Build parameter influence on strut thickness and mechanical performance in additively manufactured titanium lattice structures.

Additively manufactured lattices have been adopted in applications ranging from medical implants to aerospace components. For solid AM components, the effect of build parameters has been well studied but comparably little attention has been paid to the influence of build parameters on lattice performance. For this project, the main aim was to evaluate static compressive mechanical performance of regular and stochastic lattices as a function of build parameters. The second aim was to compare strut dimensions of the metal lattice structures as build parameters were changed. Both regular and stochastic lattices were fabricated with a designed strut diameter of either 200 µm or 300 µm on a laser powder bed fusion machine. A range of laser power (140-180 W), scan speed (1700-2100 mm/s), and laser offset (0-45 µm) were used in fabricating each lattice. Compression tests were performed following the ISO 13314 (2011) standard to measure modulus, yield strength, and ultimate compressive strength values. Laser power adjustments produced the most significant effect on lattice performance. A change of 50 W resulted in roughly a 2X increase in maximum load and modulus for both regular and stochastic lattice structures. Regular lattice structures had a higher mechanical response during the mechanical evaluation. Internal strut diameters varied between build parameters as well, with laser offset adjustments producing the most noticeable change in strut geometry between lattice samples. These findings suggest that build parameter optimization, in lieu of using OEM parameters developed for solid structures, is necessary to ensure the optimum mechanical performance of AM lattice structures.

Biomimetic tissue phantoms for neurosurgical near-infrared fluorescence imaging.

Significance: Neurosurgical fluorescence imaging is a well-established clinical approach with a growing range of indications for use. However, this technology lacks effective phantom-based tools for development, performance testing, and clinician training. Aim: Our primary aim was to develop and evaluate 3D-printed phantoms capable of optically and morphologically simulating neurovasculature under fluorescence angiography. Approach: Volumetric digital maps of the circle of Willis with basilar and posterior communicator artery aneurysms, along with surrounding cerebral tissue, were generated. Phantoms were fabricated with a stereolithography printer using custom photopolymer composites, then visualized under white light and near-infrared fluorescence imaging. Results: Feature sizes of printed components were found to be within 13% of digital models. Phantoms exhibited realistic optical properties and convincingly recapitulated fluorescence angiography scenes. Conclusions: Methods identified in this study can facilitate the development of realistic phantoms as powerful new tools for fluorescence imaging.

Benchtop assessment of sealing efficacy and breathability of additively manufactured (AM) face masks.

The onset of the 2019 novel coronavirus disease (COVID-19) led to a shortage of personal protective equipment (PPE), medical devices, and other medical supplies causing many stakeholders and the general public alike to turn to additive manufacturing (AM) as a stopgap when normally accessible devices were not available. However, without a method to test these AM constructs, there continued to be a disconnect between AM suppliers and the community's needs. The objective of this study was to characterize the pressure drop and leakage of four different publicly available AM face mask models with two filter material combinations, as well as to investigate the impact of frame modification techniques including the use of foam strips and hot-water face forming to improve fit when the masks are donned on manikin head forms. AM face mask frame designs were downloaded from public repositories during the early stages of the COVID-19 pandemic. AM face masks were fabricated and tested on manikin head forms within a custom chamber containing dry aerosolized NaCl. Pressure drops, particle penetration, and leakage were evaluated for various flow rates and NaCl concentrations. Results indicated that filter material combination and frame modification played a major role in the overall performance of the AM face masks studied. Filter material combinations showed improved performance when high filtration fabric was used, and the cross-sectional area of the fabric was increased. AM frame modifications appeared to improve AM face mask leakage performance by as much as 69.6%.

Dimensional variability characterization of additively manufactured lattice coupons.

BACKGROUND: Additive manufacturing (AM), commonly called 3D Printing (3DP), for medical devices is growing in popularity due to the technology's ability to create complex geometries and patient-matched products. However, due to the process variabilities which can exist between 3DP systems, manufacturer workflows, and digital conversions, there may be variabilities among 3DP parts or between design files and final manufactured products. The overall goal of this project is to determine the dimensional variability of commercially obtained 3DP titanium lattice-containing test coupons and compare it to the original design files. METHODS: This manuscript outlines the procedure used to measure dimensional variability of 3D Printed lattice coupons and analyze the differences in external dimensions and pore area when using laser and electron beam fabricated samples. The key dimensions measured were the bulk length, width, and depth using calipers. Strut thickness and pore area were assessed for the lattice components using optical imaging and µCT. RESULTS: Results show a difference in dimensional measurement between printed parts and the computer-designed files for all groups analyzed including the internal lattice dimensions. Measurements of laser manufactured coupons varied from the nominal by less than 0.2 mm and results show averages greater than the nominal value for length, width, and depth dimensions. Measurements of Electron Beam Melting coupons varied between 0.4 mm-0.7 mm from the nominal value and showed average lengths below the nominal dimension while the width and depths were greater than the nominal values. The length dimensions of Laser Powder Bed Fusion samples appeared to be impacted by hot isostatic press more than the width and depth dimension. When lattice relative density was varied, there appeared to be little impact on the external dimensional variability for the as-printed state. CONCLUSIONS: Based on these results, we can conclude that there are relevant variations between designed files and printed parts. However, we cannot currently state if these results are clinically relevant and further testing needs to be conducted to apply these results to real-world situations.

Dual Extrusion Patterning Drives Tissue Development Aesthetics and Shape Retention in 3D Printed Nipple-Areola Constructs.

Breast cancer and its most radical treatment, the mastectomy, significantly impose both physical transformations and emotional pain in thousands of women across the globe. Restoring the natural appearance of a nipple-areola complex directly on the reconstructed breast represents an important psychological healing experience for these women and remains an unresolved clinical challenge, as current restorative techniques render a flattened disfigured skin tab within a single year. To provide a long-term solution for nipple reconstruction, this work presents 3D printed hybrid scaffolds composed of complementary biodegradable gelatin methacrylate and synthetic non-degradable poly(ethylene) glycol hydrogels to foster the regeneration of a viable nipple-areola complex. In vitro results showcased the robust structural capacity and long-term shape retention of the nipple projection amidst internal fibroblastic contraction, while in vivo subcutaneous implantation of the 3D printed nipple-areola demonstrated minimal fibrotic encapsulation, neovascularization, and the formation of healthy granulation tissue. Envisioned as subdermal implants, these nipple-areola bioprinted regenerative grafts have the potential to transform the appearance of the newly reconstructed breast, reduce subsequent surgical intervention, and revolutionize breast reconstruction practices.

Endothelial/Mesenchymal Stem Cell Crosstalk Within Bioprinted Cocultures.

The development of viable tissue surrogates requires a vascular network that sustains cell metabolism and tissue development. The coculture of endothelial cells (ECs) and mesenchymal stem cells (MSCs), the two key players involved in blood vessel formation, has been heralded in tissue engineering (TE) as one of the most promising approaches for scaffold vascularization. However, MSCs may exert both proangiogenic and antiangiogenic role. Furthermore, it is unclear which cell type is responsible for the upregulation of angiogenic pathways observed in EC:MSC cocultures. There is disagreement on the proangiogenic action of MSCs, as they have also been shown to negatively affect the formation of capillary networks. To address these issues, we investigated the regulation of key angiogenic pathways in scaffolds hosting different EC:MSC ratios fabricated through extrusion-based bioprinting. Human ECs were cocultured with either rat or human MSCs, and the regulation of fundamental angiogenic and arteriogenic pathways was analyzed through DNA, gene, and protein expression. The use of a hybrid human/rat coculture system facilitated pinpointing each cell type role in the regulation of specific genes and showed that MSCs exert a dose-dependent inhibitory effect on the EC expression of angiogenic factors within the first 24 h. Within a week of coculture, MSCs exert a proangiogenic effect, as corroborated in human/human bioprinted cocultures. Interestingly, juxtacrine signaling promoted secretion of the angiogenic factor vascular endothelial growth factor in direct cocultures (EC and MSC co-encapsulated), while paracrine signaling encouraged secretion of the arteriogenic factor platelet-derived growth factor in indirect cocultures (adjacent bioprinting of EC-laden and MSC-laden scaffolds). Overall, the use of a bioprinted system to elucidate EC:MSC interplay allows rapid leveraging of the data for novel vascular TE applications. Despite the transitory negative effect early in the culture, MSC presence is necessary for the regulation of pathways involved in arteriogenesis. With further validation in vivo, this study provides a possible explanation to the controversial findings present in literature and shows how MSC effect on angiogenic pathway regulation mimics the dynamics of blood vessel formation reported in literature and normally occurring in vivo. Impact Statement The coculturing of endothelial cells (ECs) and mesenchymal stem cells (MSCs) holds great promise in tissue engineering for the development of prevascularized tissue constructs. Yet, different studies report conflicting results on the role of MSCs, which can either support or inhibit vasculature formation. Furthermore, it is unclear how each cell type modulates distinct pathways involved in angiogenesis when cocultured. Using bioprinted hybrid coculture systems, we show that MSCs have both a time- and dose-dependent effect on the gene and protein expression of key angiogenic and arteriogenic factors by ECs. These findings, obtained in translationally relevant setup, can readily inform the design of vascularized scaffolds.