3D printing of bone tissue engineering scaffolds

Fabrication and assessment of a novel hybrid scaffold consisted of polyurethane-gellan gum-hyaluronic acid-glucosamine for meniscus tissue engineering

The meniscus has inadequate intrinsic regenerative capacity and its damage can lead to degeneration of articular cartilage. Meniscus tissue engineering aims to restore an injured meniscus followed by returning its normal function through bioengineered scaffolds. In the present study, the structural and biological properties of 3D-printed polyurethane (PU) scaffolds dip-coated with gellan gum (GG), hyaluronic acid (HA), and glucosamine (GA) were investigated. The optimum concentration of GG was 3% (w/v) with maintaining porosity at 88.1%. The surface coating of GG-HA-GA onto the PU scaffolds increased the compression modulus from 30.30 kPa to 59.10 kPa, the water uptake ratio from 27.33% to 60.80%, degradation rate from 5.18% to 8.84%, whereas the contact angle was reduced from 104.8° to 59.3°. MTT assay, acridine orange/ethidium bromide (AO/EB) fluorescent staining, and SEM were adopted to assess the behavior of the seeded chondrocytes on scaffolds, and it was found that the ternary surface coating stimulated the cell proliferation, viability, and adhesion. Moreover, the coated scaffolds showed higher expression levels of collagen II and aggrecan genes at day 7 compared to the control groups. Therefore, the fabricated PU-3% (w/v) GG-HA-GA scaffold can be considered as a promising scaffold for meniscus tissue engineering.

Bacterial Polyglucuronic Acid/Alginate/Carbon Nanofibers Hydrogel Nanocomposite as a Potential Scaffold for Bone Tissue Engineering

3D nanocomposite scaffolds have attracted significant attention in bone tissue engineering applications. In the current study, we fabricated a 3D nanocomposite scaffold based on a bacterial polyglucuronic acid (PGU) and sodium alginate (Alg) composite with carbon nanofibers (CNFs) as the bone tissue engineering scaffold. The CNFs were obtained from electrospun polyacrylonitrile nanofibers through heat treatment. The fabricated CNFs were incorporated into a PGU/Alg polymeric solution, which was physically cross-linked using CaCl2 solution. The fabricated nanocomposites were characterized to evaluate the internal structure, porosity, swelling kinetics, hemocompatibility, and cytocompatibility. The characterizations indicated that the nanocomposites have a porous structure with interconnected pores architecture, proper water absorption, and retention characteristics. The in vitro studies revealed that the nanocomposites were hemocompatible with negligible hemolysis induction. The cell viability assessment showed that the nanocomposites were biocompatible and supported bone cell growth. These results indicated that the fabricated bacterial PGU/Alg/CNFs hydrogel nanocomposite exhibited appropriate properties and can be considered a new biomaterial for bone tissue engineering scaffolds.

Engineering 3D Printed Scaffolds with Tunable Hydroxyapatite

Orthopedic and craniofacial surgical procedures require the reconstruction of bone defects caused by trauma, diseases, and tumor resection. Successful bone restoration entails the development and use of bone grafts with structural, functional, and biological features similar to native tissues. Herein, we developed three-dimensional (3D) printed fine-tuned hydroxyapatite (HA) biomimetic bone structures, which can be applied as grafts, by using calcium phosphate cement (CPC) bioink, which is composed of tetracalcium phosphate (TTCP), dicalcium phosphate anhydrous (DCPA), and a liquid [Polyvinyl butyral (PVB) dissolved in ethanol (EtOH)]. The ink was ejected through a high-resolution syringe nozzle (210 µm) at room temperature into three different concentrations (0.01, 0.1, and 0.5) mol/L of the aqueous sodium phosphate dibasic (Na2HPO4) bath that serves as a hardening accelerator for HA formation. Raman spectrometer, X-ray diffraction (XRD), and scanning electron microscopy (SEM) demonstrated the real-time HA formation in (0.01, 0.1, and 0.5) mol/L Na2HPO4 baths. Under those conditions, HA was formed at different amounts, which tuned the scaffolds' mechanical properties, porosity, and osteoclast activity. Overall, this method may pave the way to engineer 3D bone scaffolds with controlled HA composition and pre-defined properties, which will enhance graft-host integration in various anatomic locations.

Bone Healing Materials in the Treatment of Recalcitrant Nonunions and Bone Defects

The usual treatment for bone defects and recalcitrant nonunions is an autogenous bone graft. However, due to the limitations in obtaining autogenous bone grafts and the morbidity associated with their procurement, various bone healing materials have been developed in recent years. The three main treatment strategies for bone defects and recalcitrant nonunions are synthetic bone graft substitutes (BGS), BGS combined with bioactive molecules, and BGS and stem cells (cell-based constructs). Regarding BGS, numerous biomaterials have been developed to prepare bone tissue engineering scaffolds, including biometals (titanium, iron, magnesium, zinc), bioceramics (hydroxyapatite (HA)), tricalcium phosphate (TCP), biopolymers (collagen, polylactic acid (PLA), polycaprolactone (PCL)), and biocomposites (HA/MONs@miR-34a composite coating, Bioglass (BG)-based ABVF-BG (antibiotic-releasing bone void filling) putty). Bone tissue engineering scaffolds are temporary implants that promote tissue ingrowth and new bone regeneration. They have been developed to improve bone healing through appropriate designs in terms of geometric, mechanical, and biological performance. Concerning BGS combined with bioactive molecules, one of the most potent osteoinductive growth factors is bone morphogenetic proteins (BMPs). In recent years, several natural (collagen, fibrin, chitosan, hyaluronic acid, gelatin, and alginate) and synthetic polymers (polylactic acid, polyglycolic acid, polylactic-coglycolide, poly(e-caprolactone) (PCL), poly-p-dioxanone, and copolymers consisting of glycolide/trimethylene carbonate) have been investigated as potential support materials for bone tissue engineering. Regarding BGS and stem cells (cell-based constructs), the main strategies are bone marrow stromal cells, adipose-derived mesenchymal cells, periosteum-derived stem cells, and 3D bioprinting of hydrogels and cells or bioactive molecules. Currently, significant research is being performed on the biological treatment of recalcitrant nonunions and bone defects, although its use is still far from being generalized. Further research is needed to investigate the efficacy of biological treatments to solve recalcitrant nonunions and bone defects.

Poly-Alanine-ε-Caprolacton-Methacrylate as Scaffold Material with Tuneable Biomechanical Properties for Osteochondral Implants

An aging population and injury-related damage of the bone substance lead to an increasing need of innovative materials for the regeneration of osteochondral defects. Biodegradable polymers form the basis for suitable artificial implants intended for bone replacement or bone augmentation. The great advantage of these structures is the site-specific implant design, which leads to a considerable improvement in patient outcomes and significantly reduced post-operative regeneration times. Thus, biomechanical and biochemical parameters as well as the rate of degradation can be set by the selection of the polymer system and the processing technology. Within this study, we developed a polymer platform based on the amino acid Alanine and ε-Caprolacton for use as raw material for osteochondral implants. The biomechanical and degradation properties of these Poly-(Alanine-co-ε-Caprolacton)-Methacrylate (ACM) copolymers can be adjusted by changing the ratio of the monomers. Fabrication of artificial structures for musculo-skeletal tissue engineering was done by Two-Photon-Polymerization (2PP), which represents an innovative technique for generating defined scaffolds with tailor-made mechanical and structural properties. Here we show the synthesis, physicochemical characterization, as well as first results for structuring ACM using 2PP technology. The data demonstrate the high potential of ACM copolymers as precursors for the fabrication of biomimetic implants for bone-cartilage reconstruction.

Targeted Delivery of Chemotherapeutic Agents for Osteosarcoma Treatment

Since osteosarcoma (OS) is an aggressive bone cancer with unknown molecular pathways of etiology and pathophysiology, improving patient survival has long been a challenge. The conventional therapy is a complex multidisciplinary management that include radiotherapy, chemotherapy which followed by surgery and then post-operative adjuvant chemotherapy. However, they have severe side effects because the majority of the medicines used have just a minor selectivity for malignant tissue. As a result, treating tumor cells specifically without damaging healthy tissue is currently a primary goal in OS therapy. The coupling of chemotherapeutic drugs with targeting ligands is a unique therapy method for OS that, by active targeting, can overcome the aforementioned hurdles. This review focuses on advances in ligands and chemotherapeutic agents employed in targeted delivery to improve the capacity of active targeting and provide some insight into future therapeutic research for OS.

Surface engineering of 3D-printed scaffolds with minerals and a pro-angiogenic factor for vascularized bone regeneration

Scaffolds functionalized with biomolecules have been developed for bone regeneration but inducing the regeneration of complex structured bone with neovessels remains a challenge. For this study, we developed three-dimensional printed scaffolds with bioactive surfaces coated with minerals and platelet-derived growth factor. The minerals were homogeneously deposited on the surface of the scaffold using 0.01 M NaHCO₃ with epigallocatechin gallate in simulated body fluid solution (M2). The M2 scaffold demonstrated enhanced mineral coating amount per scaffold with a greater compressive modulus than the others which used different concentration of NaHCO₃. Then, we immobilized PDGF on the mineralized scaffold (M2/P), which enhanced the osteogenic differentiation of human adipose derived stem cells in vitro and promoted the secretion of pro-angiogenic factors. Cells cultured in M2/P showed remarkable ratio of osteocalcin- and osteopontin-positive nuclei, and M2/P-derived medium induced endothelial cells to form tubule structures. Finally, the implanted M2/P scaffolds onto mouse calvarial defects had regenerated bone in 80.8 ± 9.8% of the defect area with the arterioles were formed, after 8 weeks. In summary, our scaffold, which composed of minerals and pro-angiogenic growth factor, could be used therapeutically to improve the regeneration of bone with a highly vascularized structure. STATEMENT OF SIGNIFICANCE: Surface engineered scaffolds have been developed for bone regeneration but inducing the volumetric regeneration of bone with neovessels remains a challenge. In here, we developed 3D printed scaffolds with bioactive surfaces coated with bio-minerals and platelet-derived growth factors. We proved that the 0.01 M NaHCO₃ with polyphenol in simulated body fluid solution enhanced the deposition of bio-minerals and even distribution on the surface of scaffold. The in vitro studies demonstrated that the attached cells on the bioactive surface showed the enhanced osteogenic differentiation and secretion of pro-angiogenic factors. Finally, the scaffold with bioactive surface not only improved the regenerated volume of bone tissues but also increased neovessel formation after in vivo implantation onto mouse calvarial defect.

Bio-inspired zonal-structured matrices for bone-cartilage interface engineering

Design and development of scaffold structures for osteochondral (OC) interface regeneration is a significant engineering challenge. Recent efforts are aimed at recapitulating the unique compositional and hierarchical structure of an OC interface. Conventional scaffold fabrication techniques often have limited design control and reproducibility, and the development of OC scaffolds with zonal hierarchy and structural integrity between zones is especially challenging. In this study, a series of multi-zonal and gradient structures were designed and fabricated using three-dimensional bioprinting. We developed OC scaffolds with bi-phasic and tri-phasic configurations to support the zonal structure of OC tissue, and gradient scaffold configurations to enable smooth transitions between the zones to more closely mimic a bone-cartilage interface. A biodegradable polymer, polylactic acid, was used for the fabrication of zonal/gradient scaffolds to provide mechanical strength and support OC function. The formation of the multi-zonal and gradient scaffolds was confirmed through scanning electron microscopy imaging and micro-computed tomography scanning. Precisely controlled hierarchy with tunable porosity along the scaffold length established the formation of the bio-inspired scaffolds with different zones/gradient structure. In addition, we also developed a novel bioprinting method to selectively introduce cells into desired scaffold zones of the zonal/gradient scaffolds via concurrent printing of a cell-laden hydrogel within the porous template. Live/dead staining of the cell-laden hydrogel introduced in the cartilage zone showed uniform cell distribution with high cell viability. Overall, our study developed bio-inspired scaffold structures with structural hierarchy and mechanical integrity for bone-cartilage interface engineering.

Mechanical Property Evaluation of PLA/Soybean Oil Epoxidized Acrylate Three-Dimensional Scaffold in Bone Tissue Engineering

Recently investigated photocurable, biocompatible plant resin on tissue engineering to provide the scaffold with structural support and mechanical properties. A novel method had been used here to build our scaffold by combined the traditional three-dimensional fused deposition modeling (FDM) printing and injected the structural scaffold after fabrication with plant-based resin. The materials used are polymers a synthesized one polylactic acid and soybean oil epoxidized acrylate. The addition of soybean plant-based resin improves the adhesion and proliferation of the PLA scaffold while also providing structural support to the fabricated scaffold. The purpose of the study made optimization of printing parameters and compared different printing scaffolds to select the perfect one with preferred mechanical properties. Two designs are built (cubic design and cylinder design) to make a comparison of mechanical properties between the two designs. The novel method was used through injected soybean oil resin into the PLA scaffold by avoiding any heat and temperature rise of the resin. In the traditional method, the resin is printed using an SLA printer which exposed the resin to heating before printing, this will affect the properties of the final model in our technique temperature will eliminate by direct inject the plant-based resin into the PLA scaffold and then photocuring with ultraviolet curing device for 30 min at 405nm. Finally, the results demonstrate that after injecting PLA scaffold with soybean oil resin, the mechanical properties of the scaffold improve; additionally, the results show that the cylindrical design has more promising mechanical properties than the cubic design.

Recent advances in smart stimuli-responsive biomaterials for bone therapeutics and regeneration

Bone defects combined with tumors, infections, or other bone diseases are challenging in clinical practice. Autologous and allogeneic grafts are two main traditional remedies, but they can cause a series of complications. To address this problem, researchers have constructed various implantable biomaterials. However, the original pathological microenvironment of bone defects, such as residual tumors, severe infection, or other bone diseases, could further affect bone regeneration. Thus, the rational design of versatile biomaterials with integrated bone therapy and regeneration functions is in great demand. Many strategies have been applied to fabricate smart stimuli-responsive materials for bone therapy and regeneration, with stimuli related to external physical triggers or endogenous disease microenvironments or involving multiple integrated strategies. Typical external physical triggers include light irradiation, electric and magnetic fields, ultrasound, and mechanical stimuli. These stimuli can transform the internal atomic packing arrangements of materials and affect cell fate, thus enhancing bone tissue therapy and regeneration. In addition to the external stimuli-responsive strategy, some specific pathological microenvironments, such as excess reactive oxygen species and mild acidity in tumors, specific pH reduction and enzymes secreted by bacteria in severe infection, and electronegative potential in bone defect sites, could be used as biochemical triggers to activate bone disease therapy and bone regeneration. Herein, we summarize and discuss the rational construction of versatile biomaterials with bone therapeutic and regenerative functions. The specific mechanisms, clinical applications, and existing limitations of the newly designed biomaterials are also clarified.

Recent Advances in Enhancement Strategies for Osteogenic Differentiation of Mesenchymal Stem Cells in Bone Tissue Engineering

Although bone is an organ that displays potential for self-healing after damage, bone regeneration does not occur properly in some cases, and it is still a challenge to treat large bone defects. The development of bone tissue engineering provides a new approach to the treatment of bone defects. Among various cell types, mesenchymal stem cells (MSCs) represent one of the most promising seed cells in bone tissue engineering due to their functions of osteogenic differentiation, immunomodulation, and secretion of cytokines. Regulation of osteogenic differentiation of MSCs has become an area of extensive research over the past few years. This review provides an overview of recent research progress on enhancement strategies for MSC osteogenesis, including improvement in methods of cell origin selection, culture conditions, biophysical stimulation, crosstalk with macrophages and endothelial cells, and scaffolds. This is favorable for further understanding MSC osteogenesis and the development of MSC-based bone tissue engineering.

Photothermal scaffolds/surfaces for regulation of cell behaviors

Regulation of cell behaviors and even cell fates is of great significance in diverse biomedical applications such as cancer treatment, cell-based therapy, and tissue engineering. During the past decades, diverse methods have been developed to regulate cell behaviors such as applying external stimuli, delivering exogenous molecules into cell interior and changing the physicochemical properties of the substrates where cells adhere. Photothermal scaffolds/surfaces refer to a kind of materials embedded or coated with photothermal agents that can absorb light with proper wavelength (usually in near infrared region) and convert light energy to heat; the generated heat shows great potential for regulation of cell behaviors in different ways. In the current review, we summarize the recent research progress, especially over the past decade, of using photothermal scaffolds/surfaces to regulate cell behaviors, which could be further categorized into three types: (i) killing the tumor cells via hyperthermia or thermal ablation, (ii) engineering cells by intracellular delivery of exogenous molecules via photothermal poration of cell membranes, and (iii) releasing a single cell or an intact cell sheet via modulation of surface physicochemical properties in response to heat. In the end, challenges and perspectives in these areas are commented.

Biphasic mineralized collagen based composite scaffold for cranial bone regeneration in developing sheep

Appropriate mechanical support and excellent osteogenic capability are two essential prerequisites of customized implants for regenerating large-sized cranial bone defect. Although porous bone scaffolds have been widely proven to promote bone regeneration, their weak mechanical properties limit the clinical applications in cranioplasty. Herein, we applied two previously developed mineralized collagen-based bone scaffolds (MC), porous MC (pMC) and compact MC (cMC) to construct a biphasic MC composite bone scaffold (bMC) to repair the large-sized cranial bone defect in developing sheep. A supporting frame composed of cMC phase in the shape of tic–tac–toe structure was fabricated first and then embedded in pMC phase. The two phases had good interfacial bond, attributing to the formation of an interfacial zone. The in vivo performance of the bMC scaffold was evaluated by using a cranial bone defect model in 1-month-old sheep. The computed tomography imaging, X-ray scanning and histological evaluation showed that the pMC phase in the bMC scaffold, similar to the pMC scaffold, was gradually replaced by the regenerative bone tissues with comprehensively increased bone mineral density and complete connection of bone bridge in the whole region. The cMC frame promoted new bone formation beneath the frame without obvious degradation, thus providing appropriate mechanical protection and ensuring the structural integrity of the implant. In general, the sheep with bMC implantation exhibited the best status of survival, growth and the repair effect. The biphasic structural design may be a prospective strategy for developing new generation of cranioplasty materials to regenerate cranial bone defect in clinic.

Fabrication of Antibacterial, Osteo-Inductor 3D Printed Aerogel-Based Scaffolds by Incorporation of Drug Laden Hollow Mesoporous Silica Microparticles into the Self-Assembled Silk Fibroin Biopolymer

In this study, the novel biomimetic aerogel-based composite scaffolds through a synergistic combination of wet chemical synthesis and advanced engineering approaches have successfully designed. To this aim, initially the photo-crosslinkable methacrylated silk fibroin (SF-MA) biopolymer and methacrylated hollow mesoporous silica microcapsules (HMSC-MA) as the main constituents of the novel composite aerogels were synthesized. Afterward, by incorporation of drug-loaded HMSC-MA into the self-assembled SF-MA, printable gel-based composite inks are developed. By exploiting micro-extrusion-based three-dimensional (3D) printing, SF-MA-HMSC composite gels are printed by careful controlling their viscosity to provide a means to control the shape fidelity of the resulted printed gel constructs. The developed scaffold has shown a multitude of interesting biophysical and biological performances. Namely, thanks to the photo-crosslinking of the gel components during the 3D printing, the scaffolds become mechanically more stable than the pristine SF scaffolds. Also, freeze-casting the printed constructs generates further interconnectivity in the printed pore struts resulting in the scaffolds with hierarchically organized porosities necessary for cell infiltration and growth. Importantly, HMSC incorporated scaffolds promote antibacterial drug delivery, cellular ingrowth and proliferation, promoting osteoblastic differentiation by inducing the expression of osteogenic markers and matrix mineralization. Finally, the osteoconductive, -inductive, and anti-infective composite aerogels are expected to act as excellent bone implanting materials with an extra feature of local and sustained release of drug for efficient therapy of bone-related diseases.

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.

Recent approaches towards bone tissue engineering

Bone tissue engineering approaches have evolved towards addressing the challenges of tissue mimetic requirements over the years. Different strategies have been combining scaffolds, cells, and biologically active cues using a wide range of fabrication techniques, envisioning the mimicry of bone tissue. On the one hand, biomimetic scaffold-based strategies have been pursuing different biomaterials to produce scaffolds, combining with diverse and innovative fabrication strategies to mimic bone tissue better, surpassing bone grafts. On the other hand, biomimetic scaffold-free approaches mainly foresee replicating endochondral ossification, replacing hyaline cartilage with new bone. Finally, since bone tissue is highly vascularized, new strategies focused on developing pre-vascularized scaffolds or pre-vascularized cellular aggregates have been a motif of study. The recent biomimetic scaffold-based and scaffold-free approaches in bone tissue engineering, focusing on materials and fabrication methods used, are overviewed herein. The biomimetic vascularized approaches are also discussed, namely the development of pre-vascularized scaffolds and pre-vascularized cellular aggregates.

Electrospun Nanofibers for Bone Regeneration: From Biomimetic Composition, Structure to Function

In recent years, a variety of novel materials and processing technologies have been developed to prepare tissue engineering scaffolds for bone defect repair. Among them, nanofibers fabricated via electrospinning technology...

Nanomicelles-in-Coaxial Nanofibers with Exit Channels as Transdermal Delivery Platform for Smoking Cessation

Smoking has turned to a life-threatening habit; that is why many nicotine-replacement therapies (NRTs) were reported for smoking cessation including chewing gums, nicotine patches, lozenges, mouth sprays, inhalers and nasal...

3D-Printed PCL Scaffolds Coated with Nanobioceramics Enhance Osteogenic Differentiation of Stem Cells

With advances in bone tissue engineering, various materials and methods have been explored to find a better scaffold that can help in improving bone growth and regeneration. Three-dimensional (3D) printing by fused deposition modeling can produce customized scaffolds from biodegradable polyesters such as polycaprolactone (PCL). Although the fabricated PCL scaffolds exhibited a lack of bioactivity and poor cell attachment on their surfaces, herein, using a simple postfabrication modification method with hydroxyapatite (HA) and bioglasses (BGs), we obtained better cell proliferation and attachment. Biological behavior and osteosupportive capacity of the 3D-printed scaffolds including PCL, PCL/HA, PCL/BG, and PCL/HA/BG were evaluated in this study, while human adipose tissue-derived mesenchymal stem cells (hADSCs) were cultured on the scaffolds. The cell morphology, attachment, and proliferation were investigated using scanning electron microscopy (SEM), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, and 4',6-diamidino-2-phenylindole (DAPI) staining. In the next step, the ability of stem cells to differentiate into osteoblasts was evaluated by measuring alkaline phosphatase (ALP) activity, calcium deposition, and bone-related gene and protein expression. In the end, the expression levels of miR-20a, miR-125a, and their target genes were also investigated as positive and negative regulators in osteogenesis pathways. The results showed that the coated scaffolds with bioceramics present a more appropriate surface for cell adhesion and proliferation, as well as efficient potential in inducing osteoconduction and osteointegration compared to PCL alone and control. The PCL/HA/BG scaffold exhibited higher in vitro cell viability and bone formation compared to the other groups, which can be due to the synergistic effect of HA and BG. On the whole, this tricomponent 3D-printing scaffold has a promising prospect for bone tissue engineering applications.

Synthesis of Silica-Based Solid-Acid Catalyst Material as a Potential Osteochondral Repair Model In Vitro

For osteochondral damage, the pH value change of the damaged site will influence the repair efficacy of the patient. For better understanding the mechanism of the acid-base effect, the construction of in vitro model is undoubtedly a simple and interesting work to evaluate the influence. Here, a novel porous silica-based solid-acid catalyst material was prepared by additive manufacturing technology, exhibiting improved eliminating effects of the residue. SEM, FTIR, and TGA were used to characterize the morphology, structure, and thermal stability of the synthesized 3D material. The reaction between 4-methoxybenzyl alcohol and 3, 4-dihydro-2H-pyran was used as a template reaction to evaluate the eliminating performance of the 3D porous material. Solvents were optimized, and three reaction groups in the presence of 3D SiO2, 3D SiO2-SO3H, and 3D SiO2-NH-SO3H, as well as one without catalyst, were compared. In addition, in consideration of the complicated situation of the physiological environment in vivo, universality of the synthesized 3D SiO2-NH-SO3H catalyst material was studied with different alcohols. The results showed that the sulfonic acid-grafted 3D material had excellent catalytic performance, achieving a yield over 95% in only 20 min. Besides, the catalyst material can be recycled at least 10 times, with yields still higher than 90%. Such a solid catalyst material is expected to have great potential in additive manufacturing because the catalyst material is easy-recyclable, renewable and biocompatible. The 3D material with connective channels may also be utilized as an in vitro model for environment evaluation of osteochondral repair in the future.

Applying extrusion-based 3D printing technique accelerates fabricating complex biphasic calcium phosphate-based scaffolds for bone tissue regeneration

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Biphasic calcium phosphates offer a chemically similar biomaterial to the natural bone, which can significantly accelerate bone formation and reconstruction.

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Robocasting is a suitable technique to produce porous scaffolds supporting cell viability, proliferation, and differentiation.

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This review discusses materials and methods utilized for BCP robocasting, considering recent advancements and existing challenges in using additives for bioink preparation.

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Commercialization and marketing approach, in-vitro and in-vivo evaluations, biologic responses, and post-processing steps are also investigated.

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Possible strategies and opportunities for the use of BCP toward injured bone regeneration along with clinical applications are discussed.

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The study proposes that BCP possesses an acceptable level of bone substituting, considering its challenges and struggles.

Background

Aim of review

Key scientific concepts of review

Perspective of the GEMSTONE Consortium on Current and Future Approaches to Functional Validation for Skeletal Genetic Disease Using Cellular, Molecular and Animal-Modeling Techniques

The availability of large human datasets for genome-wide association studies (GWAS) and the advancement of sequencing technologies have boosted the identification of genetic variants in complex and rare diseases in the skeletal field. Yet, interpreting results from human association studies remains a challenge. To bridge the gap between genetic association and causality, a systematic functional investigation is necessary. Multiple unknowns exist for putative causal genes, including cellular localization of the molecular function. Intermediate traits ("endophenotypes"), e.g. molecular quantitative trait loci (molQTLs), are needed to identify mechanisms of underlying associations. Furthermore, index variants often reside in non-coding regions of the genome, therefore challenging for interpretation. Knowledge of non-coding variance (e.g. ncRNAs), repetitive sequences, and regulatory interactions between enhancers and their target genes is central for understanding causal genes in skeletal conditions. Animal models with deep skeletal phenotyping and cell culture models have already facilitated fine mapping of some association signals, elucidated gene mechanisms, and revealed disease-relevant biology. However, to accelerate research towards bridging the current gap between association and causality in skeletal diseases, alternative in vivo platforms need to be used and developed in parallel with the current -omics and traditional in vivo resources. Therefore, we argue that as a field we need to establish resource-sharing standards to collectively address complex research questions. These standards will promote data integration from various -omics technologies and functional dissection of human complex traits. In this mission statement, we review the current available resources and as a group propose a consensus to facilitate resource sharing using existing and future resources. Such coordination efforts will maximize the acquisition of knowledge from different approaches and thus reduce redundancy and duplication of resources. These measures will help to understand the pathogenesis of osteoporosis and other skeletal diseases towards defining new and more efficient therapeutic targets.

Design of 3D Scaffolds for Hard Tissue Engineering: From Apatites to Silicon Mesoporous Materials

Advanced bioceramics for bone regeneration constitutes one of the pivotal interests in the multidisciplinary and far-sighted scientific trajectory of Prof. Vallet Regí. The different pathologies that affect osseous tissue substitution are considered to be one of the most important challenges from the health, social and economic point of view. 3D scaffolds based on bioceramics that mimic the composition, environment, microstructure and pore architecture of hard tissues is a consolidated response to such concerns. This review describes not only the different types of materials utilized: from apatite-type to silicon mesoporous materials, but also the fabrication techniques employed to design and adequate microstructure, a hierarchical porosity (from nano to macro scale), a cell-friendly surface; the inclusion of different type of biomolecules, drugs or cells within these scaffolds and the influence on their successful performance is thoughtfully reviewed.

BEM evaluation of surface octahedral strains and internal strain gradients in 3D-printed scaffolds used for bone tissue regeneration

Most of the mechnoregulatory computational models appearing so far in tissue engineering for bone healing predictions, utilize as regulators for cell differentiation mainly the octahedral volume strains and the interstitial fluid velocity calculated at any point of the fractured bone area and controlled by empirical constants concerning these two parameters. Other stimuli like the electrical and chemical signaling of bone constituents are covered by those two regulatory fields. It is apparent that the application of the same mechnoregulatory computational models for bone healing predictions in scaffold-aided regeneration is questionable since the material of a scaffold disturbs the signaling pathways developed in the environment of bone fracture. Thus, the goal of the present work is to evaluate numerically two fields developed in the body of two different compressed scaffolds, which seem to be proper for facilitating cell sensing and improving cell viability and cell seeding efficiency. These two fields concern the surface octahedral strains that the cells attached to the scaffold can experience and the internal strain gradients that create electrical pathways due to flexoelectric phenomenon. Both fields are evaluated with the aid of the Boundary Element Method (BEM), which is ideal for evaluating with high accuracy surface strains and stresses as well as strain gradients appearing throughout the analyzed elastic domain.

An advanced method to design graded cylindrical scaffolds with versatile effective cross-sectional mechanical properties

The selection of the most-suited bone scaffold for a given clinical application is challenging, and has motivated numerous studies. They are mostly based on the characterization of cellular structures, generated from the three-dimensional repetition of a unit cell. However, the interest of circular graded bone scaffolds has been emphasized since they facilitate nutrient transport from the periphery to the core of the scaffold. In the present contribution, we present an advanced and versatile method to design graded circular porous 2D structures based on the conformal mapping of unit cells. We propose a method to generate 3D porous scaffolds by a multilayer repetition of the circular cross-section, resulting in tunable anisotropy depending on the clinical application. We then analyze the link between the porosities of the obtained structures and their effective elastic mechanical cross-sectional properties, making use of a novel and computationally efficient method allowing exhaustive parametric studies. The comparison of various conformal transformations and unit cell designs emphasizes the extent of mechanical properties and porosities that may be reached for a given constitutive material, including non-standard mechanical properties that open large perspectives towards the development of self-fitting scaffolds.

Fabrication and properties of PLA/nano-HA composite scaffolds with balanced mechanical properties and biological functions for bone tissue engineering application

Repair of critical bone defects is a challenge in the orthopedic clinic. 3D printing is an advanced personalized manufacturing technology that can accurately shape internal structures and external contours. In this study, the composite scaffolds of polylactic acid (PLA) and nano-hydroxyapatite (n-HA) were manufactured by the fused deposition modeling (FDM) technique. Equal mass PLA and n-HA were uniformly mixed to simulate the organic and inorganic phases of natural bone. The suitability of the composite scaffolds was evaluated by material characterization, mechanical property, and in vitro biocompatibility, and the osteogenesis induction in vitro was further tested. Finally, the printed scaffold was implanted into the rabbit femoral defect model to evaluate the osteogenic ability in vivo. The results showed that the composite scaffold had sufficient mechanical strength, appropriate pore size, and biocompatibility. Most importantly, the osteogenic induction performance of the composite scaffold was significantly better than that of the pure PLA scaffold. In conclusion, the PLA/n-HA scaffold is a promising composite biomaterial for bone defect repair and has excellent clinical transformation potential.

3D-printed Mg-incorporated PCL-based scaffolds: A promising approach for bone healing

3D-printed scaffolds have been developed as potential therapeutic strategies in bone tissue engineering. Mg/PCL biomaterials have been attracted much attention owing to biocompatibility, biodegradability as well as tunable mechanical properties. In this work, we developed 3D-printed customized Mg/PCL composite scaffolds with enhanced osteogenesis and biomineralization. Mg microparticles embedded in PCL-based scaffolds took a positive role in the improvement of biocompatibility, biomineralization, and biodegradable abilities. When incorporated with 3 wt% Mg, PCL-based scaffolds exhibited the optimal bone repairing ability in vitro and in vivo. The in vitro experiments indicated that 3 Mg/PCL scaffolds had improved mechanical properties, good biocompatibility, enhanced osteogenic and angiogenic activities. Besides, the in vivo studies demonstrated that Mg/PCL scaffolds promoted tissue ingrowth and new bone formation. In sum, these findings indicated that 3D-printed cell-free Mg/PCL scaffolds are promising strategies for bone healing application.

Nanomaterials-Upconverted Hydroxyapatite for Bone Tissue Engineering and a Platform for Drug Delivery

Hydroxyapatite is a basic mineral that is very important to the human body framework. Recently, synthetic hydroxyapatite (SHA) and its nanocomposites (HANs) are the subject of intense research for bone tissue engineering and drug loading system applications, due to their unique, tailor-made characteristics, as well as their similarities with the bone mineral component in the human body. Although hydroxyapatite has good biocompatibility and osteoconductive characteristics, the poor mechanical strength restricts its use in non-load-bearing applications. Consequently, a rapid increase in reinforcing of other nanomaterials into hydroxyapatite for the formation of HANs could improve the mechanical properties. Most of the research reported on the success of other nanomaterials such as metals, ceramics and natural/synthetic polymers as additions into hydroxyapatite is reviewed. In addition, this review also focuses on the addition of various substances into hydroxyapatite for the formation of various HANs and at the same time to try to minimize the limitations so that various bone tissue engineering and drug loading system applications can be exploited.

Bioactive Ceramic Scaffolds for Bone Tissue Engineering by Powder Bed Selective Laser Processing: A Review

The implementation of a powder bed selective laser processing (PBSLP) technique for bioactive ceramics, including selective laser sintering and melting (SLM/SLS), a laser powder bed fusion (L-PBF) approach is far more challenging when compared to its metallic and polymeric counterparts for the fabrication of biomedical materials. Direct PBSLP can offer binder-free fabrication of bioactive scaffolds without involving postprocessing techniques. This review explicitly focuses on the PBSLP technique for bioactive ceramics and encompasses a detailed overview of the PBSLP process and the general requirements and properties of the bioactive scaffolds for bone tissue growth. The bioactive ceramics enclosing calcium phosphate (CaP) and calcium silicates (CS) and their respective composite scaffolds processed through PBSLP are also extensively discussed. This review paper also categorizes the bone regeneration strategies of the bioactive scaffolds processed through PBSLP with the various modes of functionalization through the incorporation of drugs, stem cells, and growth factors to ameliorate critical-sized bone defects based on the fracture site length for personalized medicine.

A 3D printed Ga containing scaffold with both anti-infection and bone homeostasis-regulating properties for the treatment of infected bone defects

Large bone defects face a high risk of infection, which can also lead to bone homeostasis disorders. This seriously hinders the bone healing process; therefore, the help of a dual-functional scaffold that has both anti-infection and bone-homeostasis-regulating capacities is needed in the treatment of infected bone defects. In this study, a 3D printed dual-functional scaffold composed of poly-ε-caprolactone (PCL), mesoporous bioactive glasses (MBG), and gallium (Ga) was produced. In vitro experiments demonstrated the excellent antibacterial ability of the PCL/MBG/Ga scaffold against methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). The scaffold also significantly inhibited osteoclastic activity and promoted osteogenic differentiation. Furthermore, a rabbit model with an infected bone defect in the radius was used to evaluate the in vivo bone healing capability of PCL/MBG/Ga. The results demonstrate that the PCL/MBG/Ga scaffold can significantly accelerate bone healing and prevent bone resorption, suggesting its potential for application in repairing infected bone defects.

3D Printing of Antibacterial, Biocompatible, and Biomimetic Hybrid Aerogel-Based Scaffolds with Hierarchical Porosities via Integrating Antibacterial Peptide-Modified Silk Fibroin with Silica Nanostructure

Scaffold-mediated tissue engineering has become a golden solution for the regeneration of damaged bone tissues that lack self-regeneration capability. A successful scaffold in bone tissue engineering comprises a multitude of suitable biological, microarchitectural, and mechanical properties acting as different signaling cues for the cells to mediate the new tissue formation. Therefore, careful design of bioactive scaffold macro- and microstructures in multiple length scales and biophysical properties fulfilling the tissue repair demands are necessary yet challenging to achieve. Herein, we have developed an antibacterial and biocompatible silica-silk fibroin (SF) gel-based ink through novel yet simple chemical approaches of sol-gel and self-assembly followed by processing the obtained gels as three-dimensional (3D) hybrid aerogel-based scaffolds exploiting the advanced materials design approaches of micro-extrusion-based 3D printing, and directional freeze-casting/drying approaches. As the main constituent of the hybrid biocompatible scaffold of this study, we used the SF extracted from Bombyx mori silkworm cocoon. However, to increase the cell responsivity and bactericidal efficiency of the final scaffold, thiol-ended antimicrobial and cell adhesive peptide sequence (SH-CM-RGD) was conjugated to silica-SF hybrid gels via covalent attachment using a spacer molecule through either preprint (prior to sol-gel) or during the post-printing steps on the previously printed silica-SF gel. In the next step, the hybrid Silica-SF-CM-RGD hydrogel ink was 3D-printed into the construct with interconnected porous structure with hierarchically organized porosity and a combination of several promising properties. Namely, due to the covalent linkage of the antibacterial peptide to the SF, the scaffold shows potent bactericidal efficiency toward Gram-positive and Gram-negative bacteria. Moreover, nanostructured silica components in the 3D-printed composites could intertwine with SF-CM-RGD to support the mechanical properties in the final scaffold and the final osteoconductivity of the scaffold. This study supports the promising properties of 3D-printed silica-SF-based hybrid aerogels constructs for repairing bone defect.

Bioactive Calcium Phosphate-Based Composites for Bone Regeneration

Calcium phosphates (CaPs) are widely accepted biomaterials able to promote the regeneration of bone tissue. However, the regeneration of critical-sized bone defects has been considered challenging, and the development of bioceramics exhibiting enhanced bioactivity, bioresorbability and mechanical performance is highly demanded. In this respect, the tuning of their chemical composition, crystal size and morphology have been the matter of intense research in the last decades, including the preparation of composites. The development of effective bioceramic composite scaffolds relies on effective manufacturing techniques able to control the final multi-scale porosity of the devices, relevant to ensure osteointegration and bio-competent mechanical performance. In this context, the present work provides an overview about the reported strategies to develop and optimize bioceramics, while also highlighting future perspectives in the development of bioactive ceramic composites for bone tissue regeneration.

Three-dimensional-poly(lactic acid) scaffolds coated with gelatin/magnesium-doped nano-hydroxyapatite for bone tissue engineering

BACKGROUND

Treatment of critical-sized bone defects has progressively evolved over the years from metallic implants to more ingenious three-dimensional-based scaffolds. The use of three-dimensional scaffolds for bone regeneration from biodegradable polymers like poly(lactic acid) (PLA) is gaining popularity. Scaffolds with surface functionalization using gelatin (Gel) have the advantages of biocompatibility and cell adhesion. Nano-hydroxyapatite (nHAp) is one of the most promising implant materials utilized in orthopaedics. The osteogenic potential of the nHAp can be improved by the substitution of magnesium (Mg) ions onto the crystal lattice of nHAp. Thus, the goal of this work was to make three-dimensional-PLA scaffolds covered with Gel/Mg-nHAp for osteogenic effect.

METHODS AND RESULTS

The designed three-dimensional-PLA/Gel/Mg-nHAp scaffolds were attributed to various characterizations for the examination of their physicochemical, mechanical properties, cyto-compatibility, and biodegradability as well as their ability to promote osteogenesis in vitro. Mouse mesenchymal stem cells (mMSCs) were cytocompatible with these scaffolds. The osteogenic potential of three-dimensional-PLA/Gel/Mg-nHAp scaffolds employing mMSCs was validated at the cellular and molecular levels. The three-dimensional-PLA/Gel/Mg-nHAp scaffolds stimulated the differentiation of mMSCs towards osteoblastic lineage.

CONCLUSION

Based on these findings, we suggest that the three-dimensional-PLA/Gel/Mg-nHAp scaffolds' osteogenic capability may be advantageous in the mending of bone defects in orthopedic applications.

3D Printed Composite Scaffolds in Bone Tissue Engineering: A systematic review

OBJECTIVE

This study aimed to analyze the effect of fabrication factors on both biological and physico-chemical features of 3-dimensional (3D) printed composite scaffolds.

METHOD

Electronic search was done according to the PRISMA guideline in PubMed and Scopus databases limited to English articles published until May 2021.Studies in which composite scaffolds were fabricated through computer-aided design and computer-aided manufacturing (CAD-CAM)-based methods were included.Articles regarding the features of the scaffolds fabricated through indirect techniques were excluded.

RESULTS

Full text of 121 studies were reviewed, and 69 met the inclusion criteria. According to analyzed studies, PCL and HA were the most commonly used polymer and ceramic,respectively. Besides,the Solvent-based technique was the most commonly used composition technique, which enabled preparing blends with high concentrations of ceramic materials. The most common fabrication method used in the included studies was Fused deposition modeling (FDM).The addition of bio-ceramics enhanced the mechanical features and the biological behaviors of the printed scaffolds in a ratio-dependent manner. However,studies that analyzed the effect of ceramic weight ratio showed that scaffolds with the highest ceramic content did not necessarily possess the optimal biological and non-biological features.

CONCLUSION

The biological and physico-chemical behaviors of the scaffold can be affected by pre-printing factors, including utilized materials, composition techniques, and fabrication methods. Fabricating scaffolds with high mineral content as of the natural bone may not provide the optimal condition for bone formation. Therefore, it is recommended that future studies compare the efficiency of different kinds of biomaterials rather than different weight ratios of one type.

3D-printed biphasic scaffolds for the simultaneous regeneration of osteochondral tissues

Osteochondral tissue engineering (OCTE) involves the simulation of highly complex tissues with disparate biomechanical properties. OCTE is regarded as the best option for treating osteochondral defects, most of the drawbacks of current treatment methodologies can be addressed by this method. In recent years, the conventional scaffolds used in cartilage and bone regeneration are gradually being replaced by 3D printed scaffolds (3DP). In the present study, we devised the strategy of 3D printing for fabricating biphasic and integrated scaffolds that are loaded with bioactive factors for enhancing the osteochondral tissue regeneration. Polycaprolactone (PCL) and poly(lactic-co-glycolic acid) (PLGA), is used along with bioactive factors (chondroitin sulphate and beta-tricalcium phosphate (βTCP)) for the upper cartilage and lower bone layer respectively. The 3D printed bi-layered scaffolds with varying infill density, to mimic the native tissue, are not previously explored for OCTE. Hence, we tested the simultaneous osteochondrogenic differentiation inducing potential of the aforesaid 3D printed biphasic scaffoldsin vitro, using rabbit adipose derived mesenchymal stem cells (ADMSCs). Further, the biphasic scaffolds were highly cytocompatible, with excellent cell adhesion properties and cellular morphology. Most importantly, these biphasic scaffolds directed the simultaneous differentiation of a single stem cell population in to two cell lineages (simultaneous differentiation of rabbit ADMSCs into chondrocytes and osteoblasts). Further, these scaffolds enhanced the production of ECM and induced robust expression of marker genes that is specific for respective cartilage and bone layers. The 3D printed OCTE scaffold of our study hence can simulate the native osteochondral unit and could be potential futuristic biomimetic scaffold for osteochondral defects. Furtherin vivostudies are warranted.

Mesenchymal Stem Cells, Bioactive Factors, and Scaffolds in Bone Repair: From Research Perspectives to Clinical Practice

Mesenchymal stem cell-based therapies are promising tools for bone tissue regeneration. However, tracking cells and maintaining them in the site of injury is difficult. A potential solution is to seed the cells onto a biocompatible scaffold. Construct development in bone tissue engineering is a complex step-by-step process with many variables to be optimized, such as stem cell source, osteogenic molecular factors, scaffold design, and an appropriate in vivo animal model. In this review, an MSC-based tissue engineering approach for bone repair is reported. Firstly, MSC role in bone formation and regeneration is detailed. Secondly, MSC-based bone tissue biomaterial design is analyzed from a research perspective. Finally, examples of animal preclinical and human clinical trials involving MSCs and scaffolds in bone repair are presented.

3D printing of lubricative stiff supramolecular polymer hydrogels for meniscus replacement

3D printing of a stiff and lubricative hydrogel-based meniscus substitute has been challenging since printability and stiffness compromise each other. In this work, based on an upgraded self-thickening and self-strengthening strategy, a unique multiple H-bonding monomer N-acryloylsemicarbazide (NASC) is firstly copolymerized with a super-hydrophilic monomer carboxybetaine acrylamide (CBAA) in dimethyl sulfoxide (DMSO)/H2O to form a soft poly(NASC-co-CBAA) gel, in which PCBAA serves to weaken the H-bonding interaction and avoid hydrophobic phase separation. The poly(NASC-co-CBAA) gel is then loaded with concentrated NASC and CBAA, followed by heating to form a thickening sol ink, which is printed into different objects that are further photoirradiated to initiate the copolymerization of entrapped NASC and CBAA, resulting in the formation of a high performance hydrogel with a Young's modulus of 10.98 MPa, tensile strength of 1.87 MPa and tearing energy of 5333 J m-2 after DMSO is completely replaced with water, due to the re-establishment of NASC H-bonds. Importantly, PCBAA affords high lubricity in printed hydrogels. The printed PNASC-PCBAA meniscus substitute can substitute rabbit's native meniscus and ameliorate the cartilage surface wear within a set 12-week time window, portending great potential as a meniscal substitute and other soft-supporting tissue scaffolds.

Immunopolarization-regulated 3D printed-electrospun fibrous scaffolds for bone regeneration

Three-dimension (3D)-printed bioscaffolds are precise and personalized for bone regeneration. However, customized 3D scaffolds may activate the immune response in vivo and consequently impede bone formation. In this study, with layer-by-layer deposition and electrospinning technology to control the physical structure, 3D-printed PCL scaffolds with PLLA electrospun microfibrous (3D-M-EF) and nanofibrous (3D-N-EF) composites were constructed, and their immunomodulatory effect and the subsequent osteogenic effects were explored. Compared to 3D-N-EF scaffolds, 3D-M-EF scaffolds polarized more RAW264.7 cells toward alternatively activated macrophages (M2), as demonstrated by increased M2 and deceased classically activated macrophage (M1) phenotypic marker expression in the cells. In addition, the 3D-M-EF scaffolds shifted RAW264.7 cells to the M2 phenotype through PI3K/AKT signaling and enhanced VEGF and BMP-2 expression. Conditional medium from the RAW264.7 cells seeded in 3D-M-EF scaffolds promoted osteogenesis of MC3T3-E1 cells. Furthermore, in vivo study of repairing rat calvarial defects, the 3D-M-EF scaffolds increased the polarization of M2 macrophages, enhanced angiogenesis, and accelerated new bone formation. Collectively, our data suggested that well-designed 3D-M-EF scaffolds are favorable for osteogenesis through regulation of M2 polarization. Therefore, it is potential to utilize the physical structure of 3D-printed scaffolds to manipulate the osteoimmune environment to promote bone regeneration.

Direct 3D Printing of Seashell Precursor toward Engineering a Multiphasic Calcium Phosphate Bone Graft

Multiphasic calcium phosphate (Ca-P) has widely been explored for bone graft replacement. This study represents a simple method of developing osteoinductive scaffolds by direct printing of seashell resources. The process demonstrates a coagulation-assisted extrusion-based three-dimensional (3D) printing process for rapid fabrication of multiphasic calcium phosphate-incorporated 3D scaffolds. These scaffolds demonstrated an interconnected open porous architecture with improved compressive strength and higher surface area. Multiphasic calcium phosphate (Ca-P) and hydroxyapatite present in the multi-scalar naturally resourced scaffold displayed differential protein adsorption, thus facilitating cell adhesion, migration, and differentiation, resulting in enhanced deposition of the extracellular matrix. The microstructural and physicochemical attributes of the scaffolds also lead to enhanced stem cell differentiation as witnessed from gene and protein expression analysis. Furthermore, the histological study of subcutaneous implantation evidently portrays promising biocompatibility without foreign body reaction. Neo-tissue in-growth was manifested with abundant blood vessels, thus indicative of excellent vascularization. Notably, cartilaginous and proteoglycan-rich tissue deposition indicated ectopic bone formation via an endochondral ossification pathway. The hierarchical interconnected porous architectural tribology accompanied with multiphasic calcium phosphate composition manifests its successful implication in enhancing stem cell differentiation and promoting excellent tissue in-growth, thus making it a plausible alternative in bone tissue engineering applications.

State-of-the-art of 3D printing technology of alginate-based hydrogels-An emerging technique for industrial applications

Recently, three-dimensional (3D) printing (also known as additive manufacturing) has received unprecedented consideration in various fields owing to many advantages compared to conventional manufacturing equipment such as reduced fabrication time, one-step production, and the ability for rapid prototyping. This promising technology, as the next manufacturing revolution and universal industrial method, allows the user to fabricate desired 3D objects using a layer-by-layer deposition of material and a 3D printer. Alginate, a versatile polysaccharide derived from seaweed, is popularly used for this advanced bio-fabrication technique due to its printability, biodegradability, biocompatibility, excellent availability, low degree of toxicity, being a relatively inexpensive, rapid gelation in the presence of Ca²⁺ divalent, and having fascinating chemical structure. In recent years, 3D printed alginate-based hydrogels have been prepared and used in various fields including tissue engineering, water treatment, food, electronics, and so forth. Due to the prominent role of 3D printed alginate-based materials in diverse fields. So, this review will focus and highlight the latest and most up-to-date achievements in the field of 3D printed alginate-based materials in biomedical, food, water treatment, and electronics.

Applications of 3D Bio-Printing in Tissue Engineering and Biomedicine

In recent years, 3D bio-printing technology has developed rapidly and become an advanced bio-manufacturing technology. At present, 3D bio-printing technology has been explored in the fields of tissue engineering, drug testing and screening, regenerative medicine and clinical disease research and has achieved many research results. Among them, the application of 3D bio-printing technology in tissue engineering has been widely concerned by researchers, and it contributing many breakthroughs in the preparation of tissue engineering scaffolds. In the future, it is possible to print fully functional tissues or organs by using 3D bio-printing technology which exhibiting great potential development prospects in th applications of organ transplantation and human body implants. It is expected to solve thebiomedical problems of organ shortage and repair of damaged tissues and organs. Besides,3Dbio-printing technology will benefit human beings in more fields. Therefore, this paper reviews the current applications, research progresses and limitations of 3D bio-printing technology in biomedical and life sciences, and discusses the main printing strategies of 3D bio-printing technology. And, the research emphases, possible development trends and suggestions of the application of 3D bio-printing are summarized to provide references for the application research of 3D bio-printing.

A Review on Hydrogels with Photothermal Effect in Wound Healing and Bone Tissue Engineering

Photothermal treatment (PTT) is a promising strategy to deal with multidrug-resistant bacteria infection and promote tissue regeneration. Previous studies demonstrated that hyperthermia can effectively inhibit the growth of bacteria, whereas mild heat can promote cell proliferation, further accelerating wound healing and bone regeneration. Especially, hydrogels with photothermal properties could achieve remotely controlled drug release. In this review, we introduce a photothermal agent hybrid in hydrogels for a photothermal effect. We also summarize the potential mechanisms of photothermal hydrogels regarding antibacterial action, angiogenesis, and osteogenesis. Furthermore, recent developments in photothermal hydrogels in wound healing and bone regeneration applications are introduced. Finally, future application of photothermal hydrogels is discussed. Hydrogels with photothermal effects provide a new direction for wound healing and bone regeneration, and this review will give a reference for the tissue engineering.

Effect of Morphological Characteristics and Biomineralization of 3D-Printed Gelatin/Hyaluronic Acid/Hydroxyapatite Composite Scaffolds on Bone Tissue Regeneration

The use of porous three-dimensional (3D) composite scaffolds has attracted great attention in bone tissue engineering applications because they closely simulate the major features of the natural extracellular matrix (ECM) of bone. This study aimed to prepare biomimetic composite scaffolds via a simple 3D printing of gelatin/hyaluronic acid (HA)/hydroxyapatite (HAp) and subsequent biomineralization for improved bone tissue regeneration. The resulting scaffolds exhibited uniform structure and homogeneous pore distribution. In addition, the microstructures of the composite scaffolds showed an ECM-mimetic structure with a wrinkled internal surface and a porous hierarchical architecture. The results of bioactivity assays proved that the morphological characteristics and biomineralization of the composite scaffolds influenced cell proliferation and osteogenic differentiation. In particular, the biomineralized gelatin/HA/HAp composite scaffolds with double-layer staggered orthogonal (GEHA20-ZZS) and double-layer alternative structure (GEHA20-45S) showed higher bioactivity than other scaffolds. According to these results, biomineralization has a great influence on the biological activity of cells. Hence, the biomineralized composite scaffolds can be used as new bone scaffolds in bone regeneration.

3D Printing of Micro- and Nanoscale Bone Substitutes: A Review on Technical and Translational Perspectives

Recent developments in three-dimensional (3D) printing technology offer immense potential in fabricating scaffolds and implants for various biomedical applications, especially for bone repair and regeneration. As the availability of autologous bone sources and commercial products is limited and surgical methods do not help in complete regeneration, it is necessary to develop alternative approaches for repairing large segmental bone defects. The 3D printing technology can effectively integrate different types of living cells within a 3D construct made up of conventional micro- or nanoscale biomaterials to create an artificial bone graft capable of regenerating the damaged tissues. This article reviews the developments and applications of 3D printing in bone tissue engineering and highlights the numerous conventional biomaterials and nanomaterials that have been used in the production of 3D-printed scaffolds. A comprehensive overview of the 3D printing methods such as stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM), and ink-jet 3D printing, and their technical and clinical applications in bone repair and regeneration has been provided. The review is expected to be useful for readers to gain an insight into the state-of-the-art of 3D printing of bone substitutes and their translational perspectives.