Unraveling the influence of channel size and shape in 3D printed ceramic scaffolds on osteogenesis.

Bone has the capacity to regenerate itself for relatively small defects; however, this regenerative capacity is diminished in critical-size bone defects. The development of synthetic materials has risen as a distinct strategy to address this challenge. Effective synthetic materials to have emerged in recent years are bioceramic implants, which are biocompatible and highly bioactive. Yet nothing suitable for the repair of large bone defects has made the transition from laboratory to clinic. The clinical success of bioceramics has been shown to depend not only on the scaffold's intrinsic material properties but also on its internal porous geometry. This study aimed to systematically explore the implications of varying channel size, shape, and curvature in tissue scaffolds on in vivo bone regeneration outcomes. 3D printed bioceramic scaffolds with varying channel sizes (0.3 mm to 1.5 mm), shapes (circular vs rectangular), and curvatures (concave vs convex) were implanted in rabbit femoral defects for 8 weeks, followed by histological evaluation. We demonstrated that circular channel sizes of around 0.9 mm diameter significantly enhanced bone formation, compared to channel with diameters of 0.3 mm and 1.5 mm. Interestingly, varying channel shapes (rectangular vs circular) had no significant effect on the volume of newly formed bone. Furthermore, the present study systematically demonstrated the beneficial effect of concave surfaces on bone tissue growth in vivo, reinforcing previous in silico and in vitro findings. This study demonstrates that optimizing architectural configurations within ceramic scaffolds is crucial in enhancing bone regeneration outcomes. STATEMENT OF SIGNIFICANCE: Despite the explosion of work on developing synthetic scaffolds to repair bone defects, the amount of new bone formed by scaffolds in vivo remains suboptimal. Recent studies have illuminated the pivotal role of scaffolds' internal architecture in osteogenesis. However, these investigations have mostly remained confined to in silico and in vitro experiments. Among the in vivo studies conducted, there has been a lack of systematic analysis of individual architectural features. Herein, we utilized bioceramic 3D printing to conduct a systematic exploration of the effects of channel size, shape, and curvature on bone formation in vivo. Our results demonstrate the significant influence of channel size and curvature on in vivo outcomes. These findings provide invaluable insights into the design of more effective bone scaffolds.

Progress in Nanostructured Mechano-Bactericidal Polymeric Surfaces for Biomedical Applications.

Bacterial infections and antibiotic resistance remain significant contributors to morbidity and mortality worldwide. Despite recent advances in biomedical research, a substantial number of medical devices and implants continue to be plagued by bacterial colonisation, resulting in severe consequences, including fatalities. The development of nanostructured surfaces with mechano-bactericidal properties has emerged as a promising solution to this problem. These surfaces employ a mechanical rupturing mechanism to lyse bacterial cells, effectively halting subsequent biofilm formation on various materials and, ultimately, thwarting bacterial infections. This review delves into the prevailing research progress within the realm of nanostructured mechano-bactericidal polymeric surfaces. It also investigates the diverse fabrication methods for developing nanostructured polymeric surfaces with mechano-bactericidal properties. We then discuss the significant challenges associated with each approach and identify research gaps that warrant exploration in future studies, emphasizing the potential for polymeric implants to leverage their distinct physical, chemical, and mechanical properties over traditional materials like metals.

Multifunctional nacre-like materials.

Nacre, the iridescent inner layer of seashells, displays an exceptional combination of strength and toughness due to its 'brick-wall' architecture. Significant research has been devoted to replicating nacre's architecture and its associated deformation and failure mechanisms. Using the resulting materials in applications necessitates adding functionalities such as self-healing, force sensing, bioactivity, heat conductivity and resistance, transparency, and electromagnetic interference shielding. Herein, progress in the fabrication, mechanics, and multi-functionality of nacre-like materials, particularly over the past three years is systematically and critically reviewed. The fabrication techniques reviewed include 3D printing, freeze-casting, mixing/coating-assembling, and laser engraving. The mechanical properties of the resulting materials are discussed in comparison with their constituents and previously developed nacre mimics. Subsequently, the progress in incorporating multifunctionalities and the resulting physical, chemical, and biological properties are evaluated. We finally provide suggestions based on 3D/4D printing, advanced modelling techniques, and machine elements to make reprogrammable nacre-like components with complex shapes and small building blocks, tackling some of the main challenges in the science and translation of these materials.

Discovering an unknown territory using atom probe tomography: Elemental exchange at the bioceramic scaffold/bone tissue interface.

Here we report the first atom probe study to reveal the atomic-scale composition of in vivo bone formed in a bioceramic scaffold (strontium-hardystonite-gahnite) after 12-month implantation in a large bone defect in sheep tibia. The composition of the newly formed bone tissue differs to that of mature cortical bone tissue, and elements from the degrading bioceramic implant, particularly aluminium (Al), are present in both the newly formed bone and in the original mature cortical bone tissue at the perimeter of the bioceramic implant. Atom probe tomography confirmed that the trace elements are released from the bioceramic and are actively transported into the newly formed bone. NanoSIMS mapping, as a complementary technique, confirmed the distribution of the released ions from the bioceramic into the newly formed bone tissue within the scaffold. This study demonstrated the combined benefits of atom probe and nanoSIMS in assessing nanoscopic chemical composition changes at precise locations within the tissue/biomaterial interface. Such information can assist in understanding the interaction of scaffolds with surrounding tissue, hence permitting further iterative improvements to the design and performance of biomedical implants, and ultimately reducing the risk of complications or failure while increasing the rate of tissue formation. STATEMENT OF SIGNIFICANCE: The repair of critical-sized load-bearing bone defects is a challenge, and precisely engineered bioceramic scaffold implants is an emerging potential treatment strategy. However, we still do not understand the effect of the bioceramic scaffold implants on the composition of newly formed bone in vivo and surrounding existing mature bone. This article reports an innovative route to solve this problem, the combined power of atom probe tomography and nanoSIMS is used to spatially define elemental distributions across bioceramic implant sites. We determine the nanoscopic chemical composition changes at the Sr-HT Gahnite bioceramic/bone tissue interface, and importantly, provide the first report of in vivo bone tissue chemical composition formed in a bioceramic scaffold.

Protocol for Cell Colonization and Comprehensive Monitoring of Osteogenic Differentiation in 3D Scaffolds Using Biochemical Assays and Multiphoton Imaging.

The goal of bone tissue engineering is to build artificial bone tissue with properties that closely resemble human bone and thereby support the optimal integration of the constructs (biografts) into the body. The development of tissues in 3D scaffolds includes several complex steps that need to be optimized and monitored. In particular, cell-material interaction during seeding, cell proliferation and cell differentiation within the scaffold pores play a key role. In this work, we seeded two types of 3D-printed scaffolds with pre-osteoblastic MC3T3-E1 cells, proliferated and differentiated the cells, before testing and adapting different assays and imaging methods to monitor these processes. Alpha-TCP/HA (α-TCP with low calcium hydroxyapatite) and baghdadite (Ca3ZrSi2O9) scaffolds were used, which had comparable porosity (~50%) and pore sizes (~300-400 µm). Cell adhesion to both scaffolds showed ~95% seeding efficiency. Cell proliferation tests provided characteristic progression curves over time and increased values for α-TCP/HA. Transmitted light imaging displayed a homogeneous population of scaffold pores and allowed us to track their opening state for the supply of the inner scaffold regions by diffusion. Fluorescence labeling enabled us to image the arrangement and morphology of the cells within the pores. During three weeks of osteogenesis, ALP activity increased sharply in both scaffolds, but was again markedly increased in α-TCP/HA scaffolds. Multiphoton SHG and autofluorescence imaging were used to investigate the distribution, morphology, and arrangement of cells; collagen-I fiber networks; and hydroxyapatite crystals. The collagen-I networks became denser and more structured during osteogenic differentiation and appeared comparable in both scaffolds. However, imaging of the HA crystals showed a different morphology between the two scaffolds and appeared to arrange in the α-TCP/HA scaffolds along collagen-I fibers. ALP activity and SHG imaging indicated a pronounced osteo-inductive effect of baghdadite. This study describes a series of methods, in particular multiphoton imaging and complementary biochemical assays, to validly measure and track the development of bone tissue in 3D scaffolds. The results contribute to the understanding of cell colonization, growth, and differentiation, emphasizing the importance of optimal media supply of the inner scaffold regions.

Personalized 3D printed bone scaffolds: A review.

3D printed bone scaffolds have the potential to replace autografts and allografts because of advantages such as unlimited supply and the ability to tailor the scaffolds' biochemical, biological and biophysical properties. Significant progress has been made over the past decade in additive manufacturing techniques to 3D print bone grafts, but challenges remain in the lack of manufacturing techniques that can recapitulate both mechanical and biological functions of native bones. The purpose of this review is to outline the recent progress and challenges of engineering an ideal synthetic bone scaffold and to provide suggestions for overcoming these challenges through bioinspiration, high-resolution 3D printing, and advanced modeling techniques. The article provides a short overview of the progress in developing the 3D printed scaffolds for the repair and regeneration of critical size bone defects. STATEMENT OF SIGNIFICANCE: Treatment of critical size bone defects is still a tremendous clinical challenge. To address this challenge, diverse sets of advanced manufacturing approaches and materials have been developed for bone tissue scaffolds. 3D printing has sparked much interest because it provides a close control over the scaffold's internal architecture and in turn its mechanical and biological properties. This article provides a critical overview of the relationships between material compositions, printing techniques, and properties of the scaffolds and discusses the current technical challenges facing their successful translation to the clinic. Bioinspiration, high-resolution printing, and advanced modeling techniques are discussed as future directions to address the current challenges.

Design and evaluation of 3D-printed Sr-HT-Gahnite bioceramic for FDA regulatory submission: A Good Laboratory Practice sheep study.

There is an unmet clinical need for a spinal fusion implant material that recapitulates the biological and mechanical performance of natural bone. We have developed a bioceramic, Sr-HT-Gahnite, which has been identified as a potential fusion device material. This material has the capacity to transform the future of the global interbody devices market, with follow on social, economic, and environmental benefits, rooted in its remarkable combination of mechanical properties and bioactivity. In this study, and in line with FDA requirements, the in vivo preclinical systemic biological safety of a Sr-HT-Gahnite interbody fusion device is assessed over 26 weeks in sheep under good laboratory practice (GLP). Following the in-life phase, animals are assessed for systemic biological effects via blood haematology and clinical biochemistry, strontium dosage analysis in the blood and wool, and histopathology examination of the distant organs including adrenals, brain, heart, kidneys, liver, lungs and bronchi, skeletal muscle, spinal nerves close to the implanted sites, ovaries, and draining lymph nodes. Our results show that no major changes in blood haematology or biochemistry parameters are observed, no systemic distribution of strontium to the blood and wool, and no macroscopic or histopathological abnormalities in the distant organs when Sr-HT-Gahnite was implanted, compared to baseline and control values. Together, these results indicate the systemic safety of the Sr-HT-Gahnite interbody fusion device. The results of this study extend to the systemic safety of other Sr-HT-Gahnite implanted medical devices in contact with bone or tissue, of similar size and manufactured using the described processes. STATEMENT OF SIGNIFICANCE: This paper is considered original and innovative as it is the first that thoroughly reports the systemic biological safety of previously undescribed bioceramic material, Sr-HT-Gahnite. The study has been performed under good laboratory practice, in line with FDA requirements for assessment of a new interbody fusion device, making the results broadly applicable to the translation of sheep models to the human cervical spine; and also the translation of Sr-HT-Gahnite as a biomaterial for use in additional applications. We expect this study to be of broad interest to the readership of Acta Biomaterilia. Its findings are directly applicable to researchers and clinicians working in bone repair and the development of synthetic biomaterials.

Rationally-designed self-shaped ceramics through heterogeneous green body compositions.

Forming ceramics into rationally-designed and complex shapes without compromising their mechanical properties is a major challenge. Here, we demonstrate self-shaping of ceramics through sequential stereolithographic printing of ceramic resins into components with a heterogeneous concentration of ceramic particles, resulting in well-defined anisotropic shrinkage and, consequently, shape changes during sintering. The method is versatile and scalable and results in well-controlled shape changes in ceramics through bending, folding, twisting, and combinations of these mechanisms. The density measurements and mechanical tests show that the stresses resulting from the self-shaping mechanisms do not significantly affect the physical and mechanical properties of the ceramics. Together with the experiments, we developed a material- and scale-independent mechanical model based on linear elasticity that predicted shape changes accurately. The model can serve as a design tool to guide the selection of particle concentrations to realize the desired shapes in a broad range of ceramics.

Segmentations in fins enable large morphing amplitudes combined with high flexural stiffness for fish-inspired robotic materials.

Fish fins do not contain muscles, yet fish can change their shape with high precision and speed to produce large and complex hydrodynamic forces-a combination of high morphing efficiency and high flexural stiffness that is rare in modern morphing and robotic materials. These "flexo-morphing" capabilities are rare in modern morphing and robotic materials. The thin rays that stiffen the fins and transmit actuation include mineral segments, a prominent feature whose mechanics and function are not fully understood. Here, we use mechanical modeling and mechanical testing on 3D-printed ray models to show that the function of the segmentation is to provide combinations of high flexural stiffness and high morphing amplitude that are critical to the performance of the fins and would not be possible with rays made of a continuous material. Fish fin-inspired designs that combine very soft materials and very stiff segments can provide robotic materials with large morphing amplitudes and strong grasping forces.

Development of a bioactive and radiopaque bismuth doped baghdadite ceramic for bone tissue engineering.

Baghdadite (Ca3ZrSi2O9, BAG), is a Zr-doped calcium silicate that has outstanding bioactivity both in vitro and in vivo. Bioceramic scaffolds should be sufficiently radiopaque to be distinguishable in vivo from surrounding bone structures. To enhance the radiopacity of BAG, this study investigated the effect of incorporating bismuth ions into its crystalline structure (BixCa3-xZrSi2O9, x = 0, 0.1, 0.2, 0.5; BAG, Bi0.1-BAG, Bi0.2-BAG, Bi0.5-BAG, respectively). Monophasic baghdadite was retained after bismuth ion incorporation up to x = 0.2 at calcination temperatures of 1350 °C. When pressed and sintered, energy dispersive x-ray spectroscopy showed that BAG and Bi0.1-BAG retained crystalline homogeneity, but Bi0.2-BAG formed zirconium-rich crystalline regions. BAG, Bi0.1-BAG and Bi0.2-BAG exhibited non-degradation after 56 days of immersion in culture medium. Bi0.1-BAG exhibited the lowest change in culture medium pH (+0.0), compared to BAG (+0.7) and Bi0.2-BAG (+0.2) after 56 days of culture media immersion. Bi0.1-BAG exhibited similar strength and modulus to BAG (σ: 200-290 MPa; E: 4-5 GPa), and significantly higher compressive strength and modulus versus Bi0.2-BAG (σ: 150-200 MPa; E: 3.5-4 GPa) across 56 days of aqueous immersion. In vitro studies using primary human bone derived cells (HOBs) demonstrated a significant increase in HOBs proliferation when cultured on Bi0.1-BAG for seven days compared to BAG and Bi0.2-BAG. Importantly, Bi0.1-BAG showed increased radiopacity by ~33%, when compared to BAG, and by ~115% when compared to biphasic calcium phosphate. The properties of Bi0.1-BAG show promise for its use as a bioactive ceramic with sufficient radiopacity for treatment of bone defects.

Influence of carbon dot synthetic parameters on photophysical and biological properties.

Recently, carbon dots (CDs) have been widely investigated for biological applications in imaging. One-step hydrothermal synthesis is considered to be one of the most promising methods for the synthesis of CDs, due to its simple and rapid manipulation, flexible selection of ingredients, environmentally friendly conditions, and low-cost. A number of synthetic and post-synthetic parameters, including solvent, heating time, dopant quantity, and particle size distribution, play a crucial role in controlling the size and surface structure of CDs, which ultimately have influence on their photophysical and biological behavior. Despite the crucial role of each of these parameters in defining the yield and nature of synthesized CDs, they have not previously been rigorously optimized, particularly with respect to desired biological applications. Herein, we report our comprehensive optimization of the parameters employed for the hydrothermal synthesis of CDs to gain a better understanding of the effect of these parameters on optical properties, cytotoxicity, and cellular uptake efficiency. Furthermore, this work will open up new pathways toward the design of CDs with physiochemical properties tailored for specific biomedical applications such as bioimaging.

A comparative study of nano-fillers to improve toughness and modulus of polymer-derived ceramics.

Brittleness is a major limitation of polymer-derived ceramics (PDCs). Different concentrations of three nanofillers (carbon nanotubes, Si3N4 and Al2O3 nanoparticles) were evaluated to improve both toughness and modulus of a commercial polysilazane (PSZ) PDC. The PSZs were thermally cross-linked and pyrolyzed under isostatic pressure in nitrogen. A combination of mechanical, chemical, density, and microscopy characterizations was used to determine the effects of these fillers. Si3N4 and Al2O3 nanoparticles (that were found to be active fillers) were more effective than nanotubes and improved the elastic modulus, hardness, and fracture toughness (JIC) of the PDC by ~ 1.5 ×, ~ 3 ×, and ~ 2.5 ×, respectively. Nanotubes were also effective in maintaining the integrity of the samples during pyrolysis. The modulus and hardness of PDCs correlated positively with their apparent density; this can provide a fast way to assess future PDCs. The improvement in fracture toughness was attributed to crack deflection and bridging observed in the micro-indentation cracks in the modified PDCs. The specific toughness of the modified PDCs was 4 × higher than that of high-purity alumina, and its specific modulus reached that of commercially available technical ceramics. These PDCs can also easily take different shapes and therefore are of interest in protective armor, propulsion, thermal protection, device packaging and biomaterial systems.

Personalized Baghdadite scaffolds: stereolithography, mechanics and in vivo testing.

An ongoing challenge in the field of orthopedics is to produce a clinically relevant synthetic ceramic scaffold for the treatment of 'critical-sized' bone defects, which cannot heal without intervention. We had developed a bioactive ceramic (baghdadite, Ca3ZrSi2O9) and demonstrated its outstanding bioactivity using traditional manufacturing techniques. Here, we report on the development of a versatile stereolithography printing technology that enabled fabrication of anatomically-shaped and -sized Baghdadite scaffolds. We assessed the in vivo bioactivity of these scaffolds in co-delivering of bone morphogenetic protein-2 (BMP2) and zoledronic acid (ZA) through bioresorbable coatings to induce bone formation and increase retention in a rat model of heterotopic ossification. Micro-computed tomography, histology, mechanical tests pre- and post-implantation, and mechanical modelling were used to assess bone ingrowth and its effects on the mechanics of the scaffolds. Bone ingrowth and the consequent mechanical properties of the scaffolds improved with increasing BMP2 dose. Co-delivery of ZA with BMP2 further improved this outcome. The significant bone formation within the scaffolds functionalized with 10 µg BMP2 and 2 µg ZA made them 2.3 × stiffer and 2.7 × stronger post-implantation and turned these inherently brittle scaffolds into a tough and deformable material. The effects of bone ingrowth on the mechanical properties of scaffolds were captured in a mechanical model that can be used in future clinical studies for non-destructive evaluation of scaffold's stiffness and strength as new bone forms. These results support the practical utilization of our versatile stereolithographic printing methods and BMP2/ZA functionalization to create fit-for-purpose personalized implants for clinical trials. STATEMENT OF SIGNIFICANCE: In this study, we addressed a long-standing challenge of developing a ceramic printing technology that enables fabrication of customizable anatomically-shaped and -sized bioceramic scaffolds with precise internal architectures using an inexpensive desktop printer. We also addressed another challenge related to delivery of pharmaceuticals. BMP2, currently available as a bone-inducing bioactive protein, is clinically administered in a collagen scaffold that has limited moldability and poor mechanical properties. The comparably stiffer and stronger 3D printed personalized Baghdadite scaffolds developed here can be readily functionalized with bioresorbable coatings containing BMP2 ± ZA. These innovations considerably improve on the prior art and are scalable for use in human surgery.

Simultaneous improvements of strength and toughness in topologically interlocked ceramics.

Topologically interlocked materials (TIMs) are an emerging class of architectured materials based on stiff building blocks of well-controlled geometries which can slide, rotate, or interlock collectively providing a wealth of tunable mechanisms, precise structural properties, and functionalities. TIMs are typically 10 times more impact resistant than their monolithic form, but this improvement usually comes at the expense of strength. Here we used 3D printing and replica casting to explore 15 designs of architectured ceramic panels based on platonic shapes and their truncated versions. We tested the panels in quasi-static and impact conditions with stereoimaging, image correlation, and 3D reconstruction to monitor the displacements and rotations of individual blocks. We report a design based on octahedral blocks which is not only tougher (50×) but also stronger (1.2×) than monolithic plates of the same material. This result suggests that there is no upper bound for strength and toughness in TIMs, unveiling their tremendous potential as structural and multifunctional materials. Based on our experiments, we propose a nondimensional "interlocking parameter" which could guide the exploration of future architectured systems.

Fabrication, testing and modeling of a new flexible armor inspired from natural fish scales and osteoderms.

Crocodiles, armadillo, turtles, fish and many other animal species have evolved flexible armored skins in the form of hard scales or osteoderms, which can be described as hard plates of finite size embedded in softer tissues. The individual hard segments provide protection from predators, while the relative motion of these segments provides the flexibility required for efficient locomotion. In this work, we duplicated these broad concepts in a bio-inspired segmented armor. Hexagonal segments of well-defined size and shape were carved within a thin glass plate using laser engraving. The engraved plate was then placed on a soft substrate which simulated soft tissues, and then punctured with a sharp needle mounted on a miniature loading stage. The resistance of our segmented armor was significantly higher when smaller hexagons were used, and our bio-inspired segmented glass displayed an increase in puncture resistance of up to 70% compared to a continuous plate of glass of the same thickness. Detailed structural analyses aided by finite elements revealed that this extraordinary improvement is due to the reduced span of individual segments, which decreases flexural stresses and delays fracture. This effect can however only be achieved if the plates are at least 1000 stiffer than the underlying substrate, which is the case for natural armor systems. Our bio-inspired system also displayed many of the attributes of natural armors: flexible, robust with 'multi-hit' capabilities. This new segmented glass therefore suggests interesting bio-inspired strategies and mechanisms which could be systematically exploited in high-performance flexible armors. This study also provides new insights and a better understanding of the mechanics of natural armors such as scales and osteoderms.