Noncovalent Targeting of Nanocarriers to Immune Cells with Polyphosphoester-Based Surfactants in Human Blood Plasma

Advanced Biomaterials Derived from Functional Polyphosphoesters: Synthesis, Properties, and Biomedical Applications

Polyphosphoesters (PPEs) represent an innovative class of biodegradable polymers, with the phosphate ester serving as the core repeating unit of their polymeric backbone. Recently, biomaterials derived from functionalized PPEs have garnered significant interest in biomedical applications because of their commendable biocompatibility, biodegradability, and the capacity for functional modification. This review commences with a brief overview of synthesis methodologies and the distinctive properties of PPEs, including thermoresponsiveness, degradability, stealth effect, and biocompatibility. Subsequently, the review delves into the latest applications of PPEs-based nanocarriers for drug or gene delivery and PPEs-based polymeric prodrugs and scaffolds in the biomedical field, presenting several illustrative examples for each application. By encapsulating the advancements of recent years, this review aims to offer an enhanced understanding and serve as a reference for the synthesis and biomedical applications of functional PPEs.

Polymer Brushes on Nanoparticles for Controlling the Interaction with Protein-Rich Physiological Media

The interaction of nanoparticles (NPs) with biological environments triggers the formation of a protein corona (PC), which significantly influences their behavior in vivo. This review explores the evolving understanding of PC formation, focusing on the opportunity for decreasing or suppressing protein-NP interactions by macromolecular engineering of NP shells. The functionalization of NPs with a dense, hydrated polymer brush shell is a powerful strategy for imparting stealth properties in order to elude recognition by the immune system. While poly(ethylene glycol) (PEG) has been extensively used for this purpose, concerns regarding its stability and immunogenicity have prompted the exploration of alternative polymers. The stealth properties of brush shells can be enhanced by tailoring functionalities and structural parameters, including the molar mass, grafting density, and polymer topology. Determining correlations between these parameters and biopassivity has enabled us to obtain polymer-grafted NPs with high colloidal stability and prolonged circulation time in biological media.

The Yin and Yang of the protein corona on the delivery journey of nanoparticles

Nanoparticles-based drug delivery systems have attracted significant attention in biomedical fields because they can deliver loaded cargoes to the target site in a controlled manner. However, tremendous challenges must still be overcome to reach the expected targeting and therapeutic efficacy in vivo. These challenges mainly arise because the interaction between nanoparticles and biological systems is complex and dynamic and is influenced by the physicochemical properties of the nanoparticles and the heterogeneity of biological systems. Importantly, once the nanoparticles are injected into the blood, a protein corona will inevitably form on the surface. The protein corona creates a new biological identity which plays a vital role in mediating the bio-nano interaction and determining the ultimate results. Thus, it is essential to understand how the protein corona affects the delivery journey of nanoparticles in vivo and what we can do to exploit the protein corona for better delivery efficiency. In this review, we first summarize the fundamental impact of the protein corona on the delivery journey of nanoparticles. Next, we emphasize the strategies that have been developed for tailoring and exploiting the protein corona to improve the transportation behavior of nanoparticles in vivo. Finally, we highlight what we need to do as a next step towards better understanding and exploitation of the protein corona. We hope these insights into the "Yin and Yang" effect of the protein corona will have profound implications for understanding the role of the protein corona in a wide range of nanoparticles.

Bioengineering CXCR4-overexpressing cell membrane functionalized ROS-responsive nanotherapeutics for targeting cerebral ischemia-reperfusion injury

Rationale: As a potentially life-threatening disorder, cerebral ischemia-reperfusion (I/R) injury is associated with significantly high mortality, especially the irreversible brain tissue damage associated with increased reactive oxygen radical production and excessive inflammation. Currently, the insufficiency of targeted drug delivery and “on-demand” drug release remain the greatest challenges for cerebral I/R injury therapy. Bioengineered cell membrane-based nanotherapeutics mimic and enhance natural membrane functions and represent a potentially promising approach, relying on selective interactions between receptors and chemokines and increase nanomedicine delivery efficiency into the target tissues.

Methods: We employed a systematic method to synthesize biomimetic smart nanoparticles. The CXCR4-overexpressing primary mouse thoracic aorta endothelial cell (PMTAEC) membranes and RAPA@HOP were extruded through a 200 nm polycarbonate porous membrane using a mini-extruder to harvest the RAPA@BMHOP. The bioengineered CXCR4-overexpressing cell membrane-functionalized ROS-responsive nanotherapeutics, loaded with rapamycin (RAPA), were fabricated to enhance the targeted delivery to lesions with pathological overexpression of SDF-1.

Results: RAPA@BMHOP exhibited a three-fold higher rate of target delivery efficacy via the CXCR4/SDF-1 axis than its non-targeting counterpart in an in vivo model. Additionally, in response to the excessive pathological ROS, nanotherapeutics could be degraded to promote “on-demand” cargo release and balance the ROS level by p-hydroxy-benzyl alcohol degradation, thereby scavenging excessive ROS and suppressing the free radical-induced focal damage and local inflammation. Also, the stealth effect of cell membrane coating functionalization on the surface resulted in extended circulation time and high stability of nanoparticles.

Conclusion: The biomimetic smart nanotherapeutics with active targeting, developed in this study, significantly improved the therapeutic efficacy and biosafety profiles. Thus, these nanoparticles could be a candidate for efficient therapy of cerebral I/R injury.

Polyphosphoester surfactants as general stealth coatings for polymeric nanocarriers

Opsonization of nanocarriers is one of the most important biological barriers for controlled drug delivery. The typical way to prevent such unspecific protein adsorption and thus fast clearance by the immune system is the covalent modification of drug delivery vehicles with poly(ethylene glycol) (PEG), so-called PEGylation. Recently, polyphosphoesters (PPEs) were identified as adequate PEG substitutes, however with the benefits of controllable hydrophilicity, additional chemical functionality, or biodegradability. Here, we present a general strategy by non-covalent adsorption of different nonionic PPE-surfactants to nanocarriers with stealth properties. Polyphosphoester surfactants with different binding motifs were synthesized by anionic ring-opening polymerization of cyclic phosphates or phosphonates and well-defined polymers were obtained. They were evaluated with regard to their cytotoxicity, protein interactions, and corona formation and their cellular uptake. We proved that all PPE-surfactants have lower cytotoxicity as the common PEG-based surfactant (Lutensol® AT 50) and that their hydrolysis is controlled by their chemical structure. Two polymeric nanocarriers, namely polystyrene and poly(methyl methacrylate), and bio-based and potentially biodegradable hydroxyethyl starch nanocarriers were coated with the PPE-surfactants. All nanocarriers exhibited reduced protein adsorption after coating with PPE-surfactants and a strongly reduced interaction with macrophages. This general strategy allows the transformation of polymeric nanocarriers into camouflaged nanocarriers and by the chemical versatility of PPEs will allow the attachment of additional moieties for advanced drug delivery.

Engineering at the nano-bio interface: harnessing the protein corona towards nanoparticle design and function

Unpredictable and uncontrollable protein adsorption on nanoparticles remains a considerable challenge to achieving effective application of nanotechnologies within biological environments. Nevertheless, engineered nanoparticles offer unprecedented functionality and control in probing and altering biological systems. In this review, we highlight recent advances in harnessing the "protein corona" formed on nanoparticles as a handle to tune functional properties of the protein-nanoparticle complex. Towards this end, we first review nanoparticle properties that influence protein adsorption and design strategies to facilitate selective corona formation, with the corresponding characterization techniques. We next focus on literature detailing corona-mediated functionalities, including stealth to avoid recognition and sequestration while in circulation, targeting of predetermined in vivo locations, and controlled activation once localized to the intended biological compartment. We conclude with a discussion of biocompatibility outcomes for these protein-nanoparticle complexes applied in vivo. While formation of the nanoparticle-corona complex may impede our control over its use for the projected nanobiotechnology application, it concurrently presents an opportunity to create improved protein-nanoparticle architectures by exploiting natural or guiding selective protein adsorption to the nanoparticle surface.

Cubosomes stabilized by a polyphosphoester-analog of Pluronic F127 with reduced cytotoxicity

Lyotropic liquid crystalline nanoparticles with bicontinuous cubic internal nanostructure, known as cubosomes, have been proposed as nanocarriers in various medical applications. However, as these nanoparticles show a certain degree of cytotoxicity, particularly against erythrocytes, their application in systemic administrations is limited to date. Intending to produce a more biocompatible formulation, we prepared cubosomes for the first time stabilized with a biodegradable polyphosphoester-analog of the commonly used Pluronic F127. The ABA-triblock copolymer poly(methyl ethylene phosphate)-block-poly(propylene oxide)-block-poly(methyl ethylene phosphate) (PMEP-b-PPO-b-PMEP) was prepared by organocatalyzed ring-opening polymerization of MEP. The cytotoxic features of the resulting formulation were investigated against two different cell lines (HEK-293 and HUVEC) and human red blood cells. The response of the complement system was also evaluated. Results proved the poly(phosphoester)-based formulation was significantly less toxic than that prepared using Pluronic F127 with respect to all the tested cell lines and, more importantly, hemolysis assay and complement system activation tests demonstrated its very high hemocompatibility. The potentially biodegradable poly(phosphoester)-based cubosomes represent a new and versatile platform for preparation of functional and smart nanocarriers.

Main-Chain Phosphorus-Containing Polymers for Therapeutic Applications

Polymers in which phosphorus is an integral part of the main chain, including polyphosphazenes and polyphosphoesters, have been widely investigated in recent years for their potential in a number of therapeutic applications. Phosphorus, as the central feature of these polymers, endears the chemical functionalization, and in some cases (bio)degradability, to facilitate their use in such therapeutic formulations. Recent advances in the synthetic polymer chemistry have allowed for controlled synthesis methods in order to prepare the complex macromolecular structures required, alongside the control and reproducibility desired for such medical applications. While the main polymer families described herein, polyphosphazenes and polyphosphoesters and their analogues, as well as phosphorus-based dendrimers, have hitherto predominantly been investigated in isolation from one another, this review aims to highlight and bring together some of this research. In doing so, the focus is placed on the essential, and often mutual, design features and structure-property relationships that allow the preparation of such functional materials. The first part of the review details the relevant features of phosphorus-containing polymers in respect to their use in therapeutic applications, while the second part highlights some recent and innovative applications, offering insights into the most state-of-the-art research on phosphorus-based polymers in a therapeutic context.

Construction of polyphosphoesters with the main chain of rigid backbones and stereostructures via organocatalyzed ring-opening polymerization

A highly stereoregular polyphosphoester with a rigid cyclohexylene structure in the main chain was constructed via ring-opening polymerization (ROP) in the presence of an organic catalyst system.