Elements of Polymer Science
E. Desmond Goddard, James V. Gruber in Principles of Polymer Science and Technology in Cosmetics and Personal Care, 1999
Linear chains may also be arranged at short intervals along a single main chain via trifunctional branch points. These “comb” polymers can be synthesized by polymerization of macromers (a monomer consisting of a polymerizable group linked to a short polymer chain) or by grafting (13). Branched polymers contain branch points (junctions) that connect three or four subchains, which may be side chains or parts of a main chain. Polymers are statistically branched if side chains of different lengths are irregularly distributed along the main chain. These polymers resemble trees. In star polymers (14) three or more branches sprout from a common core. Star polymers with multifunctional ends on the arms can add additional monomers. The resulting polymers, known as dendrimers (15), can be considered as tree polymers with regular sequences of branches or star polymers with subsequent secondary branches.
Nanoparticle-Based Molecular Imaging in Living Subjects
Martin G. Pomper, Juri G. Gelovani, Benjamin Tsui, Kathleen Gabrielson, Richard Wahl, S. Sam Gambhir, Jeff Bulte, Raymond Gibson, William C. Eckelman in Molecular Imaging in Oncology, 2008
Dendrimers, which are dendritric molecules reminiscent of trees (and termed such accordingly), generally remain without a precise, consistent definition in the literature. At their most basic, they are repeatedly branching structures comprising monomeric units of any chemical structure—they are thus by definition a form of polymer. However, dendrimers are considered here outside the purview of linear or block (co)polymer nanostructures because of their multifunctional status and intricate potential geometries. These features are conducive to therapeutic delivery and imaging as molecule carriers; indeed, dendrimers’ biocompatibility, versatility, and size make them ideal nanostructures in many ways. The precision with which dendrimers can be assembled at the nanoscale with respect to size, shape, surface chemistry, solubility, and amenability to decoration with desired imaging and therapeutic molecules make these innately modular nanoparticles clinically attractive (34). It is clear that the key physical and medical properties of dendrimers are intimately related to their structure, which is a function of the chemical methods and components used in their construction. Properties such as the specific utility, encapsulation parameters, and performance of dendrimers have been reviewed well elsewhere (34–36).
Nanomaterials in Chemotherapy
D. Sakthi Kumar, Aswathy Ravindran Girija in Bionanotechnology in Cancer, 2023
Dendrimers are unimolecular, highly branched, and three-dimensional polymers (Figure 8.7), which can be synthesized from monomeric units by adding new branches in a step-by-step manner until a uniform tree-like structure is formed. Depending on the branching architecture, one can design perfect dendrimers, dendrons, dendronized polymers, and hyperbranched polymers. A typical dendrimer possesses unique nanoarchitecture with an average diameter of 1–10 nm, low viscosity, high solubility, high surface functionality, and biocompatibility. Due to the presence of active termini on its surface, easy functionalization is possible in dendrimers. In comparison to linear polymers, dendritic polymer architecture is advantageous for drug delivery applications [162]. For example, due to its defined multivalency and drug conjugation, the addition of targeting ligand and/or solubilizing modalities can be incorporated in a single dendrimer. Dendrimer-based drug carriers showed extended circulation time and altered biodistribution profiles compared to bare drugs in preclinical animal models.
Small interfering RNA-based nanotherapeutics for treating skin-related diseases
Published in Expert Opinion on Drug Delivery, 2023
Yen-Tzu Chang, Tse-Hung Huang, Ahmed Alalaiwe, Erica Hwang, Jia-You Fang
Dendrimers are a novel generation of polymeric-based nanoparticles that promote the cutaneous absorption of small-molecular drugs and macromolecules. This polymer-based nanosystem exhibits a tree-like polymer structure to facilely modify the nanoparticle size. Dendrimers are comprised of three topological fragments: a focal core, building blocks with some interior layers having repeating units, and multiple peripheral functional groups. These branched polymers manifest special qualities of nanoscale diameter, multivalency, surface functionalization, and low polydispersity [59]. Dendrimers can interact with SC lipids to improve drug permeation. Charged dendrimers are reported to denature keratin in the SC layer to increase the transcellular diffusion of penetrants [60]. The high density of the cationic charge renders multiple attaching sites for siRNA molecules. The protection of RNA-based agents from nuclease is also a major concern in nucleic acid delivery. It has been proven that the complexation of siRNA molecules with dendrimers protects nucleic acids from enzymatic degradation [61]. The abundant tertiary amines in dendrimers promote the endosomal escape of siRNAs via a proton sponge effect [62]. It is expected that tertiary amines are protonated inside the endosomes. This effect disintegrates the endosome membrane, activating the release of cargos.
The development of peptide- and oligonucleotide-based drugs to prevent the formation of abnormal tau in tauopathies
Published in Expert Opinion on Drug Discovery, 2023
Madia Lozupone, Vittorio Dibello, Rodolfo Sardone, Fabio Castellana, Roberta Zupo, Luisa Lampignano, Ilaria Bortone, Roberta Stallone, Mario Altamura, Antonello Bellomo, Antonio Daniele, Vincenzo Solfrizzi, Francesco Panza
ASOs in general are unable to cross cellular membranes and blood-tissue barriers, such as the BBB, which is only permeable to lipophilic molecules of molecular weight<600 Da. Furthermore, ASOs must resist/escape intracellular degradation mechanisms, primarily with endogenous nucleases. There are three predominant strategies for the effective delivery of ASOs: (1) direct chemical alteration of the ASO molecule; (2) conjugation with specific targeting molecules, and (3) encapsulation in non-viral vesicles [123]. Within the CNS, increased efficiency in ASO delivery, protection from degradation, shielding the negative charge for more efficient cellular uptake, and lower immunogenicity can all be achieved through the encapsulation of ASOs in non-viral vectors including polymers. Also, polycationic dendrimers, which are highly branched polymers with easily modifiable surfaces, can be used as potential nonviral transfection nanocarriers [124].
Drip irrigation biofouling with treated wastewater: bacterial selection revealed by high-throughput sequencing
Published in Biofouling, 2019
Kévin Lequette, Nassim Ait-Mouheb, Nathalie Wéry
Drippers and irrigation pipes are made of polyethylene. Some microorganisms are able to colonise and alter polyethylene surfaces by modifying the functional groups on the surface, the surface topography or the hydrophobicity/hydrophilicity of the surface (Restrepo-Flórez et al. 2014). These changes can facilitate bacterial attachment to the surface and thus biofilm development on polyethylene surfaces. There are several types of polyethylene according to their density or degree of branching. For instance, Aeromonas and Nocardia were found in pipe and dripper biofilms whereas only the genus Pseudomonas was observed in dripper biofilms (Figure 5). These genera have polyethylene biodegradation abilities (Restrepo-Flórez et al. 2014). In the current study, no information was available concerning the material properties of the pipes and drippers. Nevertheless, this parameter might explain the presence of these bacterial genera in the pipe and dripper biofilms. An investigation of the effect of the material properties of polyethylene on the microbial communities would therefore improve present knowledge regarding biofouling processes in drip irrigation systems.
Related Knowledge Centers
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