System integration and demonstration of adhesive bonded high temperature aluminum alloys for aerospace structure, phase 2

Adhesive bonding materials and processes were evaluated for assembly of future high-temperature aluminum alloy structural components such as may be used in high-speed civil transport aircraft and space launch vehicles. A number of candidate high-temperature adhesives were selected and screening tests were conducted using single lap shear specimens. The selected adhesives were then used to bond sandwich (titanium core) test specimens, adhesive toughness test specimens, and isothermally aged lap shear specimens. Moderate-to-high lap shear strengths were obtained from bonded high-temperature aluminum and silicon carbide particulate-reinforced (SiC(sub p)) aluminum specimens. Shear strengths typically exceeded 3500 to 4000 lb/in(sup 2) and flatwise tensile strengths exceeded 750 lb/in(sup 2) even at elevated temperatures (300 F) using a bismaleimide adhesive. All faceskin-to-core bonds displayed excellent tear strength. The existing production phosphoric acid anodize surface preparation process developed at Boeing was used, and gave good performance with all of the aluminum and silicon carbide particulate-reinforced aluminum alloys investigated. The results of this program support using bonded assemblies of high-temperature aluminum components in applications where bonding is often used (e.g., secondary structures and tear stoppers)

The effects of aircraft fuel and fluids on the strength properties of Resin Transfer Molded (RTM) composites

The resin transfer molding (RTM) process offers important advantages for cost-effective composites manufacturing, and consequently has become the subject of intense research and development efforts. Several new matrix resins have been formulated specifically for RTM applications in aircraft and aerospace vehicles. For successful use on aircraft, composite materials must withstand exposure to the fluids in common use. The present study was conducted to obtain comparative screening data on several state-ofthe-art RTM resins after environmental exposures were performed on RTM composite specimens. Four graphite/epoxy composites and one graphite/bismaleimide composite were tested; testing of two additional graphite epoxy composites is in progress. Zero-deg tension tests were conducted on specimens machined from eight-ply (+45-deg, -45-deg) laminates, and interlaminar shear tests were conducted on 32-ply 0-deg laminate specimens. In these tests, the various RTM resins demonstrated widely different strengths, with 3501-6 epoxy being the strongest. As expected, all of the matrix resins suffered severe strength degradation from exposure to methylene chloride (paint stripper). The 3501-6 epoxy composites exhibited about a 30 percent drop in tensile strength in hot, wet tests. The E905-L epoxy exhibited little loss of tensile strength (less than 8 percent) after exposure to water. The CET-2 and 862 epoxies as well as the bismaleimide exhibited reduced strengths at elevated temperature after exposure to oils and fuel. In terms of the percentage strength reductions, all of the RTM matrix resins compared favorably with 3501-6 epoxy

Resin transfer molding of textile composites

The design and manufacture of textile composite panels, tubes, and angle sections that were provided to NASA for testing and evaluation are documented. The textile preform designs and requirements were established by NASA in collaboration with Boeing and several vendors of textile reinforcements. The following four types of preform architectures were used: stitched uniweave, 2D-braids, 3D-braids, and interlock weaves. The preforms consisted primarily of Hercules AS4 carbon fiber; Shell RSL-1895 resin was introduced using a resin transfer molding process. All the finished parts were inspected using ultrasonics

Three-dimensional in vitro follicle growth: overview of culture models, biomaterials, design parameters and future directions

In vitro ovarian follicle culture is a new frontier in assisted reproductive technology with tremendous potential, especially for fertility preservation. Folliculogenesis within the ovary is a complex process requiring interaction between somatic cell components and the oocyte. Conventional two-dimensional culture on tissue culture substrata impedes spherical growth and preservation of the spatial arrangements between oocyte and surrounding granulosa cells. Granulosa cell attachment and migration can leave the oocyte naked and unable to complete the maturation process. Recognition of the importance of spatial arrangements between cells has spurred research in to three-dimensional culture system. Such systems may be vital when dealing with human primordial follicles that may require as long as three months in culture. In the present work we review pertinent aspects of in vitro follicle maturation, with an emphasis on tissue-engineering solutions for maintaining the follicular unit during the culture interval. We focus primarily on presenting the various 3-dimensional culture systems that have been applied for in vitro maturation of follicle:oocyte complexes. We also try to present an overview of outcomes with various biomaterials and animal models and also the limitations of the existing systems

Three dimensional culture of fresh and vitrified mouse pre-antral follicles in a hyaluronan-based hydrogel: a preliminary investigation of a novel biomaterial for in vitro follicle maturation

Abstract Background Folliculogenesis within the ovary requires interaction between somatic cell components and the oocyte. Maintenance of 3-dimensional (3-D) architecture and granulosa-oocyte interaction may be critical for successful in vitro maturation of follicles. Testing of novel biomaterials for the 3-D culture of follicles may ultimately lead to a culture model that can support the longer in vitro culture intervals needed for in vitro maturation of human oocytes from ovarian tissue biopsies. Methods A novel tyramine-based hyaluronan (HA) hydrogel was tested for its biocompatibility with ovarian follicles. The HA was prepared at concentrations from 2 to 5 mg/ml. HA hydrogel was also formulated and tested with matrix proteins (ECM). Enzymatically isolated pre-antral follicles from the ovaries of 10–12 day SJL pups were divided amongst control (CT) and HA treatments. The growth of both fresh and vitrified follicles was assessed after encapsulation in the hydrogel. The basal culture medium was MEM alpha supplemented with FSH, LH, ITS and 5% FBS. Maturation was triggered by addition of hCG and EGF after in vitro culture (IVC). Outcome parameters monitored were follicle morphology, survival after IVC, antrum formation, GVBD and MII formation. Differences between treatments were analyzed. Results HA and ECM-HA encapsulated follicles looked healthy and maintained their 3-D architecture during IVC. In control cultures, the follicles flattened and granulosa:oocyte connections appeared fragile. Estradiol secretion per follicle was significantly higher by Day 12 in ECM-HA compared to HA or CT (4119, 703 and 1080 pg/ml, respectively). HA and ECM-HA cultured follicles had similar survival rates (62% and 54%, respectively), percent GV breakdown (96–97%), MII formation (47–48%) and oocyte diameters at the end of IVC. Control cultures differed significantly in percent GVBD (85%) and MII formation (67%) . Vitrified-warmed follicles encapsulated in HA had an oocyte maturation rate to MII of 54% as compared to 57% in non-embedded follicles. Conclusions Initial testing of this new and unique HA-based hydrogel was quite promising. The ease of follicle encapsulation in HA, its optical transparency and ability to be molded combined with its support of follicle growth, estradiol secretion and resumption of meiosis make this HA-hydrogel particularly attractive as model for 3-D ovarian follicle culture.</p