Multifunctional Poly(ethylene glycol): Synthesis, Characterization, and Potential Applications of Dendritic–Linear–Dendritic Block Copolymer Hybrids

Dendritic-Linear Copolymer and Dendron Lipid Nanoparticles for Drug and Gene Delivery

Polymers constitute a diverse class of macromolecules that have demonstrated their unique advantages to be utilized for drug or gene delivery applications. In particular, polymers with a highly ordered, hyperbranched structure─"dendrons"─offer significant benefits to the design of such nanomedicines. The incorporation of dendrons into block copolymer micelles can endow various unique properties that are not typically observed from linear polymer counterparts. Specifically, the dendritic structure induces the conical shape of unimers that form micelles, thereby improving the thermodynamic stability and achieving a low critical micelle concentration (CMC). Furthermore, through a high density of highly ordered functional groups, dendrons can enhance gene complexation, drug loading, and stimuli-responsive behavior. In addition, outward-branching dendrons can support a high density of nonfouling polymers, such as poly(ethylene glycol), for serum stability and variable densities of multifunctional groups for multivalent cellular targeting and interactions. In this paper, we review the design considerations for dendron-lipid nanoparticles and dendron micelles formed from amphiphilic block copolymers intended for gene transfection and cancer drug delivery applications. These technologies are early in preclinical development and, as with other nanomedicines, face many obstacles on the way to clinical adoption. Nevertheless, the utility of dendron micelles for drug delivery remains relatively underexplored, and we believe there are significant and dramatic advancements to be made in tumor targeting with these platforms.

Remdesivir-loaded bis-MPA hyperbranched dendritic nanocarriers for pulmonary delivery

Remdesivir is the only clinically available antiviral drug for the treatment of COVID-19. However, its very limited aqueous solubility confines its therapeutic activity and the development of novel inhaled nano-based drug delivery systems of remdesivir for enhanced lung tissue targeting and efficacy is internationally pursued. In this work 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) hyperbranched dendritic nano-scaffolds were employed as nanocarriers of remdesivir. The produced nano-formulations, empty and loaded, consisted of monodisperse nanoparticles with spherical morphology and neutral surface charge and sizes ranging between 80 and 230 nm. The entrapment efficiency and loading capacity of the loaded samples were 82.0% and 14.1%, respectively, whereas the release of the encapsulated drug was complete after 48 h. The toxicity assays in healthy MRC-5 lung diploid fibroblasts and NR8383 alveolar macrophages indicated their suitability as potential remdesivir carriers in the respiratory system. The novel nano-formulations are non-toxic in both tested cell lines, with IC₅₀ values higher than 400 μΜ after 72 h treatment. Moreover, both free and encapsulated remdesivir exhibited very similar IC₅₀ values, at the range of 80-90 μM, while its aqueous solubility was increased, overall presenting a suitable profile for application in inhaled delivery of therapeutics.

Dendritic Hydrogels Induce Immune Modulation in Human Keratinocytes and Effectively Eradicate Bacterial Pathogens

Infections caused by antibiotic-resistant bacteria are globally a major threat, leading to high mortality rates and increased economic burden. Novel treatment strategies are therefore urgently needed by healthcare providers to protect people. Biomaterials that have inherent antibacterial properties and do not require the use of antibiotics present an attractive and feasible avenue to achieve this goal. Herein, we demonstrate the effect of a new class of cationic hydrogels based on amino-functional hyperbranched dendritic-linear-dendritic copolymers (HBDLDs) exhibiting excellent antimicrobial activity toward a wide range of clinical Gram-positive and Gram-negative bacteria, including drug-resistant strains isolated from wounds. Intriguingly, the hydrogels can induce the expression of the antimicrobial peptides RNase 7 and psoriasin, promoting host-mediated bacterial killing in human keratinocytes (HaCaT). Moreover, treatment with the hydrogels decreased the proinflammatory cytokine IL-1β, reactive nitrogen species (NO), and mitochondrial reactive oxygen species (ROS) in S. aureus-infected HaCaT cells, conjunctively resulting in reduced inflammation.

Synthesis and Characterization of Cationic Dendrimer-PDMS Hybrids

A modular strategy for the synthesis of dendron-linear polymer hybrids comprised of a flexible polydimethylsiloxane (PDMS) midblock with cationic 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) dendron end groups is developed. The invention of a scalable methodology to access quaternary ammonium carboxylate building blocks and their direct use in esterification chemistry enables rapid access to cationic bis-MPA dendrons. The convergent click coupling of highly charged dendrons to hydrophobic PDMS chain-ends gives a 12-membered family of hybrids that are comprised of different dendron generations (G1-3) and quaternary ammonium alkyl chain lengths (C4 , C8 , C12 , C16 ). This provides a library of materials with variable hydrophobicity, charge density, and chain-end valency. The physical behavior of the dendron-linear PDMS hybrid copolymers significantly changes after introduction of the cationic dendron end-groups and leads to soft-solid materials as a result of inhibited chain mobility. These PDMS-dendron hybrids are expected to behave as surface-active antimicrobial additives in bulk cross-linked silicone systems.

Off-Stoichiometric Thiol-Ene Chemistry to Dendritic Nanogel Therapeutics

A novel platform of dendritic nanogels is herein presented, capitalizing on the self-assembly of allyl-functional polyesters based on dendritic-linear-dendritic amphiphiles followed by simple cross-linking with complementary monomeric thiols via UV initiated off-stoichiometric thiol-ene chemistry. The facile approach enabled multigram creation of allyl reactive nanogel precursors, in the size range of 190-295 nm, being readily available for further modifications to display a number of core functionalities while maintaining the size distribution and characteristics of the master batch. The nanogels are evaluated as carriers of a spread of chemotherapeutics by customizing the core to accommodate each individual cargo. The resulting nanogels are biocompatible, displaying diffusion controlled release of cargo, maintained therapeutic efficacy, and decreased cargo toxic side effects. Finally, the nanogels are found to successfully deliver pharmaceuticals into a 3D pancreatic spheroids tumor model.

Controlled ATRP Synthesis of Novel Linear-Dendritic Block Copolymers and Their Directed Self-Assembly in Breath Figure Arrays

Herein, we report the formation and characterization of novel amphiphilic linear-dendritic block copolymers (LDBCs) composed of hydrophilic dendritic poly(ether-ester), PEE, blocks and hydrophobic linear poly(styrene), PSt. The LDBCs are synthesized via controlled atom transfer radical polymerization (ATRP) initiated by a PEE macroinitiator. The copolymers formed have narrow molecular mass distributions and are designated as LGn-PSt Mn, in which LG represents the PEE fragment, n denotes the generation of the dendron (n = 1⁻3), and Mn refers to the average molecular mass of the LDBC (Mn = 3.5⁻68 kDa). The obtained LDBCs are utilized to fabricate honeycomb films by a static "breath figure" (BF) technique. The copolymer composition strongly affects the film morphology. LDBCs bearing acetonide dendron end groups produce honeycomb films when the PEE fraction is lower than 20%. Pore uniformity increases as the PEE content decreases. For LDBCs with hydroxyl end groups, only the first generation LDBCs yield BF films, but with a significantly smaller pore size (0.23 μm vs. 1⁻2 μm, respectively). Although higher generation LDBCs with free hydroxyl end groups fail to generate honeycomb films by themselves, the use of a cosolvent or addition of homo PSt leads to BF films with a controllable pore size (3.7⁻0.42 μm), depending on the LDBC content. Palladium complexes within the two triazole groups in each of the dendron's branching moieties can also fine-tune the morphology of the BF films.

Effects of molecular weight distribution on the self-assembly of end-functionalized polystyrenes

The molecular weight distribution of hydroxyl-end-functionalized polystyrenes shows effects on the self-assembly of patterned porous films and the mechanical strength.

Recent Advances in Dendritic Macromonomers for Hydrogel Formation and Their Medical Applications

Hydrogels represent one of the most important classes of biomaterials and are of interest for various medical applications including wound repair, tissue engineering, and drug release. Hydrogels possess tunable mechanical properties, biocompatibility, nontoxicity, and similarity to natural soft tissues. The need for hydrogels with specific properties, based on the design requirements of the in vitro, in vivo, or clinical application, motivates researchers to develop new synthetic approaches and cross-linking methodologies to form novel hydrogels with unique properties. The use of dendritic macromonomers represents one elegant strategy for the formation of hydrogels with specific properties. Specifically, the uniformity of dendrimers combined with the control of their size, architecture, density, and surface groups make them promising cross-linkers for hydrogel formation. Over the last two decades, a large variety of dendritic-based hydrogels are reported for their potential use in the clinic. This review describes the state of the art with these different dendritic hydrogel formulations including their design requirements, the synthetic routes, the measurement and determination of their properties, the evaluation of their in vitro and in vivo performances, and future perspectives.

Synthesis, nanoprecipitation and pH sensitivity of amphiphilic linear-dendritic hybrid polymers and hyperbranched-polydendrons containing tertiary amine functional dendrons

The combination of linear polymers with dendritic chain-ends has led to numerous studies of linear-dendritic polymer hybrid materials. Interchain branching within the linear segment of these materials has recently extended this concept to the formation of soluble hyperbranched-polydendrons. Here, the introduction of amphiphilicity into hyperbranched-polydendrons has been achieved for the first time through the use of tertiary amine functional dendritic chain-ends and branched hydrophobic polymer segments. The synthesis and aqueous nanoprecipitation of these branched materials is compared with their linear-dendritic polymer analogues, showing that chain-end chemistry/generation, precipitation medium pH and polymer architecture are all capable of influencing the ability to generate nanoparticles, the resulting nanoparticle diameter and dispersity, and subsequent response to changes in pH.

Synthesis, characterization and association behavior of linear-dendritic amphiphilic diblock copolymers based on poly(ethylene oxide) and a dendron derived from 2,2′-bis(hydroxymethyl)propionic acid

Two new amphiphilic linear-dendritic block copolymers have been synthesized and characterized. And their association behaviors have also been studied.

Polyamidoamine and polyglycerol; their linear, dendritic and linear–dendritic architectures as anticancer drug delivery systems

This review covers the latest advances in the conjugation of chemotherapeutics such as doxorubicin, paclitaxel, methotrexate, fluorouracil and cisplatin to dendritic polymers, including polyamidoamine dendrimers, hyperbranched polyglycerols and their linear analogues, with a focus on their cytotoxicity, biodistribution and biodegradability.

The dendrimer paradox – high medical expectations but poor clinical translation

This review was written with the intention to critically evaluate the status of dendrimers as drug carriers and find answers as to why this class of compounds has not translated into the clinic despite 40 years of research.

Functional porous membranes from amorphous linear dendritic polyester hybrids

Non-toxic and functional linear dendritic hybrids were synthesized and exploited to generate reactive porous membranes for straightforward functionalization in aqueous media.

Multiple interfaces in self-assembled breath figures

Progress in the breath figure method is reviewed by emphasizing the role of the multiple interfaces and the applications of honeycomb films in separation, biocatalysis, biosensing, templating, stimuli-responsive surfaces and adhesive surfaces.

Convenient divergent synthesis of linear-dendron block polyphosphoesters via acyclic diene metathesis polymerization

ADMET polymerization was successfully applied for the synthesis of linear-dendritic polyphosphoester structures by using macromolecular chain stoppers.