Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. In order to fit functional demand, materials with desired physical, chemical, biological, biomechanical and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

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Biomedical Applications of Biodegradable Polymers

Functional π-Gelators and Their Applications

Increasing power and energy demands for next-generation portable and flexible electronics such as roll-up displays, photovoltaic cells, and wearable devices have stimulated intensive efforts to explore flexible, lightweight and environmentally friendly energy storage devices. Flexible solid-state supercapacitors (SCs) have attracted increasing interest because they can provide substantially higher specific/volumetric energy density compared to conventional capacitors. Additionally, flexible solid-state SCs are typically small in size, highly reliable, light-weight, easy to handle, and have a wide range of operation temperatures. In this regard, solid-state SCs hold great promise as new energy storage devices for flexible and wearable electronics. In this article, we review recent achievements in the design, fabrication and characterization of flexible solid-state SCs. Moreover, we also discuss the current challenges and future opportunities for the development of high-performance flexible solid-state SCs.

Flexible solid-state supercapacitors: design, fabrication and applications

Clinical applications of current photodynamic therapy (PDT) agents are often limited by their low singlet oxygen ((1)O2) quantum yields, as well as by photobleaching and poor biocompatibility. Here we present a new PDT agent based on graphene quantum dots (GQDs) that can produce (1)O2 via a multistate sensitization process, resulting in a quantum yield of ~1.3, the highest reported for PDT agents. The GQDs also exhibit a broad absorption band spanning the UV region and the entire visible region and a strong deep-red emission. Through in vitro and in vivo studies, we demonstrate that GQDs can be used as PDT agents, simultaneously allowing imaging and providing a highly efficient cancer therapy. The present work may lead to a new generation of carbon-based nanomaterial PDT agents with overall performance superior to conventional agents in terms of (1)O2 quantum yield, water dispersibility, photo- and pH-stability, and biocompatibility.

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A graphene quantum dot photodynamic therapy agent with high singlet oxygen generation

Polymeric materials with antimicrobial activity

With the increasing antibiotic resistance of microorganisms, there is a growing interest in the design and development of new materials that are effective in killing bacteria to replace conventional antibiotics. Herein, a new anionic water-soluble polythiophene (PTP) and a cationic porphyrin (TPPN) are synthesized and characterized. They can form a complex through electrostatic interactions, and efficient energy transfer from PTP to TPPN occurs upon irradiation under white light (400-800 nm). The energy of TPPN transfers to triplet by intersystem crossing, followed by sensitization of oxygen molecule to enhance the efficiency of singlet oxygen generation related to TPPN itself. The positive charges of PTP/TPPN complex promote its adsorption to the negatively charged bacteria membranes of gram-negative Escherichia coli and gram-positive Bacillus subtilis through electrostatic interactions, and the singlet oxygen effectively kills the bacteria. The photosensitized inactivation of bacteria for the PTP/TPPN complex is efficient, and about 70% reduction of bacterial viability is observed after only 5 min of irradiation with white light at a fluence rate of 90 mW x cm(-2) (27 J x cm(-2)). The technique provides a promising application in photodynamic inactivation of bacteria on the basis of enhanced energy transfer offered by light-harvesting conjugated polymers.

Conjugated polymer/porphyrin complexes for efficient energy transfer and improving light-activated antibacterial activity

We prepared a new conjugated polymer nanoparticle with the size of about 50 nm that is prepared by electrostatic assembly of cationic conjugated polymer PFO and anionic poly(l-glutamic acid) conjugated with anticancer drug doxorubicin (PFO/PG-Dox). The PFO exhibits good fluorescence quantum yield, photostability, and little cytotoxicity to meet the essential requests for cell imaging. In PFO/PG-Dox nanoparticles, the fluorescence of PFO is highly quenched by Dox by electron transfer mechanism, and thus the PFO is in the fluorescence "turn-off' state. After PFO/PG-Dox nanoparticles are exposed to carboxypeptidase or are taken up by cancer cells, the poly(l-glutamic acid) is hydrolysed to release the Dox, inducing the activation of PFO fluorescence to "turn-on" state. This multifunctional nanoparticle system can deliver Dox to targeted cancer cells and monitor the Dox release based on fluorescence "turn-on" signal of PFO, which concurrently images the cancer cells. The present work opens the door for new functional studies of conjugated polymer in simultaneous imaging and disease therapeutics.

Conjugated Polymer Nanoparticles for Drug Delivery and Imaging

Design Guidelines For Conjugated Polymers With Light‐Activated Anticancer Activity

A fluorescent film sensor was prepared by chemical modification of a polyfluorene derivative on a glass-plate surface. X-ray photoelectron spectroscopy and ellipsometry measurements demonstrate the covalent attachment of the polyfluorene derivative to the glass-plate surface. The sensor was used to detect Cu2+ ions in aqueous solution by a mechanism exploiting fluorescence quenching of conjugated polymers. Among the tested metal ions, the film sensor presents good selectivity towards Cu2+ ions. Further experiments show that the sensing process is reversible. Moreover, sensory microarrays based on conjugated polymers targeting Cu2+ ions are constructed, which display similar sensing performance to that of the film sensor. The structural motif in which conjugated polymers are covalently confined to a solid substrate surface offers several attractive advantages for sensing applications. First, in comparison with film sensors in which small fluorescent molecules are employed as sensing elements, the sensitivity of our new film sensor is enhanced due to the signal-amplifying effect of the conjugated polymers. Second, the film sensors or microarrays can be used in aqueous environments, which is crucial for their potential use in a wide range of real-world systems. Since the sensing process is reversible, the sensing materials can be reused. Third, unlike physically coated polymer chains, the covalent attachment of the grafted chains onto a material surface precludes desorption and imparts long-term stability of the polymer chains.

Hongwei Tang

Papers

Conjugated polymer/porphyrin complexes for efficient energy transfer and improving light-activated antibacterial activity

Conjugated Polymer Nanoparticles for Drug Delivery and Imaging

Design Guidelines For Conjugated Polymers With Light‐Activated Anticancer Activity

Development of Film Sensors Based on Conjugated Polymers for Copper (II) Ion Detection

Fluorescent DNA–poly(phenylenevinylene) hybrid hydrogels for monitoring drug release