Multi-Material Stereolithography: Spatially-Controlled Bioactive Poly(Ethylene Glycol) Scaffolds for Tissue Engineering

Challenges remain in tissue engineering to control the spatial and temporal mechanical and biochemical architectures of scaffolds. Unique capabilities of stereolithography (SL) for fabricating multi-material spatially-controlled bioactive scaffolds were explored in this work. To accomplish multi-material builds with implantable materials, a new mini-vat setup was designed, constructed and placed on top of the existing build platform to allow for accurate and selfaligning X-Y registration during fabrication. Precise quantities of photocrosslinkable solution were added to and removed from the mini-vat using micro-pipettes. The mini-vat setup allowed the part to be easily removed and rinsed and different photocrosslinkable solutions could be easily removed and added to the vat to aid in multi-material fabrication. Two photocrosslinkable hydrogel biopolymers, poly(ethylene glycol dimethacrylate) (PEG-dma, molecular wt 1,000) and poly(ethylene glycol)-diacrylate (PEG-da, molecular wt 3,400), were used as the primary scaffold materials, and controlled concentrations of fluorescently labeled dextran or bioactive PEG were prescribed and fabricated in different regions of the scaffold using SL. The equilibrium swelling behavior of the two biopolymers after SL fabrication was determined and used to design constructs with the specified dimensions at the swollen state. Two methods were used to measure the spatial gradients enabled by this process with multi-material spatial control successfully demonstrated down to 500-µm. First, the presence of the fluorescent component in specific regions of the scaffold was analyzed with fluorescent microscopy. Second, human dermal fibroblast cells were seeded on top of the fabricated scaffolds with selective bioactivity, and phase contrast microscopy images were used to show specific localization of cells in the regions patterned with bioactive PEG. The use of multi-material SL and the relative ease of conjugating different bioactive ligands or growth factors to PEG allows for the fabrication of tailored three-dimensional constructs with specified spatially-controlled bioactivity.Mechanical Engineerin

Hydrogels in Stereolithography

The use of stereolithography (SL) for fabricating complex three-dimensional (3D) tissue engineered scaffolds of aqueous poly(ethylene glycol) (PEG) hydrogel solutions is described. The primary polymer used in the study was PEG-dimethacrylate (PEG-dma) with an average molecular weight (MW) of 1000 in distilled water with the photoinitiator Irgacure 2959 (I-2959). Successful layered manufacturing (LM) with embedded channel architecture required investigation of the photopolymerization characteristics of the PEG solution (measured as hydrogel thickness or cure depth) as a function of photoinitiator concentration and laser energy dosage for a specific photoinitiator type and polymer concentration in solution. Hydrogel thickness was a strong function of PI concentration and energy dosage. Curves of hydrogel thickness were utilized to successfully plan, perform, and demonstrate layered manufacturing of highly complex hydrogel scaffold structures, including structures with internal channels of various orientations. Successful fabrication of 3D, multi-layered bioactive PEG scaffolds containing cells was accomplished using a slightly modified commercial SL system (with 325 nm wavelength laser) and procedure. Human dermal fibroblast (HDF) cells were encapsulated in PEG hydrogels using small concentrations (~ 5 mg/ml) of acryloyl-PEG-RGDS (MW 3400) added to the photopolymerizable PEG solution to promote cell attachment. HDF cells were combined with the PEG solution, photocrosslinked using SL, and successfully shown to survive the fabrication process. The combined use of SL and photocrosslinkable biomaterials such as PEG makes it possible to fabricate complex 3D scaffolds that provide site-specific and tailored mechanical properties (i.e., multiple polymer materials) with a polymer matrix that allows transport of nutrients and waste at the macroscale and facilitates cellular processes at the microscale through precisely placed bioactive agents.Mechanical Engineerin

Assessment and Applications of the Conversion of Chemical Energy to Mechanical Energy Using Model Rocket Engines

To provide the first-year engineering students with a hands-on experience in an engineering application using both chemistry and physics, this team project uses a set of chemical and physical energy concepts and MS Excel based analysis. The main objective of the project is to calculate how much of the potential maximum possible chemical energy is converted into propulsion when using model rocket engines with solid fuel. The secondary objective is to determine the effects of increasing conversion rates on the performance of a model rocket. The solid fuel or propellant used in common model rocket engines is black powder. Compared to composite and hybrid engines, engines with black powder are cheaper and easier to ignite. Affordability of this propellant has made it possible to test fire many engines of different sizes. In addition, solid model rocket engines provide a good analogy to solid rocket boosters used in some of today’s launch vehicles. Rockets are momentum engines, thus, it is unusual to consider them in terms of energy, but energy is felt by observers even in model rocket launches. Total impulse is the measure of momentum imparted to the vehicle and depends on several processes including the chemical energy of the propellant and the useful kinetic energy of the exhaust. The project centers around calculation of the total energy released by the combustion of the reactants in model rocket engines of various types (A through F). The propulsion energy is a small fraction of the total energy released during combustion where a significant part of the total is lost heat. Many students enjoyed this activity as they learned how to code several sets of chemical balance and physical energy equations using MS Excel. Each team wrote a detailed technical report that explains the overall project. They used field pictures and the graphs to illustrate various parts of the project. They also included an essay on alternative propulsion means to explore the outer Solar system and beyond. An anonymous learning survey was developed, implemented, and analyzed to assess the educational effect of this project. The survey results and anecdotal evidence show this was a good and a challenging learning experience that was also too demanding for some of the students

\u3ci\u3eCreating the Fleet Maker\u3c/i\u3e - Lessons Learned from the First Series of Workshops on Maker Concepts for Active Duty Personnel

The US Navy has supported research related to the 3D printing or Additive Manufacturing area for more than 20 years. More recently, efforts like the Print the Fleet initiative and Marine Makers are exploring ways to design and create solutions to future problems with the possibility of reducing maintenance costs, increasing equipment readiness, and improving combat effectiveness. The Creating the Fleet Maker project is an effort supported by the Navy and Marine Corps Science, Technology, Engineering and Mathematics Education, Outreach and Workforce Program of the Office of Naval Research. It examines the concept of making in order to develop skills for active duty personnel in 3D printing, computer aided design, and reverse engineering. As part of the Creating the Fleet Maker project, educational materials, and handson activities, based on STEM concepts, were developed for a 2-day workshop. During the first year of the project, a series of five workshops were delivered, with a total of 92 active activeduty sailors attending the workshops. This paper presents the lessons learned during the first series of workshops, including successes, challenges encountered, how these challenges were overcome, as well as areas for improvement as the project enters its second year. Results from the workshop assessments are very positive with the majority of sailors reporting an improvement in their knowledge of the concepts covered during the workshop, as well as in the skills for 3D printing, computer aided design, and reverse engineering. Furthermore, attendees reported interest in taking part in an extended version of the workshop or having it as part of their regular naval training

Fused Deposition Modeling of Polymethylmethacrylate for Use in Patient-Specific Reconstructive Surgery

facial reconstruction and as bone cement and antibiotic-impregnated spacers in orthopaedics. The polymerization of PMMA in-situ causes tissue necrosis and other complications due to the long surgical times associated with mixing and shaping the PMMA. PMMA is a thermoplastic acrylic resin suitable for extrusion in FDM thus 3D anatomical models can be fabricated prior to surgery directly from medical imaging data. The building parameters required for successful FDM fabrication with medical-grade PMMA filament (1/16”Ø) were developed using an FDM 3000. It was found that a liquefier and envelope temperature of 235ºC and 55ºC, respectively, as well as increasing the model feed rate by 60%, were necessary to properly and consistently extrude the PMMA filament. Scaffolds with different porosities and fabrication conditions (tip wipe frequency and layer orientation) were produced, and their compressive mechanical properties were examined. Results show that both the tip wipe frequency (1 wipe every layer or 1 wipe every 10 layers) and layer orientation (transverse or axial with respect to the applied compressive load) used to fabricate the scaffolds, as well as the porosity of the scaffold had an effect on the mechanical properties. The samples fabricated with the high tip frequency had a larger compressive strength and modulus (Compressive strength: 16 ± 0.97 vs. 13 ± 0.71 MPa, Modulus: 370 ± 14 vs. 313 ± 29 MPa, for samples fabricated in the transverse orientation with 1 tip wipe per layer or 1 tip wipe per 10 layers, respectively). Also, the samples fabricated in the transverse orientation had a larger compressive strength and modulus than the ones fabricated in the axial orientation (Compressive strength: 16±0.97 vs. 13±0.83 MPa, Modulus: 370±14 vs. 281±22 MPa, for samples fabricated with 1 tip wipe per layer, in the transverse and axial orientation, respectively). Overall, the compressive strain for the samples fabricated with the four different conditions ranged from 8 – 12%. In regards to the porosity of the samples, in general, the stiffness, yield strength and yield strain decreased when the porosity increased (Compressive strength: 12±0.71 – 7±0.95 MPa, Modulus: 248±10 – 165±16 MPa, Strain: 7±1.5 – 5±1% for samples with a porosity ranging from 55 – 70%). The successful FDM fabrication of patient-specific, 3D PMMA implants with varying densities, including the model of a structure to repair a cranial defect and the model of a femur, was demonstrated. This work shows that customized structures with varying porosities to achieve tailored properties can be designed and directly fabricated using FDM and PMMA.Mechanical Engineerin

Impact of Bioinspired Robots on Veterans Pursuing STEM Degrees

The gap in the area of advanced manufacturing skilled workforce and the efforts in guiding veterans towards STEM careers are merged in the NSF funded project presented in this paper. While most of the products and STEM educational programs focused on a maker concept that are currently available are specifically designed for young population, at various K-12 grade levels, to increase their interest in STEM and engineering careers in particular, there is a limited availability of such programs to address adult population. The study presented in this paper focuses on developing and implementing a series of workshops for veterans, using bio-inspired robots as a learning platform. The design, making and controlling of bio-inspired robots require knowledge of mechanical, electrical, computer, and material science engineering, and have the potential to spark interest in a wide variety of engineering pathways. The paper discusses the topics covered by the workshops, the scaffolding of the activities, and the assessment conducted on how the bio-inspired robotics activities may influence veterans’ attitude towards advanced manufacturing careers

Active Duty Training For Support of Navy\u27s Additive Manufacturing Strategy

Additive manufacturing has recently gained the attention of multiple stakeholders, including those in the advanced manufacturing industry, research and government labs, academia, and the Navy community. Various efforts within the Navy focus on studying the best way for parts to be built and repaired for marine and naval vessels. Rapid manufacturing of spare components is particularly important for sailors, especially while deployed on warships, as they often do not have timely access to spare parts from the supply chain. For that purpose, a multidisciplinary team of engineering and education faculty have developed a series of workshops to train on-duty sailors in designing, testing, reverse engineering, and printing parts needed for their daily operations. The workshop has modules focused on rapid prototyping, reverse engineering, computer aided design, material testing, product data management, and product lifecycle management. The Office of Naval Research Workforce Development program funds this program

DeapSECURE Computational Training for Cybersecurity: Third-Year Improvements and Impacts

The Data-Enabled Advanced Training Program for Cybersecurity Research and Education (DeapSECURE) was introduced in 2018 as a non-degree training consisting of six modules covering a broad range of cyberinfrastructure techniques, including high performance computing, big data, machine learning and advanced cryptography, aimed at reducing the gap between current cybersecurity curricula and requirements needed for advanced research and industrial projects. By its third year, DeapSECURE, like many other educational endeavors, experienced abrupt changes brought by the COVID-19 pandemic. The training had to be retooled to adapt to fully online delivery. Hands-on activities were reformatted to accommodate self-paced learning. In this paper, we describe and assess the third and fourth years of the project and compare them with the first half of the project, which implemented in-person instruction. We also indicate major improvements and present future opportunities for this training program to advance the cybersecurity field

Learning in Informal Environments Through Engineering Activities Through the Partnership with the Girl Scouts

More affordable and portable robots have enabled easier access for outreach activities to happen in different environments. However, exposure to robotics often relies on seeing robots in action, such as industrial robotics and robots that are used for research purposes. Old Dominion University’s College of Engineering and Technology in Norfolk, Virginia recently signed a partnership agreement with the Girl Scouts of Colonial Coast as one of the focused outreach strategies that target the female population. Various events are held on campus in the Hampton Roads residential area located in the southeastern United States, which has a population of around 2 million people. Through this method, elementary age girls can be exposed to engineering content by attending events that are held on the university campus and lead by faculty along with graduate and undergraduate students. This paper showcases one such learning activity through an informal setting activity designed for the K-5 elementary grade levels. In this case, Girl Scouts in the following groups: Daisies, Brownies, and Juniors. Similar activities can be delivered on any other college campus that offers majors related to the area of mechanical engineering / mechanical engineering technology; civil engineering / civil engineering technology; and electrical engineering / electrical engineering technology

DeapSECURE Computational Training for Cybersecurity Students: Improvements, Mid-Stage Evaluation, and Lessons Learned

DeapSECURE is a non-degree computational training program that provides a solid high-performance computing (HPC) and big-data foundation for cybersecurity students. DeapSECURE consists of six modules covering a broad spectrum of topics such as HPC platforms, big-data analytics, machine learning, privacy-preserving methods, and parallel programming. In the second year of this program, to improve the learning experience, we implemented a number of changes, such as grouping modules into two broad categories, big-data and HPC ; creating a single cybersecurity storyline across the modules; and introducing post-workshop (optional) hackshops. Two major goals of these changes are, firstly, to effectively engage students to maintain high interest and attendance in such a non-degree program, and, secondly, to increase knowledge and skill acquisition. To assess the program, and in particular the changes made in the second year, we evaluated and compared the execution and outcomes of the training in Year 1 and Year 2. The assessment data shows that the implemented changes have partially achieved our goals, while simultaneously providing indications where we can further improve. The development of a fully on-line training mode is planned for the next year, along with a reproducibility pilot study to broaden the subject domain from cybersecurity to other areas, such as computations with sensitive data