Russo, Maria
(2017)
A microfluidic platform to design crosslinked hydrogel nanoparticles for enhanced MRI.
[Tesi di dottorato]
Abstract
The Ph.D. thesis work entitled “A Microfluidic Platform to design crosslinked hydrogel nanoparticles for enhanced MRI” exploits a microfluidic Flow Focusing approach to develop intravascularly, injectable and completely biocompatible hydrogel nanoparticles, entrapping a clinically approved Magnetic Resonance Imaging (MRI) Contrast Agent (CA), Gd-DTPA.
Despite their widespread use, Gd-based CAs still suffer from several limitations such as low efficacy, toxic effects and lack of tissue specificity. Indeed, their relaxivity is still far away from the theoretical limits, and they present nephrotoxicity and heavy allergic effects. Furthermore, recent studies have reported the risk of intracranial deposition of elemental gadolinium in neuronal tissues after Gd-based CAs administration, even in patients with normal renal and hepatobiliary function and after only one MRI scan. Furthermore, Food and Drug Administration (FDA) alarmed the medical community about the risk of deposition, recommending the healthcare professionals to limit the use of Gd-based CAs unless necessary, with potential negative impact on the early diagnosis of several pathologies (www.FDA.GOV.com/safety announcement 7-27-2015). In this perspective, the opportunity to provide a formulation able to overcome several of these limitations is of great interest to the scientific and the medical community. Therefore, it is essential to highlight the need to build up not only a new system but also a biocompatible probe with higher relaxivity able potentially to protect the chelate around Gd ions from transmetallation phenomena and control the accumulation and the clearance of the Gd-based CAs in a specific organ.
Recent advancements in imaging diagnostics have focused on the use of nanostructures that entrap MRI CAs without the need to modify chemically the compounds approved in clinical use. However, the exploitation of microfluidic technology for their controlled and continuous production is still missing.
Here, crosslinked Hyaluronic Acid Nanoparticles (cHANPs) entrapping Gd-DTPA are synthesized through a controlled nanoprecipitation in a microfluidic Flow Focusing approach. This microfluidic process facilitates a high degree of control over particle synthesis, enabling the production of monodisperse particles as small as 35 nm. Furthermore, the interference of Gd-DTPA during polymer precipitation is overcome by finely tuning process parameters and leveraging the use of hydrophilic-lipophilic balance (HLB) of surfactants and pH conditions. For both production strategies proposed to design Gd-loaded cHANPs, a boosting of the relaxation rate T1 is observed since a T1 of 1562 is achieved with a 10 μM of Gd-loaded cHANPs while a similar value is reached with 100 μM of the clinical relevant Gd-DTPA in solution. To explain the increase in Gd-DTPA relaxivity, hydrogel structural parameters of cHANPs are investigated to control the hydration of Gd-DTPA subjected to the osmotic pressure deriving from elastodynamics of swollen gels, which establishes an equilibrium able to boost relaxometric properties of Gd-DTPA without chemical modification of the chelate. This capability, here called Hydrodenticity, is defined in terms of crosslink density and mesh size, tunable through our Microfluidic Flow-Focusing approach.
Furthermore, the same microfluidic platform is enforced to entrap simultaneously several diagnostic agents within the cHANPs for multimodal imaging applications and later, PEGylation of the nanoparticles is performed to improve the long circulation and the stability of the cHANPs in clinical applications. Also a new combination of biomaterials, thiolated HA (HA-SH) and mPEG-Vinylsulfone (PEG-VS), is presented in this work by optimizing the same microfluidic approach, proving the flexibility of the proposed system by applying our strategies to different materials. In this last case, the simultaneous reaction of the HA-SH and PEG-VS is conducted to produce in a one-step strategy the PEGylated cHANPs encapsulating directly one or more active compounds. Moreover, the achieved results extend the knowledge of the versatility and the ability that microfluidics can exert.
The strength of our scientific work lies in the fact that our method allows a strict control of the characteristics of the biopolymer nanoparticles and the entrapment of the Gd-DTPA, showing a low polydispersity of nanoparticles and a high encapsulation efficiency, as well as easy recovery of the obtained particles, without long and expensive purification steps. Additionally, their physicochemical properties are modulated to prove to be useful in the MRI field.
Finally, this work contributes to overcome several of the both physical and biological limits regarding the clinical use of the CAs. We have proved that it is possible to increase the relaxivity by tuning the structural parameters of hydrogel nanoparticles, and, at the same time, improve potentially the tissue specificity, stability of the chelates, imaging diagnostic acquisition and reduce the administration dosage. The developed microfluidic strategies allow a fine tuning of the formulations, and it can be easily applied to different polymers and materials or a combination of materials involved in nanomedicine field making a library of personalized nanostructures.
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