Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Development of a synthetic small calibre vascular bypass graft

Polyurethanes are an attractive class of material for bioprosthesis development due to the ability to manipulate their elasticity and strength. However, their use as long term biological implants is hampered by biodegradation. A novel polyurethane has been developed which incorporates nano-engineered polyhedral oligomeric silsesquioxane within poly(carbonate-urea) urethane to improve the biostability of the latter. Previous investigators have found this material to be cytocompatible and to have low thrombogenicity. The medium and long term clinical results of currently available prosthetic small calibre vascular bypass grafts are poor, due to neo-intimal hyperplasia associated with their non-compliant properties. The investigation reported here commences with the benchtop manufacture of compliant small calibre grafts using an original extrusion- phase inversion technique. The reproducibility of the technique as well as the effect on the pore structure of different coagulation conditions is demonstrated. Fundamental mechanical characterisation of the grafts produced is then presented, by way of tensillometry to demonstrate the viscous and elastic properties of the material. These are made more relevant to the clinical setting with functional mechanical characterisation of the grafts, showing graft compliance in a biomimetic flow circuit along with viscoelastic hysteresis, along with burst pressure testing. An examination of burst pressure testing methodology is also shown, in the light of the various non-standardised strategies reported in the graft-testing literature. Mechanical characterisation shows the short-term safety for use, but durability studies in the biological haemodynamic environment serve to assess longer term fatigability as well as confirming biostability. This has been reported using a stringent ovine carotid interposition model which remained patent over the full investigation period representing at least 45 million pulsatile cycles. Physico-chemical analysis; integrity of the structure, microstructure and ultrastructure; preservation of mechanical properties and immunohistological analysis were used to examine the grafts after implantation to show their healing properties and biostability

Direct Laser Writing of Proteins and Synthetic Photoresists for Neuronal Cell Growth Guidance

In vitro cell culture platforms are important tools for the study of neural functions in health and disease. The formation of controlled neuronal networks increases the robustness of the results, which facilitates the transition of the results to in vivo. Controlled cell growth on predefined axes can be achieved via chemical or topographical cues, such as the microscale patterns of celladhesive peptides or physically confining 3D microstructures. Computer-assisted laser-based fabrication techniques such as direct laser writing by two-photon polymerization (2PP-DLW) offer a versatile tool to fabricate such controlled cell culture platforms with highly ordered geometries in the size scale of natural 3D cell environments. 2PP-DLW is a sequential fabrication technique based on the phenomenon of two-photon absorption (2PA) by photoinitiator molecules, which initiates radical chain-growth polymerization that converts small, unsaturated monomer molecules from a liquid state to solid macromolecules. The 2PP-DLW technique allows the fabrication of complex features including internal walls, overhangs, or tortuous channels with feature sizes in the µm and sub-µm range.In this thesis, 2PP-DLW was used to fabricate microscale chemical and topographical guidance cues for neuronal cells. The main goal was to find appropriate photosensitive materials for the microstructures, to optimize the 2PP-DLW processing parameters for different materialphotoinitiator combinations, and to design and fabricate several novel microstructures to be tested with human pluripotent stem cell (hPSC)-derived neuronal cells. As hPSCs can be differentiated into several cell types, such as neurons, astrocytes, and oligodendrocytes, they offer a promising cell source for cell culture models. Overall, four different custom-built 2PP-DLW fabrication setups based on either Nd:YAG or Ti:sapphire lasers were used for the polymerization experiments. First, the processability of photosensitive custom-synthetized methacrylated poly(caprolactone) oligomer (PCL-o) and commercial poly(ethylene glycol)diacrylate (PEGda) were studied together with Irgacure®127 photoinitiator. Although both PCL-o and PEGda could be successfully fabricated into simple microstructures with a picosecond Nd:YAG laser, the PCL-o required the use of very slow scanning speed in order to achieve complete polymerization. Thus, it was concluded that the fabrication of larger or more complex structures from PCL-o was not feasible. The inability of PEGda and PCL-o to support the migration or functionality of neuronal cells make them therefore poor candidates for cell culture purposes.Next, avidin and biotinylated bovine serum albumin (bBSA) proteins together with flavin mononucleotide (FMN) photosensitizer were fabricated into surface patterns using several protein concentrations in combination with different average laser power and scanning speed values to determine the range of fabrication conditions suitable for protein crosslinking. It was demonstrated that the bioactivity of proteins is retained during the exposure to the high laser intensities required for photocrosslinking with the Nd:YAG laser. Avidin and bBSA together with Irgacure® 2959 photoinitiator were also photocrosslinked into 2D single neuron guidance patterns, functionalized ii with extracellular matrix-derived peptides, and used for the study of cell growth guidance with hPSC-derived neuronal cells for 14 days. As several difficulties were encountered during the fabrication of the protein patterns and cell culture experiment, proteins were excluded from any further studies and replaced with the commercially available hybrid polymer-ceramic Ormocomp® that possesses superior photocrosslinking properties.Ormocomp® combined with Irgacure®127 was fabricated into 3D confinement microstructures and 3D tubular microtowers with or without intraluminal guidance cues. The applicability of the confinement structures to control the location of neurons and to direct the growth of neurites on predefined axes was evaluated during the cell culture experiments. The functionality of three different microtower designs for the long-term 3D culturing of human neuronal cells and their ability to orient neurites was assessed with a four-week cell culture study. The observations achieved in this thesis support the use of the microtower-based platform for long-term cell culture as the microtowers were proven to facilitate neurite orientation and 3D network formation via suspended neurite bridges. Thus, the proposed microstructure-based culturing concept could in future be used as a substitute for the hydrogel matrices commonly used to mechanically support the formation of 3D cell networks

Direct Laser Writing of Proteins and Synthetic Photoresists for Neuronal Cell Growth Guidance

In vitro cell culture platforms are important tools for the study of neural functions in health and disease. The formation of controlled neuronal networks increases the robustness of the results, which facilitates the transition of the results to in vivo. Controlled cell growth on predefined axes can be achieved via chemical or topographical cues, such as the microscale patterns of celladhesive peptides or physically confining 3D microstructures. Computer-assisted laser-based fabrication techniques such as direct laser writing by two-photon polymerization (2PP-DLW) offer a versatile tool to fabricate such controlled cell culture platforms with highly ordered geometries in the size scale of natural 3D cell environments. 2PP-DLW is a sequential fabrication technique based on the phenomenon of two-photon absorption (2PA) by photoinitiator molecules, which initiates radical chain-growth polymerization that converts small, unsaturated monomer molecules from a liquid state to solid macromolecules. The 2PP-DLW technique allows the fabrication of complex features including internal walls, overhangs, or tortuous channels with feature sizes in the µm and sub-µm range.In this thesis, 2PP-DLW was used to fabricate microscale chemical and topographical guidance cues for neuronal cells. The main goal was to find appropriate photosensitive materials for the microstructures, to optimize the 2PP-DLW processing parameters for different materialphotoinitiator combinations, and to design and fabricate several novel microstructures to be tested with human pluripotent stem cell (hPSC)-derived neuronal cells. As hPSCs can be differentiated into several cell types, such as neurons, astrocytes, and oligodendrocytes, they offer a promising cell source for cell culture models. Overall, four different custom-built 2PP-DLW fabrication setups based on either Nd:YAG or Ti:sapphire lasers were used for the polymerization experiments. First, the processability of photosensitive custom-synthetized methacrylated poly(caprolactone) oligomer (PCL-o) and commercial poly(ethylene glycol)diacrylate (PEGda) were studied together with Irgacure®127 photoinitiator. Although both PCL-o and PEGda could be successfully fabricated into simple microstructures with a picosecond Nd:YAG laser, the PCL-o required the use of very slow scanning speed in order to achieve complete polymerization. Thus, it was concluded that the fabrication of larger or more complex structures from PCL-o was not feasible. The inability of PEGda and PCL-o to support the migration or functionality of neuronal cells make them therefore poor candidates for cell culture purposes.Next, avidin and biotinylated bovine serum albumin (bBSA) proteins together with flavin mononucleotide (FMN) photosensitizer were fabricated into surface patterns using several protein concentrations in combination with different average laser power and scanning speed values to determine the range of fabrication conditions suitable for protein crosslinking. It was demonstrated that the bioactivity of proteins is retained during the exposure to the high laser intensities required for photocrosslinking with the Nd:YAG laser. Avidin and bBSA together with Irgacure® 2959 photoinitiator were also photocrosslinked into 2D single neuron guidance patterns, functionalized ii with extracellular matrix-derived peptides, and used for the study of cell growth guidance with hPSC-derived neuronal cells for 14 days. As several difficulties were encountered during the fabrication of the protein patterns and cell culture experiment, proteins were excluded from any further studies and replaced with the commercially available hybrid polymer-ceramic Ormocomp® that possesses superior photocrosslinking properties.Ormocomp® combined with Irgacure®127 was fabricated into 3D confinement microstructures and 3D tubular microtowers with or without intraluminal guidance cues. The applicability of the confinement structures to control the location of neurons and to direct the growth of neurites on predefined axes was evaluated during the cell culture experiments. The functionality of three different microtower designs for the long-term 3D culturing of human neuronal cells and their ability to orient neurites was assessed with a four-week cell culture study. The observations achieved in this thesis support the use of the microtower-based platform for long-term cell culture as the microtowers were proven to facilitate neurite orientation and 3D network formation via suspended neurite bridges. Thus, the proposed microstructure-based culturing concept could in future be used as a substitute for the hydrogel matrices commonly used to mechanically support the formation of 3D cell networks

The Transmission Electron Microscope

The book "The Transmission Electron Microscope" contains a collection of research articles submitted by engineers and scientists to present an overview of different aspects of TEM from the basic mechanisms and diagnosis to the latest advancements in the field. The book presents descriptions of electron microscopy, models for improved sample sizing and handling, new methods of image projection, and experimental methodologies for nanomaterials studies. The selection of chapters focuses on transmission electron microscopy used in material characterization, with special emphasis on both the theoretical and experimental aspect of modern electron microscopy techniques. I believe that a broad range of readers, such as students, scientists and engineers will benefit from this book

Design and fabrication of biocompatible scaffolds for the regeneration of tissues

Regenerative medicine and tissue engineering attempt to repair or improve the biological functions of tissues that have been damaged or have ceased to perform their role through three main components: a biocompatible scaffold, cellular component and bioactive molecules. Nanotechnology provide a toolbox of innovative scaffold fabrication procedures in regenerative medicine. In fact, nanotechnology, using manufacturing techniques such as conventional and unconventional lithography, allows fabricating supports with different geometries and sizes as well as displaying physical chemical properties tunable over different length scales. Soft lithography techniques allow to functionalize the support by specific molecules that promote adhesion and control the growth of cells. Understanding cell response to scaffold, and viceversa, is a key issue; here we show our investigation of the essential features required for improving the cell-surface interaction over different scale lengths. The main goal of this thesis has been to devise a nanotechnology-based strategy for the fabrication of scaffolds for tissue regeneration. We made four types of scaffolds, which are able to accurately control cell adhesion and proliferation. For each scaffold, we chose properly designed materials, fabrication and characterization techniques

Index to 1983 NASA Tech Briefs, volume 8, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1983 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences