Humidity-Triggered Relaxation of Polyelectrolyte Complexes as a Robust Approach to Generate Extracellular Matrix Biomimetic Films

Robust, Sprayable, and Multifunctional Hydrogel Coating through a Polycation Reinforced (PCR) Surface Bridging Strategy

The sprayable hydrogel coatings that can establish robust adhesion onto diverse materials and devices hold enormous potential; however, a significant challenge persists due to monomer hydration, which impedes even coverage during spraying and induces inadequate adhesion post-gelation. Herein, a polycation-reinforced (PCR) surface bridging strategy is presented to achieve tough and sprayable hydrogel coatings onto diverse materials. The polycations offer superior wettability and instant electrostatic interactions with plasma-treated substrates, facilitating an effective spraying application. This PCR-based hydrogel coatings demonstrate tough adhesion performance to inert PTFE and silicone, including remarkable shear strength (161 ± 49 kPa for PTFE), interfacial toughness (198 ± 27 J m-2 for PTFE), and notable tolerance to cyclic tension (10 000 cycles, 200% strain, silicone). Meanwhile, this method can be applied to various hydrogel formulations, offering diverse functionalities, including underwater adhesion, lubrication, and drug delivery. Furthermore, the PCR concept enables the conformal construction of durable hydrogel coatings onto sophisticated medical devices like cardiovascular stents. Given its simplicity and adaptability, this approach paves an avenue for incorporating hydrogels onto solid surfaces and potentially promotes untapped applications.

Recent Developments in Layer-by-Layer Assembly for Drug Delivery and Tissue Engineering Applications

Surfaces with biological functionalities are of great interest for biomaterials, tissue engineering, biophysics, and for controlling biological processes. The layer-by-layer (LbL) assembly is a highly versatile methodology introduced 30 years ago, which consists of assembling complementary polyelectrolytes or biomolecules in a stepwise manner to form thin self-assembled films. In view of its simplicity, compatibility with biological molecules, and adaptability to any kind of supporting material carrier, this technology has undergone major developments over the past decades. Specific applications have emerged in different biomedical fields owing to the possibility to load or immobilize biomolecules with preserved bioactivity, to use an extremely broad range of biomolecules and supporting carriers, and to modify the film's mechanical properties via crosslinking. In this review, the focus is on the recent developments regarding LbL films formed as 2D or 3D objects for applications in drug delivery and tissue engineering. Possible applications in the fields of vaccinology, 3D biomimetic tissue models, as well as bone and cardiovascular tissue engineering are highlighted. In addition, the most recent technological developments in the field of film construction, such as high-content liquid handling or machine learning, which are expected to open new perspectives in the future developments of LbL, are presented.

Microporous Polyelectrolyte Complexes by Hydroplastic Foaming

Polyelectrolyte complexes (PECs) have emerged as an attractive category of materials for their water processability and some similarities to natural biopolymers. Herein, we employ the intrinsic hydroplasticity of PEC materials to enable the generation of porous structures with the aid of gas foaming. Such foamable materials are fabricated by simply mixing polycation, polyanion, and a UV-initiated chemical foaming agent in an aqueous solution, followed by molding into thin films. The gas foaming of the PEC films can be achieved upon exposure to UV illumination under water, where the films are plasticized and the gaseous products from the photolysis of foaming agents afford the formation, expanding, and merging of numerous bubbles. The porosity and morphology of the resulting porous films can be customized by tuning film composition, foaming conditions, and especially the degree of plasticizing effect, illustrating the high flexibility of this hydroplastic foaming method. Due to the rapid initiation of gas foaming, the present method enables the formation of porous structures via an instant one-step process, much more efficient than those existing strategies for porous PEC materials. More importantly, such a pore-forming mechanism might be extended to other hydroplastic materials (e.g., biopolymers) and help to yield hydroplasticity-based processing strategies.

A Perspective on the Glass Transition and the Dynamics of Polyelectrolyte Multilayers and Complexes

Polyelectrolyte multilayers (PEMs) or polyelectrolyte complexes (PECs), formed by layer-by-layer assembly or the mixing of oppositely charged polyelectrolytes (PEs) in aqueous solution, respectively, have potential applications in health, energy, and the environment. PEMs and PECs are very tunable because their structure and properties are influenced by factors such as pH, ionic strength, salt type, humidity, and temperature. Therefore, it is increasingly important to understand how these factors affect PECs and PEMs on a molecular level. In this Feature Article, we summarize our contributions to the field in the development of approaches to quantify the swelling, thermal properties, and dynamic mechanical properties of PEMs and PECs. First, the role of water as a plasticizer and in the glass-transition temperature (Tg) in both strong poly(diallyldimethylammonium)/poly(sodium 4-styrenesulfonate) (PDADMA/PSS) and weak poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) systems is presented. Then, factors influencing the dynamics of PECs and PEMs are discussed. We also reflect on the swelling of PEMs in response to different salts and solvent additives. Last, the nature of water's microenvironment in PEMs/PECs is discussed. A special emphasis is placed on experimental techniques, along with molecular simulations. Taken together, this review presents an outlook and offers recommendations for future research directions, such as studying the additional effects of hydrogen-bonding hydrophobic interactions.

Quenching the Macroporous Collapse of Polyelectrolyte Multilayer Films for Repeated Drug Loading

Macroporous structures can be developed within polyelectrolyte multilayer films for efficient drug loading, but these structures tend to collapse or fracture during conventional drying procedures. Herein, a facile dehydrating method for macroporous polyelectrolyte multilayer films is proposed using solvent exchange to ethanol and then spontaneous evaporation. During these processes, the collapse of the macroporous structures can be effectively avoided, which can be ascribed to a combined effect of two factors. On one hand, capillary pressure during ethanol evaporation is relatively small since the surface tension of ethanol is much lower than that of water. On the other hand, solvent exchange suppresses the interdiffusion of polyelectrolytes and substantially increases the mechanical strength of the macroporous films, more than three orders of magnitude, making the pore walls highly tolerant of the capillary pressure. The stability of macroporous polyelectrolyte films to ethanol enables the repeated wicking from the ethanol solution of drugs, leading to a higher loading beyond previous studies. Such a high loading is favorable for the long-term release of drugs from the surfaces of modified substrates and maintaining a local drug concentration above the minimum effective concentration.

Biomedical polymers: synthesis, properties, and applications

Biomedical polymers have been extensively developed for promising applications in a lot of biomedical fields, such as therapeutic medicine delivery, disease detection and diagnosis, biosensing, regenerative medicine, and disease treatment. In this review, we summarize the most recent advances in the synthesis and application of biomedical polymers, and discuss the comprehensive understanding of their property-function relationship for corresponding biomedical applications. In particular, a few burgeoning bioactive polymers, such as peptide/biomembrane/microorganism/cell-based biomedical polymers, are also introduced and highlighted as the emerging biomaterials for cancer precision therapy. Furthermore, the foreseeable challenges and outlook of the development of more efficient, healthier and safer biomedical polymers are discussed. We wish this systemic and comprehensive review on highlighting frontier progress of biomedical polymers could inspire and promote new breakthrough in fundamental research and clinical translation.

Mir-22-incorporated polyelectrolyte coating prevents intima hyperplasia after balloon-induced vascular injury

Drug-coated balloons (DCB) offer potential to deliver drugs to treat coronary lesions but without leaving permanent implants behind. Paclitaxel and sirolimus are anti-proliferation drugs that are commonly used by commercially...

Fabrication of "Spongy Skin" on Diversified Materials Based on Surface Swelling Non-Solvent-Induced Phase Separation

Porous surfaces have attracted tremendous interest for customized incorporation of functional agents on biomedical devices. However, the versatile preparation of porous structures on complicated devices remains challenging. Herein, we proposed a simple and robust method to fabricate "spongy skin" on diversified polymeric substrates based on non-solvent-induced phase separation (NIPS). Through the swelling and the subsequent phase separation process, interconnected porous structures were directly formed onto the polymeric substrates. The thickness and pore size could be regulated in the ranges of 5-200 and 0.3-0.75 μm, respectively. The fast capillary action of the porous structure enabled controllable loading and sustained release of ofloxacin and bovine albumin at a high loading dosage of 79.9 and 24.1 μg/cm², respectively. We verified that this method was applicable to diversified materials including polymethyl methacrylate, polystyrene, thermoplastic polyurethane, polylactide acid, and poly(lactic-co-glycolic acid) and can be realized onto TCPS cell culture plates. This NIPS-based method is promising to generate porous surfaces on medical devices for incorporating therapeutic agents.

miR-22 eluting cardiovascular stent based on a self-healable spongy coating inhibits in-stent restenosis

The in-stent restenosis (IRS) after the percutaneous coronary intervention contributes to the major treatment failure of stent implantation. MicroRNAs have been revealed as powerful gene medicine to regulate endothelial cells (EC) and smooth muscle cells (SMC) in response to vascular injury, providing a promising therapeutic candidate to inhibit IRS. However, the controllable loading and eluting of hydrophilic bioactive microRNAs pose a challenge to current lipophilic stent coatings. Here, we developed a microRNA eluting cardiovascular stent via the self-healing encapsulation process based on an amphipathic poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCL-PEG-PCL, PCEC) triblock copolymer spongy network. The miR-22 was used as a model microRNA to regulate SMC. The dynamic porous coating realized the uniform and controllable loading of miR-22, reaching the highest dosage of 133 pmol cm-2. We demonstrated that the sustained release of miR-22 dramatically enhanced the contractile phenotype of SMC without interfering with the proliferation of EC, thus leading to the EC dominating growth at an EC/SMC ratio of 5.4. More importantly, the PCEC@miR-22 coated stents showed reduced inflammation, low switching of SMC phenotype, and low secretion of extracellular matrix, which significantly inhibited IRS. This work provides a simple and robust coating platform for the delivery of microRNAs on cardiovascular stent, which may extend to other combination medical devices, and facilitate practical application of bioactive agents in clinics.

A facile method for high-throughput screening of drug-eluting coatings in droplet microarrays based on ultrasonic spray deposition

Coating modification such as drug-eluting coating is one of the most important approaches for the functionalization of biomedical devices. However, the throughputs are limited in conventional coating methods and the concept of miniaturization is rarely fulfilled. A droplet microarray (DMA), as a unique high-throughput platform, can avoid cross-contamination and reduce the consumption of materials which is inherently suitable for coating research yet is difficult to apply with coating materials via traditional methods. Here, we bring up a facile method based on ultrasonic spray deposition to integrate coating materials into a DMA. Several common polymer materials were selected to fabricate a DMA, and the obtained DMA showed the ability to anchor water droplets and form specific patterns. Coating arrays with a typical sandwich structure were also prepared for the high-throughput screening of drug-eluting coatings to demonstrate the potential of the platform in coating research. This developed method is efficient and compatible and enriches the choices of materials that can be applied in DMAs.

Dual pH-/thermo-responsive chitosan-based hydrogels prepared using "click" chemistry for colon-targeted drug delivery applications

A dual pH-/thermo-responsive hydrogel was designed based on a polyelectrolyte complex of polyacrylic acid (PAA) and norbornene-functionalized chitosan (CsNb), which was synergized with chemical crosslinking using bistetrazine-poly(N-isopropyl acrylamide) (bisTz-PNIPAM). The thermo-responsive polymeric crosslinker, bisTz-PNIPAM, was synthesized via reversible addition-fragmentation transfer polymerization of NIPAM. FTIR, XRD, rheological and morphological analyses demonstrated the successful formation of the polyelectrolyte network. The highly porous structure generated through the in-situ "click" reaction between Tz and Nb resulted in a higher drug loading (29.35 %). The hydrogel (COOH/NH₂ mole ratio of 3:1) exhibited limited drug release (8.5 %) of 5-ASA at a pH of 2.2, but it provided an almost complete release (92 %) at pH 7.4 and 37 °C within 48 h due to the pH responsiveness of PAA, hydrogel porosity, and shrinkage behavior of PNIPAM. The hydrogels were biodegradable and non-toxic against human fibroblast cells, suggesting their considerable potential for a colon-targeted drug delivery system.

Hierarchical Capillary Coating to Biofunctionlize Drug-Eluting Stent for Improving Endothelium Regeneration

The drug-eluting stent (DES) has become one of the most successful and important medical devices for coronary heart disease, but yet suffers from insufficient endothelial cell (EC) growth and intima repair, eventually leading to treatment failure. Although biomacromolecules such as vascular endothelial growth factor (VEGF) would be promising to promote the intima regeneration, combining hydrophilic and vulnerable biomacromolecules with hydrophobic drugs as well as preserving the bioactivity after harsh treatments pose a huge challenge. Here, we report on a design of hierarchical capillary coating, which composes a base solid region and a top microporous region for incorporating rapamycin and VEGF, respectively. The top spongy region can guarantee the efficient, safe, and controllable loading of VEGF up to 1 μg/cm² in 1 minute, providing a distinctive real-time loading capacity for saving the bioactivity. Based on this, we demonstrate that our rapamycin-VEGF hierarchical coating impressively promoted the competitive growth of endothelial cells over smooth muscle cells (ratio of EC/SMC~25) while relieving the adverse impact of rapamycin to ECs. We further conducted the real-time loading of VEGF on stents and demonstrate that the hierarchical combination of rapamycin and VEGF showed remarkable endothelium regeneration while maintaining a very low level of in-stent restenosis. This work paves an avenue for the combination of both hydrophobic and hydrophilic functional molecules, which should benefit the next generation of DES and may extend applications to diversified combination medical devices.