Hydrothermal processing of 3D-printed calcium phosphate scaffolds enhances bone formation in vivo: a comparison with biomimetic treatment

Three-Dimensional Printed Patient-Specific Vestibular Augmentation: A Case Report

Background: The anterior maxilla is challenging regarding aesthetic rehabilitation. Current bone augmentation techniques are complex and 3D-printed bioceramic bone grafts can simplify the intervention. Aim: A four-teeth defect in the anterior maxilla was reconstructed with a 3D-printed synthetic patient-specific bone graft in a staged approach for dental implant delivery. Methods: The bone graft was designed using Cone-Beam Computed Tomography (CBCT) images. The bone graft was immobilized with fixation screws. Bone augmentation was measured on CBCT images at 11 days and 8 and 13 months post-surgery. A biopsy sample was retrieved at reentry (10 months post-augmentation) and evaluated by histological and micro-computed tomography assessments. The definitive prosthesis was delivered 5 months post-reentry and the patient attended a visit 1-year post-loading. Results: A total bone width of 8 mm was achieved (3.7 mm horizontal bone gain). The reconstructed bone remained stable during the healing period and was sufficient for placing two dental implants (with an insertion torque > 35 N·cm). The fractions of new bone, bone graft, and soft tissue in the biopsy were 40.77%, 41.51%, and 17.72%, respectively. The histological assessment showed no signs of encapsulation, and mature bone was found in close contact with the graft, indicating adequate biocompatibility and suggesting osteoconductive properties of the graft. At 1-year post-loading, the soft tissues were healthy, and the dental implants were stable. Conclusions: The anterior maxilla's horizontal ridge can be reconstructed using a synthetic patient-specific 3D-printed bone graft in a staged approach for implant placement. The dental implants were stable and successful 1-year post-loading.

Toughening 3D printed biomimetic hydroxyapatite scaffolds: Polycaprolactone-based self-hardening inks

The application of 3D printing to calcium phosphates has opened unprecedented possibilities for the fabrication of personalized bone grafts. However, their biocompatibility and bioactivity are counterbalanced by their high brittleness. In this work we aim at overcoming this problem by developing a self-hardening ink containing reactive ceramic particles in a polycaprolactone solution instead of the traditional approach that use hydrogels as binders. The presence of polycaprolactone preserved the printability of the ink and was compatible with the hydrolysis-based hardening process, despite the absence of water in the ink and its hydrophobicity. The microstructure evolved from a continuous polymeric phase with loose ceramic particles to a continuous network of hydroxyapatite nanocrystals intertwined with the polymer, in a configuration radically different from the polymer/ceramic composites obtained by fused deposition modelling. This resulted in the evolution from a ductile behavior, dominated by the polymer, to a stiffer behavior as the ceramic phase reacted. The polycaprolactone binder provides two highly relevant benefits compared to hydrogel-based inks. First, the handleability and elasticity of the as-printed scaffolds, together with the proven possibility of eliminating the solvent, opens the door to implanting the scaffolds freshly printed once lyophilized, while in a ductile state, and the hardening process to take place inside the body, as in the case of calcium phosphate cements. Second, even with a hydroxyapatite content of more than 92 wt.%, the flexural strength and toughness of the scaffolds after hardening are twice and five times those of the all-ceramic scaffolds obtained with the hydrogel-based inks, respectively. STATEMENT OF SIGNIFICANCE: Overcoming the brittleness of ceramic scaffolds would extend the applicability of synthetic bone grafts to high load-bearing situations. In this work we developed a 3D printing ink by replacing the conventional hydrogel binder with a water-free polycaprolactone solution. The presence of polycaprolactone not only enhanced significantly the strength and toughness of the scaffolds while keeping the proportion of bioactive ceramic phase larger than 90 wt.%, but it also conferred flexibility and manipulability to the as-printed scaffolds. Since they are able to harden upon contact with water under physiological conditions, this opens up the possibility of implanting them immediately after printing, while they are still in a ductile state, with clear advantages for fixation and press-fit in the bone defect.

The Preparation and Characterization of Chitosan/Calcium Phosphate Composite Microspheres for Biomedical Applications

In this study, we successfully prepared porous composite microspheres composed of hydroxyapatite (HAp), di-calcium phosphate di-hydrated (DCPD), and chitosan through the hydrothermal method. The chitosan played a crucial role as a chelating agent to facilitate the growth of related calcium phosphates. The synthesized porous composite microspheres exhibit a specific surface area of 38.16 m2/g and a pore volume of 0.24 cm3/g, with the pore size ranging from 4 to 100 nm. Given the unique properties of chitosan and the exceptional porosity of these composite microspheres, they may serve as carriers for pharmaceuticals. After being annealed, the chitosan transforms into a condensed form and the DCPD transforms into Ca2P2O7 at 300 °C. Then, the Ca2P2O7 initially combines with HAp to transform into β tricalcium phosphate (β-TCP) at 500 °C where the chitosan is also completely combusted. Finally, the microspheres are composed of Ca2P2O7, β-TCP, and HAp, also making them suitable for applications such as injectable bone graft materials.

High-aspect-ratio nanostructured hydroxyapatite: towards new functionalities for a classical material

Hydroxyapatite-based materials have been widely used in countless applications, such as bone regeneration, catalysis, air and water purification or protein separation. Recently, much interest has been given to controlling the aspect ratio of hydroxyapatite crystals from bulk samples. The ability to exert control over the aspect ratio may revolutionize the applications of these materials towards new functional materials. Controlling the shape, size and orientation of HA crystals allows obtaining high aspect ratio structures, improving several key properties of HA materials such as molecule adsorption, ion exchange, catalytic reactions, and even overcoming the well-known brittleness of ceramic materials. Regulating the morphogenesis of HA crystals to form elongated oriented fibres has led to flexible inorganic synthetic sponges, aerogels, membranes, papers, among others, with applications in sustainability, energy and catalysis, and especially in the biomedical field.

FePSe3 -Nanosheets-Integrated Cryogenic-3D-Printed Multifunctional Calcium Phosphate Scaffolds for Synergistic Therapy of Osteosarcoma

Clinical treatment of osteosarcoma encounters great challenges of postsurgical tumor recurrence and extensive bone defect. To develop an advanced artificial bone substitute that can achieve synergistic bone regeneration and tumor therapy for osteosarcoma treatment, a multifunctional calcium phosphate composite enabled by incorporation of bioactive FePSe3 -nanosheets within the cryogenic-3D-printed α-tricalcium phosphate scaffold (TCP-FePSe3 ) is explored. The TCP-FePSe3 scaffold exhibits remarkable tumor ablation ability due to the excellent NIR-II (1064 nm) photothermal property of FePSe3 -nanosheets. Moreover, the biodegradable TCP-FePSe3 scaffold can release selenium element to suppress tumor recurrence by activating of the caspase-dependent apoptosis pathway. In a subcutaneous tumor model, it is demonstrated that tumors can be efficiently eradicated via the combination treatment with local photothermal ablation and the antitumor effect of selenium element. Meanwhile, in a rat calvarial bone defect model, the superior angiogenesis and osteogenesis induced by TCP-FePSe3 scaffold have been observed in vivo. The TCP-FePSe3 scaffold possesses improved capability to promote the repair of bone defects via vascularized bone regeneration, which is induced by the bioactive ions of Fe, Ca, and P released during the biodegradation of the implanted scaffolds. The TCP-FePSe3 composite scaffolds fabricated by cryogenic-3D-printing illustrate a distinctive strategy to construct multifunctional platform for osteosarcoma treatment.

Functional engineering strategies of 3D printed implants for hard tissue replacement

Three-dimensional printing technology with the rapid development of printing materials are widely recognized as a promising way to fabricate bioartificial bone tissues. In consideration of the disadvantages of bone substitutes, including poor mechanical properties, lack of vascularization and insufficient osteointegration, functional modification strategies can provide multiple functions and desired characteristics of printing materials, enhance their physicochemical and biological properties in bone tissue engineering. Thus, this review focuses on the advances of functional engineering strategies for 3D printed biomaterials in hard tissue replacement. It is structured as introducing 3D printing technologies, properties of printing materials (metals, ceramics and polymers) and typical functional engineering strategies utilized in the application of bone, cartilage and joint regeneration.

Scaffold-based bone tissue engineering in microgravity: potential, concerns and implications

One of humanity's greatest challenges is space exploration, which requires an in-depth analysis of the data continuously collected as a necessary input to fill technological gaps and move forward in several research sectors. Focusing on space crew healthcare, a critical issue to be addressed is tissue regeneration in extreme conditions. In general, it represents one of the hottest and most compelling goals of the scientific community and the development of suitable therapeutic strategies for the space environment is an urgent need for the safe planning of future long-term manned space missions. Osteopenia is a commonly diagnosed disease in astronauts due to the physiological adaptation to altered gravity conditions. In order to find specific solutions to bone damage in a reduced gravity environment, bone tissue engineering is gaining a growing interest. With the aim to critically investigate this topic, the here presented review reports and discusses bone tissue engineering scenarios in microgravity, from scaffolding to bioreactors. The literature analysis allowed to underline several key points, such as the need for (i) biomimetic composite scaffolds to better mimic the natural microarchitecture of bone tissue, (ii) uniform simulated microgravity levels for standardized experimental protocols to expose biological materials to the same testing conditions, and (iii) improved access to real microgravity for scientific research projects, supported by the so-called democratization of space.

Calcium Phosphate-Based Biomaterials for Bone Repair

Traumatic, tumoral, and infectious bone defects are common in clinics, and create a big burden on patient's families and society. Calcium phosphate (CaP)-based biomaterials have superior properties and have been widely used for bone defect repair, due to their similarities to the inorganic components of human bones. The biological performance of CaPs, as a determining factor for their applications, are dependent on their physicochemical properties. Hydroxyapatite (HAP) as the most thermally stable crystalline phase of CaP is mostly used in the form of ceramics or composites scaffolds with polymers. Nanostructured CaPs with large surface areas are suitable for drug/gene delivery systems. Additionally, CaP scaffolds with hierarchical nano-/microstructures have demonstrated excellent ability in promoting bone regeneration. This review focuses on the relationships and interactions between the physicochemical/biological properties of CaP biomaterials and their species, sizes, and morphologies in bone regeneration, including synthesis strategies, structure control, biological behavior, and the mechanisms of CaP in promoting osteogenesis. This review will be helpful for scientists and engineers to further understand CaP-based biomaterials (CaPs), and be useful in developing new high-performance biomaterials for bone repair.

3D printing with star-shaped strands: A new approach to enhance in vivo bone regeneration

Concave surfaces have shown to promote bone regeneration in vivo. However, bone scaffolds obtained by direct ink writing, one of the most promising approaches for the fabrication of personalized bone grafts, consist mostly of convex surfaces, since they are obtained by microextrusion of cylindrical strands. By modifying the geometry of the nozzle, it is possible to print 3D structures composed of non-cylindrical strands and favor the presence of concave surfaces. In this work, we compare the in vivo performance of 3D-printed calcium phosphate scaffolds with either conventional cylindrical strands or star-shaped strands, in a rabbit femoral condyle model. Monocortical defects, drilled in contralateral positions, are randomly grafted with the two scaffold configurations, with identical composition. The samples are explanted eight weeks post-surgery and assessed by μ-CT and resin-embedded histological observations. The results reveal that the scaffolds containing star-shaped strands have better osteoconductive properties, guiding the newly formed bone faster towards the core of the scaffolds, and enhance bone regeneration, although the increase is not statistically significant (p > 0.05). This new approach represents a turning point towards the optimization of pore shape in 3D-printed bone grafts, further boosting the possibilities that direct ink writing technology offers for patient-specific applications.

Implementation of bactericidal topographies on biomimetic calcium phosphates and the potential effect of its reactivity

Since the discovery that nanostructured surfaces were able to kill bacteria, many works have been published focusing on the design of nanopatterned surfaces with antimicrobial properties. Synthetic bone grafts, based on calcium phosphate (CaP) formulations, can greatly benefit from this discovery if adequate nanotopographies can be developed. However, CaP are reactive materials and experience ionic exchanges when placed into aqueous solutions which may in turn affect cell behaviour and complicate the interpretation of the bactericidal results. The present study explores the bactericidal potential of two nanopillared CaP prepared by hydrolysis of two different sizes of α-tricalcium phosphate (α-TCP) powders under biomimetic or hydrothermal conditions. A more lethal bactericidal response toward Pseudomonas aeruginosa (~75% killing efficiency of adhered bacteria) was obtained from the hydrothermally treated CaP which consisted in a more irregular topography in terms of pillar size (radius: 20-60 nm), interpillar distances (100-1500 nm) and pillar distribution (pillar groups forming bouquets) than the biomimetically treated one (radius: 20-40 nm and interpillar distances: 50-200 nm with a homogeneous pillar distribution). The material reactivity was greatly influenced by the type of medium (nutrient-rich versus nutrient-free) and the presence or not of bacteria. A lower reactivity and superior bacterial attachment were observed in the nutrient-free medium while a lower attachment was observed for the nutrient rich medium which was explained by a superior reactivity of the material paired with the lower tendency of planktonic bacteria to adhere on surfaces in the presence of nutrients. Importantly, the ionic exchanges produced by the presence of materials were not toxic to planktonic cells. Thus, we can conclude that topography was the main contributor to mortality in the bacterial adhesion tests.