Cynthia M. Gomes

3D-printed silicate porous bioceramics using a non-sacrificial preceramic polymer binder

Silicate bioceramics possess an excellent bioactivity; however, shaping them into complex geometries is still challenging. Therefore, this paper aims to present a new strategy for the shaping of a bioglass-ceramic with controlled geometry and properties starting from a glass powder combined with a preceramic polymer, i.e. a silicon resin, and reactive fillers. The powder-based three-dimensional (3D)-printing of wollastonite (CaSiO3)-based silicate bioceramic parts was demonstrated in this work. The resin plays a dual role, as it not only acts as a non-sacrificial binder for the filler powders in the printing process but it also reacts with the fillers to generate the desired bioceramic phases. The mechanical and physical properties, i.e. ball-on-three-balls test, density, porosity and morphology, were evaluated in 3D-printed discs. These samples possessed a total porosity around 64 vol% and a biaxial flexural strength around 6 MPa. The raw materials used in this work also enabled the 3D-printing of scaffolds possessing a designed multi-scale porosity, suitable bioceramic phase assemblage and a compressive strength of 1 MPa (for cylindrical scaffolds with total porosity ~80 vol%). Solubility in TRIS/HCl and in vitro assays, i.e. viability, cytotoxicity and apoptosis assays, were also performed. In vitro tests indicated good cell viability and no cytotoxicity effect on the cells.

Laminated object manufacturing of LZSA glass‐ceramics

Purpose – This paper seeks to detail the fabrication of a glass‐ceramic substrate, based on the LiO2‐ZrO2‐SiO2‐Al2O3 (LZSA) system, by laminated object manufacturing (LOM) using water‐based cast tapes.Design/methodology/approach – Small amounts of ZrSiO4 were added to control the thermal expansion coefficient (TEC) of the original glass‐ceramic (LZSA5Zr: LZSA+5 wt% ZrSiO4). In order to verify the influence of the amount and nature of crystalline phases on the thermal and dielectric behavior of the material, LZSA and LZSA5Zr laminates were sintered at 700°C for 30 min and crystallized at either 800 or 850°C for 30 min.Findings – LZSA laminates (sintered and crystallized at 700 and 800°C, respectively) exhibited a relative density of ∼90 percent, a dielectric constant of 8.39, a dielectric loss tangent of 0.031 and TEC of 5.5×10−6 K−1 (25‐550°C). The addition of 5 wt% ZrSiO4 to original LZSA glass‐ceramics led to a nearly constant TEC value of 6×10−6 K−1 throughout the whole temperature interval (25‐800°C)....

Powder-Bed Stabilization for Powder-Based Additive Manufacturing

The most successful additive manufacturing (AM) technologies are based on thelayer-by-layer depositionof a flowable powder. Although considered as the third industrial revolution, one factor still limiting these processes to become completely autonomous is the often necessary build-up of support structures. Besides the prevention of lateral shifts of the part during the deposition of layers, the support assures quality and stability to the built process. The loose powder itself surrounding the built object, or so-called powder-bed, does not provide this sustenance in most existent technology available. Here we present a simple but effective and economical method for stabilizing the powder-bed, preventing distortions in the geometry with no need for support structures. This effect, achieved by applying an air flow through the powder-bed, is enabling an entirely autonomous generation of parts and is a major contribution to all powder-based additive manufacturing technologies. Moreover, it makes powder-based AM independent of gravitational forces, which will facilitate crafting items in space from a variety of powdery materials.

Calcium Alkaline Phosphate Scaffolds for Bone Regeneration 3D-Fabricated by Additive Manufacturing

Calcium alkaline phosphate granulates can be used for substitution of several bone defects but for the reconstruction of large skeletal parts in the maxillofacial and orthopaedic fields fitted scaffolds are preferable. Within the additive manufacturing methods, the 3D printing process offers exciting opportunities to generate defined porous scaffolds. We used a R1 printer from ProMetal Company, USA, for producing scaffolds directly from a ceramic powder. For this direct free form fabrication technology the powder has to possess a lot of specific properties both for the generation of a stable green body and also for the subsequent sintering preparation. For this printing process we prepared different granules in a fluidized bed process containing Ca2KNa(PO4)2 as main crystalline phase. Granules were characterized by different methods and several sieve fractions were used for preparing disc like and cylindrical parts. The suitability of granules for this printing process was determined by porosity and strength of produced bodies. Next to granules’ performance both of these properties can be directly influenced by 3D printing process parameters. With knowledge of suitable process parameters scaffolds with different porosity in a respective desired design can be created. In this study, cylindrical scaffolds with graded porosity were produced for bone regeneration of segmental defects in maxillofacial surgery and dental implantology by tissue engineering.

Deflocculation of triaxial ceramic suspensions using a mixture design approach)

The evaluation of the rheological properties of suspensions is an important step in the ceramic slurries development. Mainly in wet processing, the rheological factor can be a limitation to the employment of determined raw material as well as the deflocculant agent. In this sense, the integrated approach of triaxial ceramics formulation and the mixture design come as an important aid to decrease the number of experiments necessary to determine the optimum properties of a system, which can be physical or rheological properties. The present work is directed towards to study the deflocculation of triaxial ceramic slurries (clay/feldspar/quartz) obtained from the mixture design, through the determination of a mathematical model that represents the ideal deflocculant concentration presented by each ceramic composition of the triaxial diagram. Aqueous suspensions (55% solids content) were prepared, using dehydrated sodium silicate (1.3 silica modulus) as deflocculant agent. Deflocculation curves were obtained. The results showed that the increase on clay mineral fraction lead the suspensions to higher deflocculant consumption.

An Intrinsic Angiogenesis Approach and Varying Bioceramic Scaffold Architecture Affect Blood Vessel Formation in Bone Tissue Engineering In Vivo

Early establishment of angiogenesis is critical for bone tissue engineering. Recently, a technique was introduced, which is based on the idea of using axial vascularization of the host tissues in engineered grafts, namely the “intrinsic angiogenesis chamber” technique, which utilizes an artery and a vein to construct an AV-Bundle. The aim of this study was to evaluate the effect of varying scaffold architecture of calcium alkali orthophosphate scaffolds (CAOP), resulting from two different fabrication procedures, namely 3D printing (RP) or a Schwarzwalder-Somers replica technique (SSM), on angiogenesis in vivo when combining a microvascular technique with bioceramic scaffolds colonized with stem cells for bone tissue engineering. 32 adult female Wistar rats, in which critical size segmental discontinuity defects 6 mm in length were created in the left femur, were divided into 4 groups, group 1 received a RP scaffold colonized with rat stem cells after 7d of dynamic cell culture and an AV-Bundle (AVB), group 2 a SSM scaffold with rat stem cells after 7d of dynamic cell culture and an AVB, group 3 a RP control scaffold (without cells and AVB), group 4 a SSM control scaffold (without cells and AVB). After 3 and 6 months, angiomicro-CT after perfusion with a contrast agent, image reconstruction, histomorphometric and immunohistochemical analysis utilizing antibodies to collagen IV, vWF and CD-31 were performed. At 6 months, a statistically significant higher blood vessel volume%, blood vessel surface/volume, blood vessel thickness, blood vessel density and blood vessel linear density was observed with RP scaffolds with cells and AVB than with the other groups. At 6 mths, RP with cells and AVB displayed the highest expression of collagen IV (score 2.75), CD31 (score 2.75) and vWF (score 2.6), which is indicative of highly dense blood vessels. Both angio-CT and immunohistochemical analysis demonstrated that AVB is an efficient technique for achieving scaffold vascularization in critical size segmental defects after 3 and 6 months of implantation.

Development of a synthetic tissue engineered 3D printed bioceramic-based bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro.

Over the last decade there have been increasing efforts to develop three‐dimensional (3D) scaffolds for bone tissue engineering from bioactive ceramics with 3D printing emerging as a promising technology. The overall objective of the present study was to generate a tissue engineered synthetic bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro, thereby mimicking the advantageous properties of autogenous bone grafts and facilitating usage for reconstructing segmental discontinuity defects in vivo. To this end, 3D scaffolds were developed from a silica‐containing calcium alkali orthophosphate, using, first, a replica technique – the Schwartzwalder–Somers method – and, second, 3D printing, (i.e. rapid prototyping). The mechanical and physical scaffold properties and their potential to facilitate homogenous colonization by osteogenic cells and extracellular bone matrix formation throughout the porous scaffold architecture were examined. Osteoblastic cells were dynamically cultured for 7 days on both scaffold types with two different concentrations of 1.5 and 3 × 109 cells/l. The amount of cells and bone matrix formed and osteogenic marker expression were evaluated using hard tissue histology, immunohistochemical and histomorphometric analysis. 3D‐printed scaffolds (RPS) exhibited more micropores, greater compressive strength and silica release. RPS seeded with 3 × 109 cells/l displayed greatest cell and extracellular matrix formation, mineralization and osteocalcin expression. In conclusion, RPS displayed superior mechanical and biological properties and facilitated generating a tissue engineered synthetic bone graft in vitro, which mimics the advantageous properties of autogenous bone grafts, by containing homogenously distributed terminally differentiated osteoblasts and mineralizing bone matrix and therefore is suitable for subsequent in vivo implantation for regenerating segmental discontinuity bone defects. Copyright

Advances in Additive Manufacturing Processes and Materials

Additivemanufacturing (AM), also known as rapid prototyping or 3Dprinting, generally refers to techniques that produce three-dimensional parts by adding material gradually in a layer by layer fashion. In this sense, AMdiffers fundamentally from forming and subtractive techniques. This special issue intends to put together research and developments in AM, particularly related to new manufacturing processes and/or to alternative feedstock materials and products. Polymer and metal-based raw materials and products have been extensively investigated inAMtechniques. Recently, ceramic, glass, and composite materials have been additionally used both in commercial and in innovative AM processes. The material compositions and processing steps used for shaping or finishing the structure of AM products are responsible for final properties and performance. Recent advances in sensors, micromechanics, computational modelling, and simulation have enhanced AM technologies. As complex parts become easier to build and the equipment and skills needed to build them become more and more common, innovative approaches are achievable. Additionally, this evolution opens up new fields of application,moving it from being a prototyping tool to a final productmanufacturing process (rapidmanufacturing). This special issue explores the development of new products and applications throughAMprocesses. Selected investigations contributed to this issue with original research that analyze feedstock materials, process parameters, and their effects onmechanical, physical, and other properties in prototypes or customized parts fabricated by AM techniques. The topics presented in this issue include diverse materialsmanufactured by representative AMprocesses, as summarized below:

Development of a synthetic tissue engineered three-dimensional printed bioceramic-based bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro : Development of a synthetic tissue engineered 3D printed bioceramic bone graft

Over the last decade there have been increasing efforts to develop three‐dimensional (3D) scaffolds for bone tissue engineering from bioactive ceramics with 3D printing emerging as a promising technology. The overall objective of the present study was to generate a tissue engineered synthetic bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro, thereby mimicking the advantageous properties of autogenous bone grafts and facilitating usage for reconstructing segmental discontinuity defects in vivo. To this end, 3D scaffolds were developed from a silica‐containing calcium alkali orthophosphate, using, first, a replica technique – the Schwartzwalder–Somers method – and, second, 3D printing, (i.e. rapid prototyping). The mechanical and physical scaffold properties and their potential to facilitate homogenous colonization by osteogenic cells and extracellular bone matrix formation throughout the porous scaffold architecture were examined. Osteoblastic cells were dynamically cultured for 7 days on both scaffold types with two different concentrations of 1.5 and 3 × 109 cells/l. The amount of cells and bone matrix formed and osteogenic marker expression were evaluated using hard tissue histology, immunohistochemical and histomorphometric analysis. 3D‐printed scaffolds (RPS) exhibited more micropores, greater compressive strength and silica release. RPS seeded with 3 × 109 cells/l displayed greatest cell and extracellular matrix formation, mineralization and osteocalcin expression. In conclusion, RPS displayed superior mechanical and biological properties and facilitated generating a tissue engineered synthetic bone graft in vitro, which mimics the advantageous properties of autogenous bone grafts, by containing homogenously distributed terminally differentiated osteoblasts and mineralizing bone matrix and therefore is suitable for subsequent in vivo implantation for regenerating segmental discontinuity bone defects. Copyright

Development of a Synthetic Tissue Engineered 3D Printed Calciumalkaliphosphate-Based Bone Graft with Homogenously Distributed Osteoblasts and Mineralizing Bone Matrix In Vitro

Over the last decade there have been increasing efforts to develop adequate 3D scaffolds for bone tissue engineering from bioactive ceramics with 3D printing emerging as a promising technology. The overall objective of the present study was to generate a tissue engineered synthetic bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro, thereby mimicking the advantageous properties of autogenous bone grafts and facilitating usage for reconstructing segmental discontinuity defects in vivo. To this end, 3D scaffolds were developed from a silica containing calciumalkaliorthophosphate (code: GB9S14) utilizing two different fabrication processes, first a replica technique (SSM), and second 3D printing (RP). The mechanical and physical properties of the scaffolds (porosity, compressive strength, solubility) and their potential to facilitate homogenous colonization by osteogenic cells and extracellular bone matrix formation throughout the porous scaffold architecture prior to in vivo implantation were examined. To this end, murine osteoblastic cells (MT3T3-E1) were dynamically seeded and cultured for 7 days on both scaffold types under perfusion with two different concentrations of 1.5 and 3x106 cells per ml. The amount of cells and extracellular matrix formed and osteogenic marker expression were evaluated using hard tissue histology, immunohistochemical and histomorphometric analysis. SSM scaffolds (SSMS) displayed a significantly greater total porosity (86.9%) than RP scaffolds (RPS) (50%), while RPS exhibited significantly more open micropores, greater compressive strength and silica release. RPS seeded with a 3x106 cells per ml displayed greatest cell and extracellular matrix formation, mineralization and osteocalcin expression. In conclusion, RPS displayed superior mechanical and biological properties and facilitated generating a tissue engineered synthetic bone graft in vitro, which mimics the advantageous properties of autogenous bone grafts, by containing homogenously distributed terminally differentiated osteoblasts and mineralizing bone matrix and therefore is suitable for subsequent in vivo implantation for regenerating segmental discontinuity bone defects.