Firas Awaja

Functionalized, biocompatible, and impermeable nanoscale coatings for PEEK

Biologically compatible coatings that provide hermetic seal could resolve a major technological hurdle in the attempt to replace metals with polymers for biochips and active medical implants. The use of amorphous carbon/diamond like carbon (a-C:H) coatings to hermetically seal and biologically enhance polyether-ether-ketone (PEEK) for biomedical device integration in the human body was investigated. The PEEK coating functionality (sp3/sp2 ratio), hardness and thickness (70-200nm) were controlled, by varying H2 and N2 concentration during the plasma operation with CH4. a-C:H coatings having the highest indentation modulus of 13.5GPa, originate out of a CH4 (90%) rich composition. Even in a mixture of 70/30 H2/CH4 the hardness is 4.76GPa, corresponding to hard and dense coatings. In all tested conditions of deposition coatings hardens was sufficient for the purpose of PEEK implants modification. The synthesized (a-C:H) nanoscale coatings were not water permeable as measured by the hydrolysis test, resolving the traditional challenge of swelling in wet environment. The hardness of the coatings showed strong correlations with the thickness, surprisingly however, with no correlations with the sp3/sp2 ratio. Selected non water permeable nanoscale coating on PEEK showed strong bioactivity by being viable for human osteoblast (hFOB) and human fibroblast (hGF) cells without toxicity issues. No correlation was observed between the coatings sp3/sp2 ratio and biological performance.

Dynamic adhesive environment alters the differentiation potential of young and ageing mesenchymal stem cells

Engineering dynamic stem cell niche-like environment offers opportunity to obtain better control of the fate of stem cells. We identified, for the first time, that periodic changes in the adhesive environment of human adipose derived mesenchymal stem cells (ADSCs) alters dramatically their asymmetric division but not their ability for symmetric renewal. Hereby, we used smart thermo-responsive polymer (PNIPAM) to create a dynamic adhesive environment for ADSCs by applying periodic temperature cycles to perturb adsorbed adhesive proteins to substratum interaction. Cumulative population doubling time (CPDT) curves showed insignificant decline in the symmetric cell growth studied for up to 13th passages accompanied with small changes in the overall cell morphology and moderately declined fibronectin (FN) matrix deposition probably as a functional consequence of ADSCs ageing. However, a substantial alteration in the differentiation potential of ADSCs from both early and late passages (3rd and 14th, respectively) was found when the cells were switched to osteogenic differentiation conditions. This behavior was evidenced by the significantly altered alkaline phosphatase activity and Ca deposition (Alizarin red) assayed at 3, 14 and 21day in comparison to the control samples of regular TC polystyrene processed under same temperature settings.

Self-bonding of PEEK for active medical implants applications

In an effort to select the best possible medical grade of polyether ether ketone (PEEK) for active medical implants application, it was necessary to inspect surface thermodynamic properties of different grades and correlate with self-bonding (autohesion) strength. Autohesion is the process of choice for encapsulating active medical implants made of PEEK. Temperature modulated DSC was used to investigate crystallinity and thermal events of range of medical grade PEEK (semi-crystalline, amorphous, semi-crystalline with amorphous surface, minerals and black masterbatch filled). Lab shear test was used to measure autohesive forces between PEEK samples pressed at moderate temperature (200 °C) and pressure. Samples with higher mobile amorphous region (MAF) and lower degree of crystallinity (Wc) resulted in higher autohesivce bonding strength. However, semi crystalline PEEK with surfaces that showed high MAF and low Wc resulted in higher autohesive bonding strength when compared with crystalline samples. The presence of fillers (minerals and black masterbatch) in the crystalline structure doubled the autohesive bonding strength values of the semi-crystalline sample. The presence of large crystalline region and a larger portion of the rigid amorphous region acted negatively on autohesion strength. Semi-crystalline PEEK with a special manufacturing procedure to produce amorphous surface produced the best choice among the PEEK grades. This grade have the desired thermodynamical properties in the bulk while exhibiting best surface adhesion strength.