Controlling the Cell-Adhesion Properties of Poly(acrylic acid)/Polyacrylamide Hydrogen-Bonded Multilayers

Design of a UCST Polymer with Strong Hydrogen Bonds and Reactive Moieties for Facile Polymer-Protein Hybridization

Polymer-protein hybrids have been extensively used in biomedical fields. Polymers with upper critical solution temperature (UCST) behaviors can form a hydrated coacervate phase below the cloud point (T_cp), providing themselves the opportunity to directly capture hydrophilic proteins and form hybrids in aqueous solutions. However, it is always a challenge to obtain a UCST polymer that could aggregate at a high temperature at a relatively low concentration and also efficiently bind with proteins. In this work, a UCST polymer reactive with proteins was designed, and its temperature responsiveness and protein-capture ability were investigated in detail. The polymer was synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylamide (AAm) and N-acryloxysuccinimide (NAS). Interestingly, taking advantage of the partial hydrolysis of NAS into acrylic acid (AAc), the obtained P(AAm-co-NAS-co-AAc) polymer exhibited an excellent UCST behavior and possessed good protein-capture ability. It showed a relatively higher T_cp (81 °C) at a lower concentration (0.1 wt %) and quickly formed polymer-protein hybrids with high protein loading and without losing protein bioactivity, and both the polymer and polymer-protein nanoparticles showed good cytocompatibility. All the findings are attributed to the unique structure of the polymer, which provided not only the strong and stable hydrogen bonds but also the quick and mild reactivity. The work offers an easy and mild strategy for polymer-protein hybridization directly in aqueous solutions, which may find applications in biomedical fields.

Photopolymerizable Biomaterials and Light-Based 3D Printing Strategies for Biomedical Applications

Since the advent of additive manufacturing, known commonly as 3D printing, this technology has revolutionized the biofabrication landscape and driven numerous pivotal advancements in tissue engineering and regenerative medicine. Many 3D printing methods were developed in short course after Charles Hull first introduced the power of stereolithography to the world. However, materials development was not met with the same enthusiasm and remained the bottleneck in the field for some time. Only in the past decade has there been deliberate development to expand the materials toolbox for 3D printing applications to meet the true potential of 3D printing technologies. Herein, we review the development of biomaterials suited for light-based 3D printing modalities with an emphasis on bioprinting applications. We discuss the chemical mechanisms that govern photopolymerization and highlight the application of natural, synthetic, and composite biomaterials as 3D printed hydrogels. Because the quality of a 3D printed construct is highly dependent on both the material properties and processing technique, we included a final section on the theoretical and practical aspects behind light-based 3D printing as well as ways to employ that knowledge to troubleshoot and standardize the optimization of printing parameters.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

pH Responsiveness of Multilayered Films and Membranes Made of Polysaccharides

We investigated the pH-dependent properties of multilayered films made of chitosan (CHI) and alginate (ALG) and focused on their postassembly response to different pH environments using a quartz crystal microbalance with dissipation monitoring (QCM-D), swelling studies, ζ potential measurements, and dynamic mechanical analysis (DMA). In an acidic environment, the multilayers presented lower dissipation values and, consequently, higher moduli when compared with the values obtained for the pH used during the assembly (5.5). When the multilayers were exposed to alkaline environments, the opposite behavior occurred. These results were further corroborated by the ability of this multilayered system to exhibit a reversible swelling-deswelling behavior within the pH range from 3 to 9. The changes in the physicochemical properties of the multilayer system were gradual and different from those of individual solubilized polyelectrolytes. This behavior is related to electrostatic interactions between the ionizable groups combined with hydrogen bonding and hydrophobic interactions. Beyond the pH range of 3-9, the multilayers were stabilized by genipin cross-linking. The multilayered films also became more rigid while the pH responsiveness conferred by the ionizable moieties of the polyelectrolytes was preserved. This work demonstrates the versatility and feasibility of LbL methodology to generate inherently pH stimulus-responsive nanostructured films. Surface functionalization using pH responsiveness endows several biomedical applications with abilities such as drug delivery, diagnostics, microfluidics, biosensing, and biomimetic implantable membranes.

Injectable hydrogels based on poly(ethylene glycol) and derivatives as functional biomaterials

The design criteria for injectable, in situ-gelling hydrogels are reviewed in conjunction with highlights on recent progress in the preparation of injectable PEG and PEG-analogue poly(oligoethylene glycol methacrylate) (POEGMA) hydrogels.

Surface modulation of complex stiffness via layer-by-layer assembly as a facile strategy for selective cell adhesion

A facile approach to achieve selective cell adhesion by modulating surface complex stiffness based on layer-by-layer assembly is reported.

Effects of anionic surfactants on the water permeability of a model stratum corneum lipid membrane

The stratum corneum (SC) is the ourtermost layer of the epidermis and has a brick-and-mortar-like structure, in which multilamellar lipid bilayers surround flattened dead cells known as corneocytes. The SC lipid membranes provide the main pathway for the transport of water and other substances through the SC. While the physicochemical properties of the SC can be affected by exogenous materials such as surfactants, little is known about how the water barrier function of the SC lipid membranes is compromised by common surfactants. Here, we study the effect of common anionic surfactants on the water permeability of a model SC lipid membrane using a quartz crystal microbalance with dissipation monitoring (QCM-D). Particularly, the effect of sodium dodecyl sulfate (SDS) and sodium lauryl ether sulfate (SLES) is compared. These two surfactants share commonality in their molecular structure: sulfate in the polar headgroup and the same apolar tail. The mass of the lipid membranes increases after the surfactant treatment at or above the critical micelle concentration (CMC) of the surfactants due to their absorption into the membranes. The incorporation of the surfactants into the lipid membranes is also accompanied by partial dissolution of the lipids from the model SC lipid membranes as confirmed by Fourier-transform infrared (FT-IR) spectroscopy. Although the water sorption of pure SDS is much lower than that of pure SLES, the water sorption of SDS-treated membranes increases significantly similar to that of SLES-treated membranes. By combining QCM-D and FT-IR spectroscopy, we find that the chain conformational order and stiffness of the lipid membranes decrease after SDS treatment, resulting in the increased water sorption and diffusivity. In contrast, the conformational order and stiffness of the SLES-treated lipid membranes increase, suggesting that the increased water sorption capacity of SLES-treated lipid membranes is due to the hygroscopic nature of SLES.

Facile fabrication of ultrathin antibacterial hydrogel films via layer-by-layer “click” chemistry

Ultrathin antibacterial hydrogel films were prepared via layer-by-layer “click” chemistry.