The Design of Printed Hybrid Constructs to Serve as Cartilage Templates for Bone Repair

With an estimated annual incidence of over 2.2 million cases across the world, critical size bone defects pose an unmet challenge requiring improved therapeutic strategies. Current clinical solutions, namely autologous and allogeneic grafts, are associated with a number of complications which include supply shortage, donor site morbidity and immune rejection. Given the poor vascularization observed with bioresorbable bone template scaffolds, some have turned to engineering the endogenous repair pathway by developing implantable cartilage templates susceptible to the bone transformation process known as endochondral ossification seen in native defects. Yet considerations relating to the implants' mechanical behavior, porosity and swelling, all of which are crucial to mimicking the endochondral ossification process, remain largely unaddressed in past studies. Through a parameter-driven preliminary study, we have devised a method to improve spatial resolution and property modulation by incorporating additive manufacturing into the fabrication process of cartilage templates destined for ossification-mediated defect repair. Based on our findings that hydrogel extrusion introduces structural discontinuities leading to excessive swelling and time-dependent mechanical deformation, we advance a biofabrication method involving (1) the 3D printing of a porous hybrid construct comprised of a stiff polycaprolactone network interwoven with sacrificial poly(ethylene glycol) material, (2) the casting of a cell-laden hydrogel material into the primary porous network, and (3) the evacuation of the sacrificial poly(ethylene glycol) material to create a secondary porous network. The architecture of the generated templates was modulated by varying the widths of the secondary pores and hydrogel struts. Generated templates were subjected to geometric analysis by photography, porosity evaluation by micro-computed tomography, stress relaxation testing and a swelling study. The incorporation of a stiff network constrained swelling by more than half, while decreased porosity-to-hydrogel content ratios mitigated time-dependent deformation.M.S., Biomedical Engineering -- Drexel University, 201

A micromirror array with annular partitioning for high-speed random-access axial focusing

Dynamic axial focusing functionality has recently experienced widespread incorporation in microscopy, augmented/virtual reality (AR/VR), adaptive optics, and material processing. However, the limitations of existing varifocal tools continue to beset the performance capabilities and operating overhead of the optical systems that mobilize such functionality. The varifocal tools that are the least burdensome to drive (ex: liquid crystal, elastomeric or optofluidic lenses) suffer from low (~ 100 Hz) refresh rates. Conversely, the fastest devices sacrifice either critical capabilities such as their dwelling capacity (ex: acoustic gradient lenses or monolithic micromechanical mirrors) or low operating overhead (e.g., deformable mirrors). Here, we present a general-purpose random-access axial focusing device that bridges these previously conflicting features of high speed, dwelling capacity and lightweight drive by employing low-rigidity micromirrors that exploit the robustness of defocusing phase profiles. Geometrically, the device consists of an 8.2 mm diameter array of piston-motion and 48 um-pitch micromirror pixels that provide 2pi phase shifting for wavelengths shorter than 1 100 nm with 10-90 % settling in 64.8 us (i.e., 15.44 kHz refresh rate). The pixels are electrically partitioned into 32 rings for a driving scheme that enables phase-wrapped operation with circular symmetry and requires less than 30 V per channel. Optical experiments demonstrated the array's wide focusing range with a measured ability to target 29 distinct, resolvable depth planes. Overall, the features of the proposed array offer the potential for compact, straightforward methods of tackling bottlenecked applications including high-throughput single-cell targeting in neurobiology and the delivery of dense 3D visual information in AR/VR.Comment: 38 pages, 8 figure

A micromirror array with annular partitioning for high-speed random-access axial focusing.

Dynamic axial focusing functionality has recently experienced widespread incorporation in microscopy, augmented/virtual reality (AR/VR), adaptive optics and material processing. However, the limitations of existing varifocal tools continue to beset the performance capabilities and operating overhead of the optical systems that mobilize such functionality. The varifocal tools that are the least burdensome to operate (e.g. liquid crystal, elastomeric or optofluidic lenses) suffer from low (≈100 Hz) refresh rates. Conversely, the fastest devices sacrifice either critical capabilities such as their dwelling capacity (e.g. acoustic gradient lenses or monolithic micromechanical mirrors) or low operating overhead (e.g. deformable mirrors). Here, we present a general-purpose random-access axial focusing device that bridges these previously conflicting features of high speed, dwelling capacity and lightweight drive by employing low-rigidity micromirrors that exploit the robustness of defocusing phase profiles. Geometrically, the device consists of an 8.2 mm diameter array of piston-motion and 48-μm-pitch micromirror pixels that provide 2π phase shifting for wavelengths shorter than 1100 nm with 10-90% settling in 64.8 μs (i.e., 15.44 kHz refresh rate). The pixels are electrically partitioned into 32 rings for a driving scheme that enables phase-wrapped operation with circular symmetry and requires <30 V per channel. Optical experiments demonstrated the array's wide focusing range with a measured ability to target 29 distinct resolvable depth planes. Overall, the features of the proposed array offer the potential for compact, straightforward methods of tackling bottlenecked applications, including high-throughput single-cell targeting in neurobiology and the delivery of dense 3D visual information in AR/VR