In situ 4D tomography image analysis framework to follow sintering within 3D-printed glass scaffolds

We propose a novel image analysis framework to automate analysis of X-ray microtomography images of sintering ceramics and glasses, using open-source toolkits and machine learning. Additive manufacturing (AM) of glasses and ceramics usually requires sintering of green bodies. Sintering causes shrinkage, which presents a challenge for controlling the metrology of the final architecture. Therefore, being able to monitor sintering in 3D over time (termed 4D) is important when developing new porous ceramics or glasses. Synchrotron X-ray tomographic imaging allows in situ, real-time capture of the sintering process at both micro and macro scales using a furnace rig, facilitating 4D quantitative analysis of the process. The proposed image analysis framework is capable of tracking and quantifying the densification of glass or ceramic particles within multiple volumes of interest (VOIs) along with structural changes over time using 4D image data. The framework is demonstrated by 4D quantitative analysis of bioactive glass ICIE16 within a 3D-printed scaffold. Here, densification of glass particles within 3 VOIs were tracked and quantified along with diameter change of struts and interstrut pore size over the 3D image series, delivering new insights on the sintering mechanism of ICIE16 bioactive glass particles in both micro and macro scale

Ductile silica/methacrylate hybrids for bone regeneration

Bioglass® was the first synthetic material capable of bonding with bone without fibrous encapsulation, and fulfils some of the criteria of an ideal synthetic bone graft. However, it is brittle and toughness is required. Here, we investigated hybrids consisting of co-networks of high cross-linking density polymethacrylate and silica (class II hybrid) as a potential new generation of scaffold materials. Poly(3-(methoxysilyl)propyl methacrylate) (pTMSPMA) and tetraethyl orthosilicate (TEOS) were used as sol–gel precursors and hybrids were synthesised with different inorganic to organic ratios (Ih). The hybrids were nanoporous, with a modal pore diameter of 1 nm. At Ih = 50%, the release of silica was controlled by varying the molecular weight of pTMSPMA while retaining a specific surface area above 100 m2 g−1. Strain to failure increased to 14.2%, for Ih = 50% using a polymer of 30 kDa, compared to 4.5% for pure glass. The modulus of toughness (UT) increased from 0.73 (pure glass) to 2.64 GPa. Although, the hybrid synthesised in this report did not contain calcium, pTMSPMA/SiO2 hybrid was found to nucleate bone-like mineral on its surface after 1 week of immersion in simulated body fluid (SBF), whereas pure silica sol–gel glass did not. This increase in apatite forming ability was due to the ion–dipole complexation of calcium with the ester moieties of the polymer that were exposed after release of soluble silica from TEOS. No adverse cytotoxicity for MC3T3-E1 osteoblast-like cells was detected and improved cell attachment was observed, compared to a pure silica gel. pTMSPMA/SiO2 hybrids have potential for the regeneration of hard tissue as they overcome the major drawbacks of pure inorganic substrates while retaining cell attachment

Detection and tracking volumes of interest in 3D printed tissue engineering scaffolds using 4D imaging modalities.

Additive manufacturing (AM) platforms allow the production of patient tissue engineering scaffolds with desirable architectures. Although AM platforms offer exceptional control on architecture, post-processing methods such as sintering and freeze-drying often deform the printed scaffold structure. In-situ 4D imaging can be used to analyze changes that occur during post-processing. Visualization and analysis of changes in selected volumes of interests (VOIs) over time are essential to understand the underlining mechanisms of scaffold deformations. Yet, automated detection and tracking of VOIs in the 3D printed scaffold over time using 4D image data is currently an unsolved image processing task. This paper proposes a new image processing technique to segment, detect and track volumes of interest in 3D printed tissue engineering scaffolds. The method is validated using a 4D synchrotron sourced microCT image data captured during the sintering of bioactive glass scaffolds in-situ. The proposed method will contribute to the development of scaffolds with controllable designs and optimum properties for the development of patient-specific scaffolds

In-vitro cell interaction and apatite forming ability in simulated body fluid of ICIE16 and 13-93 bioactive glass coatings deposited by an emerging suspension high velocity oxy fuel (SHVOF) thermal spray

ICIE16 and 13-93 bioactive glasses have been proposed as alternative chemically stable compositions in physiological fluid keeping bioactivity comparable to Bioglass®. ICIE16 and 13-93 bioactive glasses coatings were produced via an emerging suspension high-velocity oxy-fuel (SHVOF) thermal spraying technique. Suspensions of ICIE16 and 13-93 with 10 wt% solid loading in isopropanol (IPA) and water were used to produce coatings on AISI304 stainless steel using a flame power of 50 kW and 75 kW. For both glass formulations, the coatings deposited at a lower flame power were more porous, less hard, and less rough (~6% porous and 242 HV) than the coatings obtained at a higher flame power (~4% porosity and 300 HV). ICIE16 coatings showed more dissolution in SBF (simulated body fluid) than the 13-93 coatings. Moreover, the 13-93 glass coating sprayed at 75 kW showed the highest stability in SBF since only 2% of the coating was resorbed in SBF after 7 days of immersion and revealed apatite precipitation after 7 days. In-vitro cell tests, using MG63 cells, showed good cell attachment and proliferation on the surfaces of the coatings, revealing good cytocompatibility. The 13-93 coating sprayed at 75 kW revealed the highest cell proliferation after 7 days of incubation. This can be attributed to the higher surface roughness of the coating (Ra = 6.5 ± 0.6 μm)

Four-dimensional imaging and quantification of viscous flow sintering within a 3D printed bioactive glass scaffold using synchrotron X-ray tomography

Bioglass® was the first material to form a stable chemical bond with human tissue. Since its discovery, a key goal was to produce three-dimensional (3D) porous scaffolds which can host and guide tissue repair, in particular, regeneration of long bone defects resulting from trauma or disease. Producing 3D scaffolds from bioactive glasses is challenging because of crystallization events that occur while the glass particles densify at high temperatures. Bioactive glasses such as the 13–93 composition can be sintered by viscous flow sintering at temperatures above the glass transition onset (T_{g}) and below the crystallization temperature (T_{c}). There is, however, very little literature on viscous flow sintering of bioactive glasses, and none of which focuses on the viscous flow sintering of glass scaffolds in four dimensions (4D) (3D + time). Here, high-resolution synchrotron-sourced X-ray computed tomography (sCT) was used to capture and quantify viscous flow sintering of an additively manufactured bioactive glass scaffold in 4D. In situ sCT allowed the simultaneous quantification of individual particle (local) structural changes and the scaffold's (global) dimensional changes during the sintering cycle. Densification, calculated as change in surface area, occurred in three distinct stages, confirming classical sintering theory. Importantly, our observations show for the first time that the local and global contributions to densification are significantly different at each of these stages: local sintering dominates stages 1 and 2, while global sintering is more prevalent in stage 3. During stage 1, small particles coalesced to larger particles because of their higher driving force for viscous flow at lower temperatures, while large angular particles became less faceted (angular regions had a local small radius of curvature). A transition in the rate of sintering was then observed in which significant viscous flow occurred, resulting in large reduction of surface area, total strut volume, and interparticle porosity because the majority of the printed particles coalesced to become continuous struts (stage 2). Transition from stage 2 to stage 3 was distinctly obvious when interparticle pores became isolated and closed, while the sintering rate significantly reduced. During stage 3, at the local scale, isolated pores either became more spherical or reduced in size and disappeared depending on their initial morphology. During stage 3, sintering of the scaffolds continued at the strut level, with interstrut porosity reducing, while globally the strut diameter increased in size, suggesting overall shrinkage of the scaffold with the flow of material via the strut contacts. This study provides novel insights into viscous flow in a complex non-idealized construct, where, locally, particles are not spherical and are of a range of sizes, leading to a random distribution of interparticle porosity, while globally, predesigned porosity between the struts exists to allow the construct to support tissue growth. This is the first time that the three stages of densification have been captured at the local and global scales simultaneously. The insights provided here should accelerate the development of 3D bioactive glass scaffolds

In situ 4D tomography image analysis framework to follow sintering within 3D-printed glass scaffolds

We propose a novel image analysis framework to automate analysis of X-ray microtomography images of sintering ceramics and glasses, using open-source toolkits and machine learning. Additive manufacturing (AM) of glasses and ceramics usually requires sintering of green bodies. Sintering causes shrinkage, which presents a challenge for controlling the metrology of the final architecture. Therefore, being able to monitor sintering in 3D over time (termed 4D) is important when developing new porous ceramics or glasses. Synchrotron X-ray tomographic imaging allows in situ, real-time capture of the sintering process at both micro and macro scales using a furnace rig, facilitating 4D quantitative analysis of the process. The proposed image analysis framework is capable of tracking and quantifying the densification of glass or ceramic particles within multiple volumes of interest (VOIs) along with structural changes over time using 4D image data. The framework is demonstrated by 4D quantitative analysis of bioactive glass ICIE16 within a 3D-printed scaffold. Here, densification of glass particles within 3 VOIs were tracked and quantified along with diameter change of struts and interstrut pore size over the 3D image series, delivering new insights on the sintering mechanism of ICIE16 bioactive glass particles in both micro and macro scales

Cobalt containing glass fibres and their synergistic effect on the HIF-1 pathway for wound healing applications

Introduction and Methods: Chronic wounds are a major healthcare problem, but their healing may be improved by developing biomaterials which can stimulate angiogenesis, e.g. by activating the Hypoxia Inducible Factor (HIF) pathway. Here, novel glass fibres were produced by laser spinning. The hypothesis was that silicate glass fibres that deliver cobalt ions will activate the HIF pathway and promote the expression of angiogenic genes. The glass composition was designed to biodegrade and release ions, but not form a hydroxyapatite layer in body fluid. Results and Discussion: Dissolution studies demonstrated that hydroxyapatite did not form. When keratinocyte cells were exposed to conditioned media from the cobalt-containing glass fibres, significantly higher amounts of HIF-1α and Vascular Endothelial Growth Factor (VEGF) were measured compared to when the cells were exposed to media with equivalent amounts of cobalt chloride. This was attributed to a synergistic effect of the combination of cobalt and other therapeutic ions released from the glass. The effect was also much greater than the sum of HIF-1α and VEGF expression when the cells were cultured with cobalt ions and with dissolution products from the Co-free glass, and was proven to not be due to a rise in pH. The ability of the glass fibres to activate the HIF-1 pathway and promote VEGF expression shows the potential for their use in chronic wound dressings