1. New insights into the degradation of biocompatible drug carriers :
Single particle kinetic degradation analysis by Raman microscopy
X. Li1, L. Lachmanski2, S. Safi2, C. Serre3, J. Zhang4, R. Gref1
1Institut des Sciences Moléculaires d'Orsay, UMR 8412, Université Paris- Saclay, Orsay, 91405, France
2 Malvern Instruments , 30 rue Jean Rostand, Orsay, 91405, France
3Institut Lavoisier de Versailles, UMR 8180, Université Paris-Saclay, 78000, France
4 Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai , China.
Objectives
Metal-organic frameworks (MOFs) based on porous iron (III) polycarboxylates have emerged as a new class of versatile, biodegradable and non-toxic drug carriers1,2. Because of their high pore volumes and surface areas, MOFs were shown to load unprecedented amounts (within the wt % range) of a series of drugs able to efficiently penetrate within the porous MOF structures. Using newly developed advanced methodologies, this study aims gaining new insights into the degradation behavior of MOF micro- and nanoparticles.
For this, Malvern’s Morphology G3-ID was used as a powerful versatile tool that combines particle counting, morphological image analysis and chemical identification capabilities. In this study the G3-ID was used to follow the degradation of single particle in the visible range using image analysis through intensity mean statistics. The mechanistic aspects of degradation were also investigated through a spectroscopic approach by Raman mapping of the same single microparticle.
Preparation of MOFs: MIL100 (Fe)
Materials
Porosity– BET areas of 1490 ± 100 m2·g-1 for nanoMOFs accurately measured by Porosimetry ( )
Size – DLS and Transmission Electron Microscopy (TEM)
Structure – X-ray powder diffraction, infrared spectroscopy, TEM
Composition – Thermogravimetric analysis 
MIL100 iron-trimesate MOFs was synthesized by hydrothermal reaction.
NanoMOFs (200 nm)
Microwave (CEM Mars 5) assisted synthesis
MicroMOFs ( µm)
Teflon reactor
Characterization of MOFs: MIL100 (Fe)
Degradation of nanoMOFs
200 nm A
200 nm B
Trimesate linker is quickly released after particle incubation in PBS, and XRPD pattern was modified3.
However, there is only a slight modification of the particle size as confirmed by both DLS and TEM investigations.
During particle incubation in water, no changes in particle size, shape, crystallinity nor morphology were detected.
Phosphate ions from the incubation media competitively replaced the trimesate linked to progressively degrade the 3D structure.
TEM images of nanoMOFs before (A) and after (B) incubation in PBS for 4 h
XRPD pattern
Degradation analysis of microMOFs
2.Single particle kinetic degradation analysis
3. Degradation during the coating process
1. Morphological investigations
cyclodextrin-phosphates (CD-P) was used to coat microMOFs taking advantade of the interaction between phosphate and the particles.
Morphologi G3-ID
The degradation analysis was conducted by Malvern’s Morphologi G3-ID, which combines automated static imaging features with chemical identification of individual particles using Raman spectroscopy. It allows both statistic particle characterization of overall samples and single particle tracking to get an in-depth understanding of their particulate samples.
Schematic representation (A) and confocal reconstituted envelope (B) of a microMOFs crystal coated with rhodamine-labelled cyclodextrin-phosphates (CD-P) 2
The degradation mechanism shown by Raman spectra:
1000 cm-1 and 800 cm-1: aromatic ring finger print (trimesate)→ trimesate release
210 cm-1: ordered crystalline iron-based structure → amorphous phase formation
cm-1: lattice vibrations and network binding modes →change in the coordination environment, indicating iron-phosphate complex
The morphological investigations were performed for microMOFs before and after degradation in PBS. About 5000 particles were observed and the size of microMOFs is between µm.
Coating with CD-P did not induce particle degradation, as assessed by identical Raman spectra and no color change. This could be explained by the fact that bulky CDs are not able to penetrate within the 3D structure of MIL100. They are only adsorbed at the surface forming a stable coating in biological media due to cooperative anchoring of several phosphate units grafted to one CD molecule
The size distribution of microMOFs is almost the same before (green) and after (red) incubated in PBS for 10 days.
However, a clear color change and spectra modification were observed during the degradation.
Kinetic analysis:
Fast phase in the first few hours, showing sharp increase in intensity and surface area, but with overlooked color change;
Stable phase. showing increasing intensity and color change
Conclusion. The combination of static microscopy and Raman spectroscopy was a powerful tool to assess the homogeneity in chemical composition and morphology of particles by analyzing individually each particle. Of upmost interest, it was possible to detect modifications of the chemical composition on different regions on the same particle during degradation. Besides, it was possible to accurately detect chemical changes during coating processes.
References
[1] Horcajada, P. et al Porous metal–organic-framework nanoscale carriers as a potential platform for drug delivery and imaging. Nat. Mater. 9,
[2] Agostoni, V. et al A “green” strategy to construct non-covalent, stable and bioactive coatings on MOF nanoparticles. Scientific Reports ; DOI : /srep07925.
[3] Agostoni, V. et al Towards an improved anti-HIV activity of NRTI via metal-organic frameworks nanoparticles. Adv Healthc Mater. 2,