Bioceramic scaffolds with triply periodic minimal surface architectures guide early-stage bone regeneration

Piezoelectricity Promotes 3D-Printed BTO/β-TCP Composite Scaffolds with Excellent Osteogenic Performance

Piezoelectricity is reported to be able to promote bone scaffolds with excellent osteogenic performance. Herein, barium titanate/β-tricalcium phosphate (BTO/β-TCP) piezoelectric composite scaffolds were 3D printed, and their osteogenic performances were investigated in detail. The fabrication of BTO/β-TCP piezoelectric composite scaffolds employed cutting-edge DLP 3D printing technology. The scaffolds, featuring a triply periodic minimal surface (TPMS) design with a porosity of 60%, offered a unique structural framework. A comprehensive assessment of the composition, piezoelectric properties, and mechanical characteristics of the BTO/β-TCP scaffolds was conducted. Notably, an increase in the BTO volume fraction from 50 to 80 vol % within the scaffolds led to a reduction in compressive strength, decreasing from 2.47 to 1.74 MPa. However, this variation was accompanied by a substantial enhancement in the piezoelectric constant d33, soaring from 1.4 pC/N to 21.6 pC/N. Utilizing mouse osteoblasts (MC3T3-E1) in a live/dead cell staining assay, under the influence of external ultrasound, demonstrated the commendable biocompatibility of these piezoelectric composite ceramic bone scaffolds. Furthermore, thorough analyses of alkaline phosphatase (ALP) activity and polymerase chain reaction (PCR) findings provided compelling evidence of the scaffolds' superior osteogenic properties, underpinning their effectiveness at the cellular protein and gene levels. In conclusion, this study offers a groundbreaking strategy for the employment of BTO/β-TCP piezoelectric composite scaffolds in bone implant applications, harnessing their unique blend of biocompatibility, piezoelectricity, and osteogenic potential.

Enhancing Osteogenesis and Mechanical Properties through Scaffold Design in 3D Printed Bone Substitutes

In the context of regenerative medicine, the design of scaffolds to possess excellent osteogenesis and appropriate mechanical properties has gained significant attention in bone tissue engineering. In this review, we categorized materials into metallic, inorganic, nonmetallic, organic polymer, and composite materials. This review provides a more integrated and multidimensional analysis of scaffold design for bone tissue engineering. Unlike previous works that often focus on single aspects, such as material type or fabrication technique, our review takes a broader approach. It analyzes the interaction between scaffold materials, 3D printing techniques, scaffold structural designs, modification methods, porosities, and pore sizes, and the composition of materials (particularly composite materials). Meanwhile, it focuses on their impacts on scaffolds' osteogenic potential and mechanical performance. This review also provides suggested ranges for porosity and pore size for different materials and outlines recommended surface modification methods. This approach not only consolidates current knowledge but also highlights the interdependencies among various factors affecting scaffold efficacy, offering deeper insights into optimization strategies tailored for specific clinical conditions. Furthermore, we introduce recent advancements in innovative 3D printing techniques and novel composite materials, which are rarely addressed in previous reviews, thereby providing a forward-looking perspective that informs future research directions and clinical applications.

Understanding the relationship between pore structure and properties of triply periodic minimal surface bone scaffolds

The number of patients with bone defects caused by trauma and diseases has been increasing year by year. The treatment of bone defects remains a major challenge in clinical practice. Bone scaffolds are increasingly favored for repairing bones, with triply periodic minimal surface (TPMS) scaffolds emerging as a popular option due to their superior performance. The aim of this review is to highlight the crucial influence of pore structure on the properties of TPMS bone scaffolds, offering important insights for their innovation and production. It briefly examines various elements that influence the properties of TPMS bone scaffolds, such as pore shape, porosity, pore diameter, and curvature. By analyzing these elements, this review serves as a valuable reference for upcoming research and practical implementations in the field of bone tissue engineering.

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.

Design of 3D printing osteotomy block for foot based on triply periodic minimal surface

The ankle joint, which connects the lower limbs and the sole of the foot, is prone to sprain during walking and sports, which leads to ankle arthritis. Supratroleolar osteotomy is an ankle preserving operation for the treatment of ankle arthritis, in which the osteotomy is an important fixing and supporting part. In order to avoid stress shielding effect as much as possible, the osteotomy block is designed as a porous structure. In this study, the osteotomy block was designed based on three-period minimal surface, and the designed structure was manufactured by 3D printing. The mechanical properties of different structures were studied by mechanical test and finite element simulation. In mechanical tests, the Gyroid structure showed a progressive failure mechanism from bottom to bottom, while the Diamond structure showed a shear failure zone at 45° Angle, which was not conducive to energy absorption and was more prone to brittle fracture than the Gyroid structure. Therefore, the Gyroid structure is valuable for further research in the development of porous osteotomy.

Biomimetic Bone-Like Composite Hydrogel Scaffolds Composed of Collagen Fibrils and Natural Hydroxyapatite for Promoting Bone Repair

Bone is a complex organic-inorganic composite tissue composed of ∼30% organics and ∼70% hydroxyapatite (HAp). Inspired by this, we used 30% collagen and 70% HAp extracted from natural bone using the calcination method to generate a biomimetic bone composite hydrogel scaffold (BBCHS). In one respect, BBCHS, with a fixed proportion of inorganic and organic components similar to natural bone, exhibits good physical properties. In another respect, the highly biologically active and biocompatible HAp from natural bone effectively promotes osteogenic differentiation, and type I collagen facilitates cell adhesion and spreading. Additionally, the well-structured porosity of the BBCHS provides sufficient growth space for bone marrow mesenchymal stem cells (BMSCs) while promoting substance exchange. Compared to the control group, the new bone surface of the defective location in the B-HA70+Col group is increased by 3.4-fold after 8 weeks of in vivo experiments. This strategy enables the BBCHS to closely imitate the chemical makeup and physical structure of natural bone. With its robust biocompatibility and osteogenic activity, the BBCHS can be easily adapted for a wide range of bone repair applications and offers promising potential for future research and development.

Prioritizing Biomaterial Driven Clinical Bioactivity Over Designing Intricacy during Bioprinting of Trabecular Microarchitecture: A Clinician's Perspective

Bone tissue engineering has witnessed a historical shift from three perspectives. From a biomaterial perspective, materials have now become smarter and dynamic; from a bioengineering perspective the bioprinting techniques have now advanced to 4D bioprinting; and from a clinical perspective scaffold bioactivity has progressed toward enhanced osteoinductive scaffolds driven by intricate biomechanical, biophysical, biochemical, and biological cues. Though all of these advancements are indicative of improvised scaffold engineering, a pivotal question regarding the critical role and need of designing and replicating the intricacies of trabecular microarchitecture for enhanced, clinically appreciable osteoangiogenicity needs to be answered. This review hence critically evaluates the rationale and the need of investing substantial effort into designing complex microarchitectures amidst the era of "smart biomaterials" and dynamic 4D bioprinting aimed toward enhancing clinically appreciable bioactivity. The article explores the concept of integrating intricate designs into a scaffold microarchitecture to bolster bioactivity and the practical challenges encountered in 3D bioprinting of complex designs and meticulously examines the pivotal role of biomaterials in scaffold bioactivity, proposing a comprehensive approach to bioprinting geared toward achieving clinical bioactivity and striking a judicious balance between design intricacy and functional outcomes in bone bioprinting.

3D Printed Porous Zirconia Biomaterials based on Triply Periodic Minimal Surfaces Promote Osseointegration In Vitro by Regulating Osteoimmunomodulation and Osteo/Angiogenesis

The triply periodic minimal surface (TPMS) is a highly useful structure for bone tissue engineering owing to its nearly nonexistent average surface curvature, high surface area-to-volume ratio, and exceptional mechanical energy absorption properties. However, limited literature is available regarding bionic zirconia implants using the TPMS structure for bone regeneration. Herein, we employed the digital light processing (DLP) technology to fabricate four types of zirconia-based TPMS structures: P-cell, S14, IWP, and Gyroid. For cell proliferation, the four porous TPMS structures outperformed the solid zirconia group (P-cell > S14 > Gyroid > IWP > ZrO2). In vitro assessments on the biological responses and osteogenic properties of the distinct porous surfaces identified the IWP and Gyroid structures as promising candidates for future clinical applications of porous zirconia implants because of their superior osteogenic capabilities (IWP > Gyroid > S14 > P-cell > ZrO2) and mechanical properties (ZrO2 > IWP > Gyroid > S14 > P-cell). Furthermore, the physical properties of the IWP/Gyroid surface had more substantial effects on bone immune regulation by reducing macrophage M1 phenotype polarization while increasing M2 phenotype polarization compared with the solid zirconia surface. Additionally, the IWP and Gyroid groups exhibited enhanced immune osteogenesis and angiogenesis abilities. Collectively, these findings highlight the substantial impact of topology on bone/angiogenesis and immune regulation in promoting bone integration.

Additively manufactured porous scaffolds by design for treatment of bone defects

There has been increasing attention to produce porous scaffolds that mimic human bone properties for enhancement of tissue ingrowth, regeneration, and integration. Additive manufacturing (AM) technologies, i.e., three dimensional (3D) printing, have played a substantial role in engineering porous scaffolds for clinical applications owing to their high level of design and fabrication flexibility. To this end, this review article attempts to provide a detailed overview on the main design considerations of porous scaffolds such as permeability, adhesion, vascularisation, and interfacial features and their interplay to affect bone regeneration and osseointegration. Physiology of bone regeneration was initially explained that was followed by analysing the impacts of porosity, pore size, permeability and surface chemistry of porous scaffolds on bone regeneration in defects. Importantly, major 3D printing methods employed for fabrication of porous bone substitutes were also discussed. Advancements of MA technologies have allowed for the production of bone scaffolds with complex geometries in polymers, composites and metals with well-tailored architectural, mechanical, and mass transport features. In this way, a particular attention was devoted to reviewing 3D printed scaffolds with triply periodic minimal surface (TPMS) geometries that mimic the hierarchical structure of human bones. In overall, this review enlighten a design pathway to produce patient-specific 3D-printed bone substitutions with high regeneration and osseointegration capacity for repairing large bone defects.

Design and fabrication of biomimicking radially graded scaffolds via digital light processing 3D printing for bone regeneration

Scaffolds are an essential component in bone tissue engineering (BTE). However, most of the current BTE scaffolds are homogeneous structures and do not resemble the graded architectures of native bone. In the current study, four types of biomimicking scaffold designs based on gyroid (G) and primitive (P) units with radially graded pore sizes were devised, and scaffolds of these designs with two porosity groups (65 vol% and 75 vol%) were fabricated via digital light processing (DLP) 3D printing using biphasic calcium phosphate (BCP). Scaffolds of the gyroid-gyroid (G-G) design displayed better dimensional accuracy, compressive property, and cell proliferation rate than gyroid-primitive (G-P), primitive-gyroid (P-G), and primitive-primitive (P-P) scaffolds. Subsequently, graded G-G scaffolds with different porosities were fabricated and the relationship between compressive strength and porosity was determined. Furthermore, the sintered BCP bioceramics fabricated via current manufacturing process exhibited excellent biocompatibility and bioactivity, indicating their high potential for BTE.