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S58 Oral and Poster Presentations / Journal of Biomechanics 43S1 (2010) S23–S74
limited work on the microstructure, configuration and mechanism
of deformation of hydrogels have been reported in literature.
Therefore, the design of theoretic models and finite element
simulation analysis of auxetic hydrogel is significant to predict its
mechanical behaviours and to guide the material selection, design
and processing. A novel centresymmetric honeycomb structure with
fillings in three types of shape and packing pattern is designed,
constructed and evaluated. The assumptions of the model are
made on the basis of the preparation process, the microstructure
characteristics and experimental analysis of polyvinyl alcohol
hydrogel with three-dimension porous structure, in comparison
with the classical hexagonal honeycomb configurations.
Based on the theoretical and numerical analysis, the results show
that the effective density and the Poisson’s ratio vary as functions
of the configuration parameters of a centresymmetric honeycomb
unit cell, such as the isosceles trapezoid cell short length (L2),
the base angle (q1) and circular cell inner diameter (R2). The
honeycomb structure without fillings has the negative Poisson’s
ratio regardless the changes of the configuration parameters.
The fillings in forms of different unit shapes (circular and
hexagonal) and packing orders are proposed to represent the
dispersion medium (water) in hydrogels. In the case of the circular
filling (the unit structure thickness, t, <5mm) in square packing,
the centresymmetric honeycomb structure possess the negative
Poisson’s ratio on condition that large parameters, L2, q1 and R2,
are chosen. In another case of the hexagonal close-packing filling,
the centresymmetric honeycomb structure possess the negative
Poisson’s ratio if small values of L2, q1 and R2 are defined.
Acknowledgments: This study is financially supported by National
Natural Science Foundation of China Project (Grant No. 50773004)
M-16
A New Tool to Assess Corrosion and Metal Ion Release in
Artificial Hip Joints
Y. Yan, A. Neville, J. Hesketh, D. Dowson, S. Williams, J. Fisher.
University of Leeds, UK
Concern for the use of Metal-on-Metal hip prostheses has been
expressed about the potential problems which may arise in later
years due to the increased amount of metal ions and the number
of very fine metallic wear particles generated. The release of
metal ions is electrochemical in nature (corrosion). Hip simulators
have been extensively used to study wear. To date, all the work
on hip simulators has been focused on mechanical damage –
wear. However, hip implants operate in a corrosive and biological
environment and corrosion plays a key role in the total material
degradation processes. There has been no attempt to measure the
interactions (biotribocorrosion) between corrosion and tribology
in situ in simulated body fluids using a hip simulator. There are
no reports that identify what damage is due to pure mechanical
processes and corrosion processes in a hip simulator. This abstract
describes the first instrumentation of an integrated hip joint
simulator to provide corrosion measurements under dynamic
loading and movements. It is a pioneering study to determine
damage in real time. The contribution of corrosion-related damage
to the total material degradation is quantified. The open circuit
potential results are reported to assess the corrosion regime in
the absence and presence of movement at the bearing surfaces.
The importance of these measurements is that the real damage
mechanisms can be assessed as a function of the operating cycle.
Links of lab tests with clinical data will be discussed.
M-17
Strontium Bioactive Glass Coatings for Medical Implants
N. Lotfibakhshaiesh, E. Gentleman, M.M. Stevens, R. Hill. Imperial
College London, UK
Introduction: Metallic prosthetic implants are widely used to treat
joint and skeletal injuries. However, some implants can fail because
the metal alloys used do not bond with bone. Bioactive glass (BG)
coatings may offer a solution to this problem as they form a strong
bond with living tissue and have the added benefit that their
dissolution ions stimulate cell activity. Sr can be substituted for
calcium in BGs creating a material that may combine the bone
remodelling benefits of Sr ions with the well-established bone
stimulatory action of bioactive glass. The aim of this study is to
develop Sr containing BG coatings on metallic surfaces to bond to
an implant as an effective biomaterial choice for a range of bone
regeneration therapies.
Materials and Methods: BG in the system: SiO2-MgO-Na2O-K2O-
ZnO-P2O5-CaO with 0, 10, and 50 of the Ca being replaced by Sr
were prepared by a melt-quench route. A degradation study was
carried out in simulated body fluids. Silicon (Si), Phosphorus (P),
Calcium (Ca) and Sr were checked at different time periods.
Produced glasses were combined with RPMI media. The human
osteosarcoma cell line, Saos-2, was seeded in Sr substituted
medium. Cell metabolic activity was measured using the tetrazole
MTT. BGs were coated on to the surface of Ti6AL4V coupons and
Saos-2 cells were seeded on BG coatings and viability was assessed
with a Live/Dead stain.
Results: Glass dissolution leads to a rise of all the ion concentrations
in solution. MTT activity increased in all samples with time in
culture until 14 days. Saos-2 cultured treated with Sr-substituted
BGs had higher MTT activities than controls. Live/Dead staining
showed that cells were alive on all coating materials.
Discussion and Conclusions: Substituting strontium for calcium
increases the dissolution of the glass releasing in more ions
in solution. These ions may tend to enhance the metabolic
activity of Saos-2 cells, which may lead to an increase in
mineralization. As BGs are a well-studied biomaterial system
capable of controlled ion release and are deliverable as coatings
or scaffolds substitution of strontium for calcium in bioactive
glasses may be an effective strategy for creating materials for bone
repair/regeneration therapies.
M-18
Carbon Nanotube-Reinforced Hydroxyapatite Biocomposite
Coatings by Hydrothermal Synthesis and Electrophoretic
Deposition (EPD)
C. Kaya1, C.B. Ustundag1, F. Kaya2. 1Yildiz Technical University,
Turkey; 2Zonguldak Karaelmas University, Turkey
Carbon nanotubes (CNTs) show outstanding mechanical, physical
and electrical properties and they are interesting reinforcing
elements for a variety of materials, which includes also materials
for biomedical applications. One significant drawback of using
CNTs in liquid media is the non-wetting character of as-fabricated
CNT surfaces, therefore, CNT surfaces must be modified with
functional groups (for example with OH or COOH groups) to achieve
homogeneous CNT dispersions. Typically, CNTs are functionalized
by immersing them in an acid mixture (H2SO4+HNO3), however
it has been shown that this process may create surface defects
on CNT surfaces resulting in significant property degradation. In
the present work, an alternative functionalization process based on
hydrothermal processing is shown, which utilizes a suspension that
contains CNTs and a mixture of calcium acetate (Ca (CH3COO)3)
and phosphoric acid (H3PO4), which are the precursors to produce
stoichiometric hydroxyapatite (HA) at 200°C for 2h. The ultimate
objective is the development of CNT-hydroxyapatite (HA) nano-
composite powder mixtures exhibiting a highly homogeneous
dispersion of CNTs. The microstructure of CNT-HA mixtures
obtained under hydrothermal conditions was characterized by a
range of techniques including XRD, TEM and FEG SEM. Utilizing
the CNT-HA mixed powders, well dispersed colloidal suspensions
were prepared and used to coat various biomedical Ti alloys
using electrophoretic deposition (EPD). The characterization of the
bioactive coatings based on CNT reinforced HA will be presented