Glen A. Livesay

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.

Peak Torque and Rotational Stiffness Developed at the Shoe-Surface Interface The Effect of Shoe Type and Playing Surface

Background Shoe-surface interactions have been implicated in the high number of noncontact knee injuries suffered by athletes at all levels. Purpose To examine shoe-surface interactions on newer field designs and compare these with more traditional shoe-surface combinations. The peak torque and rotational stiffness (the rate at which torque is developed under rotation) were determined. Study Design Controlled laboratory study. Methods A device was constructed to measure the torque versus applied rotation developed between different shoe-surface combinations. Data were collected on 5 different playing surfaces (natural grass, Astroturf, 2 types of Astroplay, and FieldTurf), using 2 types of shoes (grass and turf), under a compressive load of 333 N. Results The highest peak torques were developed by the grass shoe–FieldTurf tray and the turf shoe–Astroturf field combinations. The lowest peak torques were developed on the grass field. The turf shoe–Astroturf combination exhibited a rotational stiffness nearly double that of any other shoe-surface combinations. Conclusion The differences in the rotational stiffness across all 10 shoe-surface combinations were greater than those of the peak torques. It is possible that rotational stiffness may provide a new criterion for the evaluation of shoe-surface interface. Clinical Relevance An improved understanding of shoe-surface interactions remains a critical need to improve the design of shoe-surface combinations with the goal of meeting player needs while minimizing injury potential.

Development of Ligament-Like Structural Organization and Properties in Cell-Seeded Collagen Scaffolds in vitro

Acute anterior cruciate ligament (ACL) injuries lead to poor joint function, instability, and eventually osteoarthritis if left untreated. Current surgical treatment options are not ideal; however, tissue engineering may provide mechanically sound, biocompatible reconstructions. Collagen fiber scaffolds were combined with fibroblast-seeded collagen gels and maintained in culture for up to 20 days. The tensile and viscoelastic behavior of the constructs closely mimicked that of natural ligament. Constructs’ mechanical and viscoelastic properties did not degrade over time in culture, and peak stress was significantly higher for constructs with embedded fibroblasts. Immunocytochemical and histological analyses demonstrated cell proliferation and ligament-like organization. We have created an engineered tissue that closely approaches key mechanical and viscoelastic properties of the ACL, does not degrade after 20 days in culture, and is histologically similar to the native tissue. This study should aid in developing effective treatments for ACL injury.

Short Collagen Fibers Provide Control of Contraction and Permeability in Fibroblast-Seeded Collagen Gels

Tissue engineering may allow for the reconstruction of breast, facial, skin, and other soft tissue defects in the human body. Cell-seeded collagen gels are a logical choice for creating soft tissues because they are biodegradable, mimic the natural tissue, and provide a three-dimensional environment for the cells. The main drawback associated with this approach, however, is the subsequent contraction of the gel by the constituent cells, which severely reduces permeability, initiates apoptosis, and precludes control of the resulting shape and size of the construct. In this study, type I collagen gels were seeded with fibroblasts and cast either with or without the addition of short collagen fibers. Gel contraction was monitored and permeability was assessed after 7 and 14 days in culture. The addition of short collagen fibers both significantly limited contraction and increased permeability of fibroblast-seeded collagen gels. The addition of short collagen fibers had no detrimental effect on cell proliferation, and there were a high number of viable fibroblasts in gels with fibers and gels without fibers. Gels containing short collagen fibers demonstrated permeabilities that were 100 to 1000 times greater than controls and also closely maintained their casting dimensions (never less than 96% of original). By limiting contraction and maintaining permeability, the incorporation of short collagen fibers should enable the creation of larger constructs by allowing for greater nutrient diffusion, and permit the creation of more complicated shapes during gel casting.

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.

Geometric morphometric analyses of hominid proximal femora: Taxonomic and phylogenetic considerations

The proximal femur has long been used to distinguish fossil hominin taxa. Specifically, the genus Homo is said to be characterized by larger femoral heads, shorter femoral necks, and more lateral flare of the greater trochanter than are members of the genera Australopithecus or Paranthropus. Here, a digitizing arm was used to collect landmark data on recent human (n=82), chimpanzee (n=16), and gorilla (n=20) femora and casts of six fossil hominin femora in order to test whether one can discriminate extant and fossil hominid (sensu lato) femora into different taxa using three-dimensional (3D) geometric morphometric analyses. Twenty proximal femoral landmarks were chosen to best quantify the shape differences between hominin genera. These data were first subjected to Procrustes analysis. The resultant fitted coordinate values were then subjected to PCA. PC scores were used to compute a dissimilarity matrix that was subjected to cluster analyses. Results indicate that one can easily distinguish Homo, Pan, and Gorilla from each other based on proximal femur shape, and one can distinguish Pliocene and Early Pleistocene hominin femora from those of recent Homo. It is more difficult to distinguish Early Pleistocene Homo proximal femora from those of Australopithecus or Paranthropus, but cluster analyses appear to separate the fossil hominins into four groups: an early australopith cluster that is an outlier from other fossil hominins; and two clusters that are sister taxa to each other: a late australopith/Paranthropus group and an early Homo group.

Operating curves to characterize the contraction of fibroblast-seeded collagen gel/collagen fiber composite biomaterials: effect of fiber mass.

Background: Collagen is a well-established and important biomaterial that could be used to help meet significant medical needs for various soft-tissue replacements. Many efforts to create engineered soft-tissue constructs by seeding cells within collagen gels have been hampered because constituent cells contract collagen gels over time, resulting in a construct that is only a fraction of the original size and that contains a cell population that has suffered a large degree of cell death. However, the presence of embedded short collagen fibers has been shown to significantly limit contraction and dramatically enhance permeability in fibroblast-seeded collagen gels. Methods: Five volume fractions of short collagen fibers were embedded in fibroblast-seeded collagen gels. Collagen gel contraction (n ≥ 4 for all groups) and cell viability (n ≥ 3 for all groups) were examined after up to 2 weeks in culture. Results: The present study demonstrated that increasing the volume fraction of short collagen fibers in fibroblast-seeded collagen gels correspondingly reduced the amount of gel contraction without negatively impacting cell viability after 2 weeks of culture. Furthermore, operating curves that describe the quantitative relationships between the contraction of fibroblast-seeded collagen gel/collagen fiber composite biomaterials, time in culture, and volume fraction of embedded fibers were obtained. Conclusion: The resulting operating curves enable investigators to tailor initial fabrication procedures to ultimately yield cell-seeded collagen composites of specifically desired sizes—a critical step toward developing clinically useful engineered soft-tissue constructs.

Work in progress — Rules of engagement: Student interest and learning in hands-on laboratory experiences

In order to evaluate the impact of hands-on experiences on student learning, the authors developed and delivered five one-hour supplemental learning sessions to a group of approximately 25 students over two consecutive years. During the sessions, student groups participated in a total of 16 hands-on activities, ranging in length from 5 to 20 minutes each. The primary objective of the activities was to emphasize concepts that students were learning about in a transport phenomena course. Pre- and post-testing indicated that during both years, the sessions helped students learn. In the second year, students were surveyed to attempt to elucidate causes for their engagement levels with the various activities. Student ratings of their interest in an activity and their perception of the learning value of an activity were usually positively correlated. Both student interest and student perception of learning values were positively correlated to improved scores from pre- to post-testing for activities.

Development of a New Device for In-Vitro Simulation of Upper Extremity Fractures

Upper extremity fractures are common among all age groups, and distal radius fractures are the most prevalent type of fracture among individuals younger than 75 [1]. In 1999 the US Consumer Product Safety Commission estimated that approximately 117,000 emergency room visits were the result of a fall event at a playground [2]. The increased popularity of activities such as inline skating, snowboarding and skateboarding in the aging population has been correlated with increased numbers of upper extremity fractures, as these activities have a high fracture risk [3]. While personal protective equipment such as wrist guards and elbow pads may alter fracture risk, little is known about fall biomechanics and the effects of a fall arrest on the upper extremity.Copyright

Functional Evaluation of Soft Tissue Insertions to Bone

Soft tissue insertions into bone are of critical importance in transmitting forces from ligaments and tendons to bone, and thus are crucial in joint stability and musculoskeletal motion. Despite their importance, there exists no established experimental method for rigorously determining their function. Previous studies [1–3] have established the pull-out test as the standard method of evaluating the mechanical function of soft-tissue insertions, however, as this method tests response at a single orientation it may not capture the overall function of soft-tissue insertions.Copyright