In vitro biological evaluation of high molecular weight hyperbranched polyglycerols
Introduction
Hyperbranched polymers that can be prepared in a convenient single step make them potential alternatives to dendrimers in applications where a precise structure is not necessary [1]. These applications include viscosity modification and cross linking where the polymer characteristics such as globular structure, low viscosity and the large number of functional groups are exploited [2]. Initially polydispersities were large but more recent theoretical and experimental work has shown that controlled polymerization of AB2 monomers is possible by slow monomer addition [3]. In particular, synthesis of hyperbranched polyglycerols (HPGs) with low polydispersities and predetermined molecular weights were reported using anionic ring opening multibranching polymerization of glycidol with slow monomer addition and partial deprotonation of the initiator [4]. The structure of the polymers is shown in Fig. 1. Recently we reported the synthesis of very high molecular weight HPGs with low polydispersities using high monomer to initiator ratios in the presence and absence of emulsifying solvents [5]. Narrowly polydisperse HPGs (polydispersity index (PDI)=Mw/Mn=1.1–1.4, where Mw and Mn are the weight and number average molecular weights, respectively) were synthesized using dioxane as emulsifying agent. Broader molecular weight distributions with low molecular weight fractions were obtained when diglyme was used although the low molecular weight fractions could be removed by dialysis. We prepared a series of polymers with various molecular weights with a relatively low PDI=1.1–1.8 and the Mw range up to 1,475,000. As the number of functional hydroxyl groups approximately equals the degree of polymerization, synthesis of higher molecular weight HPGs is of significant interest as such materials have numerous potential applications and have properties likely unattainable in a practical sense by other approaches, given the complexity inherent in synthesizing higher generation dendrimers. Such polymers, with low intrinsic viscosity and a very large number of derivatizable hydroxyl groups, would seem to be excellent candidates for applications in nanotechnology and in nanomedicine.
Due to their structural similarities to poly(ethylene glycol) (PEG) and polysaccharides, polyglycerols (PGs) are also expected to be biocompatible [6]. The availability of multiple functional groups in the HPG class of polyether polyols is an advantage in pharmaceutical and medical applications compared to linear PEG. An additional advantage is that HPG is thermally and oxidatively more stable than PEG [7] and of much lower viscosity for comparable molecular weights, potentially opening up the concentration range over which these polyethers can be used. Recently we reported the biocompatibility of low molecular weight polymers (Mn∼3000) using several in vitro techniques and animal toxicity studies where HPGs were found to be as biocompatible as PEG, suggesting that these robust polymers are promising biomaterials [8]. The biocompatibility of polymers is a function of molecular weight, however, as volume exclusion, cell aggregation, polymer adsorption and solution viscosity all increase strongly with molecular weight. In addition, in the case of HPGs, the large number of functional end groups could potentially affect interactions with biological macromolecules or cells. We therefore selected two high molecular weight HPGs and studied their biocompatibility properties in detail using a variety of in vitro techniques. The results are reported in this article.
Tests of coagulation (prothrombin time (PT), activated partial thromboplastin time (APTT), and plasma recalcification time (PRT), thrombelastograph parameters (TEG)), platelet activation (PAC-1, fibrinogen and CD62 expression), complement activation (C3a levels), red blood cell aggregation, plasma protein precipitation as well as cytotoxicity experiments were conducted.
Section snippets
Materials
All chemicals were purchased from Sigma-Aldrich Canada Ltd. (Oakville, ON) and used without further purification except glycidol (96%) which was purified by vacuum distillation and stored over molecular sieves in a refrigerator (2–4 °C). 1,1,1-tris(hydroxymethyl)propane (Fluka) and potassium methylate solution (25 wt% in methanol, Fluka) were used as supplied. Anhydrous diglyme and dioxane were also obtained from Aldrich and used without further drying. For the in vitro biocompatibility testing
Results and discussion
HPGs are thought to be a promising candidate for biotechnology applications [6]. Detailed descriptions of their synthesis, biocompatibility and applications have been reported [4], [7], [8]. However the data available to date were limited to low molecular weight fractions (Mn⩽20,000). Very recently we reported the synthesis and solution properties of several HPGs with molecular weights as high as 700,000 (Mn) [5]. We have found that narrowly polydispersed polymers can be synthesized using
Conclusions
High molecular weight hyperbranched PGs appear to have very little effect on a variety of measures of biocompatibility in vitro. Although they are of high molecular weight, the inherently compact hyperbranched structure removes many of the disadvantages associated with the exposure of high molecular weight linear polymers to blood and cells. In fact, the HPGs behave in solution more like proteins than linear polymers. The high molecular weight means there are a large number of reactive sites
References (27)
- et al.
Hyperbranched polymers: from synthesis to applications
Prog Polym Sci
(2004) - et al.
Dendritic polyglycerol: a new versatile biocompatible material
Rev Mol Biotech
(2002) - et al.
The hydrodynamic radii of macromolecules and their effect on red blood cell aggregation
Biophys J
(2004) - et al.
Dendrimers: relationship between structure and biocompatibility in vitro and preliminary studies on the biodistribution of 125I-labeled polyamidoamine dendrimers in vivo
J Control Release
(2000) - et al.
Biomaterial-associated thrombosis: roles of coagulation factors, complement, platelets and leukocytes
Biomaterials
(2004) - et al.
Changes in the platelet membrane glycoprotein Iib–IIIa complex during platelet activation
J Biol Chem
(1985) - et al.
Biomaterials for blood-contacting applications
Biomaterials
(1994) Precipitation of proteins with polyethylene glycol
Methods Enzymol
(1990)- et al.
Designing dendrimers for biological applications
Nat Biotechnol
(2005) - et al.
Hyperbranched polymers prepared via the core-dilution/slow addition technique: computer simulation of molecular weight distribution and degree of branching
Macromolecules
(1998)
Controlled synthesis of hyperbranched polyglycerols by ring-opening multibranching polymerization
Macromolecules
Synthesis, characterization, and viscoelastic properties of high molecular weight hyperbranched polyglycerols
Macromolecules
Self-assembled monolayers of dendritic polyglycerol derivatives on gold that resist the adsorption of proteins
Chem-A Eur J
Cited by (218)
A universal multivalent hyperbranched delivery platform for circumventing multidrug resistance via double camouflage and rapid bonding with cell
2023, Journal of Drug Delivery Science and TechnologyPreparation, characterization and targeted antitumor effects of polyglycerol-hyaluronic acid functionalized tungsten oxide nanocomposites
2023, Materials Today CommunicationsDrug–polymer conjugates: Challenges, opportunities, and future prospects in clinical trials
2023, Polymer-Drug Conjugates: Linker Chemistry, Protocols and ApplicationsIn vitro biocompatibility evaluations of pH-sensitive Bi<inf>2</inf>MoO<inf>6</inf>/NH<inf>2</inf>-GO conjugated polyethylene glycol for release of daunorubicin in cancer therapy
2023, Colloids and Surfaces B: BiointerfacesCitation Excerpt :The samples were taken after incubating them at 37 °C for 2 h. The concentration of C3/C4 was investigated after the incubation, and compared with the control in order to evaluate the nanocarrier activation of the complement system [46]. XRD analysis was used to study the purity and crystal structure of the products Fig. (2a).
Water-soluble ZnO quantum dots modified by polyglycerol: The pH-sensitive and targeted fluorescent probe for delivery of an anticancer drug
2022, Journal of Drug Delivery Science and TechnologyLinear Polyglycerol for N-terminal-selective Modification of Interleukin-4
2022, Journal of Pharmaceutical Sciences