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Lancaster, PA, United States

Tohfafarosh M.,Drexel University | Baykal D.,Exponent, Inc. | Kiel J.W.,Exponent, Inc. | Mansmann K.,Formae Inc. | And 2 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2016

Hydrogels are known to possess cartilage-like mechanical and lubrication properties; however, hydrogel sterilization is challenging. Cyborgel™, a proprietary hydrogel, is intended for use as a cartilage replacement implant. This study evaluated the effect of 30-35kGy e-beam and gamma radiation on the polymer swell ratio, and the mechanical, chemical and tribological behavior of this hydrogel. Three different formulations were mechanically tested, and material parameters were identified using finite element analysis. FTIR spectroscopy was used to investigate chemical changes. Wear test was carried out for 2 million cycles in bovine serum, followed by 2 million cycles in distilled water. No significant difference was found in the swell ratio, mechanical and tribological properties of control hydrogel samples and those exposed to e-beam or gamma radiation; however, chemical spectra of e-beam sterilized samples revealed minor changes, which were absent in unsterilized and gamma sterilized samples. © 2015 Elsevier Ltd. Source

Baykal D.,Drexel University | Underwood R.J.,Exponent, Inc. | Mansmann K.,Formae Inc. | Marcolongo M.,Drexel University | And 2 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2013

Characterizing hydrogels using a biphasic cartilage model, which can predict their behavior based on structural properties, such as permeability and aggregate modulus, may be useful for comparing active lubrication modes of cartilage and hydrogels for the design of articular cartilage implants. The effects of interstitial fluid pressurization, inherent matrix viscoelasticity and tension-compression nonlinearity on mechanical properties of the biphasic material were evaluated by linear biphasic (KLM), biphasic poroviscoelastic (BPVE) and linear biphasic with anisotropy cartilage models, respectively. The BPVE model yielded the lowest root mean square error and highest coefficient of determination when predicting confined and unconfined compression stress-relaxation response of hydrogels (n=15): 0.220±0.316. MPa and 0.93±0.08; and 0.017±0.008. MPa and 0.98±0.01 respectively. Since the differences in error between models were not statistically significant, the simplest model we considered, KLM model, was sufficient to predict the mechanical response of this family of hydrogels. The coefficient of friction (COF) of a hydrogel-ceramic articulation was measured at varying loads and pressures to explore the full range of lubrication behavior of hydrogel. Material parameters obtained by biphasic models correlated with COF. Based on the linear biphasic model, COF correlated positively with aggregate modulus (spearman's rho=0.5; p<0.001) and velocity (rho=0.3; p<0.001), and negatively with permeability (rho=-0.3; p<0.001) and load (rho=-0.6; p<0.001). Negative correlation of COF with load and positive correlation with velocity indicated that hydrogel-ceramic articulation was separated by a fluid film. These results together suggested that interstitial fluid pressurization was dominant in the viscoelasticity and lubrication properties of this biphasic material. © 2013 Elsevier Ltd. Source

Formae Inc. | Date: 2011-11-09

Medical, surgical and orthopaedic implants made of artificial materials.

Baykal D.,Drexel University | Day J.S.,Drexel University | Day J.S.,Exponent, Inc. | Jaekel D.J.,Drexel University | And 4 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2012

Characterizing the wear behavior of hydrogel articulations is problematic and a standardized method has not yet been developed. The aims of this study were to evaluate the wear resistance of hydrogel-on-hydrogel articulations and to assess the suitability of a submerged measurement technique as a practical and non-destructive method in quantifying their wear rates. Five hydrogel bearings were tested for 5 million cycles using a pin-on-disk tester. As the test progressed, the coefficient of friction increased (Spearman's rho=0.76; p<0.001) while the surfaces of the pins were burnished (Spearman's rho=-0.31; p<0.001) and those of the disks got rougher (Spearman's rho=0.19; p<0.01). Environmental scanning electron microscopy analysis showed no evidence of gross wear and revealed similar surface morphology between contacting and non-contacting regions of specimens. These results support the finding of low wear, which were -1.4±8.3 and 6.6±35.3mm3/MC based on submerged and wet weights, respectively. Pins displayed higher wear than disks based on submerged weights. This was anticipated since surfaces of pins were constantly under load and cross-shear while only a portion of the disk in contact with the pin was loaded at a given time. Wet weights, on the other hand, indicated higher wear for disks than pins. In addition, submerged weights yielded a lower standard error of the mean in wear rates than wet weights, 3.7 and 14.6mm3/MC, respectively. These results indicated that submerged weights were more suitable than wet weights in quantifying wear of hydrogels in spite of unwanted effects of swelling. © 2012 Elsevier Ltd. Source

Flexible cartilage-replacing implants are disclosed that use either or both of (1) enlarged peripheral rim components, and/or (2) elongated flexible reinforcing members that are embedded around the peripheral edge of an implant device. These types of anchoring devices, especially when used in combination, can provide flexible implants that can be implanted arthroscopically into synovial joints, for complete replacement of damaged cartilage segments.

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