Biocompatible Composite Filaments Printable by Fused Deposition Modelling Technique: Selection of Tuning Parameters by Influence of Biogenic Hydroxyapatite and Graphene Nanoplatelets Ratios.

The proposed strategy for the extrusion of printable composite filaments follows the favourable association of biogenic hydroxyapatite (HA) and graphene nanoplatelets (GNP) as reinforcement materials for a poly(lactic acid) (PLA) matrix. HA particles were chosen in the <40 µm range, while GNP were selected in the micrometric range. During the melt-mixing incorporation into the PLA matrix, both reinforcement ratios were simultaneously modulated for the first time at different increments. Cylindrical composite pellets/test samples were obtained only for the mechanical and wettability behaviour evaluation. The Fourier-transformed infrared spectroscopy depicted two levels of overlapping structures due to the solid molecular bond between all materials. Scanning electron microscopy and surface wettability and mechanical evaluations vouched for the (1) uniform/homogenous dispersion/embedding of HA particles up to the highest HA/GNP ratio, (2) physical adhesion at the HA-PLA interface due to the HA particles' porosity, (3) HA-GNP bonding, and (4) PLA-GNP synergy based on GNP complete exfoliation and dispersion into the matrix.

Selection Route of Precursor Materials in 3D Printing Composite Filament Development for Biomedical Applications.

Additive manufacturing or 3D printing technologies might advance the fabrication sector of personalised biomaterials with high-tech precision. The selection of optimal precursor materials is considered the first key-step for the development of new printable filaments destined for the fabrication of products with diverse orthopaedic/dental applications. The selection route of precursor materials proposed in this study targeted two categories of materials: prime materials, for the polymeric matrix (acrylonitrile butadiene styrene (ABS), polylactic acid (PLA)); and reinforcement materials (natural hydroxyapatite (HA) and graphene nanoplatelets (GNP) of different dimensions). HA was isolated from bovine bones (HA particles size < 40 µm, <100 µm, and >125 µm) through a reproducible synthesis technology. The structural (FTIR-ATR, Raman spectroscopy), morphological (SEM), and, most importantly, in vitro (indirect and direct contact studies) features of all precursor materials were comparatively evaluated. The polymeric materials were also prepared in the form of thin plates, for an advanced cell viability assessment (direct contact studies). The overall results confirmed once again the reproducibility of the HA synthesis method. Moreover, the biological cytotoxicity assays established the safe selection of PLA as a future polymeric matrix, with GNP of grade M as a reinforcement and HA as a bioceramic. Therefore, the obtained results pinpointed these materials as optimal for future composite filament synthesis and the 3D printing of implantable structures.

Influence of Ceramic Particles Size and Ratio on Surface-Volume Features of the Naturally Derived HA-Reinforced Filaments for Biomedical Applications.

The intersection of the bone tissue reconstruction and additive manufacturing fields promoted the advancement to a prerequisite and new feedstock resource for high-performance bone-like-scaffolds manufacturing. In this paper, the proposed strategy was directed toward the use of bovine-bone-derived hydroxyapatite (HA) for surface properties enhancement and mechanical features reinforcement of the poly(lactic acid) matrix for composite filaments extrusion. The involvement of completely naturally derived materials in the technological process was based on factors such as sustainability, low cost, and a facile and green synthesis route. After the HA isolation and extraction from bovine bones by thermal processing, milling, and sorting, two dependent parameters­the HA particles size (<40 µm, <100 µm, and >125 µm) and ratio (0−50% with increments of 10%)­were simultaneously modulated for the first time during the incorporation into the polymeric matrix. The resulting melt mixtures were divided for cast pellets and extruded filaments development. Based on the obtained samples, the study was further designed to examine several key features by complementary surface−volume characterization techniques. Hence, the scanning electron microscopy and micro-CT results for all specimens revealed a uniform and homogenous dispersion of HA particles and an adequate adhesion at the ceramic/polymer interface, without outline pores, sustained by the shape and surface features of the synthesized ceramic particles. Moreover, an enhanced wettability (contact angle in the ~70−21° range) and gradual mechanical takeover were indicated once the HA ratio increased, independent of the particles size, which confirmed the benefits and feasibility of evenly blending the natural ceramic/polymeric components. The results correlation led to the selection of optimal technological parameters for the synthesis of adequate composite filaments destined for future additive manufacturing and biomedical applications.

Nanostructured Polyacrylamide Hydrogels with Improved Mechanical Properties and Antimicrobial Behavior.

This work proposes a simple method to obtain nanostructured hydrogels with improved mechanical characteristics and relevant antibacterial behavior for applications in articular cartilage regeneration and repair. Low amounts of silver-decorated carbon-nanotubes (Ag@CNTs) were used as reinforcing agents of the semi-interpenetrating polymer network, consisting of linear polyacrylamide (PAAm) embedded in a PAAm-methylene-bis-acrylamide (MBA) hydrogel. The rational design of the materials considered a specific purpose for each employed species: (1) the classical PAAm-MBA network provides the backbone of the materials; (2) the linear PAAm (i) aids the dispersion of the nanospecies, ensuring the systems' homogeneity and (ii) enhances the mechanical properties of the materials with regard to resilience at repeated compressions and ultimate compression stress, as shown by the specific mechanical tests; and (3) the Ag@CNTs (i) reinforce the materials, making them more robust, and (ii) imprint antimicrobial characteristics on the obtained scaffolds. The tests also showed that the obtained materials are stable, exhibiting little degradation after 4 weeks of incubation in phosphate-buffered saline. Furthermore, as revealed by micro-computed tomography, the morphometric features of the scaffolds are adequate for applications in the field of articular tissue regeneration and repair.

Fiber-Templated 3D Calcium-Phosphate Scaffolds for Biomedical Applications: The Role of the Thermal Treatment Ambient on Physico-Chemical Properties.

A successful bone-graft-controlled healing entails the development of novel products with tunable compositional and architectural features and mechanical performances and is, thereby, able to accommodate fast bone in-growth and remodeling. To this effect, graphene nanoplatelets and Luffa-fibers were chosen as mechanical reinforcement phase and sacrificial template, respectively, and incorporated into a hydroxyapatite and brushite matrix derived by marble conversion with the help of a reproducible technology. The bio-products, framed by a one-stage-addition polymer-free fabrication route, were thoroughly physico-chemically investigated (by XRD, FTIR spectroscopy, SEM, and nano-computed tomography analysis, as well as surface energy measurements and mechanical performance assessments) after sintering in air or nitrogen ambient. The experiments exposed that the coupling of a nitrogen ambient with the graphene admixing triggers, in both compact and porous samples, important structural (i.e., decomposition of ß-Ca3(PO4)2 into α-Ca3(PO4)2 and α-Ca2P2O7) and morphological modifications. Certain restrictions and benefits were outlined with respect to the spatial porosity and global mechanical features of the derived bone scaffolds. Specifically, in nitrogen ambient, the graphene amount should be set to a maximum 0.25 wt.% in the case of compact products, while for the porous ones, significantly augmented compressive strengths were revealed at all graphene amounts. The sintering ambient or the graphene addition did not interfere with the Luffa ability to generate 3D-channels-arrays at high temperatures. It can be concluded that both Luffa and graphene agents act as adjuvants under nitrogen ambient, and that their incorporation-ratio can be modulated to favorably fit certain foreseeable biomedical applications.

Considerations and Influencing Parameters in EDS Microanalysis of Biogenic Hydroxyapatite.

Calcium phosphates (CPs) used as biomaterials have been intensively studied in recent years. In most studies, the determination of the chemical composition is mandatory. Due to the versatility and possibilities of performing qualitative and quantitative compositional analyses, energy dispersive spectrometry (EDS) is a widely used technique in this regard. The range of calcium phosphates is very diverse, the first method of approximating the type of compound being EDS microanalysis, by assessing the atomic Ca/P ratio. The value of this ratio can be influenced by several factors correlated with instrumental parameters and analysed samples. This article highlights the influence of the electron beam acceleration voltage (1 kV-30 kV) and of the particle size of calcium phosphate powders on the EDS analysis results. The characterised powders were obtained from bovine bones heat-treated at 1200 °C for 2 h, which have been ground and granulometrically sorted by mechanical vibration. The granulometric sorting generated three types of samples, with particle sizes < 20 µm, < 40 µm and < 100 µm, respectively. These were morphologically and dimensionally analysed by scanning electron microscopy (SEM) and compositionally by EDS, after the spectrometer was calibrated with a standard reference material (SRM) from NIST (National Institute of Standards and Technology). The results showed that the adjusting of acceleration voltage and of the powder particle size significantly influences the spectrum profile and the results of EDS analyses, which can lead to an erroneous primary identification of the analysed calcium phosphate type.

Naturally-Derived Biphasic Calcium Phosphates through Increased Phosphorus-Based Reagent Amounts for Biomedical Applications.

Calcium carbonate from marble and seashells is an eco-friendly, sustainable, and largely available bioresource for producing natural bone-like calcium phosphates (CaPs). Based on three main objectives, this research targeted the: (i) adaptation of an indirect synthesis route by modulating the amount of phosphorus used in the chemical reaction, (ii) comprehensive structural, morphological, and surface characterization, and (iii) biocompatibility assessment of the synthesized powdered samples. The morphological characterization was performed on digitally processed scanning electron microscopy (SEM) images. The complementary 3D image augmentation of SEM results also allowed the quantification of roughness parameters. The results revealed that both morphology and roughness were modulated through the induced variation of the synthesis parameters. Structural investigation of the samples was performed by Fourier transform infrared spectroscopy and X-ray diffraction. Depending on the phosphorus amount from the chemical reaction, the structural studies revealed the formation of biphasic CaPs based on hydroxyapatite/brushite or brushite/monetite. The in vitro assessment of the powdered samples demonstrated their capacity to support MC3T3-E1 pre-osteoblast viability and proliferation at comparable levels to the negative cytotoxicity control and the reference material (commercial hydroxyapatite). Therefore, these samples hold great promise for biomedical applications.