Polymer-ceramic composites obtained as the result of a mineralization process hold great promise for the future of tissue engineering. Simulated body fluids (SBFs) are widely used for the mineralization of polymer scaffolds. In this work an exhaustive study with the aim of optimizing the mineralization process on a poly(L-lactic acid) (PLLA) macroporous scaffold has been performed. We observed that when an air plasma treatment is applied to the PLLA scaffold its hydroxyapatite nucleation ability is considerably improved. However, plasma treatment only allows apatite deposition on the surface of the scaffold but not in its interior. When a 5 wt % of synthetic hydroxyapatite (HAp) nanoparticles is mixed with PLLA a more abundant biomimetic hydroxyapatite layer grows inside the scaffold in SBF. The morphology, amount, and composition of the generated biomimetic hydroxyapatite layer on the pores' surface have been analyzed. Large mineralization times are harmful to pure PLLA as it rapidly degrades and its elastic compression modulus significantly decreases. Degradation is retarded in the composite scaffolds because of the faster and extensive biomimetic apatite deposition and the role of HAp to control the pH. Mineralized scaffolds, covered by an apatite layer in SBF, were implanted in osteochondral lesions performed in the medial femoral condyle of healthy sheep. We observed that the presence of biomimetic hydroxyapatite on the pore's surface of the composite scaffold produces a better integration in the subchondral bone, in comparison to bare PLLA scaffolds.
It has been observed that the surface of a PLLA membrane after 21 days of immersion in SBF is still not completely covered by hydroxyapatite whereas the same sample treated with plasma show a smooth layer of biomimetic hydroxyapatite. The increase of bioactivity achieved with this treatment was less important in high hydroxyapatite content composites.
Biocompatible PLLA scaffolds have been developed that can be efficiently loaded with MSCs. The scaffold supports chondrogenic differentiation and ECM deposition that improves the mechanics of the scaffold. Although this improvement does not met the expectations of a hyaline-like cartilage ECM, in part due to the lack of a mechanical stimulation, their potential use in the treatment of cartilage pathologies encourages to improve the mechanical component.
WileyDeplaine, H.; Acosta-Santamaría, VA.; Vidaurre, A.; Gómez Ribelles, JL.; Doblare Castellano, M.; Ochoa-Garrido, I.; Gallego Ferrer, G. (2014)
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AbstractA Poly(L-lactic acid) scaffold prepared by a combination of freeze extraction/porogen leaching methods was submitted to static degradation in phosphate buffered saline solution at pH=7.4 and 37 ºC for up to 12 months.After 6 months of degradation the scaffold maintained its integrity, although noticeable changes in permeability and pore size were recorded. After 12 months, SEM pictures showed that most of the trabeculae were broken and the sample disaggregates under minimum loading. Neither weight loss nor crystallinity changes in a first heating calorimetric scan were observed during the degradation experiment. However, after 12 months, a rise in crystallinity, from 13 % to 38 %, and a drop in Tg from 58 ºC to 54 ºC were measured in a second heating scan. The onset of thermal degradation moved from 300 ºC, to 210 ºC after 12 months. Although the elastic modulus suffered only a very slight reduction with degradation time, the aggregate modulus decreased 44 % after 6 months.
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