The one-step AM process is considered the goal many researchers seek in the field of Additive Manufacturing (AM) of high-technology ceramics. Among the several AM techniques, only Powder Bed Fusion ...(PBF) can directly print high-technology ceramics using one step. However, the PBF technique faces numerous challenges to efficiently be employed in the PBF of ceramics. These challenges include the formation of cracks, generated thermal stress, effective laser-powder interaction, and low acquired relative density. This study developed a new preheating mechanism for ceramic materials using two laser systems to surpass beyond these challenges and successfully print ceramics with a single-step AM method. One laser is used to preheat the powder particles before the second laser is utilised to complete the melting/sintering process. Both lasers travel along the same scanning path. There is a slight delay (0.0001 s) between the preheating laser and the melting/sintering laser to guarantee that the melting/sintering laser scans a properly preheated powder. To further facilitate testing of the preheating system, a numerical model has been developed to simulate the preheating and melting process and to acquire proper process parameters. The developed numerical model was shown to determine the correct process parameters without needing costly and time-consuming experiments. Alumina samples (10 × 10 × 6 mm
) were successfully printed using alumina powder as feedstock. The surface of the samples was nearly defect-free. The samples' relative densities exceeded 80%, the highest reported relative density for alumina produced by a single-step AM method. This discovery can significantly accelerate the transition to a one-step AM process of ceramics.
Bone is a natural nanocomposite. Its mineral component is nanocrystalline calcium phosphate apatite, whose synthetic biomimetic analogs can be prepared by wet chemistry. The initially formed ...crystals, whether biological or synthetic, exhibit very peculiar physicochemical features. In particular, they are nanocrystalline, nonstoichiometric, and hydrated. The surface of the nanocrystals is covered by a non-apatitic hydrated layer containing mobile ions, which may explain their exceptional surface reactivity. For their precipitation in vivo or in vitro, for their evolution in solution, for the 3D organization of the nanocrystals, and for their consolidation to obtain bulk ceramic materials, water appears to be a central component that has not received much attention. In this mini-review, we explore these key roles of water on the basis of physicochemical and thermodynamic data obtained by complementary tools including FTIR, XRD, ion titrations, oxide melt solution calorimetry, and cryo-FEG-SEM. We also report new data obtained by DSC, aiming to explore the types of water molecules associated with the nanocrystals. These data support the existence of two main types of water molecules associated with the nanocrystals, with different characteristics and probably different roles and functions. These findings improve our understanding of the behavior of bioinspired apatite-based systems for biomedicine and also of biomineralization processes taking place in vivo, at present and in the geologic past. This paper is thus intended to give an overview of the specificities of apatite nanocrystals and their close relationship with water.
This paper focuses on the tailoring of hydroxyapatite powders properties for the preparation of highly hydroxyapatite-loaded photocurable organic slurries. The suspensions were evaluated as feedstock ...for the production of hydroxyapatite scaffolds by stereolithography-based additive manufacturing technique. Then, a debinding-sintering process was designed to avoid the formation of cracks during the pyrolysis of the resin and sintering of the printed parts. A total porosity of 35 vol % and compression strength of 4.9 ± 0.3 MPa were obtained for the specimens printed at 45° to the building platform. A slow degradation rate was observed due to the high degree of crystallinity and intrinsic stability of the hydroxyapatite phase. The tailoring of hydroxyapatite powders was required to lower the viscosity and increase the particle stability of the suspensions. The printed hydroxyapatite scaffolds showed promising results for surgery, in the case of minor or non-load bearing implants requiring slow resorption properties.
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Rapid self-setting apatite cement (SSAC) formation from tetracalcium phosphate (TeCP) and dicalcium phosphate dihydrate (DCPD) has been investigated by an attenuated total reflection Fourier ...transform infrared (ATR-IR) spectroscopy coupled with a principal component analysis (PCA). After TeCP and DCPD were kneaded with phosphoric acid, the peaks of ATR-IR spectra for the kneaded sample shift significantly in the ranges of 2250–2400 and 850–1150 cm
−1
due to the crystalline transformation into hydroxyapatite (HAp). The PCA results indicate that the loadings of principal components 1 and 2 (PC1 and PC2, respectively) are ascribed to CO
2
and phosphate group, respectively, in the transforming cement. The PC1 score initially increases to reach a maximum at around 1000 s and then decreases. In contrast, the PC2 score increases continuously, but its increment became lesser with time. Although the profiles of PC2 score against PC1 score are similar in shape, there are deviations among the profiles obtained through quadruplicate experiments. The scores are, therefore, time differentiated, and the relationship between the differentiated scores is analyzed. The time differentiation approach is found to be useful for understanding complicated chemical reactions. The PCA results suggest that SSAC formation can be divided into three major stages. In the first stage, CO
2
concentration in the transforming cement rapidly increases, which triggers HAp crystallization. In the second stage, CO
2
concentration still increases, but its increasing rate drastically decreases; HAp crystallization continues with increasing rate. In the last stage, CO
2
concentration decreases, and HAp crystallization significantly slows down.
Direct-Powder Bed Selective Laser Processing (D-PBSLP) is considered a promising technique for the Additive Manufacturing (AM) of Silicon Carbide (SiC). For the successful D-PBSLP of SiC, it is ...necessary to understand the effects of process parameters. The process parameters are the laser power, scanning speed, hatching distance, and scanning strategies. This study investigates the effect of scanning strategies on the D-PBSLP of SiC and ensures that other process parameters are appropriately selected to achieve this. A numerical model was developed to obtain the proper process parameters for the investigation of scanning strategies in this work. Different scanning strategies available in the commercial Phoenix 3D printer manufactured by 3D Systems, such as concentric in–out, linear, inclined zigzag, and hexagonal, have been investigated. It was concluded that the zigzag strategy is the best scanning strategy, as it was seen that SiC samples could be printed at a high relative density of above 80% without a characteristic pattern on the layer’s top surface. SiC samples were successfully printed using different laser powers and scanning speeds obtained from the numerical model and zigzag strategy. Additionally, complex geometry in the form of triple periodic minimum surface (gyroid) was also successfully printed.
The rise in the number of musculoskeletal disorders (MSDs) due to an increasingly aging population has led to a growing demand for medication to prevent and treat these diseases. An increased ...interest in the development of new drugs to allow treatment of these diseases in their very early stages is currently observed. The current approach on local direct delivery of medication and key minerals to support bone repair and regeneration at the defect site, from flexible degradable devices, seems to be an effective strategy. Polylactic acid (PLA) and microspheres of hydrothermally converted coralline hydroxyapatite (cHAp) were used to develop PLA thin film composites as drug delivery systems. The PLA provided flexibility and biodegradability of the systems, while coralline hydroxyapatite provided the required calcium and phosphate ions for bone regeneration. These coralline hydroxyapatite microspheres have a unique architecture of interconnected porosity, are bioactive in nature and suitable for drug loading and controlled slow drug release. The cell attachment and morphology of the PLA thin film composites were evaluated in vitro using cell cultures of human adipose derived stem cells (hADSC). It was shown that hADSC cells exhibited a strong attachment and proliferation on PLA thin film-cHAp composites, signifying high biocompatibility and a potential for osteointegration due to the presence of HAp.
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Direct-powder bed selective laser processing (D-PBSLP) is a promising technique for the manufacturing of complex-shaped parts of Silicon Carbide (SiC) ceramic. In this work, a complex optimization of ...the process parameters was performed by numerical and experimental analysis. The numerical model was used to determine and optimize the effect of laser power, scanning speed and hatching distance at different layer thicknesses of 20, 30 and 40 µm. Regarding the experimental process parameters study, powder compaction was also studied and optimized. The optimization parameter criteria were to achieve reproducible and high relative density parts. Concerning the experimental manufacturing process, D-PBSLP of alpha-silicon carbide parts with a maximum relative density of 81% were manufactured. Moreover, the process viability can be confirmed with the manufacturing of SiC complex shapes in absence of any additives in the initial powder and without or post-treatment. The results from this study could be used as a guide for process parameters selection.
Biomimetic apatites exhibit a high reactivity allowing ion substitutions to modulate their in vivo response. We developed a novel approach combining several bioactive ions in a spatially controlled ...way in view of subsequent releases to address the sequence of events occurring after implantation, including potential microorganisms' colonization. Innovative micron-sized core-shell particles were designed with an external shell enriched with an antibacterial ion and an internal core substituted with a pro-angiogenic or osteogenic ion. After developing the proof of concept, two ions were particularly considered, Ag
in the outer shell and Cu
in the inner core. In vitro evaluations confirmed the cytocompatibility through Ag-/Cu-substituting and the antibacterial properties provided by Ag
. Then, these multifunctional "smart" particles were embedded in a polymeric matrix by freeze-casting to prepare 3D porous scaffolds for bone engineering. This approach envisions the development of a new generation of scaffolds with tailored sequential properties for optimal bone regeneration.
One major warning emerging during the first worldwide combat against healthcare-associated infections concerns the key role of the surface in the storage and transfer of the virus. Our study is based ...on the laser coating of surfaces with an inorganic/organic composite mixture of amorphous calcium phosphate–chitosan–tetracycline that is able to fight against infectious agents, but also capable of preserving its activity for a prolonged time, up to several days. The extended release in simulated fluids of the composite mixture containing the drug (tetracycline) was demonstrated by mass loss and UV–VIS investigations. The drug release profile from our composite coatings proceeds via two stages: an initial burst release (during the first hours), followed by a slower evolution active for the next 72 h, and probably more. Optimized coatings strongly inhibit the growth of tested bacteria (Enterococcus faecalis and Escherichia coli), while the drug incorporation has no impact on the in vitro composite’s cytotoxicity, the coatings proving an excellent biocompatibility sustaining the normal development of MG63 bone-like cells. One may, therefore, consider that the proposed coatings’ composition can open the prospective of a new generation of antimicrobial coatings for implants, but also for nosocomial and other large area contamination prevention.
This contribution gathers various examples illustrating the fact that nanocrystalline apatites represent a genuine multi-functionalizable platform for a wide range of biomedical applications. It is ...indeed possible to convey additional functionalities to the already appealing properties of biomimetic apatites, via appropriate ionic substitutions and/or through controlled molecular adsorptions. In link with bone regeneration, we depict here examples of enhanced osteoconduction/induction and of the addition of antibacterial features to bone implants. But we also point out the promise of apatite-based colloidal nanoparticles in other domains not related to bone, such as nanomedicine (cell diagnosis/therapy), which we address by conferring luminescence properties and by adding cell recognition abilities.
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