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

Multiparametric influence of 3D-printed organo-mineral scaffolds on bone regeneration

The development of synthetic bone substitutes that equal or exceed the efficacy of autologous graft remains challenging. In this study, a rat calvarial defect model was used as a reference to investigate the influence of composition and architecture of 3D-printed cement, with or without bioactives, on tissue regeneration. Printable cement pastes were formulated by combining hyaluronic acid and cement precursors. Cementitious scaffolds were printed with 3 different patterns. After 7 weeks of implantation with or without bone marrow, multiparametric qualitative and quantitative assessments were performed using µCT, SEM, and histology. None of the set-up strategies was as efficient as autologous cancellous bone graft to repair calvarial defects. Nonetheless, the presence of scaffold improved the skull vault closure, particularly when the scaffold was soaked in total bone marrow before implantation. No significant effect of scaffold macro-architecture was observed on tissue mineralization. Magnesium phosphate-based scaffolds (MgP) seemed to induce higher bone formation than their calcium-phosphate-based counterparts. They also displayed a quicker biodegradation and sparse remaining material was found after 7 weeks of implantation. Although further improvements are required to reach clinical settings, this study demonstrated the potential of organo-mineral cements for bone regeneration and highlighted the peculiar properties of MgP-based cements.

Regulation of bone homeostasis: signaling pathways and therapeutic targets

As a highly dynamic tissue, bone is continuously rebuilt throughout life. Both bone formation by osteoblasts and bone resorption by osteoclasts constitute bone reconstruction homeostasis. The equilibrium of bone homeostasis is governed by many complicated signaling pathways that weave together to form an intricate network. These pathways coordinate the meticulous processes of bone formation and resorption, ensuring the structural integrity and dynamic vitality of the skeletal system. Dysregulation of the bone homeostatic regulatory signaling network contributes to the development and progression of many skeletal diseases. Significantly, imbalanced bone homeostasis further disrupts the signaling network and triggers a cascade reaction that exacerbates disease progression and engenders a deleterious cycle. Here, we summarize the influence of signaling pathways on bone homeostasis, elucidating the interplay and crosstalk among them. Additionally, we review the mechanisms underpinning bone homeostatic imbalances across diverse disease landscapes, highlighting current and prospective therapeutic targets and clinical drugs. We hope that this review will contribute to a holistic understanding of the signaling pathways and molecular mechanisms sustaining bone homeostasis, which are promising to contribute to further research on bone homeostasis and shed light on the development of targeted drugs.

Electrochemical Deposition and Etching of Quasi-Two-Dimensional Periodic Membrane Structure

In this paper, two experimental procedures are reported, namely electro-deposition in the ultrathin liquid layer and chemical micro-etching. Firstly, a large area quasi-two-dimensional periodic membrane with adjustable density is deposited on a Si substrate driven by half-sinusoidal voltage, which is composed of raised ridges and a membrane between the ridges. The smaller the voltage frequency is, the larger the ridge distance is. The height of a raised ridge changes synchronously with the amplitude. The grain density distribution of membrane and raised ridge is uneven; the two structures change alternately, which is closely related to the change of growth voltage and copper ion concentration during deposition. The structural characteristics of membrane provide favorable conditions for micro-etching; stable etching speed and microscope real-time monitoring are the keys to achieve accurate etching. In the chemical micro-etching process, the membrane between ridges is removed, retaining the raised ridges, thus a large scale ordered micro-nano wires array with lateral growth was obtained. This method is simple and controllable, can be applied to a variety of substrates, and is the best choice for designing and preparing new functional materials. This experiment provides a basis for the extension of this method.

3D-printed PCL framework assembling ECM-inspired multi-layer mineralized GO-Col-HAp microscaffold for in situ mandibular bone regeneration

BACKGROUND

In recent years, natural bone extracellular matrix (ECM)-inspired materials have found widespread application as scaffolds for bone tissue engineering. However, the challenge of creating scaffolds that mimic natural bone ECM's mechanical strength and hierarchical nano-micro-macro structures remains. The purposes of this study were to introduce an innovative bone ECM-inspired scaffold that integrates a 3D-printed framework with hydroxyapatite (HAp) mineralized graphene oxide-collagen (GO-Col) microscaffolds and find its application in the repair of mandibular bone defects.

METHODS

Initially, a 3D-printed polycaprolactone (PCL) scaffold was designed with cubic disks and square pores to mimic the macrostructure of bone ECM. Subsequently, we developed multi-layer mineralized GO-Col-HAp microscaffolds (MLM GCH) to simulate natural bone ECM's nano- and microstructural features. Systematic in vitro and in vivo experiments were introduced to evaluate the ECM-inspired structure of the scaffold and to explore its effect on cell proliferation and its ability to repair rat bone defects.

RESULTS

The resultant MLM GCH/PCL composite scaffolds exhibited robust mechanical strength and ample assembly space. Moreover, the ECM-inspired MLM GCH microscaffolds displayed favorable attributes such as water absorption and retention and demonstrated promising cell adsorption, proliferation, and osteogenic differentiation in vitro. The MLM GCH/PCL composite scaffolds exhibited successful bone regeneration within mandibular bone defects in vivo.

CONCLUSIONS

This study presents a well-conceived strategy for fabricating ECM-inspired scaffolds by integrating 3D-printed PCL frameworks with multilayer mineralized porous microscaffolds, enhancing cell proliferation, osteogenic differentiation, and bone regeneration. This construction approach holds the potential for extension to various other biomaterial types.

A xonotlite nanofiber bioactive 3D-printed hydrogel scaffold based on osteo-/angiogenesis and osteoimmune microenvironment remodeling accelerates vascularized bone regeneration

BACKGROUND

Coordination between osteo-/angiogenesis and the osteoimmune microenvironment is essential for effective bone repair with biomaterials. As a highly personalized and precise biomaterial suitable for repairing complex bone defects in clinical practice, it is essential to endow 3D-printed scaffold the above key capabilities.

RESULTS

Herein, by introducing xonotlite nanofiber (Ca6(Si6O17) (OH)2, CS) into the 3D-printed silk fibroin/gelatin basal scaffold, a novel bone repair system named SGC was fabricated. It was noted that the incorporation of CS could greatly enhance the chemical and mechanical properties of the scaffold to match the needs of bone regeneration. Besides, benefiting from the addition of CS, SGC scaffolds could accelerate osteo-/angiogenic differentiation of bone mesenchymal stem cells (BMSCs) and meanwhile reprogram macrophages to establish a favorable osteoimmune microenvironment. In vivo experiments further demonstrated that SGC scaffolds could efficiently stimulate bone repair and create a regeneration-friendly osteoimmune microenvironment. Mechanistically, we discovered that SGC scaffolds may achieve immune reprogramming in macrophages through a decrease in the expression of Smad6 and Smad7, both of which participate in the transforming growth factor-β (TGF-β) signaling pathway.

CONCLUSION

Overall, this study demonstrated the clinical potential of the SGC scaffold due to its favorable pro-osteo-/angiogenic and osteoimmunomodulatory properties. In addition, it is a promising strategy to develop novel bone repair biomaterials by taking osteoinduction and osteoimmune microenvironment remodeling functions into account.

3D-printed PCL/β-TCP/CS composite artificial bone and histocompatibility study

BACKGROUND

Tissue-engineered bone materials are an effective tool to repair bone defects. In this study, a novel biodegradable polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP)/calcium sulfate (CS) composite scaffold was prepared by using three-dimensional (3D) printing technology.

METHODS

Scanning electron microscopy, gas expansion displacement, and contact goniometry were used to examine the 3D-printed PCL/β-TCP/CS composite scaffolds. The results showed that the PCL/β-TCP/CS scaffolds possessed controllable porosity, hydrophobicity, biodegradability, and suitable apatite mineralization ability. To confirm the bone regenerative properties of the fabricated composite scaffolds, scaffold extracts were prepared and evaluated for their cytotoxicity to bone marrow mesenchymal stem cells (BMSCs) and their ability to induce and osteogenic differentiation in BMSCs.

RESULTS

The PCL/β-TCP/CS composite scaffolds induced a higher level of differentiation of BMSCs than the PCL scaffolds, which occurred through the expression of bone metastasis-related genes. The New Zealand white rabbit radial defect experiment further demonstrated that PCL/β-TCP/CS scaffolds could promote bone regeneration.

CONCLUSIONS

In summary, the 3D-printed PCL/β-TCP/CS composite porous artificial bone has good cytocompatibility, osteoinductivity, and histocompatibility, which make it an ideal bone material for tissue engineering.

BMP-2 promotes fracture healing by facilitating osteoblast differentiation and bone defect osteogenesis

OBJECTIVE

To investigate the role of bone morphogenetic protein-2 (BMP-2) in promoting fracture healing in animal models.

METHODS

Mouse models with muscle bag heterotopic osteogenesis (HO) were divided into a HO control group (not implanted with 250 μg rhBMP-2 bone repairing material), and a HO observation group (implanted with 250 μg rhBMP-2 bone repairing material); while rat models with bone defect (BD) were divided into a BD control group (not implanted with 250 μg rhBMP-2 bone repairing material) and a BD observation group (implanted with 250 μg rhBMP-2 bone repairing material). At 4 weeks after HO establishment, the new bone formation at the operation site was observed through visual inspections and X-ray scanning. The content of serum alkaline phosphatase (ALP) was detected by automatic biochemical analyzer. The formation of new bone at the operative sites was observed by Hematoxylin and eosin staining and Masson staining. At 0, 2, 4 and 8 weeks after operation, the growth of the defect area and its surrounding callus were observed by X-ray scanning. At 4 and 8 weeks after bone defect establishment in the mouse models, the histological changes and osteogenesis of the bone defect site were observed.

RESULTS

The heterotopic osteogenesis experiment showed that at 4 weeks after operation, the mass at the muscle bag in the HO observation group became larger in contrast to the HO control group. X-ray scanning showed that there was obvious irregular bone shadow at the back muscle bag of mice from the HO observation group. The content of serum ALP in the HO observation group was significantly higher than that in the HO control group (all P<0.05). The muscle pocket in the HO observation group showed higher ectopic osteogenic activity comparing with the HO control group. Histological staining showed that bone tissue structure was visible in the newly regenerated bone, forming bone trabeculae and bone marrow tissue. Under the microscope, a large number of osteoblasts arranged neatly in a cubic shape presented at the edge of the new bone, and there were bone lacunae formed, and the bone tissue was in a relatively mature stage. In the rat bone defect models, X-ray scanning showed that the high-density development area was further increased. There was a large amount of callus formation in the bone defect area of the BD observation group, while the BD control group still had no high-density development. At 8 weeks after operation, the high-density development area decreased, indicating that there was partial absorption of callus, while there was still no high-density development in the BD control group. The callus of the bone defect area in the BD observation group was reduced and the defect area was gradually repaired, while the bone defect in the BD control group was still obvious and the bone repair was not completed.

CONCLUSIONS

BMP-2 could promote osteoblast differentiation and bone defect osteogenesis in vivo. Thus, it is worthy of clinical application.

A Comprehensive Mechanical Characterization of Subject-Specific 3D Printed Scaffolds Mimicking Trabecular Bone Architecture Biomechanics

This study presents a polymeric scaffold designed and manufactured to mimic the structure and mechanical compressive characteristics of trabecular bone. The morphological parameters and mechanical behavior of the scaffold were studied and compared with trabecular bone from bovine iliac crest. Its mechanical properties, such as modulus of elasticity and yield strength, were studied under a three-step monotonic compressive test. Results showed that the elastic modulus of the scaffold was 329 MPa, and the one for trabecular bone reached 336 MPa. A stepwise dynamic compressive test was used to assess the behavior of samples under various loading regimes. With microcomputed tomography (µCT), a three-dimensional reconstruction of the samples was obtained, and their porosity was estimated as 80% for the polymeric scaffold and 88% for trabecular bone. The full-field strain distribution of the samples was measured using in situ µCT mechanics and digital volume correlation (DVC). This provided information on the local microdeformation mechanism of the scaffolds when compared to that of the tissue. The comprehensive results illustrate the potential of the fabricated scaffolds as biomechanical templates for in vitro studies. Furthermore, there is potential for extending this structure and fabrication methodology to incorporate suitable biocompatible materials for both in vitro and in vivo clinical applications.

Calcium sulfate-Cu2+ delivery system improves 3D-Printed calcium silicate artificial bone to repair large bone defects

There are still limitations in artificial bone materials used in clinical practice, such as difficulty in repairing large bone defects, the mismatch between the degradation rate and tissue growth, difficulty in vascularization, an inability to address bone defects of various shapes, and risk of infection. To solve these problems, our group designed stereolithography (SLA) 3D-printed calcium silicate artificial bone improved by a calcium sulfate-Cu2+ delivery system. SLA technology endows the scaffold with a three-dimensional tunnel structure to induce cell migration to the center of the bone defect. The calcium sulfate-Cu2+ delivery system was introduced to enhance the osteogenic activity of calcium silicate. Rapid degradation of calcium sulfate (CS) induces early osteogenesis in the three-dimensional tunnel structure. Calcium silicate (CSi) which degrades slowly provides mechanical support and promotes bone formation in bone defect sites for a long time. The gradient degradation of these two components is perfectly matched to the rate of repair in large bone defects. On the other hand, the calcium sulfate delivery system can regularly release Cu2+ in the temporal and spatial dimensions, exerting a long-lasting antimicrobial effect and promoting vascular growth. This powerful 3D-printed calcium silicate artificial bone which has rich osteogenic activity is a promising material for treating large bone defects and has excellent potential for clinical application.

Review on vat photopolymerization additive manufacturing of bioactive ceramic bone scaffolds

Bone defects frequently occur in clinical settings due to trauma, disease, tumors, and other causes. The clinical use of autologous bones and allograft bone, however, has several limitations, such as limited sources, donor site morbidity, and immunological rejection. Nevertheless, there is newfound hope for regenerating and repairing bone defects through the development and integration of bone tissue engineering scaffold and additive manufacturing (AM) technology, also known as 3D printing. In particular, vat photopolymerization (VPP)-AM of bioactive ceramic bone scaffolds has garnered significant interest from interdisciplinary researchers in recent years. On the one hand, VPP-AM demonstrates clear advantages in printing accuracy and speed compared to other AM and non-AM technologies. On the other hand, bioactive ceramic materials exhibit superior bioactivity, biodegradability, and mechanical properties compared to metals, polymers, and bioinert ceramics, making them one of the most promising biomaterials for developing bone scaffolds. This paper reviews the research progress of VPP-AM of bioactive ceramic bone scaffolds, covering the process principles of various VPP-AM technologies, the performance requirements and preparation process of VPP ceramic slurry, the VPP process of bioactive ceramic bone scaffolds, and the research progress on different material types of VPP bioactive ceramic scaffolds. Firstly, we provide a brief introduction to the process principles and medical applications of various VPP technologies. Secondly, we explore the composition of the VPP ceramic slurry system, discussing the function of various components and their effects on printing quality. Thirdly, we delve into the performance requirements of bone scaffolds and summarize the research progress of VPP bioactive ceramic bone scaffolds of various material types including hydroxyapatite (HA), tricalcium phosphate (TCP), bioglass (BG), etc.; Finally, we discuss the challenges currently faced by VPP-AM bioactive ceramic bone scaffolds and propose possible development directions for the future.

A Study of the Properties of Scaffolds for Bone Regeneration Modified with Gel-like Coatings of Chitosan and Folic Acid

The research has been conducted to obtain scaffolds for cancellous bone regeneration. Polylactide scaffolds were made by the phase inversion method with a freeze-extraction variant, including gelling polylactide in its non-solvent. Substitutes made of polylactide are hydrophobic, which limits cell adhesion. For this reason, the scaffolds were modified using chitosan and folic acid by forming gel-like coatings on the surface. The modification aimed to improve the material's surface properties and increase cell adhesion. Analyses of obtained scaffolds confirmed the effectiveness of performed changes. The presence of chitosan and folic acid was confirmed in the modified scaffolds, while all scaffolds retained high open porosity, which is essential for proper cell growth inside the scaffold and the free flow of nutrients. Hydrostatic weighing showed that the scaffolds have high mass absorbability, allowing them to be saturated with biological fluids. There were also cytotoxicity tests performed on 24 h extracts of the materials obtained, which indicated a lack of cytotoxic effect.

Alignment behavior of nerve, vascular, muscle, and intestine cells in two- and three-dimensional strategies

By harnessing structural hierarchical insights, plausibly simulate better ones imagination to figure out the best choice of methods for reaching out the unprecedented developments of the tissue engineering products as a next level. Constructing a functional tissue that incorporates two-dimensional (2D) or higher dimensions requires overcoming technological or biological limitations in order to orchestrate the structural compilation of one-dimensional and 2D sheets (microstructures) simultaneously (in situ). This approach enables the creation of a layered structure that can be referred to as an ensemble of layers or, after several days of maturation, a direct or indirect joining of layers. Here, we have avoided providing a detailed methodological description of three-dimensional and 2D strategies, except for a few interesting examples that highlight the higher alignment of cells and emphasize rarely remembered facts associated with vascular, peripheral nerve, muscle, and intestine tissues. The effective directionality of cells in conjunction with geometric cues (in the range of micrometers) is well known to affect a variety of cell behaviors. The curvature of a cell's environment is one of the factors that influence the formation of patterns within tissues. The text will cover cell types containing some level of stemness, which will be followed by their consequences for tissue formation. Other important considerations pertain to cytoskeleton traction forces, cell organelle positioning, and cell migration. An overview of cell alignment along with several pivotal molecular and cellular level concepts, such as mechanotransduction, chirality, and curvature of structure effects on cell alignments will be presented. The mechanotransduction term will be used here in the context of the sensing capability that cells show as a result of force-induced changes either at the conformational or the organizational levels, a capability that allows us to modify cell fate by triggering downstream signaling pathways. A discussion of the cells' cytoskeleton and of the stress fibers involvement in altering the cell's circumferential constitution behavior (alignment) based on exposed scaffold radius will be provided. Curvatures with size similarities in the range of cell sizes cause the cell's behavior to act as if it was in an in vivo tissue environment. The revision of the literature, patents, and clinical trials performed for the present study shows that there is a clear need for translational research through the implementation of clinical trial platforms that address the tissue engineering possibilities raised in the current revision. This article is categorized under: Infectious Diseases > Biomedical Engineering Neurological Diseases > Biomedical Engineering Cardiovascular Diseases > Biomedical Engineering.

Nanoscale Morphologies on the Surface of 3D-Printed Titanium Implants for Improved Osseointegration: A Systematic Review of the Literature

Three-dimensional (3D) printing is serving as the most promising approach to fabricate personalized titanium (Ti) implants for the precise treatment of complex bone defects. However, the bio-inert nature of Ti material limits its capability for rapid osseointegration and thus influences the implant lifetime in vivo. Despite the macroscale porosity for promoting osseointegration, 3D-printed Ti implant surface morphologies at the nanoscale have gained considerable attention for their potential to improve specific outcomes. To evaluate the influence of nanoscale surface morphologies on osseointegration outcomes of 3D-printed Ti implants and discuss the available strategies, we systematically searched evidence according to the PRISMA on PubMed, Embase, Web of Science, and Cochrane (until June 2022). The inclusion criteria were in vivo (animal) studies reporting the osseointegration outcomes of nanoscale morphologies on the surface of 3D-printed Ti implants. The risk of bias (RoB) was assessed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE's) tool. The quality of the studies was evaluated using the Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines. (PROSPERO: CRD42022334222). Out of 119 retrieved articles, 9 studies met the inclusion criteria. The evidence suggests that irregular nano-texture, nanodots and nanotubes with a diameter of 40-105nm on the surface of porous/solid 3D-printed Ti implants result in better osseointegration and vertical bone ingrowth compared to the untreated/polished ones by significantly promoting cell adhesion, matrix mineralization, and osteogenic differentiation through increasing integrin expression. The RoB was low in 41.1% of items, unclear in 53.3%, and high in 5.6%. The quality of the studies achieved a mean score of 17.67. Our study demonstrates that nanostructures with specific controlled properties on the surface of 3D-printed Ti implants improve their osseointegration. However, given the small number of studies, the variability in experimental designs, and lack of reporting across studies, the results should be interpreted with caution.

Response of mesenchymal stem cells to surface topography of scaffolds and the underlying mechanisms

Mesenchymal stem/stromal cells (MSCs) serve as essential components of regenerative medicine. Their destiny is influenced by the interaction of the cells with the external environment. In addition to the biochemical cues in a microenvironment, physical cues of the topography of the surrounding materials such as the extracellular matrix emerge as a crucial regulator of stem cell destiny and function. With recent advances in technologies of materials production and surface modification, surfaces with micro/nanotopographical characteristics can be fabricated to mimic the micro/nanoscale mechanical stimuli of the extracellular matrix environment and regulate the biological behavior of cells. Understanding the interaction of cells with the topography of a surface is conducive to the control of stem cell fate for application in regenerative medicine. However, the mechanisms by which topography affects the biological behavior of stem cells have not been fully elucidated. This review will present the effects of surface topography at the nano/micrometer scale on stem cell adhesion, morphology, proliferation, migration, and differentiation. It also focuses on discussing current theories about the sensing and recognition of surface topology cues, the transduction of the extracellular cues into plasma, and the final activation of related signaling pathways and downstream gene expression in MSCs. These insights will provide a theoretical basis for the future design of biomaterial scaffolds for application in regenerative medicine and tissue engineering.

3D printing method for bone tissue engineering scaffold

3D printing technology is an emerging technology. It constructs solid bodies by stacking materials layer by layer, and can quickly and accurately prepare bone tissue engineering scaffolds with specific shapes and structures to meet the needs of different patients. The field of life sciences has received a great deal of attention. However, different 3D printing technologies and materials have their advantages and disadvantages, and there are limitations in clinical application. In this paper, the technology, materials and clinical applications of 3D printed bone tissue engineering scaffolds are reviewed, and the future development trends and challenges in this field are prospected.

Meta-analyzing the efficacy of 3D printed models in anatomy education

Three-dimensional printing models (3DPs) have been widely used in medical anatomy training. However, the 3DPs evaluation results differ depending on such factors as the training objects, experimental design, organ parts, and test content. Thus, this systematic evaluation was carried out to better understand the role of 3DPs in different populations and different experimental designs. Controlled (CON) studies of 3DPs were retrieved from PubMed and Web of Science databases, where the participants were medical students or residents. The teaching content is the anatomical knowledge of human organs. One evaluation indicator is the mastery of anatomical knowledge after training, and the other is the satisfaction of participants with 3DPs. On the whole, the performance of the 3DPs group was higher than that of the CON group; however, there was no statistical difference in the resident subgroup, and there was no statistical difference for 3DPs vs. 3D visual imaging (3DI). In terms of satisfaction rate, the summary data showed that the difference between the 3DPs group (83.6%) vs. the CON group (69.6%) (binary variable) was not statistically significant, with p > 0.05. 3DPs has a positive effect on anatomy teaching, although there are no statistical differences in the performance tests of individual subgroups; participants generally had good evaluations and satisfaction with 3DPs. 3DPs still faces challenges in production cost, raw material source, authenticity, durability, etc. The future of 3D-printing-model-assisted anatomy teaching is worthy of expectation.

The 3D-Printed Ordered Bredigite Scaffold Promotes Pro-Healing of Critical-Sized Bone Defects by Regulating Macrophage Polarization

Background

Repairing critical-sized bone defects secondary to traumatic or tumorous damage is a complex conundrum in clinical practice; in this case, artificial scaffolds exhibited preferable outcomes. Bredigite (BRT, Ca₇MgSi₄O₁₆) bioceramic possesses excellent physicochemical properties and biological activity as a promising candidate for bone tissue engineering.

Methods

Structurally ordered BRT (BRT-O) scaffolds were fabricated by a three-dimensional (3D) printing technique, and the random BRT (BRT-R) scaffolds and clinically available β-tricalcium phosphate (β-TCP) scaffolds were compared as control groups. Their physicochemical properties were characterized, and RAW 264.7 cells, bone marrow mesenchymal stem cells (BMSCs), and rat cranial critical-sized bone defect models were utilized for evaluating macrophage polarization and bone regeneration.

Results

The BRT-O scaffolds exhibited regular morphology and homogeneous porosity. In addition, the BRT-O scaffolds released higher concentrations of ionic products based on coordinated biodegradability than the β-TCP scaffolds. In vitro, the BRT-O scaffolds facilitated RWA264.7 cells polarization to pro-healing M2 macrophage phenotype, whereas the BRT-R and β-TCP scaffolds stimulated more pro-inflammatory M1-type macrophages. A conditioned medium derived from macrophages seeding on the BRT-O scaffolds notably promoted the osteogenic lineage differentiation of BMSCs in vitro. The cell migration ability of BMSCs was significantly enhanced under the BRT-O-induced immune microenvironment. Moreover, in rat cranial critical-sized bone defect models, the BRT-O scaffolds group promoted new bone formation with a higher proportion of M2-type macrophage infiltration and expression of osteogenesis-related markers. Therefore, in vivo, BRT-O scaffolds play immunomodulatory roles in promoting critical-sized bone defects by enhancing the polarization of M2 macrophages.

Conclusion

3D-printed BRT-O scaffolds can be a promising option for bone tissue engineering, at least partly through macrophage polarization and osteoimmunomodulation.

Bioprinting and biomaterials for dental alveolar tissue regeneration

Three dimensional (3D) bioprinting is a powerful tool, that was recently applied to tissue engineering. This technique allows the precise deposition of cells encapsulated in supportive bioinks to fabricate complex scaffolds, which are used to repair targeted tissues. Here, we review the recent developments in the application of 3D bioprinting to dental tissue engineering. These tissues, including teeth, periodontal ligament, alveolar bones, and dental pulp, present cell types and mechanical properties with great heterogeneity, which is challenging to reproduce in vitro. After highlighting the different bioprinting methods used in regenerative dentistry, we reviewed the great variety of bioink formulations and their effects on cells, which have been established to support the development of these tissues. We discussed the different advances achieved in the fabrication of each dental tissue to provide an overview of the current state of the methods. We conclude with the remaining challenges and future needs.

Powder 3D Printing of Bone Scaffolds with Uniform and Gradient Pore Sizes Using Cuttlebone-Derived Calcium Phosphate and Glass-Ceramic

The pore geometry of bone scaffolds has a major impact on their cellular response; for this reason, 3D printing is an attractive technology for bone tissue engineering, as it allows for the full control and design of the porosity. Calcium phosphate materials synthesized from natural sources have recently attracted a certain interest because of their similarity to natural bone, and they were found to show better bioactivity than synthetic compounds. Nevertheless, these materials are very challenging to be processed by 3D printing due to technological issues related to their nanometric size. In this work, bone scaffolds with different pore geometries, with a uniform size or with a size gradient, were fabricated by binder jetting 3D printing using a biphasic calcium phosphate (BCP) nanopowder derived from cuttlebones. To do so, the nanopowder was mixed with a glass-ceramic powder with a larger particle size (45–100 µm) in 1:10 weight proportions. Pure AP40mod scaffolds were also printed. The sintered scaffolds were shown to be composed mainly by hydroxyapatite (HA) and wollastonite, with the amount of HA being larger when the nanopowder was added because BCP transforms into HA during sintering at 1150 °C. The addition of bio-derived powder increases the porosity from 60% to 70%, with this indicating that the nanoparticles slow down the glass-ceramic densification. Human mesenchymal stem cells were seeded on the scaffolds to test the bioactivity in vitro. The cells’ number and metabolic activity were analyzed after 3, 5 and 10 days of culturing. The cellular behavior was found to be very similar for samples with different pore geometries and compositions. However, while the cell number was constantly increasing, the metabolic activity on the scaffolds with gradient pores and cuttlebone-derived powder decreased over time, which might be a sign of cell differentiation. Generally, all scaffolds promoted fast cell adhesion and proliferation, which were found to penetrate and colonize the 3D porous structure.

Multifunctional Hydroxyapatite Composites for Orthopedic Applications: A Review

Being a bioactive material, hydroxyapatite (HAp) is regarded as one of the most attractive ceramic biomaterials for bone and hard-tissue replacement and regeneration. Despite its substantial biocompatibility, osteoconductivity, and compositional similarity to that of bone, the employment of HAp is still limited in orthopedic applications due to its poor mechanical (low fracture toughness and bending strength) and antibacterial properties. These significant challenges lead to the notion of developing novel HAp-based composites via different fabrication routes. HAp, when efficaciously combined with functionally graded materials and antibacterial agents, like Ag, ZnO, Co, etc., form composites that render remarkable crack resistance and toughening, as well as enhance its bactericidal efficacy. The addition of different materials and a fabrication method, like 3D printing, greatly influence the porosity of the structure and, in turn, control cell adhesion, thereby enabling biological fixation of the material. This article encompasses an elaborate discussion on different multifunctional HAp composites developed for orthopedic applications with particular emphasis on the incorporation of functionally graded materials and antibacterial agents. The influence of 3D printing on the fabrication of HAp-based scaffolds, and the different in vitro and in vivo studies conducted on these, have all been included here. Furthermore, the present review not only provides insights and broad understanding by elucidating recent advancements toward 4D printing but also directs the reader to future research directions in design and application of HAp-based composite coatings and scaffolds.

Laser Sintering Approaches for Bone Tissue Engineering

The adoption of additive manufacturing (AM) techniques into the medical space has revolutionised tissue engineering. Depending upon the tissue type, specific AM approaches are capable of closely matching the physical and biological tissue attributes, to guide tissue regeneration. For hard tissue such as bone, powder bed fusion (PBF) techniques have significant potential, as they are capable of fabricating materials that can match the mechanical requirements necessary to maintain bone functionality and support regeneration. This review focuses on the PBF techniques that utilize laser sintering for creating scaffolds for bone tissue engineering (BTE) applications. Optimal scaffold requirements are explained, ranging from material biocompatibility and bioactivity, to generating specific architectures to recapitulate the porosity, interconnectivity, and mechanical properties of native human bone. The main objective of the review is to outline the most common materials processed using PBF in the context of BTE; initially outlining the most common polymers, including polyamide, polycaprolactone, polyethylene, and polyetheretherketone. Subsequent sections investigate the use of metals and ceramics in similar systems for BTE applications. The last section explores how composite materials can be used. Within each material section, the benefits and shortcomings are outlined, including their mechanical and biological performance, as well as associated printing parameters. The framework provided can be applied to the development of new, novel materials or laser-based approaches to ultimately generate bone tissue analogues or for guiding bone regeneration.

The Role of 3D Printing in Planning Complex Medical Procedures and Training of Medical Professionals-Cross-Sectional Multispecialty Review

Medicine is a rapidly-evolving discipline, with progress picking up pace with each passing decade. This constant evolution results in the introduction of new tools and methods, which in turn occasionally leads to paradigm shifts across the affected medical fields. The following review attempts to showcase how 3D printing has begun to reshape and improve processes across various medical specialties and where it has the potential to make a significant impact. The current state-of-the-art, as well as real-life clinical applications of 3D printing, are reflected in the perspectives of specialists practicing in the selected disciplines, with a focus on pre-procedural planning, simulation (rehearsal) of non-routine procedures, and on medical education and training. A review of the latest multidisciplinary literature on the subject offers a general summary of the advances enabled by 3D printing. Numerous advantages and applications were found, such as gaining better insight into patient-specific anatomy, better pre-operative planning, mock simulated surgeries, simulation-based training and education, development of surgical guides and other tools, patient-specific implants, bioprinted organs or structures, and counseling of patients. It was evident that pre-procedural planning and rehearsing of unusual or difficult procedures and training of medical professionals in these procedures are extremely useful and transformative.

Fabrication and Characterization of PCL/HA Filament as a 3D Printing Material Using Thermal Extrusion Technology for Bone Tissue Engineering

The most common three-dimensional (3D) printing method is material extrusion, where a pre-made filament is deposited layer-by-layer. In recent years, low-cost polycaprolactone (PCL) material has increasingly been used in 3D printing, exhibiting a sufficiently high quality for consideration in cranio-maxillofacial reconstructions. To increase osteoconductivity, prefabricated filaments for bone repair based on PCL can be supplemented with hydroxyapatite (HA). However, few reports on PCL/HA composite filaments for material extrusion applications have been documented. In this study, solvent-free fabrication for PCL/HA composite filaments (HA 0%, 5%, 10%, 15%, 20%, and 25% weight/weight PCL) was addressed, and parameters for scaffold fabrication in a desktop 3D printer were confirmed. Filaments and scaffold fabrication temperatures rose with increased HA content. The pore size and porosity of the six groups’ scaffolds were similar to each other, and all had highly interconnected structures. Six groups’ scaffolds were evaluated by measuring the compressive strength, elastic modulus, water contact angle, and morphology. A higher amount of HA increased surface roughness and hydrophilicity compared to PCL scaffolds. The increase in HA content improved the compressive strength and elastic modulus. The obtained data provide the basis for the biological evaluation and future clinical applications of PCL/HA material.

Biomechanical Analyses of Porous Designs of 3D-Printed Titanium Implant for Mandibular Segmental Osteotomy Defects

Clinically, a reconstruction plate can be used for the facial repair of patients with mandibular segmental defects, but it cannot restore their chewing function. The main purpose of this research is to design a new three-dimensionally (3D) printed porous titanium mandibular implant with both facial restoration and oral chewing function reconstruction. Its biomechanical properties were examined using both finite element analysis (FEA) and in vitro experiments. Cone beam computed tomography images of the mandible of a patient with oral cancer were selected as a reference to create 3D computational models of the bone and of the 3D-printed porous implant. The pores of the porous implant were circles or hexagons of 1 or 2 mm in size. A nonporous implant was fabricated as a control model. For the FEA, two chewing modes, namely right unilateral molar clench and right group function, were set as loading conditions. Regarding the boundary condition, the displacement of both condyles was fixed in all directions. For the in vitro experiments, an occlusal force (100 N) was applied to the abutment of the 3D-printed mandibular implants with and without porous designs as the loading condition. The porous mandibular implants withstood higher stress and strain than the nonporous mandibular implant, but all stress values were lower than the yield strength of Ti-6Al-4V (800 MPa). The strain value of the bone surrounding the mandibular implant was affected not only by the shape and size of the pores but also by the chewing mode. According to Frost's mechanostat theory of bone, higher bone strain under the porous implants might help maintain or improve bone quality and bone strength. The findings of this study serve as a biomechanical reference for the design of 3D-printed titanium mandibular implants and require confirmation through clinical investigations.

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.

Nature-Based Biomaterials and Their Application in Biomedicine

Natural polymers, based on proteins or polysaccharides, have attracted increasing interest in recent years due to their broad potential uses in biomedicine. The chemical stability, structural versatility, biocompatibility and high availability of these materials lend them to diverse applications in areas such as tissue engineering, drug delivery and wound healing. Biomaterials purified from animal or plant sources have also been engineered to improve their structural properties or promote interactions with surrounding cells and tissues for improved in vivo performance, leading to novel applications as implantable devices, in controlled drug release and as surface coatings. This review describes biomaterials derived from and inspired by natural proteins and polysaccharides and highlights their promise across diverse biomedical fields. We outline current therapeutic applications of these nature-based materials and consider expected future developments in identifying and utilising innovative biomaterials in new biomedical applications.

Recent Advances in the Treatment of Bone Metastases and Primary Bone Tumors: An Up-to-Date Review

In the last decades, the treatment of primary and secondary bone tumors has faced a slow-down in its development, being mainly based on chemotherapy, radiotherapy, and surgical interventions. However, these conventional therapeutic strategies present a series of disadvantages (e.g., multidrug resistance, tumor recurrence, severe side effects, formation of large bone defects), which limit their application and efficacy. In recent years, these procedures were combined with several adjuvant therapies, with different degrees of success. To overcome the drawbacks of current therapies and improve treatment outcomes, other strategies started being investigated, like carrier-mediated drug delivery, bone substitutes for repairing bone defects, and multifunctional scaffolds with bone tissue regeneration and antitumor properties. Thus, this paper aims to present the types of bone tumors and their current treatment approaches, further focusing on the recent advances in new therapeutic alternatives.