Novel titanium-apatite hybrid scaffolds with spongy bone-like micro architecture intended for spinal application: In vitro and in vivo study

Towards single-cell bioprinting: micropatterning tools for organ-on-chip development

Organs-on-chips (OoCs) hold promise to engineer progressively more human-relevant in vitro models for pharmaceutical purposes. Recent developments have delivered increasingly sophisticated designs, yet OoCs still lack in reproducing the inner tissue physiology required to fully resemble the native human body. This review emphasizes the need to include microarchitectural and microstructural features, and discusses promising avenues to incorporate well-defined microarchitectures down to the single-cell level. We highlight how their integration will significantly contribute to the advancement of the field towards highly organized structural and hierarchical tissues-on-chip. We discuss the combination of state-of-the-art micropatterning technologies to achieve OoCs resembling human-intrinsic complexity. It is anticipated that these innovations will yield significant advances in realization of the next generation of OoC models.

Customized Additive Manufacturing in Bone Scaffolds-The Gateway to Precise Bone Defect Treatment

In the advancing landscape of technology and novel material development, additive manufacturing (AM) is steadily making strides within the biomedical sector. Moving away from traditional, one-size-fits-all implant solutions, the advent of AM technology allows for patient-specific scaffolds that could improve integration and enhance wound healing. These scaffolds, meticulously designed with a myriad of geometries, mechanical properties, and biological responses, are made possible through the vast selection of materials and fabrication methods at our disposal. Recognizing the importance of precision in the treatment of bone defects, which display variability from macroscopic to microscopic scales in each case, a tailored treatment strategy is required. A patient-specific AM bone scaffold perfectly addresses this necessity. This review elucidates the pivotal role that customized AM bone scaffolds play in bone defect treatment, while offering comprehensive guidelines for their customization. This includes aspects such as bone defect imaging, material selection, topography design, and fabrication methodology. Additionally, we propose a cooperative model involving the patient, clinician, and engineer, thereby underscoring the interdisciplinary approach necessary for the effective design and clinical application of these customized AM bone scaffolds. This collaboration promises to usher in a new era of bioactive medical materials, responsive to individualized needs and capable of pushing boundaries in personalized medicine beyond those set by traditional medical materials.

A facile way to construct Sr-doped apatite coating on the surface of 3D printed scaffolds to improve osteogenic effect

Bone-like apatite coating fabricated by biomineralization process is a facile way for surface modification of porous scaffolds to improve interfacial behaviors and thus facilitate cell attachment, proliferation, and differentiation for bone tissue engineering. In this study, a Sr-containing calcium phosphate solution was made and used to construct a thick layer of Sr-doped bone-like apatite on the surface of 3D printed scaffolds via biomineralization process. Importantly, Sr-doped bone-like apatite could form and fully cover the 3D printed scaffolds surface in hours. The characterization results indicated that Sr2+ ions successfully replaced Ca2+ ions in bone-like apatite and the molar ratio of Sr/(Ca+Sr) was up to 8.2%. Furthermore, the Sr-doped apatite coating increased the compressive strength and Young’s modulus of composite scaffolds. The compatibility and bioactivity of mineralized scaffolds were evaluated by cell attachment, proliferation, and differentiation of MC3T3-E1 cells. It was found that Sr-doped apatite coating could gradually release Sr2+ ions and further promote cell attachment, proliferation rate, and the expression of alkaline phosphatase activity and osteogenic related genes, such as collagen type I (Col I), Runt-related transcription factor 2 (Runx-2), osteopontin, and osterix. Therefore, the Sr-doped apatite coating fabricated by this facile and rapid biomineralization process offers a new strategy to modify 3D printed porous scaffolds with significantly improved mechanical and biological properties for bone tissue engineering applications.

Effect of Hydroxyapatite Nanoparticles and Nitrogen Plasma Treatment on Osteoblast Biological Behaviors of 3D-Printed HDPE Scaffold for Bone Tissue Regeneration Applications

The need for the repair of bone defects has been increasing due to various causes of loss of skeletal tissue. High density polyethylenes (HDPE) have been used as bone substitutes due to their excellent biocompatibility and mechanical strength. In the present study, we investigated the preosteoblast cell proliferation and differentiation on the adding nano-hydroxyapatite (n-HAp) particles into HDPE scaffold and treating HDPE/n-HAp scaffolds with nitrogen (N₂) plasma. The three-dimensional (3D) HDPE/n-HAp scaffolds were prepared by fused modeling deposition 3D printer. The HDPE/n-HAp was blended with 10 wt% of n-HAp particle. The scaffold surface was reactive ion etched with nitrogen plasma to improve the preosteoblast biological response in vitro. After N₂ plasma treatment, surfaces characterizations were investigated using Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The proliferation and differentiation of preosteoblast (MC3T3-E1) cells were evaluated by MTT assay and alkaline phosphatase (ALP) activity. The incorporation of n-HAp particles and N₂ plasma surface treatment showed the improvement of biological responses of MC3T3-E1 cells in the HDPE scaffolds.

Tissue Engineering Through 3D Bioprinting to Recreate and Study Bone Disease

The applications of 3D bioprinting are becoming more commonplace. Since the advent of tissue engineering, bone has received much attention for the ability to engineer normal bone for tissue engraftment or replacement. While there are still debates on what materials comprise the most durable and natural replacement of normal tissue, little attention is given to recreating diseased states within the bone. With a better understanding of the cellular pathophysiology associated with the more common bone diseases, these diseases can be scaled down to a more throughput way to test therapies that can reverse the cellular pathophysiology. In this review, we will discuss the potential of 3D bioprinting of bone tissue in the following disease states: osteoporosis, Paget's disease, heterotopic ossification, osteosarcoma, osteogenesis imperfecta, and rickets disease. The development of these 3D bioprinted models will allow for the advancement of novel therapy testing resulting in possible relief to these chronic diseases.

Structural and Material Determinants Influencing the Behavior of Porous Ti and Its Alloys Made by Additive Manufacturing Techniques for Biomedical Applications

One of the biggest challenges in tissue engineering is the manufacturing of porous structures that are customized in size and shape and that mimic natural bone structure. Additive manufacturing is known as a sufficient method to produce 3D porous structures used as bone substitutes in large segmental bone defects. The literature indicates that the mechanical and biological properties of scaffolds highly depend on geometrical features of structure (pore size, pore shape, porosity), surface morphology, and chemistry. The objective of this review is to present the latest advances and trends in the development of titanium scaffolds concerning the relationships between applied materials, manufacturing methods, and interior architecture determined by porosity, pore shape, and size, and the mechanical, biological, chemical, and physical properties. Such a review is assumed to show the real achievements and, on the other side, shortages in so far research.

Accelerated degradation of HAP/PLLA bone scaffold by PGA blending facilitates bioactivity and osteoconductivity

The incorporation of hydroxyapatite (HAP) into poly-l-lactic acid (PLLA) matrix serving as bone scaffold is expected to exhibit bioactivity and osteoconductivity to those of the living bone. While too low degradation rate of HAP/PLLA scaffold hinders the activity because the embedded HAP in the PLLA matrix is difficult to contact and exchange ions with body fluid. In this study, biodegradable polymer poly (glycolic acid) (PGA) was blended into the HAP/PLLA scaffold fabricated by laser 3D printing to accelerate the degradation. The results indicated that the incorporation of PGA enhanced the degradation rate of scaffold as indicated by the weight loss increasing from 3.3% to 25.0% after immersion for 28 days, owing to the degradation of high hydrophilic PGA and the subsequent accelerated hydrolysis of PLLA chains. Moreover, a lot of pores produced by the degradation of the scaffold promoted the exposure of HAP from the matrix, which not only activated the deposition of bone like apatite on scaffold but also accelerated apatite growth. Cytocompatibility tests exhibited a good osteoblast adhesion, spreading and proliferation, suggesting the scaffold provided a suitable environment for cell cultivation. Furthermore, the scaffold displayed excellent bone defect repair capacity with the formation of abundant new bone tissue and blood vessel tissue, and both ends of defect region were bridged after 8 weeks of implantation.

A systematic review of preclinical in vivo testing of 3D printed porous Ti6Al4V for orthopedic applications, part I: Animal models and bone ingrowth outcome measures

For Ti6Al4V orthopedic and spinal implants, osseointegration is often achieved using complex porous geometries created via additive manufacturing (AM). While AM porous titanium (pTi) has shown clinical success, concerns regarding metallic implants have spurred interest in alternative AM biomaterials for osseointegration. Insights regarding the evaluation of these new materials may be supported by better understanding the role of preclinical testing for AM pTi. We therefore asked: (a) What animal models have been most commonly used to evaluate AM porous Ti6Al4V for orthopedic bone ingrowth; (b) What were the primary reported quantitative outcome measures for these models; and (c) What were the bone ingrowth outcomes associated with the most frequently used models? We performed a systematic literature search and identified 58 articles meeting our inclusion criteria. We found that AM pTi was evaluated most often using rabbit and sheep femoral condyle defect (FCD) models. Additional ingrowth models including transcortical and segmental defects, spinal fusions, and calvarial defects were also used with various animals based on the study goals. Quantitative outcome measures determined via histomorphometry including ''bone ingrowth'' (range: 3.92-53.4% for rabbit/sheep FCD) and bone-implant contact (range: 9.9-59.7% for rabbit/sheep FCD) were the most common. Studies also used 3D imaging to report outcomes such as bone volume fraction (BV/TV, range: 4.4-61.1% for rabbit/sheep FCD), and push-out testing for outcomes such as maximum removal force (range: 46.6-3092 N for rabbit/sheep FCD). Though there were many commonalities among the study methods, we also found significant heterogeneity in the outcome terms and definitions. The considerable diversity in testing and reporting may no longer be necessary considering the reported success of AM pTi across all model types and the ample literature supporting the rabbit and sheep as suitable small and large animal models, respectively. Ultimately, more standardized animal models and reporting of bone ingrowth for porous AM materials will be useful for future studies.

In vitro evaluation of electrochemically bioactivated Ti6Al4V 3D porous scaffolds

Triply periodic minimal surfaces (TPMS) are known for their advanced mechanical properties and are wrinkle-free with a smooth local topology. These surfaces provide suitable conditions for cell attachment and proliferation. In this study, the in vitro osteoinductive and antibacterial properties of scaffolds with different minimal pore diameters and architectures were investigated. For the first time, scaffolds with TPMS architecture were treated electrochemically by plasma electrolytic oxidation (PEO) with and without silver nanoparticles (AgNPs) to enhance the surface bioactivity. It was found that the scaffold architecture had a greater impact on the osteoblast cell activity than the pore size. Through control of the architecture type, the collagen production by osteoblast cells increased by 18.9% and by 43.0% in the case of additional surface PEO bioactivation. The manufactured scaffolds demonstrated an extremely low quasi-elastic modulus (comparable with trabecular and cortical bone), which was 5-10 times lower than that of bulk titanium (6.4-11.4 GPa vs 100-105 GPa). The AgNPs provided antibacterial properties against both gram-positive and gram-negative bacteria and had no significant impact on the osteoblast cell growth. Complex experimental results show the in vitro effectiveness of the PEO-modified TPMS architecture, which could positively impact the clinical applications of porous bioactive implants.

Prospect of Metal Ceramic (Titanium-Wollastonite) Composite as Permanent Bone Implants: A Narrative Review

This literature review discusses the influence of titanium ceramic composites as a biomaterial towards the fabrication of implants for orthopedic applications. The concept of applying metal-ceramic composites enable many novel combinations in the design and fabrication of complex materials which enhances functionality to improve cell and tissue matrix interactions particularly in the formation of bone. Specific focus is placed on its plethora of materials selected from the metals and ceramic group and identifying the optimal combination that matches them. The prospect of wollastonite as the ceramic counterpart is also highlighted. In this review, we have highlighted the different fabrication methods for such metal-ceramic materials as well as the role that these hybrids play in an in vitro and in vivo environment. Its economic potential as a bone implant material is also discussed.

Growth Factors, Carrier Materials, and Bone Repair

This chapter provides an overview of the growth factors active in bone regeneration and healing. Both normal and impaired bone healing are discussed, with a focus on the spatiotemporal activity of the various growth factors known to be involved in the healing response. The review highlights the activities of most important growth factors impacting bone regeneration, with a particular emphasis on those being pursued for clinical translation or which have already been marketed as components of bone regenerative materials. Current approaches the use of bone grafts in clinical settings of bone repair (including bone grafts) are summarized, and carrier systems (scaffolds) for bone tissue engineering via localized growth factor delivery are reviewed. The chapter concludes with a consideration of how bone repair might be improved in the future.