Development and implementation of a custom program for post hoc strain tracking in biological specimens using cross-correlation - biomed 2011.

The research presented describes the development of a custom MATLAB® program designed to examine changes in surface strain based on digital image tracking, a technique that employs markerless tracking to access regional displacement in digital images. Strain tracking is accomplished through the analysis of successive images taken during testing using a dedicated black and white camera incorporated into a tensile testing system. In the tracking program a 2-D array of grid points is mapped on the initial image from a test. Each grid point consists of a pixel array (a sub-image corresponding to a “marker”) which is then compared to consecutive images to determine the new grid point placement using cross correlation. By analyzing marker position post hoc, the number of grid points, the size of the sub-pixel array, and the spacing (longitudinal and/or regional) between grid points can be varied to account for differences in observed responses. Digital strain tracking allows for a test to be reanalyzed and eliminates the need to affix markers in specified patterns to a sample prior to testing. The new “markerless” tracking approach has been compared to the classic procedure of applying physical surface markers for tracking strain, to determine the accuracy of this technique. Preliminary testing revealed that adding texture to the specimen may be necessary (especially for low texture samples like tendons and ligaments), through the use of glitter derivatives, to increase visual contrast between multiple grid points.

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 > or = 4 for all groups) and cell viability (n > or = 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.

Collagen composite biomaterials resist contraction while allowing development of adipocytic soft tissue in vitro.

Soft tissue defects resulting from tumor resection or trauma require surgery to restore the body's contours. Because autologous tissues or synthetic implant reconstructions can be less than ideal, engineered tissues produced in vitro are being developed as alternatives. Collagen gels have been proposed for this application because they are biocompatible and can be shaped to fill a specific defect. In the present study, constructs of collagen gels with embedded short collagen fibers (which are more permeable than plain collagen gels and which maintain size and shape in culture) were seeded with preadipocytes and cultured in vitro. The addition of increasing volume fractions of embedded fibers limited cell-mediated contraction of the constructs. Including epithelial cell-seeded collagen gel layers resulted in more contraction, but still less than that observed in constructs without fibers. Constructs with embedded collagen fibers contained significantly more cells at all time points examined when compared to constructs without embedded fibers. Mature adipocytes were observed throughout constructs after 21 days in culture; spectroscopic analyses indicated lipid inclusion in constructs seeded with preadipocytes, which differed from analyses of natural porcine adipose tissue. These results support the promise of collagen composites as a biomaterial for use in producing soft tissues in vitro.

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.

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.

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.

Examining 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.