Synthesis of an Innovative Paramagnetic Porous Collagen-Based Scaffold

INTRODUCTION Magnetic responsive materials are the topic of intense research due to their potential breakthrough applications in the biomedical, coatings, microfluidics and microelectronics fields. By merging magnetic and polymer materials one can obtain composites with exceptional magnetic responsive features. Magnetic actuation provides unique capabilities as it can be spatially and temporally controlled, and can additionally be operated externally to the system, providing a non-invasive approach to remote control.[1] Porous biomaterials fabricated from natural and synthetic polymers have been intensively studied and widely used as drug delivery vehicles and scaffolds for tissue regeneration. Collagen is a natural polymer with an excellent biocompatibility and low antigenicity but with a rapid degradation and poor mechanical properties. These drawbacks limit its use in biomedical applications. In this context, a hybrid system, formed by a porous collagen scaffold and magnetite nanoparticles with a TiO2 shell (NPs@TiO2), was prepared in order to merge the potentiality of the paramagnetic material and the biocompatibility of the protein scaffold. The core/shell nanoparticles were also used as a novel crosslinker agent, as TiO2 guaranteed the binding to carboxylic groups[2] of collagen. In this way, scaffold mechanical properties and stability were also improved by the embedded nanoparticles. EXPERIMENTAL METHODS Synthesis of Porous Collagen Scaffold. An aqueous suspension of 1% w/v Type I collagen from bovine dermis was prepared by stirring for 5-6 hours at 10°C. A porous collagen scaffold was then obtained by casting, freeze-drying and dehydrothermal crosslinking (DHT). Synthesis of Porous Paramagnetic Collagen Scaffold. An aqueous solution of NPs@TiO2 was added to the collagen slurry while stirring. The suspension was then treated as reported above for the porous collagen scaffold. Characterization experiments. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetrical analysis (TGA) and swelling studies were carried out. The release of NPs@TiO2 from the collagen scaffold was studied by means of inductively coupled plasma mass spectroscopy analysis (ICP-MS). RESULTS AND DISCUSSION Paramagnetic iron oxide nanoparticles with a shell of TiO2 were incorporated within a collagen scaffold to obtain a hybrid porous material. This collagen-based matrix was highly sensitive to an external magnetic field. The optimal NPs@TiO2 concentration was determined by incorporating different amounts of nanoparticles into the collagen matrix, as quantified by means of TGA. The interaction among nanoparticles and the collagen fibers was studied by FTIR spectroscopy. As widely reported in the literature[2], TiO2 is able to bind carboxyl groups. In addition, we activated collagen carboxyl groups using N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide (EDC), to prompt the connection of these groups to the TiO2 coating. In order to evaluate the effect of NPs@TiO2 on the morphology of the collagen scaffold, scanning electron microscopy (SEM) was carried out. In the presence of NPs@TiO2, the average pore size of the collagen matrices was significantly reduced. This finding seemed to suggest that paramagnetic NPs worked as crosslinkers among the collagen fibers, inducing a rearrangement of the whole matrix. Swelling studies confirmed the fact that the NPs@TiO2, interacting with the collagen polymer matrix, played the role of crosslinkers [3]. The release of NPs@TiO2 from the matrix was monitored by incubating the samples in a phosphate buffered saline solution (pH 7.4) for 4 weeks at 37 °C. At each time point, iron release from the samples was determined using ICP-MS. The bond between NPs@TiO2 and collagen was thus found to be highly stable. CONCLUSION The results obtained in this study suggest the possibility to use a collagen matrices crosslinked with TiO2 coated paramagnetic iron oxide nanoparticles as potential biocompatible actuators that can be driven by external magnetic fields. Such characteristics make these innovative materials very appealing for different applications, such as drug delivery and tissue engineering.