Laser-generated nanoparticle polymer composites for potential applications in tissue engineering

Nanocomposites have significantly contributed in medical device fabrication, 3D bioprinting, and tissue engineering applications. Various kinds of nanocomposites are increasingly investigated to control the nanoparticles (NP) dispersion in the polymer matrix and ion release kinetics from nanoparticles that are crucial prerequisites for the utilization of composites. Laser ablation in liquids (LAL) is a promising method for uniform in situ embedding of nanoparticles into polymers to fabricate composites free from chemical additives. Previous studies demonstrated its suitability; however, systematic studies on the scale-up of these materials and details on the working mechanism are not conducted. Particularly kinetics of ion release from nanoparticle-polymer composites matrices has not been fully understood yet. In addition, the role of nanoparticles in the gelation kinetics of collagen composites is not clear. Regarding other attractive biomaterial like nanoscopic bioactive glass, the mechanisms of fabrication by picosecond (ps) and nanosecond (ns) laser fragmentation have not been explained so far.

LAL of metal targets in macromolecular solutions was employed for synthesizing Au and Fe nanoparticle-loaded nanocomposites based on alginate, collagen, and thermoplastic polyurethane (TPU). In this regard, we investigated the influence of polymer solution parameters, such as polymer types, liquid viscosity, and pH on the nanoparticle productivities and particle size. Furthermore, confocal microscopy method revealed a good three-dimensional dispersion and differentiation in parallel of laser-generated nanoparticles in the polymer that was shown to be a suitable bioink for 3D printing. Moreover, the laser fragmentation method was successfully applied to downsize bioglass particles from micrometers (3.5-11 µm) to 20-50 nm, synergistically using iron salt as the fragmentation sensitizer for in situ doping.

Metal ion release from composites and protein adsorption capacity are hypothesized to be two key processes directing cell-scaffold interactions. Interestingly, a phenomenon of total Fe ion release concentration decreased with increasing mass loadings was only found in the Fe-alginate system under static conditions, neither in the Cu/Zn-alginate nor Fe-TPU control system. The attributed kinetics of special release behaviour of iron ions from alginate gels are probably not only the redox potential of metals and metal ions diffusion, but also the solubility of nano-metal oxides and affinity of metal ions with alginate. At the minute loadings with Fe nanoparticles down to 200 ppm, bovine serum albumin (BSA) and collagen-I protein adsorption on the surface of both the alginate and TPU composites was significantly increased compared to unloaded control polymers, which could be correlated with Fe ion release and porous nature of alginate composites, but was independent of the global surface charge.

Notably, the embedded nanoparticles in polymer matrices showed significant influences on physicochemical and rheological properties. Results demonstrated that compared to alginate, the elastic modulus of nanoparticle-alginate gels was enhanced 1.5 times. Nanoparticles modified the surface charge of TPU to a more negative value. Moreover, nanoparticles enlarged the hydrogel network and increased the porosity but decreased the stiffness of alginate or alginate-fibrin blends. Meanwhile, synergetic effects of fibrin, FeNPs, and fetal bovine serum contributed to an enhanced endothelialization capacity of alginate hydrogels. These findings can pave way for the fabrication of various hydrogel-based biomaterials employed in tissue engineering.


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