Development of Polyphenol-Functionalized Gelatin-Poly(vinylpyrrolidone) IPN for Potential Biomedical Applications.

Owing to their suitable physical and chemical properties, hydrogels have been considered a convenient choice for wound dressings because of the advantages that they offer, such as maintaining the moist environment required for wound healing. In this research, interpenetrating hydrogels of polyphenol-functionalized gelatin (GE), a water-soluble protein derived from natural polymer collagen with excellent biocompatibility, no immunogenicity, and hydrophilicity, and polyvinylpyrrolidone (PVP), a hydrophilic, non-toxic, biodegradable, biocompatible polymer that is soluble in many solvents, widely used in biomedical applications, particularly as a basic material for the manufacturing of hydrogel wound dressings, were synthesized. Gallic acid (GA) was selected in this work to study whether the interpenetrating polymer networks (IPNs) synthesized can provide antioxidant properties given that this material is intended to be used as a potential wound dressing. The obtained IPN hydrogels showed improved mechanical properties in comparison with pristine gelatin network (net-GE), a porous structure, and good thermal stability for biological applications. The antioxidant capacity of the IPNs functionalized with GA was compared to Trolox standards, obtaining a radical scavenging activity (RSA%) equivalent to a Trolox concentration of 400 µM.

Determination by Relaxation Tests of the Mechanical Properties of Soft Polyacrylamide Gels Made for Mechanobiology Studies.

Following the general aim of recapitulating the native mechanical properties of tissues and organs in vitro, the field of materials science and engineering has benefited from recent progress in developing compliant substrates with physical and chemical properties similar to those of biological materials. In particular, in the field of mechanobiology, soft hydrogels can now reproduce the precise range of stiffnesses of healthy and pathological tissues to study the mechanisms behind cell responses to mechanics. However, it was shown that biological tissues are not only elastic but also relax at different timescales. Cells can, indeed, perceive this dissipation and actually need it because it is a critical signal integrated with other signals to define adhesion, spreading and even more complicated functions. The mechanical characterization of hydrogels used in mechanobiology is, however, commonly limited to the elastic stiffness (Young's modulus) and this value is known to depend greatly on the measurement conditions that are rarely reported in great detail. Here, we report that a simple relaxation test performed under well-defined conditions can provide all the necessary information for characterizing soft materials mechanically, by fitting the dissipation behavior with a generalized Maxwell model (GMM). The simple method was validated using soft polyacrylamide hydrogels and proved to be very useful to readily unveil precise mechanical properties of gels that cells can sense and offer a set of characteristic values that can be compared with what is typically reported from microindentation tests.

Building a microfluidic cell culture platform with stiffness control using Loctite 3525 glue.

The study of mechanotransduction signals and cell response to mechanical properties requires designing culture substrates that possess some, or ideally all, of the following characteristics: (1) biological compatibility and adhesive properties, (2) stiffness control or tunability in a dynamic mode, (3) patternability on the microscale and (4) integrability in microfluidic chips. The most common materials used to address cell mechanotransduction are hydrogels, due to their softness. However, they may be impractical when complex scaffolds are sought and they lack viscous dissipative properties that are very important in mechanobiology. In this work, we show that an off-the-shelf, biocompatible photosensitive glue, Loctite 3525, may be used readily in mechanobiology assays without any special treatment prior to fabrication of cell culture platforms. Despite a high (MPa) stiffness easily tunable by UV exposure time at a fixed dose, 3T3 fibroblasts showed a response to the mechanics of the material similar to that obtained on much softer (kPa) hydrogels. Loctite's viscous dissipation properties indeed seemed to be responsible for such cell mechanical response, as suggested by recent works where more complex two-phase hydrogels were employed. More interestingly, it was possible to stiffen soft Loctite substrates by post-exposing them during cell culture, to observe changes in cell spreading caused by a dynamic stiffness modification. Thanks to Loctite 3525's patternability, micropillars were also fabricated to demonstrate the compatibility with traction force microscopy studies. Finally, the glue was used as an excellent adhesion layer for hydrogels on glass or PDMS, without the need for additional treatment, enabling the easy fabrication of microfluidic chips integrating hydrogels.

Method for the Direct Fabrication of Polyacrylamide Hydrogels with Controlled Stiffness in Polystyrene Multiwell Plates for Mechanobiology Assays.

Polyacrylamide (PAA) hydrogels are now widely used in mechanobiology because the well-defined available protocols allow a robust and reproducible control of substrate stiffness within a physiological range. However, several assays require hydrogels inside traditional plastic substrates and the current methods remain relatively tedious. Here, we present a simple and direct fabrication technique that successfully attaches PAA hydrogels inside polystyrene multiwell plates and Petri dishes of different sizes. It permits a control of the Young's modulus of the gels, within the desired range for mechanobiology. Some critical steps, that had to be overcome to guarantee protein conjugation and cell attachment, are detailed, as they differ from the standardized preparation on glass substrates. To validate our process, we demonstrated that HepG2 and 3T3L1 cell lines as well as primary hepatocytes seeded on PAA gels of different stiffnesses in plastics showed a mechanical response identical to the cells cultured on traditional gels.

Progress on the Use of Commercial Digital Optical Disc Units for Low-Power Laser Micromachining in Biomedical Applications.

The development of organ-on-chip and biological scaffolds is currently requiring simpler methods for microstructure biocompatible materials in three dimensions, to fabricate structural and functional elements in biomaterials, or modify the physicochemical properties of desired substrates. Aiming at addressing this need, a low-power CD-DVD-Blu-ray laser pickup head was mounted on a programmable three-axis micro-displacement system in order to modify the surface of polymeric materials in a local fashion. Thanks to a specially-designed method using a strongly absorbing additive coating the materials of interest, it has been possible to establish and precisely control processes useful in microtechnology for biomedical applications. The system was upgraded with Blu-ray laser for additive manufacturing and ablation on a single platform. In this work, we present the application of these fabrication techniques to the development of biomimetic cellular culture platforms thanks to the simple integration of several features typically achieved with traditional, less cost-effective microtechnology methods in one step or through replica-molding. Our straightforward approach indeed enables great control of local laser microablation or polymerization for true on-demand biomimetic micropatterned designs in transparent polymers and hydrogels and is allowing integration of microfluidics, microelectronics, surface microstructuring, and transfer of superficial protein micropatterns on a variety of biocompatible materials.