Introduction: Polylactides have been widely employed in the biomedical field for several applications due to their biocompatibility and biodegradability. However some drawbacks still remain to be solved, such as lack of radiopacity, toughness and bioactivity.
In the present work, we present a strategy to overcome the aforementioned drawbacks associated to polylactides by the incorporation of polydopamine coated barium sulfate submicro-particles to the polymer matrix. On the one hand, incorporation of inorganic barium sulphate particles will enhance the radiopacity of polylactide, which otherwise cannot be detected by X-rays [1]. On the other hand, submicron-size rigid particles in a brittle matrix may induce the activation of the shear yielding mechanism leading to high levels of deformation at break [2].
Additionally, mussel inspired polydopamine coatings will favor the incorporation of biologically active molecules such as protein or peptides improving, accordingly, the bioactivity of polylactide.
Experimental Methods: Poly(D-lactide) (PDLA) samples filled with 0.5, 1, 2, 5 and 10 wt%. polydopamine-coated submicron barium sulphate particles were prepared by injection moulding. Mechanical properties of these samples were determined via tensile test and the dispersion of the particles within the polymer matrix was studied by means of SEM and TEM. Finally, AlamarBlue® and PicoGreen® assays were performed to quantify proliferation and metabolic activity of human dermal fibroblast (HDFs) seeded on these samples.
Results and Discussion:
This figure shows the stress-strain behavior of PDLA/ PD-BaSO4 composites. An impressive increment in the capability of deformation, and consequently, in the toughness of the polylactide are observed. This plastic deformation occurs because under uniaxial stress the debonded particles leave voids in the matrix and activate shear yielding of the polymer. Therefore polydopamine coated barium sulphate particles leads simultaneously to toughness (SEM image with secondary electrons, below on the left) and radiopacity (the same SEM image with backscattered electrons, below on the right) in polylactide implants.
Taken together, metabolic activity and proliferation results demonstrate that the materials employed in this work are not cytotoxic and provide a valid substrate for cells to attach and proliferate.
At the same time the polydopamine coating of these particles provide a binding site for biologically active molecules as proteins or drugs increasing the potential use of these composites as internal devices for biomedical applications.
Conclusion: In this work, brittleness associated to polylactides is overcome via the incorporation of polydopamine coated barium sulphate particles. The materials showed enhanced toughness and provide a valid substrate for cells to attach and proliferate. Besides, coating of barium sulphate particles with polydopamine provide functional groups that can act as anchorage points for further incorporation of molecules with biological activity, such as proteins or peptides.
Authors thank funding support from the Basque Government Department of Education, University and Research (consolidated research groups GIC12/161 and SAIOTEK SAI13/230); Funding from MINECO (project MAT2013-45559-P) is also acknowledged; A.L. would like to acknowledge Basque Government for the postdoctoral fellowship; SGIKER from University of the Basque Country is thanked for electron microscopy images
References:
[1] M.J. Meagher et al. J. of Nanoparticle Research 2013, 15, (12), 2146/1-2146/10
[2] F.H. Gojny et al. Composites Sci. Technol.2004, 15, 2363