Responsive Polymers as Smart Nanomaterials Enable Diverse Applications

Responsive polymers undergo reversible or irreversible physical or chemical modifications in response to a change in environment or stimulus, e.g., temperature, pH, light, and magnetic or electric fields. Polymeric nanoparticles (NPs), which constitute a diverse set of morphologies, including micelles, vesicles, and core-shell geometries, have been successfully prepared from responsive polymers and have shown great promise in applications ranging from drug delivery to catalysis. In this review, we summarize pH, thermo-, photo-, and enzymatic responsiveness for a selection of polymers. We then discuss the formation of NPs made from responsive polymers. Finally, we highlight how NPs and other nanomaterials are enabling a wide range of smart applications with improved efficiency, as well as improved sustainability and recyclability of polymeric systems.

Polymer Therapeutics: Biomarkers and New Approaches for Personalized Cancer Treatment

Polymer therapeutics (PTs) provides a potentially exciting approach for the treatment of many diseases by enhancing aqueous solubility and altering drug pharmacokinetics at both the whole organism and subcellular level leading to improved therapeutic outcomes. However, the failure of many polymer-drug conjugates in clinical trials suggests that we may need to stratify patients in order to match each patient to the right PT. In this concise review, we hope to assess potential PT-specific biomarkers for cancer treatment, with a focus on new studies, detection methods, new models and the opportunities this knowledge will bring for the development of novel PT-based anti-cancer strategies. We discuss the various "hurdles" that a given PT faces on its passage from the syringe to the tumor (and beyond), including the passage through the bloodstream, tumor targeting, tumor uptake and the intracellular release of the active agent. However, we also discuss other relevant concepts and new considerations in the field, which we hope will provide new insight into the possible applications of PT-related biomarkers.

Core–shell microspheres delivering FGF-2 and BMP-2 in different release patterns for bone regeneration

Sequential delivery of FGF-2 and BMP-2 efficiently bridged the bone defects and remodeled the bone graft.

[Stimuli-sensitive polymer systems]

The polymers can be found in different forms in solution (particles, capsules, pseudo-micelles, hydrogels…) or on surface with important prospects in many field applications. These polymer systems are particularly very good candidates to entrap, transport and deliver an active substance in biomedical applications however with many limitations on control of release of a given target. The stimuli-sensitive polymers, also called smart or environmentally sensitive polymers, present physical or chemical changes under the action of small variations of an external stimulus. This signal acts as a stimulus which causes the change of conformation and/or solvation of the macromolecular chains by modifying their various interactions. The stimuli are classified into two broad categories: physical or external stimuli: temperature, mechanical stress, light, magnetic and electric fields; chemical and biochemical or internal stimuli: pH, ionic strength, chemical molecule (glucose, redox) or biochemical (enzymes, antigens…). The use of stimuli-sensitive pathway is widely used in the literature to enhance or trigger the release of an active compound. In this paper, we present the different stimuli addressing the theoretical aspects, polymers corresponding to these stimuli. Some examples illustrate these systems for the controlled release of active compounds.

Optimization of release pattern of FGF-2 and BMP-2 for osteogenic differentiation of low-population density hMSCs

In the modern design, most delivery systems for bone regeneration focus on a single growth factor (GF) or a simple mixture of multiple GFs, overlooking the coordination of proliferation and osteogenesis induced by various factors. In this study, core-shell microspheres with poly-l-lactide core-poly(lactic-co-glycolic acid) shell were fabricated, and two GFs, basic fibroblast growth factor 2 (FGF-2) and bone morphogenetic protein 2 (BMP-2) were encapsulated into the core or/and shell. The effects of different release patterns (parallel or sequential manners) of FGF-2 and BMP-2 from these core-shell microspheres on the osteogenic differentiation of low-population density human mesenchymal stem cells (hMSCs) were investigated and the temporal organization of GF release was optimized. In vitro experiments suggested that induction of osteogenic differentiation of low-population density hMSCs by the sequential delivery of FGF-2 followed by BMP-2 from the core-shell microspheres (group S2) was much more efficient than that by the parallel release of the two factors from uniform microspheres (group U). The osteogenic induction by the sequential delivery of BMP-2 followed by FGF-2 from core-shell microspheres (group S1) was even worse than that from microspheres loaded with BMP-2 in both core and shell (group B), although comparable to the cases of parallel delivery of dual GFs (group P). This study showed the advantages of group S2 microspheres in inducing osteogenic differentiation of low-population density hMSCs and the necessity of time sequence studies in tissue engineering while multiple GFs are involved.

Stimuli-responsive polymeric nanocarriers for the controlled transport of active compounds: concepts and applications

The use of polymeric nanocarriers to transport active compounds like small-molecular drugs, peptides, or genes found an increased attention throughout the different fields of natural sciences. Not only that these nanocarriers enhance the properties of already existing drugs in terms of solubility, bioavailability, and prolonged circulation times, furthermore they can be tailor-made in such a manner that they selectively release their cargo at the desired site of action. For the triggered release, these so-called smart drug delivery systems are designed to react on certain stimuli like pH, temperature, redox potential, enzymes, light, and ultrasound. Some of these stimuli are naturally occurring in vivo, for example the difference in pH in different cellular compartments while others are caused by the disease, which is to be treated, like differences in pH and temperature in some tumor tissues. Other external applied stimuli, like light and ultrasound, allow the temporal and spatial control of the release, since they are not triggered by any biological event. This review gives a brief overview about some types of stimuli-responsive nanocarriers with the main focus on organic polymer-based systems. Furthermore, the different stimuli and the design of corresponding responsive nanocarriers will be discussed with the help of selected examples from the literature.

Novel reduction-sensitive micelles for triggered intracellular drug release

Novel reduction-sensitive micelles based on poly(ethylene oxide)-b-poly(N-methacryloyl-N'-(t-butyloxycarbonyl)cystamine) (PEO-b-PMABC) diblock copolymers were developed and applied for triggered intracellular drug release. PEO-b-PMABC block copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of MABC with dithioester-capped PEO as macroRAFT agent. Gel permeation chromatography (GPC) and (1)H NMR analysis showed that the copolymers have controlled compositions and molecular weights, indicating the living nature of polymerization. These copolymers were self-assembled into micelles. The physicochemical characteristics and reduction-sensitivity of the resultant micelles were investigated by fluorescence measurement, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The results showed that PEO-b-PMABC micelles are stable at normal physiologic condition but readily cleaved into free copolymers under reducing environment. In vitro release of doxorubicin (DOX) and cell experiments showed that the drug-loaded PEO-b-PMABC micelles accomplished much faster drug release under reducing condition and higher anticancer efficacy as compared to the control without reduction-sensitivity, indicating great potential of PEO-b-PMABC micelles for efficient intracellular drug delivery.