Lorena García-Uriostegui

Radiation grafting of N-vinylcaprolactam onto nano and macrogels of chitosan: Synthesis and characterization

The aim of this study was to synthesize chitosan hydrogels, in macro- and nano-size, grafted with N-vinylcaprolactam (NVCL) using gamma radiation, and evaluate their potential application as a drug delivery system, using 5-fluorouracil (5-FU) as a model drug. The effect of dose and monomer concentration in the grafting process was studied, and the materials were characterized by FTIR, TGA, DLS, SEM and AFM. Higher grafting percentages were observed for the nanogels system. Although both the grafted macro- and nanogels, (net-CS)-g-NVCL, showed a response to pH (4.75) and temperature (31-33°C), the nanogels showed a better swelling response to both stimuli because of their higher surface area. Both systems were able to load 5-FU in small amounts (2-3.5mgg-1) and the release was sustained for more than 12h, showing that the modified macro and nanogels can be a potential alternative for the administration of drugs.

Immobilization of liposomes on temperature-responsive polymer networks cross-linked with poly-L-lysine and grafted onto polypropylene

Immobilization of liposomes on implantable/insertable medical devices may be advantageous for the stability of liposomes and the localized release of drugs from the device to prevent/manage pathological processes. This work focuses on the preparation of polymeric systems suitable for the immobilization of drug-free and 5-fluorouracil-loaded liposomes. Polymeric systems, based on N-isopropylacrylamide (NIPAAm) and N-acryloxysuccinimide (NAS), were prepared by γ radiation with three different structures: a binary copolymer grafted onto polypropylene (PP), an interpenetrated polymer network (IPN) grafted onto PP, and an IPN hydrogel; all of them cross-linked with poly-L-lysine. Although liposome immobilization is accompanied by a lost in the 5FU entrapment efficiency, the high extent of the immobilization provides the polymeric systems with a remarkable amount of drug at their surface. These findings point out poly-L-lysine as a suitable component to endow surface-modified devices with ability to host liposomes and thus to develop drug-medical device combination products.

Lysine-Grafted MCM-41 Silica as an Antibacterial Biomaterial

This paper proposes a facile strategy for the zwitterionization of bioceramics that is based on the direct incorporation of l-lysine amino acid via the ε-amino group onto mesoporous MCM-41 materials. Fourier transform infrared (FTIR) studies of lysine-grafted MCM-41 (MCM-LYS) simultaneously showed bands at 3080 and 1540 cm−1 and bands at 1625 and 1415 cm−1 corresponding to -NH3+/COO− pairs, which demonstrate the incorporation of the amino acid on the material surface keeping its zwitterionic character. Both elemental and thermogravimetric analyses showed that the amount of grafted lysine was 8 wt. % based on the bioceramic total weight. Moreover, MCM-LYS exhibited a reduction of adhesion of S. aureus and E. coli bacteria in 33% and 50%, respectively at physiological pH, as compared with pristine MCM-41. Biofilm studies onto surfaces showed that lysine functionalization elicited a reduction of the area covered by S. aureus biofilm from 42% to only 5% (88%). This research shows a simple and effective approach to chemically modify bioceramics using single amino acids that provides zwitterionic functionality, which is useful to develop new biomaterials that are able to resist bacterial adhesion.

Polyacrylamide-coated MCM-48 mesoporous silica spheres: synthesis, characterization and drug delivery study

Mesoporous type-MCM-48 silica was grafted with polyacrylamide (PAAm) by using an azo-type initiator. The effect of monomer and initiator concentrations, reaction time, and temperature were evaluated to determine the optimal grafting conditions. Functionalized MCM-48 silicas were characterized by X-ray diffraction (XRD), infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption–desorption analyses, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which confirmed the grafting process. According to XRD, SEM and TEM results, PAAm-modified MCM-48 silica did not show changes in its morphology and mesostructure by comparing with pristine MCM-48. Also, modified silicas were tested as delivery system using nalidixic acid as drug model. MCM-48-PAAm silicas were able to load more significant amounts of nalidixic acid than the unmodified MCM-48, and showed a sustained delivery behaviour, releasing about 80% of drug.

Rheological characterization of new thermosensitive hydrogels formed by chitosan, glycerophosphate, and phosphorylated β-cyclodextrin

A novel thermosensitive hydrogel consisting of phosphorylated β-cyclodextrin (βCD-PH), β-cyclodextrin (βCD) and chitosan was prepared by embedding βCD and βCD-PH, into the well-studied chitosan/αβ-glycerophosphate system (CS/αβGP). The relevance of this work is the use of βCD-PH to partially substitute αβGP as the gelling agent. The role of βCD and βCD-PH on the rheological properties of hydrogels, gelation time, and gelation temperature were investigated. The gelation time for all the samples (CS/αβGP, CS/αβGP/βCD, and CS/αβGP/βCD-PH) was less than a minute at 37 °C, which is suitable for biomedical applications. The gelation temperature for hydrogel CS/αβGP/βCD-PH increased linearly with the addition of βCD-PH within the interval 31.8-37.3 °C, at ratios CS:βCD-PH of 1:0.5, 1:1, 1:1.5 and 1:2 (w/w). The hydrogel thus obtained has potential applications in dual drug delivery (hydrophilic and hydrophobic).

Spruce xylan/HEMA-SBA15 hybrid hydrogels as a potential scaffold for fibroblast growth and attachment

A hybrid hydrogel (GHC-SBA15) based on spruce xylan (HC), 2-hydroxyethyl methacrylate (HEMA), and mesoporous silica (SBA15) was prepared with the intended use of fibroblast attachment and growth. Xylan was functionalized with acryloyl chloride to introduce vinyl groups and was crosslinked by radical polymerization with HEMA in presence of SBA15. Infrared spectroscopy and nuclear magnetic resonance confirmed the copolymerization of HEMA with xylan. Up to 20 wt.% addition, SBA15 was homogenously incorporated in the structured hydrogel network as observed by SEM. Moreover, nitrogen adsorption-desorption, small angle X-ray scattering and transmission electron microscopy indicated that the mesoporous SBA15 framework was maintained and that the hybrid hydrogel was a physical mixture of SBA15 with the copolymer HC/HEMA. Rheological analysis revealed that addition of 20% w/w SBA15 into hydrogel enhanced significantly the mechanical properties. In addition, we demonstrate that fibroblast L929 cells grew and spread on GHC-SBA15. Cell viability was within the expected range.