Eric A. Nauman

Mechanical Characterization of Collagen Fibers and Scaffolds for Tissue Engineering

Engineered tissues must utilize scaffolding biomaterials that support desired cellular functions and possess or can develop appropriate mechanical characteristics. This study assessed properties of collagen as a scaffolding biomaterial for ligament replacements. Mechanical properties of extruded bovine achilles tendon collagen fibers were significantly affected by fiber diameter, with smaller fibers displaying higher tangent moduli and peak stresses. Mechanical properties of 125 micrometer-diameter extruded fibers (tangent modulus of 359.6+/-28.4MPa; peak stress of 36.0+/-5.4MPa) were similar to properties reported for human ligaments. Scaffolds of extruded fibers did not exhibit viscoelastic creep properties similar to natural ligaments. Collagen fibers from rat tail tendon (a well-studied comparison material) displayed characteristic strain-softening behavior, and scaffolds of rat tail fibers demonstrated a non-intuitive relationship between tangent modulus and specimen length. Composite scaffolds (extruded collagen fibers cast within a gel of Type I rat tail tendon collagen) were maintained with and without fibroblasts under standard culture conditions for 25 days; cell-incorporated scaffolds displayed significantly higher tangent moduli and peak stresses than those without cells. Because tissue-engineered products must possess appropriate mechanical as well as biological/chemical properties, data from this study should help enable the development of improved tissue analogues.

Research report: learning styles of biomedical engineering students.

AbstractExamining students’ learning styles can yield information useful to the design of learning activities, courses, and curricula. A variety of measures have been used to characterize learning styles, but the literature contains little information specific to biomedical engineering (BMEN) students. We, therefore, utilized Felder’s Index of Learning Styles to investigate the learning style preferences of BMEN students at Tulane University. Tulane BMEN students preferred to receive information visually (preferred by 88% of the student sample) rather than verbally, focus on sensory information (55%) instead of intuitive information, process information actively (66%) instead of reflectively, and understand information globally (59%) rather than sequentially. These preferences varied between cohorts (freshman, sophomore, etc.) and a significantly higher percentage of female students preferred active and sensing learning styles. Compared to other engineering student populations, our sample of Tulane BMEN students contained the highest percentage of students preferring the global learning style. Whether this is a general trend for all BMEN students or a trait specific to Tulane engineers requires further investigation. Regardless, this study confirms the existence of a range of learning styles within biomedical engineering students, and provides motivation for instructors to consider how well their teaching style engages multiple learning styles.

Differential phenotypic characteristics of heterogeneous cell population in the rabbit periosteum

Background Periosteum and periosteum-derived progenitor cells have demonstrated the potential for stimulative applications in repair of various musculoskeletal tissues. It has been found that the periosteum contains mesenchymal progenitor cells that are capable of differentiating into either osteoblasts or chondrocytes, depending on the culture conditions. Anatomically, the periosteum is a heterogeneous multilayered membrane, consisting of an outer fibrous and an inner cambium layer. The present study was designed to elucidate the phenotypic characteristics of fibrous and cambium layer cells in vitro. Methods Using a sequential enzymatic digestion method, fibrous and cambium layer cells were harvested separately from periosteum-bone explants of the proximal tibia of 6-month-old New Zealand White rabbits. Results We found that the cells from each layer showed distinct phenotypic characteristics in a primary monolayer culture system. Specifically, the cambium cells demonstrated higher osteogenic characteristics (higher alkaline phosphatase and osteocalcin levels) than the fibrous cells. However, these differences diminished with time in vitro. Interpretation Our findings suggest that the periosteum has phenotypically distinct heterogeneous cell populations. Care must be taken in order to identify and distinguish the intrinsic phenotypes of the heterogeneous periosteum-derived cell types in vitro.

A Device for Long Term, In Vitro Loading of Three-Dimensional Natural and Engineered Tissues

AbstractIn vitro studies of mechanical loads applied to three-dimensional tissue constructs are important to the design and production of functional, engineered bone tissue. This study reports the development and characterization of a mechanical device capable of subjecting a three-dimensional section of natural or engineered tissue to precise, reproducible four-point bending deformations over a range of programmable magnitudes and frequencies. To test the biological and mechanical capabilities of the system, a low-cycle (360 cycles/day), medium-range strain (2500 microstrain), long-term (16 day) loading regime was applied to rat bone marrow stromal cells cultured in porous DL-polylactic acid scaffolds. Cells proliferated in culture throughout the experiment, and with time showed an increase in alkaline phosphatase expression per cell. Calcium and phosphorus mineral deposition by the unloaded group was significantly greater (p < 0.05) than that deposited by the loaded group. The molar ratio of calcium to phosphorus in the unloaded group (0.94:1) was significantly greater (p < 0.05) than that of the loaded group (0.41:1). The loading device presented here is a tool which can be used to help elucidate contributions of mechanical loading/fatigue on biodegradable materials, as well as study the effects of mechanical loading on natural or engineered tissues in vitro.

Development and Application of a Combined Imaging and Modeling Technique for Determining Biomechanical Response of Roller Coaster Passengers

Roller Coasters are one of the most popular amusement devices in use throughout the world. In their most basic form, roller coasters consist of a track system in which a car or train rolls under the force of gravity. The major design constraints of roller coasters are determined by the level of force and acceleration that the human body can safely withstand. These forces are commonly measured in multiples of the Earth’s gravitational acceleration, and are termed “G” forces.© 2002 ASME