Alginate-waterborne polyurethane 3D bioprinted scaffolds for articular cartilage tissue engineering.

Articular cartilage defects comprise a spectrum of diseases associated with degeneration or damage of the connective tissue present in particular joints, presenting progressive osteoarthritis if left untreated. In vitro tissue regeneration is an innovative treatment for articular cartilage injuries that is attracting not only clinical attention, but also great interest in the development of novel biomaterials, since this procedure involves the formation of a neotissue with the help of material support. In this work, functional alginate and waterborne polyurethane (WBPU) scaffolds have been developed for articular cartilage regeneration using 3D bioprinting technology. The particular properties of alginate-WBPU blends, like mechanical strength, elasticity and moistening, mimic the original cartilage tissue characteristics, being ideal for this application. To fabricate the scaffolds, mature chondrocytes were loaded into different alginate-WBPU inks with rheological properties suitable for 3D bioprinting. Bioinks with high alginate content showed better 3D printing performance, as well as structural integrity and cell viability, being most suitable for scaffolds fabrication. After 28 days of in vitro cartilage formation experiments, scaffolds containing 3.2 and 6.4 % alginate resulted in the maintenance of cell number in the range of 104 chondrocytes/scaffold in differentiated phenotypes, capable of synthesizing specialized extracellular matrix (ECM) up to 6 µg of glycosaminoglycans (GAG) and thus, showing a potential application of these scaffolds for in vitro regeneration of articular cartilage tissue.

Design of drug-loaded 3D printing biomaterial inks and tailor-made pharmaceutical forms for controlled release.

Curcumin and chloramphenicol are drugs with different solubility properties in physiological conditions due to their hydrophobic and hydrophilic structure, respectively. In this work, sodium alginate-cellulose nanofibers (SA-CNF) based inks loaded with curcumin and/or chloramphenicol have been developed for syringe extrusion 3D printing technology. Printability and shape fidelity of the drug-loaded inks were analyzed through rheological characterization. Suitable drug-loaded inks were 3D printed showing shape fidelity, and samples were either freeze-dried or crosslinked with Ca2+ and air-dried to achieve functional pharmaceutical forms with different morphological characteristics. In vitro drug delivery tests were carried out from the resulted forms and it was observed that the release performed faster in freeze-dried than in Ca2+ crosslinked/air-dried ones for all cases, resulting in two different methods for controlling drug delivery over time. The differences in aqueous solubility of the drugs, the different CNF content of the inks and the surface area of the samples also played an important role during drug delivery, involving strategies to control the release over an extended duration.

3D printed alginate-cellulose nanofibers based patches for local curcumin administration.

Alginate and nanocellulose are potential biomaterials to be employed as bioinks for three-dimensional (3D) printing. Alginate-cellulose nanofibers (A-CNF) formulations with CNF amounts up to 5 wt% were developed and rheologically characterized to evaluate their printability. Results showed that formulations with less than 3 wt% CNF did not present suitable characteristics to ensure shape fidelity after printing. Selected A-CNF bioinks were 3D printed and freeze-dried to obtain porous scaffolds. Morphological and mechanical analysis were performed, showing that CNF contributed to the reinforcement of the scaffolds and modulated their porosity. The applicability for drug delivery was evaluated by the addition of curcumin to printable A-CNF formulations. The curcumin loaded bioinks were successfully 3D printed in patches and the in vitro release tests showed that alginate and CNF played an important role in curcumin stabilization, whereas the CNF content and the disintegration of the scaffold were essential in the release kinetics.

Synthesis of stimuli-responsive chitosan-based hydrogels by Diels-Alder cross-linking `click´ reaction as potential carriers for drug administration.

Stimuli-responsive chitosan-based hydrogels for biomedical applications using the Diels-Alder reaction were prepared. Furan modified chitosan (Cs-Fu) was cross-linked with polyetheramine derived bismaleimide at different equivalent ratios in order to determine the effect in the swelling and release properties on the final CsFu:BMI hydrogels. The Diels Alder cross-linking reaction was monitored by UV-vis spectroscopy and rheological measurements. Both the sol-gel transition value and the final storage modulus for the different formulations were similar and close to 40 min and 400 Pa, respectively. On the contrary, the swelling degree was found to be strongly dependent on the amount of bismaleimide, mainly in acidic medium, where the increased cross-linking reduced the swelling value in 25%, but maintaining the sustained drug release in the simulated gastrointestinal environment. Our study suggested that these DA-cross-linked chitosan hydrogels could be potential carriers for targeted drug administration.

Synthesis and characterization of a biocompatible chitosan-based hydrogel cross-linked via 'click' chemistry for controlled drug release.

A chemically cross-linked chitosan-based hydrogel was successfully synthesized through Diels-Alder (DA) reaction and characterized. The final product was obtained after different steps; on the one hand, furan-modified chitosan (Cs-Fu) was synthesized by the reaction of furfural with the free amino groups of chitosan. On the other hand, highlighting the novelty of the present research, maleimide-functionalized chitosan (Cs-AMI) was prepared by the reaction of a maleimide-modified aminoacid with the amino groups of chitosan through amide coupling. The two complementary chitosan derivatives were cross-linked to the final hydrogel network. Both modification reactions were confirmed by FTIR and 1H NMR, obtaining a degree of substitution (DS) of 31% and 26% for Cs-Fu and Cs-AMI, respectively. The as-designed hydrogel was analyzed in terms of microstructure, swelling capacity and rheological behaviour. The hydrogel showed pH-sensitivity, biocompatibility and inhibitory bacterial activity, promising features for biomedical applications, particularly for targeted-drug delivery.

Maleimide-grafted cellulose nanocrystals as cross-linkers for bionanocomposite hydrogels.

This article deals with the preparation of bionanocomposite hydrogels from natural polymers and nanoentities, an emerging class of materials for biotechnological and biomedical applications. Herein, the applicability of the Diels-Alder "click" reaction to the design of bionanocomposite hydrogels from furan modified gelatin using maleimide-functionalized cellulose nanocrystals as multifunctional cocross-linkers is demonstrated. The functionalization of cellulose nanocrystals with maleimide moieties was confirmed by XPS. The swelling and rheological properties of the resulting bionanocomposite confirmed the formation of hydrogel networks with covalently embedded nanoentities. The Diels-Alder reaction resulted in the formation of stiffer networks with lower swelling ratios due to the formation of additional cross-linking points. The designed "click" strategy proved to be a promising candidate for the formation of fully renewable bionanocomposite hydrogels.

Cellulose nanocrystals/polyurethane nanocomposites. Study from the viewpoint of microphase separated structure.

Cellulose nanocrystals (CNC) successfully obtained from microcrystalline cellulose (MCC) were dispersed in a thermoplastic polyurethane as matrix. Nanocomposites containing 1.5, 5, 10 and 30 wt% CNC were prepared by solvent casting procedure and properties of the resulting films were evaluated from the viewpoint of polyurethane microphase separated structure, soft and hard domains. CNC were effectively dispersed in the segmented thermoplastic elastomeric polyurethane (STPUE) matrix due to the favorable matrix-nanocrystals interactions through hydrogen bonding. Cellulose nanocrystals interacted with both soft and hard segments, enhancing stiffness and stability versus temperature of the nanocomposites. Thermal and mechanical properties of STPUE/CNC nanocomposites have been associated to the generated morphologies investigated by AFM images.

Surface modification of multiwalled carbon nanotubes via esterification using a biodegradable polyol.

Multiwalled carbon nanotubes (MWCNT) were surface modified firstly oxidizing them with a H2SO4/HNO3 mixture to obtain more reactive carboxylic groups on their surface and then higher functionality. Secondly the oxidized nanotubes (MWCNT-COOH) were dispersed in tetrahydrofuran (THF) and made react via esterification with a poly(hexamethylene carbonate-co-caprolactone)diol, a potentially biodegradable polyol with hydroxyl groups at its ends. Modification process steps were characterized using Fourier transform infrared spectroscopy, FT-IR, ultraviolet spectroscopy, UV, solubility in different solvents, thermo-gravimetric analysis, TGA, as well as atomic force microscopy, AFM. Results suggest that surface carboxylic groups are reactive enough to graft polymer chains onto their surface.

Effects of amine molecular structure on carbon nanotubes functionalization.

Three amines with different molecular structure, triethylenetetramine (TETA) and two polyetheramines (Jeffamine D-230 and Jeffamine T-403) were employed to functionalize multi-walled carbon nanotubes (MWCNT) previously oxidized by acid treatment. The functionalized MWCNT were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV-vis spectroscopy and the surface modification was investigated by field emission scanning electron microscopy (FE-SEM). Thermogravimetric analysis (TGA) was employed to quantify the amount of amine groups anchored to MWCNTs. The results have shown that the efficiency of amine functionalization is in the order TETA > D-230 > T-403, thus showing that amine chemical structure and molecular weight are important parameters on functionalization of carbon nanotubes.

Purification and functionalization of carbon nanotubes by classical and advanced oxidation processes.

Advanced oxidation technologies (AOT) were applied for the production of accurately controlled oxidized multi-walled carbon nanotubes. Fenton process is effective to get carboxylic (-COO- or -COOH) and OH groups on the surface of carbon nanotubes while Photofenton and UV/H2O2 processes mostly produce OH groups on surface of multiwalled carbon nanotubes (MWCNT). All of them preserve the structure of MWCNT allowing to achieve accurately controlled oxidized MWCNT. Fourier transform infrared spectroscopy (FTIR) and thermogravimetical analysis (TGA) show that the acid treatment is the more efficient technique to generate COOH groups on MWCNT surface. However, this chemical technique generates strong damages on the MWCNT structure, as demonstrated by TGA, field emission scanning electron microscopy and transmission electron microscopy results.