Biological Materials Science: Bones, Teeth and Dental Materials
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Biomaterials Committee
Program Organizers: Po-Yu Chen, National Tsing Hua University; Francois Barthelat, McGill University; Michael Porter, Clemson University; Steven Naleway, University of Utah

Tuesday 8:30 AM
February 28, 2017
Room: Pacific 15
Location: Marriott Marquis Hotel

Session Chair: Dwayne Arola, University of Washington; Michael Porter, Clemson University

8:30 AM  Invited
Improving the Performance of Dental Restorative Composites: Jamie Kruzic1; Dmytro Khvostenko2; Thomas Hilton3; Jack Ferracane3; John Mitchell4; 1UNSW Australia; 2Oregon State University; 3Oregon Health & Science University; 4Midwestern University
    While modern resin based dental restorative composites have excellent aesthetic properties, they generally have shortcomings that lead to premature failures, most commonly by secondary caries development or mechanical failure of the restoration. Strategies are needed to improve composite restoration durability without sacrificing the aesthetic properties. For mechanical performance, using a hierarchical structure of large reinforcements made from smaller nanoparticles shows promise. Fracture and fatigue crack growth experiments have demonstrated that toughening mechanisms can be achieved; however, challenges to improving mechanical performance include optimizing the microstructure morphology and getting adequate bonding of the nanoparticle agglomerate reinforcements to the resin matrix. In addition, to promote improved secondary caries resistance, composites containing bioactive glass (BAG) have been developed. Results demonstrate composites containing BAG have adequate mechanical properties and can slow bacterial biofilm penetration into gaps between the dentin and composite filling. Thus, composites containing BAG have potential to improve restoration lifetimes in vivo.

9:00 AM  
Multiscale Experiment and Computational Insight into Mechanical and Electromechanical Behavior of Collagen: Zhong Zhou1; Dong Qian1; Majid Minary2; 1University of Texas at Dallas; 2University of Texas at Dallas
    Majority of the current models of collagen assume a rod-shape molecule with homogenous mechanical properties. Recent X-ray crystallography revealed significantly different microstructures in the D-period of collagen microfibrils. We present the nanomechanics of hydrated collagen molecules through molecular dynamics simulations. The results reveal significant mechanical heterogeneity in individual collagen molecules. Additionally, we present an investigation on the molecular mechanism of piezoelectric effect in collagen using full atomistic simulation based on the experimentally verified “super-twisted” microstructure of collagen. This effect in collagen is distinctly different from organic piezoelectric crystals, given the semicrystalline molecular structure of the collagen biopolymer. Our results reveal that collagen exhibits a uniaxial polarization along the long axis of the collagen fibril. In addition, the piezoelectric effect in collagen originates at the collagen molecule level and is due to the mechanical stress-induced reorientation and magnitude change of the permanent dipoles of individual charged and polar residues.

9:20 AM  Cancelled
Nanofibrous Composites Enriched with Growth Factors for Tendon-bone Interface Regeneration: Ece Bayrak1; Burak Ozcan1; Cevat Erisken1; 1TOBB University of Economics and Technology
    Tendon injuries are among the most common trauma (>250,000/year tendon repairs performed in the US[1]). Tendon reconstruction grafts often fail to reestablish native structure, leading to recurrence rates upto 90%[2]. Objectives are; 1)fabricate PCL-based scaffolds containing TGF-β3, CTGF and nano-HA, where concentrations of CTGF and nHA change gradually, while TGF-β3 is located in the middle of the nanofibrous composites, 2)investigate stem cell behavior on these scaffolds. This design, proposed for the first time, represents a significant departure from the conventional approach, and is expected to contribute to interface regeneration. Our results showed that, nHA distribution can be accomplished across the scaffold thickness representing the structure seen in native TB interface[3]. Release studies demonstrated that TGF-β3 and CTGF can be released in a sustained manner. We are to investigate the response of stem cells for interface-related matrix formation and expression of relevant markers. These discoveries will serve as the foundation for the development of biomimetic tissue engineering technologies aimed at promoting biological graft fixation. This research is funded by TUBITAK (Project Number 115C001). [1]Gulotta+ Am J Sports Med 2009;, [2] Galatz+ J Bone Joint Surg 2004; [3]Genin+ Biophys J 2009.

9:40 AM  
Osteoporosis and Fatigue Fracture Prevention by Analysis of Bone Microdamage: Gerardo Presbitero1; David Gutierrez2; David Taylor3; 1National Autonomous University of Mexico; 2Center for Research and Advanced Studies (Cinvestav), at Monterrey, Mexico; 3Trinity College Dublin
    It is analyzed the conditions in which microcracks generated by fatigue interfiere to the fracture of bones, orienting towards the prevention of fractures of bones with osteoporosis. Mechanical tests, statistic analyzes and the development of a novel theoretical model were employed to describe the way microcracks grow towards the generation of bone fractures, basing on a concept named characteristic length. Bone mineral density and effects caused by gamma radiation for sterilization purposes of human bones used as allografts, contribute to the description of microcracks generation and growth to cause the fracture of bones. The bones weakened in their mechanical properties will fracture by fatigue in vivo conditions according to the manner in which characteristic lengths increase. The presented results will allow the development of predictions towards the prevention of fatigue fractures of bones of elderly people with osteoporosis, and will be useful for the development of new clinical approaches.

10:00 AM Break

10:15 AM  Invited
Spatial Variations in the Rate of Aging of Mineralized Tissues: Dwayne Arola1; W. Yan1; C. Montoya2; E.A. Ossa2; 1University of Washington; 2Universidad Eafit
    The biological aging of hard tissues of the human body, including bone, dentin and enamel, is of substantial importance to their fatigue and fracture behavior. Investigations performed in this area have shown that the process of aging generally involves changes to the mineral content, which impairs the mechanisms of toughening and causes an increase in fragility. A topic less frequently explored in this area is the spatial variation in biological aging of these tissues, and the contributing mechanisms. The differences between chronological and biological aging are seldom discussed, as well as the potential for accelerated aging to occur as a result of environmental and physical stimuli. This talk will review the aging of dentin and enamel of human teeth, including the changes in microstructure and their contributions to the fatigue and fracture behavior. Then the concept of accelerated aging and spatial variations in the aging process will be explored.

10:45 AM  
Time Dependent Deformation Behavior of Aged Dentin: Carolina Montoya1; Alex Ossa1; Dwayne Arola2; 1Eafit University; 2University of Washington
    The mechanical response of dentin is known to be influenced by changes in the density and diameter of its dentinal tubules (i.e porosity), and changes in chemical composition along the tooth. Several researchers have previously studied the bulk viscoelastic properties of coronal, intertubular and peritubular dentin. However, little is known about the time-dependent behavior of aged dentin and the importance of its spatial structure and composition variations. In this study, the spherical indentation response of aged coronal dentin was analyzed for outer, middle and inner dentin, and its time dependent deformation was modeled in terms of its microstructure (i.e. tubules) and chemical composition. The results showed a good agreement between experimental data and the predicted values of the time dependent behavior of the tissue. A significant decrease in the time dependent deformation response of dentin with aging was found when comparing with young samples.

11:05 AM  
The Geometric Effects of a Woodpecker’s Hyoid Apparatus for Stress Wave Mitigation: Lakiesha Williams1; Nayeon Lee1; Mark Horstemeyer1; Raj Prabhu1; Jun Liao1; Hongjoo Rhee1; Yossef Hammi1; Robert Moser2; 1Mississippi State Univ.; 2US Army Engineering Research and Development Center
    In this study a woodpecker hyoid apparatus was characterized to determine its shock mitigation mechanism using Finite Element (FE) analysis. The woodpecker’s hyoid apparatus starts at the beak tip, surrounds the woodpecker’s skull, and ends at the upper beak/front head intersection while being surrounded by muscle along the whole length. An FE model of the hyoid apparatus was created based on the geometry, microstructure, and mechanical properties garnered from our experimental measurements. We compared the impact mitigation capabilities of the hyoid apparatus with an idealized straight cylinder and a tapered cylinder. Results showed that the hyoid geometry mitigated a greater amount of pressure and impulse compared to the straight or tapered cylinders. The initially applied longitudinal wave lost its strength from attenuation and conversion to transverse shear waves. The analysis of the woodpecker’s hyoid apparatus provides a novel perspective on shock mitigation mediated by a spiral-shaped bio-composite.

11:25 AM  
Avoiding Brain Injury: A Structural Role of the Frontal Overhang on the Skull Bone of Woodpeckers: Jae-Young Jung1; Andrei Pissarenko1; Steven Naleway2; Kathryn Kang1; Nicholas Yaraghi3; Eric Bushong1; Mark Ellisman1; David Kisalius3; Marc Meyers1; Joanna McKittrick1; 1UC San Diego; 2University of Utah; 3UC Riverside
    Woodpeckers hammer at trees up to 20 times per second with a speed of 7 m/s while avoiding brain injury despite undergoing decelerations up to 1200 g. This is due to an impact-absorption system consisting of the head, beak, and (tongue) bone. This study aims to examine the relationship of structure-properties-function of the skull bone to determine its role in energy absorption and stress dissipation. We found a structural difference on woodpecker’s skull bone by having a protruded porous bone on the frontal area, the frontal overhang. From a finite element analysis, there was a lower Von Mises stress right after the frontal overhang than another model without the overhang. Moreover, the stress on the brain remained at a low level in both models with different pecking speeds. Thus, the frontal overhang structure seems to be designed to maximize energy dissipation and minimize the stress on the brain.