with second highest demand for surgeries around the globe, may lead to serious health issues and negatively influence patient lives. The advances in biomedical engineering and sciences have led to the development of several creative solutions for bone defect treatment. This review provides a brief summary of bone graft materials, an organized overview of top-down and bottom-up (bio)manufacturing approaches, plus a critical comparison between advantages and limitations of each method. We specifically discuss additive manufacturing techniques and their operation mechanisms in detail. Next, we review the hybrid methods and promising future directions for bone grafting, while giving a comprehensive US-FDA regulatory science perspective, biocompatibility concepts and assessments, and clinical considerations to translate a technology from a research laboratory to the market. The topics covered in this review could potentially fuel future research efforts in bone tissue engineering, and perhaps could also provide novel insights for other tissue engineering applications.

From 3D printing to 3D bioprinting: the material properties of polymeric material and its derived bioink for achieving tissue specific architectures

The application of 3D printing technologies fields for biological tissues, organs, and cells in the context of medical and biotechnology applications requires a significant amount of innovation in a narrow printability range. 3D bioprinting is one such way of addressing critical design challenges in tissue engineering. In a more general sense, 3D printing has become essential in customized implant designing, faithful reproduction of microenvironmental niches, sustainable development of implants, in the capacity to address issues of effective cellular integration, and long-term stability of the cellular constructs in tissue engineering. This review covers various aspects of 3D bioprinting, describes the current state-of-the-art solutions for all aforementioned critical issues, and includes various illustrative representations of technologies supporting the development of phases of 3D bioprinting. It also demonstrates several bio-inks and their properties crucial for being used for 3D printing applications. The review focus on bringing together different examples and current trends in tissue engineering applications, including bone, cartilage, muscles, neuron, skin, esophagus, trachea, tympanic membrane, cornea, blood vessel, immune system, and tumor models utilizing 3D printing technology and to provide an outlook of the future potentials and barriers.

Recent Advances in Synthetic and Natural Biomaterials-Based Therapy for Bone Defects

Synthetic and natural biomaterials are a promising alternative for the treatment of critical-sized bone defects. Several parameters such as their porosity, surface, and mechanical properties are extensively pointed out as key points to recapitulate the bone microenvironment. Many biomaterials with this pursuit are employed to provide a matrix, which can supply the specific environment and architecture for an adequate bone growth. Nevertheless, some queries remain unanswered. This review discusses the recent advances achieved by some synthetic and natural biomaterials to mimic the native structure of bone and the manufacturing technology applied to obtain biomaterial candidates. The focus of this review is placed in the recent advances in the development of biomaterial-based therapy for bone defects in different types of bone. In this context, this review gives an overview of the potentialities of synthetic and natural biomaterials: polyurethanes, polyesters, hyaluronic acid, collagen, titanium, and silica as successful candidates for the treatment of bone defects.

3D Printed SiOC(N) Ceramic Scaffolds for Bone Tissue Regeneration: Improved Osteogenic Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells

Bone tissue engineering has developed significantly in recent years as there has been increasing demand for bone substitutes due to trauma, cancer, arthritis, and infections. The scaffolds for bone regeneration need to be mechanically stable and have a 3D architecture with interconnected pores. With the advances in additive manufacturing technology, these requirements can be fulfilled by 3D printing scaffolds with controlled geometry and porosity using a low-cost multistep process. The scaffolds, however, must also be bioactive to promote the environment for the cells to regenerate into bone tissue. To determine if a low-cost 3D printing method for bespoke SiOC(N) porous structures can regenerate bone, these structures were tested for osteointegration potential by using human mesenchymal stem cells (hMSCs). This includes checking the general biocompatibilities under the osteogenic differentiation environment (cell proliferation and metabolism). Moreover, cell morphology was observed by confocal microscopy, and gene expressions on typical osteogenic markers at different stages for bone formation were determined by real-time PCR. The results of the study showed the pore size of the scaffolds had a significant impact on differentiation. A certain range of pore size could stimulate osteogenic differentiation, thus promoting bone regrowth and regeneration.

In silico and in vivo studies of the effect of surface curvature on the osteoconduction of porous scaffolds

Recent evidence shows that the curvature of porous scaffold plays a significant role in guiding tissue regeneration. However, the underlying mechanism remains controversial to date. In this study, we developed an in silico model to simulate the effect of surface curvature on the osteoconduction of scaffold implants, which comprises the primary aspects of bone regeneration. Selective laser melting was used to manufacture a titanium scaffold with channels representative of different strut curvatures for in vivo assessment. The titanium scaffold was implanted in the femur condyles of rabbits to validate the mathematical model. Simulation results suggest that the curvature affected the distribution of growth factors and subsequently induced the migration of osteoblast lineage cells and bone deposition to the locations with higher curvature. The predictions of the mathematical model are in good agreement with the in vivo assessment results, in which newly formed bone first appeared adjacent to the vertices of the major axes in elliptical channels. The mechanism of curvature-guided osteoconduction may provide a guide for the design optimization of scaffold implants to achieve enhanced bone ingrowth.

Stereolithography 3D printing technology in pharmaceuticals: a review

Three-dimensional printing (3DP) technology is an innovative tool used in manufacturing medical devices, producing alloys, replacing biological tissues, producing customized dosage forms and so on. Stereolithography (SLA), a 3D printing technique, is very rapid and highly accurate and produces finished products of uniform quality. 3D formulations have been optimized with a perfect tool of artificial intelligence learning techniques. Complex designs/shapes can be fabricated through SLA using the photopolymerization principle. Different 3DP technologies are introduced and the most promising of these, SLA, and its commercial applications, are focused on. The high speed and effectiveness of SLA are highlighted. The working principle of SLA, the materials used and applications of the technique in a wide range of different sectors are highlighted in this review. An innovative idea of 3D printing customized pharmaceutical dosage forms is also presented. SLA compromises several advantages over other methods, such as cost effectiveness, controlled integrity of materials and greater speed. The development of SLA has allowed the development of printed pharmaceutical devices. Considering the present trends, it is expected that SLA will be used along with conventional methods of manufacturing of 3D model. This 3D printing technology may be utilized as a novel tool for delivering drugs on demand. This review will be useful for researchers working on 3D printing technologies.

The effect of pores and connections geometries on bone ingrowth into titanium scaffolds: an assessment based on 3D microCT images

In order to support bone tissue regeneration, porous biomaterial implants (scaffolds) must offer chemical and mechanical properties, besides favorable fluid transport. Titanium implants provide these requirements, and depending on their microstructural parameters, the osteointegration process can be stimulated. The pore structure of scaffolds plays an essential role in this process, guiding fluid transport for neo-bone regeneration. The objective of this work was to analyze geometric and morphologic parameters of the porous microstructure of implants and analyze their influences in the bone regeneration process, and then discuss which parameters are the most fundamental. Bone ingrowths into two different sorts of porous titanium implants were analyzed after 7, 14, 21, 28, and 35 incubation days in experimental animal models. Measurements were accomplished with x-ray microtomography image analysis from rabbit tibiae, applying a pore-network technique. Taking into account the most favorable pore sizes for neo-bone regeneration, a novel approach was employed to assess the influence of the pore structure on this process: the analyses were carried out considering minimum pore and connection sizes. With this technique, pores and connections were analyzed separately and the influence of connectivity was deeply evaluated. This investigation showed a considerable influence of the size of connections on the permeability parameter and consequently on the neo-bone regeneration. The results indicate that the processing of porous scaffolds must be focused on deliver pore connections that stimulate the transport of fluids throughout the implant to be applied as a bone replacer.

Degradable RGD-Functionalized 3D-Printed Scaffold Promotes Osteogenesis

To establish an ideal microenvironment for regenerating maxillofacial defects, recent research interests have concentrated on developing scaffolds with intricate configurations and manipulating the stiffness of extracellular matrix toward osteogenesis. Herein, we propose to infuse a degradable RGD-functionalized alginate matrix (RAM) with osteoid-like stiffness, as an artificial extracellular matrix, to a rigid 3D-printed hydroxyapatite scaffold for maxillofacial regeneration. The 3D-printed hydroxyapatite scaffold was produced by microextrusion technology and showed good dimensional stability with consistent microporous detail. RAM was crosslinked by calcium sulfate to manipulate the stiffness, and its degradation was accelerated by partial oxidation using sodium periodate. The results revealed that viability of bone marrow stem cells was significantly improved on the RAM and was promoted on the oxidized RAM. In addition, the migration and osteogenic differentiation of bone marrow stem cells were promoted on the RAM with osteoid-like stiffness, specifically on the oxidized RAM. The in vivo evidence revealed that nonoxidized RAM with osteoid-like stiffness upregulated osteogenic genes but prevented ingrowth of newly formed bone, leading to limited regeneration. Oxidized RAM with osteoid-like stiffness facilitated collagen synthesis, angiogenesis, and osteogenesis and induced robust bone formation, thereby significantly promoting maxillofacial regeneration. Overall, this study supported that in the stabilized microenvironment, oxidized RAM with osteoid-like stiffness offered requisite mechanical cues for osteogenesis and an appropriate degradation profile to facilitate bone formation. Combining the 3D-printed hydroxyapatite scaffold and oxidized RAM with osteoid-like stiffness may be an advantageous approach for maxillofacial regeneration.

Chitosan-based 3D-printed scaffolds for bone tissue engineering

Despite the spontaneous regenerative properties of autologous bone grafts, this technique remains dilatory and restricted to fractures and injuries. Conventional grafting strategies used to treat bone tissue damage have several limitations. This highlights the need for novel approaches to overcome the persisting challenges. Tissue-like constructs that can mimic natural bone structurally and functionally represent a promising strategy. Bone tissue engineering (BTE) is an approach used to develop bioengineered bone with subtle architecture. BTE utilizes biomaterials to accommodate cells and deliver signaling molecules required for bone rejuvenation. Among the various techniques available for scaffold creation, 3D-printing technology is considered to be a superior technique as it enables the design of functional scaffolds with well-defined customizable properties. Among the biomaterials obtained from natural, synthetic, or ceramic origins, naturally derived chitosan (CS) polymers are promising candidates for fabricating reliable tissue constructs. In this review, the physicochemical-biological properties and applications of CS-based 3D-printed scaffolds and their future perspectives in BTE are summarized.

Gradient scaffolds for osteochondral tissue engineering and regeneration

The tissue engineering approach for repairing osteochondral (OC) defects involves the fabrication of a biological tissue scaffold that mimics the physiological properties of natural OC tissue (e.g., the gradient transition between the cartilage surface and the subchondral bone). The OC tissue scaffolds described in many research studies exhibit a discrete gradient (e.g., a biphasic or tri/multiphasic structure) or a continuous gradient to mimic OC tissue attributes such as biochemical composition, structure, and mechanical properties. One advantage of a continuous gradient scaffold over biphasic or tri/multiphasic tissue scaffolds is that it more closely mimics natural OC tissue since there is no distinct interface between each layer. Although research studies to this point have yielded good results related to OC regeneration with tissue scaffolds, differences between engineered scaffolds and natural OC tissue remain; due to these differences, current clinical therapies to repair OC defects with engineered scaffolds have not been successful. This paper provides an overview of both discrete and continuous gradient OC tissue scaffolds in terms of cell type, scaffold material, microscale structure, mechanical properties, fabrication methods, and scaffold stimuli. Fabrication of gradient scaffolds with three-dimensional (3D) printing is given special emphasis due to its ability to accurately control scaffold pore geometry. Moreover, the application of computational modeling in OC tissue engineering is considered; for example, efforts to optimize the scaffold structure, mechanical properties, and physical stimuli generated within the scaffold-bioreactor system to predict tissue regeneration are considered. Finally, challenges associated with the repair of OC defects and recommendations for future directions in OC tissue regeneration are proposed.

3D-printed gelatin methacrylate (GelMA)/silanated silica scaffold assisted by two-stage cooling system for hard tissue regeneration

Among many biomaterials, gelatin methacrylate (GelMA), a photocurable protein, has been widely used in 3D bioprinting process owing to its excellent cellular responses, biocompatibility and biodegradability. However, GelMA still shows a low processability due to the severe temperature dependence of viscosity. To overcome this obstacle, we propose a two-stage temperature control system to effectively control the viscosity of GelMA. To optimize the process conditions, we evaluated the temperature of the cooling system (jacket and stage). Using the established system, three GelMA scaffolds were fabricated in which different concentrations (0, 3 and 10 wt%) of silanated silica particles were embedded. To evaluate the performances of the prepared scaffolds suitable for hard tissue regeneration, we analyzed the physical (viscoelasticity, surface roughness, compressive modulus and wettability) and biological (human mesenchymal stem cells growth, western blotting and osteogenic differentiation) properties. Consequently, the composite scaffold with greater silica contents (10 wt%) showed enhanced physical and biological performances including mechanical strength, cell initial attachment, cell proliferation and osteogenic differentiation compared with those of the controls. Our results indicate that the GelMA/silanated silica composite scaffold can be potentially used for hard tissue regeneration.

Challenges and Innovations in Osteochondral Regeneration: Insights from Biology and Inputs from Bioengineering toward the Optimization of Tissue Engineering Strategies

Due to the extremely high incidence of lesions and diseases in aging population, it is critical to put all efforts into developing a successful implant for osteochondral tissue regeneration. Many of the patients undergoing surgery present osteochondral fissure extending until the subchondral bone (corresponding to a IV grade according to the conventional radiographic classification by Berndt and Harty). Therefore, strategies for functional tissue regeneration should also aim at healing the subchondral bone and joint interface, besides hyaline cartilage. With the ambition of contributing to solving this problem, several research groups have been working intensively on the development of tailored implants that could promote that complex osteochondral regeneration. These implants may be manufactured through a wide variety of processes and use a wide variety of (bio)materials. This review aimed to examine the state of the art regarding the challenges, advantages, and drawbacks of the current strategies for osteochondral regeneration. One of the most promising approaches relies on the principles of additive manufacturing, where technologies are used that allow for the production of complex 3D structures with a high level of control, intended and predefined geometry, size, and interconnected pores, in a reproducible way. However, not all materials are suitable for these processes, and their features should be examined, targeting a successful regeneration.

Comparative Analysis of 3D-Printed Artificial Vertebral Body Versus Titanium Mesh Cage in Repairing Bone Defects Following Single-Level Anterior Cervical Corpectomy and Fusion

Background

The aim of this study was to compare the clinical and radiological outcomes of the 3D-printed artificial vertebral body vs the titanium mesh cage in repairing bone defects for single-level anterior cervical corpectomy and fusion (ACCF).

Material/Methods

A total of 51 consecutive patients who underwent single-level ACCF in Huai’an Second People’s Hospital from July 2017 to August 2020 were retrospectively reviewed. According to the implant materials used, patients were divided into a 3D-printed artificial vertebral body group (3D-printed group) (n=20; 12 males, 8 females) and a titanium mesh cage group (TMC group) (n=31; 15 males, 16 females). General data, radiological parameters, and clinical outcomes were recorded.

Results

The rate of subsidence in the 3D-printed group (0.01, 2/20) was lower than in the TMC group (0.29, 9/31) (P<0.05). HAE and HPE of the patients in the 3D-printed group were significantly higher than those in the TMC group (P<0.05). C2–C7 Cobb angle and SA of the patients in the 3D-printed group were significantly larger than those in the TMC group (P<0.05). All patients in the 2 groups showed significant improvement in VAS, JOA, and NDI scores at 3 months and 1 year after surgery.

Conclusions

3D-printed artificial vertebral body helps maintain intervertebral height and cervical physiological curvature and is a good candidate for ACCF.

In vitro bone metastasis dwelling in a 3D bioengineered niche

Bone is the most frequent metastasis site for breast cancer. As well as dramatically increasing disease burden, bone metastases are also an indicator of poor prognosis. One of the main challenges in investigating bone metastasis in breast cancer is engineering in vitro models that replicate the features of in vivo bone environments. Such in vitro models ideally enable the biology of the metastatic cells to mimic their in vivo behavior as closely as possible. Here, taking benefit of cutting-edge technologies both in microfabrication and cancer cell biology, we have developed an in vitro breast cancer bone-metastasis model. To do so we first 3D printed a bone scaffold that reproduces the trabecular architecture and that can be conditioned with osteoblast-like cells, a collagen matrix, and mineralized calcium. We thus demonstrated that this device offers an adequate soil to seed primary breast cancer bone metastatic cells. In particular, patient-derived xenografts being considered as a better approach than cell lines to achieve clinically relevant results, we demonstrate the ability of this biomimetic bone niche model to host patient-derived xenografted metastatic breast cancer cells. These patient-derived xenograft cells show a long-term survival in the bone model and maintain their cycling propensity, and exhibit the same modulated drug response as in vivo. This experimental system enables access to the idiosyncratic features of the bone microenvironment and cancer bone metastasis, which has implications for drug testing.

Tissue Engineering and Three-Dimensional Printing in Periodontal Regeneration: A Literature Review

The three-dimensional printing of scaffolds is an interesting alternative to the traditional techniques of periodontal regeneration. This technique uses computer assisted design and manufacturing after CT scan. After 3D modelling, individualized scaffolds are printed by extrusion, selective laser sintering, stereolithography, or powder bed inkjet printing. These scaffolds can be made of one or several materials such as natural polymers, synthetic polymers, or bioceramics. They can be monophasic or multiphasic and tend to recreate the architectural structure of the periodontal tissue. In order to enhance the bioactivity and have a higher regeneration, the scaffolds can be embedded with stem cells and/or growth factors. This new technique could enhance a complete periodontal regeneration. This review summarizes the application of 3D printed scaffolds in periodontal regeneration. The process, the materials and designs, the key advantages and prospects of 3D bioprinting are highlighted, providing new ideas for tissue regeneration.

Crosslinking of Polylactide by High Energy Irradiation and Photo-Curing

Polylactide (PLA) is presently the most studied bioderived polymer because, in addition to its established position as a material for biomedical applications, it can replace mass production plastics from petroleum. However, some drawbacks of polylactide such as insufficient mechanical properties at a higher temperature and poor shape stability have to be overcome. One of the methods of mechanical and thermal properties modification is crosslinking which can be achieved by different approaches, both at the stage of PLA-based materials synthesis and by physical modification of neat polylactide. This review covers PLA crosslinking by applying different types of irradiation, i.e., high energy electron beam or gamma irradiation and UV light which enables curing at mild conditions. In the last section, selected examples of biomedical applications as well as applications for packaging and daily-use items are presented in order to visualize how a variety of materials can be obtained using specific methods.

Regeneration of critical-sized mandibular defect using a 3D-printed hydroxyapatite-based scaffold: An exploratory study

BACKGROUND

Three-dimensional (3D) printing has become an available technology to fabricate customized tissue engineering scaffolds with delicate architecture. This exploratory study aimed to evaluate the potential of a 3D-printed hydroxyapatite-based scaffold as a biomaterial for obtaining guided bone regeneration (GBR) in vivo.

METHODS

Scaffolds composed of 90% hydroxyapatite and 10% poly(lactic-co-glycolic acid) were printed using a microextrusion process to fit 4 mm diameter and 0.5 mm thick through-and-through osseous defects on the mandibular ramus of rats, with unfilled defects serving as controls. Specimens were analyzed for regeneration-associated gene expression on day 7, and micro-computed tomography (micro-CT) and histology assessments were carried out on day 28.

RESULTS

The scaffolds were 3.56 ± 0.43 mm (x-axis) and 4.02 ± 0.44 mm (y-axis) in diameter and 0.542 ± 0.035 mm thick (z-axis), with a mean pore size of 0.420 ± 0.028 × 0.328 ± 0.005 mm² . Most scaffolds fit the defects well. Type I collagen, VEGF, and Cbfa1 were upregulated in the scaffold-treated defects by day 7. By day 28, de novo osteogenesis and scaffold-tissue integration were evident in the scaffold-treated defects, and entire mineralized tissue, as well as newly formed bone, was significantly promoted, as seen in the micro-CT and histologic analyses.

CONCLUSION

The 3D-printed hydroxyapatite-based scaffold showed acceptable dimensional stability and demonstrated favorable osteoregenerative capability that fulfilled the need for GBR.

Effect of Stereolithography 3D Printing on the Properties of PEGDMA Hydrogels

Stereolithography (SLA)-based 3D printing has proven to have several advantages over traditional fabrication techniques as it allows for the control of hydrogel synthesis at a very high resolution, making possible the creation of tissue-engineered devices with microarchitecture similar to the tissues they are replacing. Much of the previous work in hydrogels for tissue engineering applications have utilised the ultraviolet (UV) chamber bulk photopolymerisation method for preparing test specimens. Therefore, it is essential to directly compare SLA 3D printing to this more traditional approach to elucidate the differences in hydrogels prepared by each fabrication method. Polyethyleneglycol dimethacrylate (PEGDMA) is an ideally suited material for a comparative study of the impact that SLA fabrication has on performance, as the properties of traditional UV chamber-cured hydrogels have been extensively characterised. The present study was conducted to compare the material properties of PEGDMA hydrogels prepared using UV chamber photopolymerisation and SLA 3D printing. From the subsequent testing, SLA-fabricated hydrogels were shown to maintain similar thermal and chemical performance to UV chamber-cured hydrogels but had a higher compressive strength and tensile stiffness, as well as increased hydrophilicity. These differences are attributed to the increased exposure to UV light SLA samples received compared to traditionally UV chamber-cured samples.

Challenges on optimization of 3D-printed bone scaffolds

Advances in biomaterials and the need for patient-specific bone scaffolds require modern manufacturing approaches in addition to a design strategy. Hybrid materials such as those with functionally graded properties are highly needed in tissue replacement and repair. However, their constituents, proportions, sizes, configurations and their connection to each other are a challenge to manufacturing. On the other hand, various bone defect sizes and sites require a cost-effective readily adaptive manufacturing technique to provide components (scaffolds) matching with the anatomical shape of the bone defect. Additive manufacturing or three-dimensional (3D) printing is capable of fabricating functional physical components with or without porosity by depositing the materials layer-by-layer using 3D computer models. Therefore, it facilitates the production of advanced bone scaffolds with the feasibility of making changes to the model. This review paper first discusses the development of a computer-aided-design (CAD) approach for the manufacture of bone scaffolds, from the anatomical data acquisition to the final model. It also provides information on the optimization of scaffold's internal architecture, advanced materials, and process parameters to achieve the best biomimetic performance. Furthermore, the review paper describes the advantages and limitations of 3D printing technologies applied to the production of bone tissue scaffolds.

Effect of the nano/microscale structure of biomaterial scaffolds on bone regeneration

Natural bone is a mineralized biological material, which serves a supportive and protective framework for the body, stores minerals for metabolism, and produces blood cells nourishing the body. Normally, bone has an innate capacity to heal from damage. However, massive bone defects due to traumatic injury, tumor resection, or congenital diseases pose a great challenge to reconstructive surgery. Scaffold-based tissue engineering (TE) is a promising strategy for bone regenerative medicine, because biomaterial scaffolds show advanced mechanical properties and a good degradation profile, as well as the feasibility of controlled release of growth and differentiation factors or immobilizing them on the material surface. Additionally, the defined structure of biomaterial scaffolds, as a kind of mechanical cue, can influence cell behaviors, modulate local microenvironment and control key features at the molecular and cellular levels. Recently, nano/micro-assisted regenerative medicine becomes a promising application of TE for the reconstruction of bone defects. For this reason, it is necessary for us to have in-depth knowledge of the development of novel nano/micro-based biomaterial scaffolds. Thus, we herein review the hierarchical structure of bone, and the potential application of nano/micro technologies to guide the design of novel biomaterial structures for bone repair and regeneration.

Multimaterial Dual Gradient Three-Dimensional Printing for Osteogenic Differentiation and Spatial Segregation

In this study of three-dimensional (3D) printed composite β-tricalcium phosphate (β-TCP)-/hydroxyapatite/poly(ɛ-caprolactone)-based constructs, the effects of vertical compositional ceramic gradients and architectural porosity gradients on the osteogenic differentiation of rabbit bone marrow-derived mesenchymal stem cells (MSCs) were investigated. Specifically, three different concentrations of β-TCP (0, 10, and 20 wt%) and three different porosities (33% ± 4%, 50% ± 4%, and 65% ± 3%) were examined to elucidate the contributions of chemical and physical gradients on the biochemical behavior of MSCs and the mineralized matrix production within a 3D culture system. By delaminating the constructs at the gradient transition point, the spatial separation of cellular phenotypes could be specifically evaluated for each construct section. Results indicated that increased concentrations of β-TCP resulted in upregulation of osteogenic markers, including alkaline phosphatase activity and mineralized matrix development. Furthermore, MSCs located within regions of higher porosity displayed a more mature osteogenic phenotype compared to MSCs in lower porosity regions. These results demonstrate that 3D printing can be leveraged to create multiphasic gradient constructs to precisely direct the development and function of MSCs, leading to a phenotypic gradient. Impact Statement In this study, three-dimensional (3D) printed ceramic/polymeric constructs containing discrete vertical gradients of both composition and porosity were fabricated to precisely control the osteogenic differentiation of mesenchymal stem cells. By making simple alterations in construct architecture and composition, constructs containing heterogenous populations of cells were generated, where gradients in scaffold design led to corresponding gradients in cellular phenotype. The study demonstrates that 3D printed multiphasic composite constructs can be leveraged to create complex heterogeneous tissues and interfaces.

In vitro and in vivo biocompatibility of calcium-phosphate scaffolds three-dimensional printed by stereolithography for bone regeneration

Stereolithography (SLA) is an interesting manufacturing technology to overcome limitations of commercially available particulated biomaterials dedicated to intra-oral bone regeneration applications. The purpose of this study was to evaluate the in vitro and in vivo biocompatibility and osteoinductive properties of two calcium-phosphate (CaP)-based scaffolds manufactured by SLA three-dimensional (3D) printing. Pellets and macro-porous scaffolds were manufactured in pure hydroxyapatite (HA) and in biphasic CaP (HA:60-TCP:40). Physico-chemical characterization was performed using micro X-ray fluorescence, scanning electron microscopy (SEM), optical interferometry, and microtomography (μCT) analyses. Osteoblast-like MG-63 cells were used to evaluate the biocompatibility of the pellets in vitro with MTS assay and the cell morphology and growth characterized by SEM and DAPI-actin staining showed similar early behavior. For in vivo biocompatibility, newly formed bone and biodegradability of the experimental scaffolds were evaluated in a subperiosteal cranial rat model using μCT and descriptive histology. The histological analysis has not indicated evidences of inflammation but highlighted close contacts between newly formed bone and the experimental biomaterials revealing an excellent scaffold osseointegration. This study emphasizes the relevance of SLA 3D printing of CaP-based biomaterials for intra-oral bone regeneration even if manufacturing accuracy has to be improved and further experiments using biomimetic scaffolds should be conducted.

A review of biomaterials scaffold fabrication in additive manufacturing for tissue engineering

The current developments in three-dimensional printing also referred as “additive manufacturing” have transformed the scenarios for modern manufacturing and engineering design processes which show greatest advantages for the fabrication of complex structures such as scaffold for tissue engineering. This review aims to introduce additive manufacturing techniques in tissue engineering, types of biomaterials used in scaffold fabrication, as well as in vitro and in vivo evaluations. Biomaterials and fabrication methods could critically affect the outcomes of scaffold mechanical properties, design architectures, and cell proliferations. In addition, an ideal scaffold aids the efficiency of cell proliferation and allows the movements of cell nutrient inside the human body with their specific material properties. This article provides comprehensive review that covers broad range of all the biomaterial types using various additive manufacturing technologies. The data were extracted from 2008 to 2018 mostly from Google Scholar, ScienceDirect, and Scopus using keywords such as “Additive Manufacturing,” “3D Printing,” “Tissue Engineering,” “Biomaterial” and “Scaffold.” A 10 years research in this area was found to be mostly focused toward obtaining an ideal scaffold by investigating the fabrication strategies, biomaterials compatibility, scaffold design effectiveness through computer-aided design modeling, and optimum printing machine parameters identification. As a conclusion, this ideal scaffold fabrication can be obtained with the combination of different materials that could enhance the material properties which performed well in optimum additive manufacturing condition. Yet, there are still many challenges from the printing methods, bioprinting and cell culturing that needs to be discovered and investigated in the future.

Fabrication and Evaluation of 3D Printed Poly(l-lactide) Scaffold Functionalized with Quercetin-Polydopamine for Bone Tissue Engineering

Quercetin (Qu), a bioflavonoid, has been reported to positively affect bone metabolism. For the first time, Qu with different concentrations was utilized to functionalize 3D-printed poly(l-lactide) (PLLA) scaffold with the aid of a polydopamine (PDA) layer through a convenient and effective way in this study. Results revealed that the coexistence of PDA and Qu can capacitate the 3D-printed PLLA scaffold to possess rougher surface, as well as better hydrophilicity and compressive properties. The resulting PDA- and Qu-modified PLLA scaffolds (Qu/PD-PLLA) can sustainably release Qu to some extent, which is more beneficial to the proliferation and attachment of MC3T3-E1 cells, upregulating ALP activity and calcium nodules as well as promoting the expression of related osteogenic genes and proteins. More significantly, such a positive impact of the Qu on the cell affinity and osteogenic activity played in a dose-dependent manner. This study revealed the potential of the 3D-printed Qu/PD-PLLA scaffolds with a certain amount of Qu as bone-repair materials.

Poly(propylene fumarate)-based materials: Synthesis, functionalization, properties, device fabrication and biomedical applications

Poly(propylene fumarate) (PPF) is a biodegradable polymer that has been investigated extensively over the last three decades. It has led many scientists to synthesize and fabricate a variety of PPF-based materials for biomedical applications due to its controllable mechanical properties, tunable degradation and biocompatibility. This review provides a comprehensive overview of the progress made in improving PPF synthesis, resin formulation, crosslinking, device fabrication and post polymerization modification. Further, we highlight the influence of these parameters on biodegradation, biocompatibility, and their use in a number of regenerative medicine applications, especially bone tissue engineering. In particular, the use of 3D printing techniques for the fabrication of PPF-based scaffolds is extensively reviewed. The recent invention of a ring-opening polymerization method affords precise control of PPF molecular mass, molecular mass distribution (Ɖ_M) and viscosity. Low Ɖ_M facilitates time-certain resorption of 3D printed structures. Novel post-polymerization and post-printing functionalization methods have accelerated the expansion of biomedical applications that utilize PPF-based materials. Finally, we shed light on evolving uses of PPF-based materials for orthopedics/bone tissue engineering and other biomedical applications, including its use as a hydrogel for bioprinting.

Comparison of Decellularized Cow and Human Bone for Engineering Bone Grafts with Human Induced Pluripotent Stem Cells

IMPACT STATEMENT

Decellularized tissue matrices are popular as scaffolding materials for tissue engineering application. However, it is unclear whether interspecies differences in tissue parameters influence the quality of tissue grafts that are engineered using human stem cells. In this study, decellularized cow and human bone scaffolds were compared for engineering bone grafts using human induced pluripotent stem cell-derived mesodermal progenitor cells and despite minor differences in architecture and mass composition, both scaffolds equally support cell viability and tissue mineralization. Decellularized cow bone scaffolds therefore represent a suitable and more affordable alternative for engineering human bone grafts for basic and applied research.

Micro-CT - a digital 3D microstructural voyage into scaffolds: a systematic review of the reported methods and results

BACKGROUND

Cell behavior is the key to tissue regeneration. Given the fact that most of the cells used in tissue engineering are anchorage-dependent, their behavior including adhesion, growth, migration, matrix synthesis, and differentiation is related to the design of the scaffolds. Thus, characterization of the scaffolds is highly required. Micro-computed tomography (micro-CT) provides a powerful platform to analyze, visualize, and explore any portion of interest in the scaffold in a 3D fashion without cutting or destroying it with the benefit of almost no sample preparation need.

MAIN BODY

This review highlights the relationship between the scaffold microstructure and cell behavior, and provides the basics of the micro-CT method. In this work, we also analyzed the original papers that were published in 2016 through a systematic search to address the need for specific improvements in the methods section of the papers including the amount of provided information from the obtained results.

CONCLUSION

Micro-CT offers a unique microstructural analysis of biomaterials, notwithstanding the associated challenges and limitations. Future studies that will include micro-CT characterization of scaffolds should report the important details of the method, and the derived quantitative and qualitative information can be maximized.

3D bioactive composite scaffolds for bone tissue engineering

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. Developing bioactive three-dimensional (3D) scaffolds to support bone regeneration has therefore become a key area of focus within bone tissue engineering (BTE). A variety of materials and manufacturing methods including 3D printing have been used to create novel alternatives to traditional bone grafts. However, individual groups of materials including polymers, ceramics and hydrogels have been unable to fully replicate the properties of bone when used alone. Favourable material properties can be combined and bioactivity improved when groups of materials are used together in composite 3D scaffolds. This review will therefore consider the ideal properties of bioactive composite 3D scaffolds and examine recent use of polymers, hydrogels, metals, ceramics and bio-glasses in BTE. Scaffold fabrication methodology, mechanical performance, biocompatibility, bioactivity, and potential clinical translations will be discussed.