Comparative Analysis of Wollastonite‐Diopside Glass‐Ceramic Structures Fabricated via Stereo‐Lithography

Abstract

One key feature of digital light processing consists of the high flexibility in the design of highly porous reticulated scaffolds. In the present paper, the authors report recent experiences concerning two glasses, both converted into wollastonite-diopside (CaSiO 3 -CaMgSi 2 O 6 ) glass-ceramics by viscous flow sintering of fine powders (<45 μm) with concurrent crystallization. Glass particles are homogeneously dispersed in a photosensitive polymer, selectively hardened, layer-by-layer, by exposure to visible light, forming diamond cell lattices. The printing accuracy is slightly influenced by the glass chemistry, whereas the shape maintenance, after firing at 1100 C, is observed for both compositions. The newly developed scaffolds are compared to other glass-ceramic scaffolds, previously developed on the basis of the starting glass: the adoption of a new design does not determine any substantial degradation of mechanical properties.

Advanced Open-Celled Structures from Low-Temperature Sintering of a Crystallization-Resistant Bioactive Glass

“…The limited morphological changes from samples in the printed state, shown in Figure 1a,b, to samples after firing, illustrated by Figure 1c, clearly show that by operating at the lower limit for pressureless sintering (with T g ~670 °C [14], the firing temperature —750 °C, i.e. T g + 80 °C, was in the range of dilatometric softening temperature), a good shape retention could be achieved despite the absence of crystallization (in previous experiments with wollastonite-diopside glass-ceramics [24] the shape was maintained as an effect of viscosity enhancement operated by intensive crystal precipitation). BGMS10 was evidently a ‘long’ glass, i.e., not exhibiting an abrupt decrease of viscosity with increasing temperature above T g .…”

“…A first series of investigations concerned the application of stereolithography to BGMS10, starting from a diamond cell design recently tested for wollastonite-diopside glass-ceramics [24], as illustrated by Figure 1. The particular design, maximizing the bending of thin struts, was chosen specifically to verify the resistance of BGMS10 to viscous collapse upon firing.…”

“…The saving of structural integrity can be understood from the results of mechanical testing. The diamond cell structure had been selected also as an example of ‘bending dominated’ design [24]. According to Gibson and Ashby [35], the crushing of brittle solids with such morphology, causing the systematic buckling of the struts, is described by a simple equation: σ c = 0.2·σ bend ·(ρ rel ) 1.5 where σ c represents the compressive strength, σ bend is the bending strength of the solid phase, and ρ rel is the relative density (ratio between geometric and true densities).…”

“…Samples with non-stochastic porosity were manufactured by using DLP (digital light processing), in analogy with previous experiences [23,24]. Fine glass powders were suspended in a commercially available photocurable acrylic polymer (Tripropylene glycol diacrylate, Robot Factory S.R.L., Mirano, Italy), already comprising a suitable photo-initiator and photo-absorber, for a solid load of 60 wt.…”

“…The use of sacrificial organic binders is fundamental; among them, photocurable resins are undoubtedly precious in enabling the manufacturing of scaffolds with non-stochastic porosity by means of high-resolution stereolithography 3D printing [19]. When considering suspensions of fine glass particles in photocurable resin (i.e., a bi-phasic mixture), instead of photocurable liquid (a monophasic system), the resolution is obviously conditioned by the particle size and by light scattering at the liquid–particle interfaces [20,21,22]; anyway, highly uniform samples, even with complex geometries, were successfully obtained starting from glass undergoing sinter-crystallization [23,24]. The sudden increase of viscosity, caused by crystal precipitation, prevented any collapse of cellular structure upon firing.…”