Hydrophobically derivatized hyperbranched polyglycerol as a human serum albumin substitute

Basement Membrane Mimetic Hydrogel Cooperates with Rho-Associated Protein Kinase Inhibitor to Promote the Development of Acini-Like Salivary Gland Spheroids

Successful engineering of functional salivary glands necessitates the creation of cell-instructive environments for ex vivo expansion and lineage specification of primary human salivary gland stem cells (hS/PCs). Herein, basement membrane mimetic hydrogels were prepared using hyaluronic acid, cell adhesive peptides, and hyperbranched polyglycerol (HPG), with or without sulfate groups, to produce "hyperGel+" or "hyperGel", respectively. Differential scanning fluorescence experiments confirmed the ability of the sulphated HPG precursor to stabilize fibroblast growth factor 10. The hydrogels were nanoporous, cytocompatibile and cell-permissive, enabling the development of multicellular hS/PC spheroids in 14 days. Incorporation of sulfated HPG species in the hydrogel enhanced cell proliferation. Culture of hS/PCs in hyperGel+ in the presence of a Rho kinase inhibitor, Y-27632 (Y-27), led to the development of spheroids with a central lumen, increased the expression of acinar marker aquaporin-3 at the transcript level (AQP3), and decreased the expression of ductal marker keratin 7 at both the transcript (KRT7) and the protein levels (K7). Reduced expression of transforming growth factor beta (TGF-β) targets SMAD2/3 was also observed in Y27-treated cultures, suggesting attenuation of TGF-β signaling. Thus, hyperGel+ cooperates with the ROCK inhibitor to promote the development of lumened spheroids with enhanced expression of acinar markers.

Preclinical PET Imaging and Toxicity Study of a 68Ga-Functionalized Polymeric Cardiac Blood Pool Agent

Cardiac blood pool imaging is currently performed almost exclusively with 99mTc-based compounds and SPECT/CT imaging. Using a generator-based PET radioisotope has a few advantages, including not needing nuclear reactors to produce it, obtaining better resolution in humans, and potentially reducing the radiation dose to the patient. When the shortlived radioisotope 68Ga is used, it can be applied repeatedly on the same day—for example, for the detection of bleeding. Our objective was to prepare and evaluate a long-circulating polymer functionalized with gallium for its biodistribution, toxicity, and dosimetric properties. A 500 kDa hyperbranched polyglycerol was conjugated to the chelator NOTA and radiolabeled rapidly at room temperature with 68Ga. It was then injected intravenously into a rat, and gated imaging allowed us to easily observe wall motion and cardiac contractility, confirming the suitability of this radiopharmaceutical for cardiac blood pool imaging. Internal radiation dose calculations showed that the radiation doses that patients would receive from the PET agent would be 2.5× lower than those from the 99mTc agent. A complete 14-day toxicology study in rats concluded that there were no gross pathology findings, changes in body or organ weights, or histopathological events. This radioactive-metal-functionalized polymer might be a suitable non-toxic agent to advance for clinical application.

Recent Progress in Nanomaterial-Based Biosensors and Theranostic Nanomedicine for Bladder Cancer

Bladder cancer (BCa) is one of the most expensive and common malignancies in the urinary system due to its high progression and recurrence rate. Although there are various methods, including cystoscopy, biopsy, and cytology, that have become the standard diagnosis methods for BCa, their intrinsic invasive and inaccurate properties need to be overcome. The novel urine cancer biomarkers are assisted by nanomaterials-based biosensors, such as field-effect transistors (FETs) with high sensitivity and specificity, which may provide solutions to these problems. In addition, nanomaterials can be applied for the advancement of next-generation optical imaging techniques and the contrast agents of conventional techniques; for example, magnetic resonance imaging (MRI) for the diagnosis of BCa. Regarding BCa therapy, nanocarriers, including mucoadhesive nanoparticles and other polymeric nanoparticles, successfully overcome the disadvantages of conventional intravesical instillation and improve the efficacy and safety of intravesical chemotherapy for BCa. Aside from chemotherapy, nanomedicine-based novel therapies, including photodynamic therapy (PDT), photothermal therapy (PTT), chemodynamic therapy (CDT), sonodynamic therapy (SDT), and combination therapy, have afforded us new ways to provide BC therapy and hope, which can be translated into the clinic. In addition, nanomotors and the nanomaterials-based solid tumor disassociation strategy provide new ideas for future research. Here, the advances in BCa diagnosis and therapy mentioned above are reviewed in this paper.

Hydrotropic Hydrogels Prepared from Polyglycerol Dendrimers: Enhanced Solubilization and Release of Paclitaxel

Polyglycerol dendrimers (PGD) exhibit unique properties such as drug delivery, drug solubilization, bioimaging, and diagnostics. In this study, PGD hydrogels were prepared and evaluated as devices for controlled drug release with good solubilization properties. The PGD hydrogels were prepared by crosslinking using ethylene glycol diglycidylether (EGDGE). The concentrations of EGDGE and PGDs were varied. The hydrogels were swellable in ethanol for loading paclitaxel (PTX). The amount of PTX in the hydrogels increased with the swelling ratio, which is proportional to EGDGE/OH ratio, meaning that heterogeneous crosslinking of PGD made high dense region of PGD molecules in the matrix. The hydrogels remained transparent after loading PTX and standing in water for one day, indicating that PTX was dispersed in the hydrogels without any crystallization in water. The results of FTIR imaging of the PTX-loaded PGD hydrogels revealed good dispersion of PTX in the hydrogel matrix. Sixty percent of the loaded PTX was released in a sink condition within 90 min, suggesting that the solubilized PTX would be useful for controlled release without any precipitation. Polyglycerol dendrimer hydrogels are expected to be applicable for rapid release of poorly water-soluble drugs, e.g., for oral administration.

Modification of carbon-based nanomaterials by polyglycerol: recent advances and applications

Hyperbranched polymers, a subclass of dendritic polymers, mimic nature's components such as trees and nerves. Hyperbranched polyglycerol (HPG) is a hyperbranched polyether with outstanding physicochemical properties, including high water-solubility and functionality, biocompatibility, and an antifouling feature. HPG has attracted great interest in the modification of different objects, in particular carbon-based nanomaterials. In this review, recent advances in the synthesis and application of HPG to modify carbon-based nanomaterials, including graphene, carbon nanotubes, fullerene, nanodiamonds, carbon dots, and carbon fibers, are reviewed.

Gram Scale Synthesis of Dual-Responsive Dendritic Polyglycerol Sulfate as Drug Delivery System

Biocompatible polymers with the ability to load and release a cargo at the site of action in a smart response to stimuli have attracted great attention in the field of drug delivery and cancer therapy. In this work, we synthesize a dual-responsive dendritic polyglycerol sulfate (DR-dPGS) drug delivery system by copolymerization of glycidol, ε-caprolactone and an epoxide monomer bearing a disulfide bond (SSG), followed by sulfation of terminal hydroxyl groups of the copolymer. The effect of different catalysts, including Lewis acids and organic bases, on the molecular weight, monomer content and polymer structure was investigated. The degradation of the polymer backbone was proven in presence of reducing agents and candida antarctica Lipase B (CALB) enzyme, which results in the cleavage of the disulfides and ester bonds, respectively. The hydrophobic anticancer drug Doxorubicin (DOX) was loaded in the polymer and the kinetic assessment showed an enhanced drug release with glutathione (GSH) or CALB as compared to controls and a synergistic effect of a combination of both stimuli. Cell uptake was studied by using confocal laser scanning microscopy with HeLa cells and showed the uptake of the Dox-loaded carriers and the release of the drug into the nucleus. Cytotoxicity tests with three different cancer cell lines showed good tolerability of the polymers of as high concentrations as 1 mg mL-1, while cancer cell growth was efficiently inhibited by DR-dPGS@Dox.

Role of stealth lipids in nanomedicine-based drug carriers

The domain of nanomedicine owns a wide-ranging variety of lipid-based drug carriers, and novel nanostructured drug carriersthat are further added to this range every year. The primary goal behind the exploration of any new lipid-based nanoformulation is the improvement of the therapeutic index of the concerned drug molecule along with minimization in the associated side-effects. However, for maintaining a sustained delivery of these intravenously injected lipoidal nanomedicines to the targeted tissues and organ systems in the body, longer circulation in the bloodstream, as well as their stability, are important. After administration, upon recognition as foreign entities in the body, these systems are rapidly cleared by the cells associated with the mononuclear phagocyte system. In order to provide these lipid-based systems with long circulation characteristics, techniques such as coating of the lipoidal surface with an inert polymeric material like polyethylene glycol (PEG) assists in imparting 'stealth properties' to these nanoformulations for avoiding recognition by the macrophages of the immune system. In this review, detailed importance is given to the hydrophilic PEG polymer and the role played by PEG-linked lipid polymers in the field of nanomedicine-based drug carriers. The typical structure and classification of stealth lipids, clinical utility, assemblage techniques, physicochemical characterization, and factors governing the in-vivo performance of the PEG-linked lipids containing formulations will be discussed. Eventually, the novel concept of accelerated blood clearance (ABC) phenomenon associated with the use of PEGylated therapeutics will be deliberated.

Evaluation of hyperbranched polyglycerol for cold perfusion and storage of donor kidneys in a pig model of kidney autotransplantation

Hyperbranched polyglycerol (HPG) is a biocompatible polyether polymer that is a potential colloid component in a preservation solution for suppressing interstitial edema during cold storage of a donor organ. This study evaluated the outcomes of kidney transplants after cold perfusion and storage with a HPG‐based preservation solution (HPGS) in a pig model of kidney autotransplantation. The left kidneys of farm pigs (weighing 35–45 kg) were perfused with and stored in either cold HPGS or standard UW solution (UWS), followed by transplantation to the right side after right nephrectomy. The survival and function of transplants were determined by the urine output, and serum creatinine (SCr) and blood urea nitrogen (BUN) of recipients. Transplant injury was examined by histological analysis. Here, we showed that there was no significant difference between HPGS and UWS in the prevention of tissue edema, but HPGS was more effective than UWS for initial blood washout of kidney perfusion and for the prevention of cold ischemia injury during cold storage. After autotransplantation, the kidneys preserved with HPGS (HPG group) had better functional recovery than those with UWS (UW group), indicated by significantly more urine output and lower levels of SCr and BUN. The survived grafts in HPG group had less tissue damage than those in UW group. In conclusion, as compared to the UWS the HPGS has less negative impact on kidney cold ischemia during cold storage, resulting in improving immediate functional recovery after transplantation, suggesting that HPG is a promising colloid for donor kidney preservation.

Antimicrobial Peptides: Diversity, Mechanism of Action and Strategies to Improve the Activity and Biocompatibility In Vivo

Antibiotic resistance is projected as one of the greatest threats to human health in the future and hence alternatives are being explored to combat resistance. Antimicrobial peptides (AMPs) have shown great promise, because use of AMPs leads bacteria to develop no or low resistance. In this review, we discuss the diversity, history and the various mechanisms of action of AMPs. Although many AMPs have reached clinical trials, to date not many have been approved by the US Food and Drug Administration (FDA) due to issues with toxicity, protease cleavage and short half-life. Some of the recent strategies developed to improve the activity and biocompatibility of AMPs, such as chemical modifications and the use of delivery systems, are also reviewed in this article.

Hyperbranched polyglycerol derivatives exhibiting normal or abnormal thermoresponsive behaviours in water: facile preparation and investigation by turbidimetry and fluorescence techniques

Polymers exhibiting an abnormal thermoresponsive behaviour, in which increase in the polymer concentration in water leads to an increase in the phase transition temperature, are few, and no plausible strategy has been addressed to prepare these polymers. For illuminating a feasible common strategy to prepare polymers with an abnormal thermoresponsive behaviour, in this study, we systematically prepared a series of hyperbranched polyglycerol (HPG) derivatives through a facile esterification reaction between HPG and aliphatic acids having different carbon numbers (X). Turbidimetry measurements demonstrate that thermoresponsive HPGs can be obtained only when HPGs are conjugated with aliphatic units of X ≤ 8. The conjugation of HPG with aliphatic units of X ≤ 4 resulted in thermoresponsive HPGs with a normal thermoresponsive behaviour. For the preparation of thermoresponsive HPGs with an abnormal thermoresponsive behaviour, X should be controlled in the range of 5-8. Fluorescence measurements with nile red as the fluorescent probe demonstrate that the existence of relatively strong hydrophobic interaction is a key factor to ensure that the polymer exhibits an abnormal thermoresponsive behaviour in water. Moreover, turbidimetry and fluorescence techniques are complementary for measuring the phase transition behaviour and suitable for different polymer concentration regions.

Hyperbranched polyglycerols: recent advances in synthesis, biocompatibility and biomedical applications

Hyperbranched polyglycerol is one of the most widely studied biocompatible dendritic polymer and showed promising applications. Here, we summarized the recent advancements in the field.

Stimuli-responsive biodegradable and gadolinium-based poly[N-(2-hydroxypropyl) methacrylamide] copolymers: their potential as targeting and safe magnetic resonance imaging probes

Functionalized and biodegradable block pHPMA copolymer–gadolinium conjugates demonstrated good biocompatibility, high T₁ relaxivity, and enhanced tumor signal intensity for MRI.

Hyperbranched polyglycerol is superior to glucose for long-term preservation of peritoneal membrane in a rat model of chronic peritoneal dialysis

Background

Replacing glucose with a better biocompatible osmotic agent in peritoneal dialysis (PD) solutions is needed in PD clinic. We previously demonstrated the potential of hyperbranched polyglycerol (HPG) as a replacement for glucose. This study further investigated the long-term effects of chronic exposure to HPG as compared to a glucose-based conventional PD solution on peritoneal membrane (PM) structure and function in rats.

Methods

Adult male Wistar rats received once-daily intraperitoneal injection of 10 mL of HPG solution (1 kDa, HPG 6%) compared to Physioneal™ 40 (PYS, glucose 2.27%) or electrolyte solution (Control) for 3 months. The overall health conditions were determined by blood chemistry analysis. The PM function was determined by ultrafiltration, and its injury by histological and transcriptome-based pathway analyses.

Results

Here, we showed that there was no difference in the blood chemistry between rats receiving the HPG and the Control, while PYS increased serum alkaline phosphatase, globulin and creatinine and decreased serum albumin. Unlike PYS, HPG did not significantly attenuate PM function, which was associated with smaller change in both the structure and the angiogenesis of the PM and less cells expressing vascular endothelial growth factor, α-smooth muscle actin and MAC387 (macrophage marker). The pathway analysis revealed that there were more inflammatory signaling pathways functioning in the PM of PYS group than those of HPG or Control, which included the signaling for cytokine production in both macrophages and T cells, interleukin (IL)-6, IL-10, Toll-like receptors, triggering receptor expressed on myeloid cells 1 and high mobility group box 1.

Conclusions

The results from this experimental study indicate the superiority of HPG to glucose in the preservation of the peritoneum function and structure during the long-term PD treatment, suggesting the potential of HPG as a novel osmotic agent for PD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-1098-z) contains supplementary material, which is available to authorized users.

Erythrocyte interactions - Comparison of the aggregation power of polymer molecules used in medicine - Not only size does matter

BACKGROUND

Different colloids are used as a part of solutions for fluid resuscitation and organ preservation: hydroxyethyl starches (HES), dextran (Dx), polyethylene glycols (PEG), polyvinyl pyrrolidone (PVP). Some of the problems associated with their application are addressed to alteration in erythrocyte (ERY) rheology.

OBJECTIVE

We intended to estimate in vitro and compare the aggregation power (AP) of these molecules related to ERY interactions.

METHODS

Washed human ERY are used during the study. The zeta sedimentation technique is used to quantify the cell aggregation. Zeta sedimentation ratio (ZSR) based indices (AI) are calculated. The hydrodynamic radius (Rh) of the polymer molecules is determined using viscometry.

RESULTS

For all polymers tested a linear range in the relationship AI - concentration was found. The slope of the calculated line was interpreted as measure of the molecule's AP. The following ranking was obtained: PEG >PVP >DX >HES. Within the same chemical type of polymer, increasing Rh of the molecules leads to elevated AI. Comparison of the AP of molecules with similar Rh reveals a significant dependence on their chemical nature.

CONCLUSIONS

Our results show that molecule's AP is significantly dependent on their chemical nature - i.e. not only molecular size does matter.

Advantages of replacing hydroxyethyl starch in University of Wisconsin solution with hyperbranched polyglycerol for cold kidney perfusion

BACKGROUND

Efficient and effective perfusion during organ procurement is required for the best prevention of donor organ injury preceding transplantation. However, current organ preservation solutions, including hydroxyethyl starch (HES)-based University of Wisconsin (UW) solution, do not always yield the best outcomes. Our previous study demonstrated that replacing HES with hyperbranched polyglycerol (HPG) reduced donor heart injury during cold storage. The current research was designed to examine the advantages of HPG-based solution for cold kidney perfusion.

METHODS

Perfusion efficiency of HPG versus UW solution was tested using mouse kidneys at 4°C. The blood washout was evaluated by using a semiquantitative scoring system and tissue damage by histologic analysis. The interaction of HPG or UW solution with human red blood cells (RBCs) was examined by measuring RBC sedimentation and aggregation.

RESULTS

The lower viscosity of HPG solution was correlated with faster and more efficient perfusion through donor kidneys as compared with UW. HPG solution was also more effective than UW in removing RBCs from the kidney and was associated with less tissue damage to donor kidneys. In vitro UW solution caused significant RBC sedimentation and hyperaggregation, whereas HPG showed minimal impact on RBC sedimentation and prevented RBC aggregation.

CONCLUSIONS

This experimental study demonstrated that compared with UW, HPG solution was more efficient and effective in the removal of the blood from donor kidneys and offered better protection from donor tissue damage, suggesting that the HPG solution is a promising candidate to supplant standard UW solution for donor kidney perfusion in transplantation.

Progesterone binding nano-carriers based on hydrophobically modified hyperbranched polyglycerols

Progesterone (Pro) is a potent neurosteroid and promotes recovery from moderate Traumatic Brain Injury but its clinical application is severely impeded by its poor water solubility. Here we demonstrate that reversibly binding Pro within hydrophobically modified hyperbranched polyglycerol (HPG-Cn-MPEG) enhances its solubility, stability and bioavailability. Synthesis, characterization and Pro loading into HPG-Cn-MPEG is described. The release kinetics are correlated with structural properties and the results of Differential Scanning Calorimetry studies of a family of HPG-Cn-MPEGs of varying molecular weight and alkylation. While the maximum amount of Pro bound correlates well with the amount of alkyl carbon per molecule contributing to its hydrophobicity, the dominant first order rate constant for Pro release correlates strongly with the amount of structured or bound water in the dendritic domain of the polymer. The results provide evidence to justify more detailed studies of interactions with biological systems, both single cells and in animal models.

Hemoglobin-Based Nanoarchitectonic Assemblies as Oxygen Carriers

Safe and effective artificial oxygen carriers are the subject of great interest due to the problems of traditional blood transfusion and enormous demand in clinical use. In view of its unique oxygen-transport ability and normal metabolic pathways, hemoglobin is regarded as an ideal oxygen-carrying unit. With advances in nano-biotechnology, hemoglobin assemblies as artificial oxygen carriers achieve great development. Here, recent progress on hemoglobin-based oxygen carriers is highlighted in view of two aspects: acellular hemoglobin-based oxygen carriers and cellular hemoglobin-based oxygen carriers. These novel oxygen carriers exhibit advantages over traditional carriers and will greatly promote research on reliable and feasible oxygen carriers.

Hemocompatibility evaluation in vitro of methoxy polyethyleneglycol-polycaprolactone copolymer solutions

Amphiphilic block copolymer methoxy polyethyleneglycol-polycaprolactone (mPEG-PCL) has attracted interest in the biomedical field, due to its water solubility and biodegradability. Nevertheless, the blood safety of mPEG-PCL copolymers has not been investigated in detail. Because mPEG-PCL copolymers introduced in vivo would inevitably interact with blood tissue, an investigation of possible interactions of mPEG-PCL with key blood components is crucial. We studied the effects of two mPEG-PCL copolymer solutions on blood coagulation, the morphology and lysis of human red blood cells (RBCs), the structure of plasma fibrinogen, complement activation, and platelet aggregation. We found that higher concentrations of the mPEG-PCL copolymers impaired blood clotting, and the copolymers had little impact on the morphology or lysis of RBCs. From the spectroscopy results, the copolymers affected the local microstructure of fibrinogen. The copolymers significantly activated the complement system in a concentration-dependent way. At higher concentrations, the copolymers impaired platelet aggregation, which may have been mediated by an inhibition of the arachidonic acid pathway. These findings provide important information that may be useful for the molecular design and biomedical applications of mPEG-PCL copolymers. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 802-812, 2016.

Multi-modal magnetic resonance imaging and histology of vascular function in xenografts using macromolecular contrast agent hyperbranched polyglycerol (HPG-GdF)

Macromolecular gadolinium (Gd)-based contrast agents are in development as blood pool markers for MRI. HPG-GdF is a 583 kDa hyperbranched polyglycerol doubly tagged with Gd and Alexa 647 nm dye, making it both MR and histologically visible. In this study we examined the location of HPG-GdF in whole-tumor xenograft sections matched to in vivo DCE-MR images of both HPG-GdF and Gadovist. Despite its large size, we have shown that HPG-GdF extravasates from some tumor vessels and accumulates over time, but does not distribute beyond a few cell diameters from vessels. Fractional plasma volume (fPV) and apparent permeability-surface area product (aPS) parameters were derived from the MR concentration-time curves of HPG-GdF. Non-viable necrotic tumor tissue was excluded from the analysis by applying a novel bolus arrival time (BAT) algorithm to all voxels. aPS derived from HPG-GdF was the only MR parameter to identify a difference in vascular function between HCT116 and HT29 colorectal tumors. This study is the first to relate low and high molecular weight contrast agents with matched whole-tumor histological sections. These detailed comparisons identified tumor regions that appear distinct from each other using the HPG-GdF biomarkers related to perfusion and vessel leakiness, while Gadovist-imaged parameter measures in the same regions were unable to detect variation in vascular function. We have established HPG-GdF as a biocompatible multi-modal high molecular weight contrast agent with application for examining vascular function in both MR and histological modalities.

Effect of cyclodextrins on the structure and functions of blood components in vitro

Cyclodextrins have been extensively used in various biomedical and pharmaceutical applications. In these applications, cyclodextrins administered in vivo would inevitably enter blood stream. However, there is not enough information on the hemocompatibility of cyclodextrins until now. In this study, we investigated the influences of cyclodextrins (α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin) on human blood components and functions in vitro, that is, morphology and lysis of red blood cells, structure and conformation of fibrinogen, complement activation, and blood coagulation. It was found that 10 mg/mL of α- or β-cyclodextrins caused abnormal red blood cell morphology and serious hemolysis, while γ-cyclodextrin at 10 mg/mL did not impair red blood cell membrane morphology and integrity. The three cyclodextrins at up to 10 mg/mL affected the local microstructure but did not change the conformation of fibrinogen. The three cyclodextrins from 0.01 to 1 mg/mL all significantly activated the complement system in a concentration-dependent way. The three cyclodextrins at up to 5 mg/mL in blood plasma did not cause significantly different coagulation times compared with the negative control. In addition, the three cyclodextrins at up to 5 mg/mL in whole blood did not cause abnormal coagulation parameters. These results provide significant information on blood safety of the three cyclodextrins for their biomedical and pharmaceutical applications.

Polymeric nanocarriers for the treatment of systemic iron overload

Desferrioxamine (DFO), deferiprone (L1) and desferasirox (ICL-670) are clinically approved iron chelators used to treat secondary iron overload. Although iron chelators have been utilized since the 1960s and there has been much improvement in available therapy, there is still the need for new drug candidates due to limited long-term efficacy and drug toxicity. Moreover, all currently approved iron chelators are of low molecular weight (MW) (<600 Da) and the objectives reported for the "ideal" chelator of low MW, including possessing the ability to promote iron excretion without causing toxic side effects, has proven difficult to realize in practice. With prolonged iron chelator use, patients may develop toxicities or become insensitive. In contrast, the limited research that has been geared towards developing higher MW, polymeric, long circulating iron chelators has shown promise. The inherent potential of polymeric iron chelators toward longer plasma half-lives and reduction in toxicity provides optimism and may be a significant addition to the currently available low MW iron chelators. This article reviews knowledge pertaining to this theme, highlights some unique advantages that these nanomedicines have in treating systemic iron overload as well as their potential utility in the treatment of other disease states.

Polymeric nanocarriers for the treatment of systemic iron overload

Desferrioxamine (DFO), deferiprone (L1) and desferasirox (ICL-670) are clinically approved iron chelators used to treat secondary iron overload. Although iron chelators have been utilized since the 1960s and there has been much improvement in available therapy, there is still the need for new drug candidates due to limited long-term efficacy and drug toxicity. Moreover, all currently approved iron chelators are of low molecular weight (MW) (<600 Da) and the objectives reported for the “ideal” chelator of low MW, including possessing the ability to promote iron excretion without causing toxic side effects, has proven difficult to realize in practice. With prolonged iron chelator use, patients may develop toxicities or become insensitive. In contrast, the limited research that has been geared towards developing higher MW, polymeric, long circulating iron chelators has shown promise. The inherent potential of polymeric iron chelators toward longer plasma half-lives and reduction in toxicity provides optimism and may be a significant addition to the currently available low MW iron chelators. This article reviews knowledge pertaining to this theme, highlights some unique advantages that these nanomedicines have in treating systemic iron overload as well as their potential utility in the treatment of other disease states.

Hyperbranched polyglycerol as a colloid in cold organ preservation solutions

Hydroxyethyl starch (HES) is a common colloid in organ preservation solutions, such as in University of Wisconsin (UW) solution, for preventing graft interstitial edema and cell swelling during cold preservation of donor organs. However, HES has undesirable characteristics, such as high viscosity, causing kidney injury and aggregation of erythrocytes. Hyperbranched polyglycerol (HPG) is a branched compact polymer that has low intrinsic viscosity. This study investigated HPG (MW-0.5 to 119 kDa) as a potential alternative to HES for cold organ preservation. HPG was synthesized by ring-opening multibranching polymerization of glycidol. Both rat myocardiocytes and human endothelial cells were used as an in vitro model, and heart transplantation in mice as an in vivo model. Tissue damage or cell death was determined by both biochemical and histological analysis. HPG polymers were more compact with relatively low polydispersity index than HES in UW solution. Cold preservation of mouse hearts ex vivo in HPG solutions reduced organ damage in comparison to those in HES-based UW solution. Both size and concentration of HPGs contributed to the protection of the donor organs; 1 kDa HPG at 3 wt% solution was superior to HES-based UW solution and other HPGs. Heart transplants preserved with HPG solution (1 kDa, 3%) as compared with those with UW solution had a better functional recovery, less tissue injury and neutrophil infiltration in syngeneic recipients, and survived longer in allogeneic recipients. In cultured myocardiocytes or endothelial cells, significantly more cells survived after cold preservation with the HPG solution than those with the UW solution, which was positively correlated with the maintenance of intracellular adenosine triphosphate and cell membrane fluidity. In conclusion, HPG solution significantly enhanced the protection of hearts or cells during cold storage, suggesting that HPG is a promising colloid for the cold storage of donor organs and cells in transplantation.

Impact of dendritic polymers on nanomaterials

Primary/secondary covalent/non-covalent interactions between dendritic polymers and nanomaterials can change the physicochemical properties, such as shape, of the obtained hybrid nanomaterials.

Supramolecular hydrogels co-loaded with camptothecin and doxorubicin for sustainedly synergistic tumor therapy

A supramolecular hydrogel was prepared to encapsulate and release both camptothecin and doxorubicin in a controlled manner for sustainedly synergistic tumor therapy.

Bioapplications of hyperbranched polymers

The recent research progress in biological and biomedical applications of hyperbranched polymers has been summarized in this review.

Surface engineering of liposomes for stealth behavior

Liposomes are used as a delivery vehicle for drug molecules and imaging agents. The major impetus in their biomedical applications comes from the ability to prolong their circulation half-life after administration. Conventional liposomes are easily recognized by the mononuclear phagocyte system and are rapidly cleared from the blood stream. Modification of the liposomal surface with hydrophilic polymers delays the elimination process by endowing them with stealth properties. In recent times, the development of various materials for surface engineering of liposomes and other nanomaterials has made remarkable progress. Poly(ethylene glycol)-linked phospholipids (PEG-PLs) are the best representatives of such materials. Although PEG-PLs have served the formulation scientists amazingly well, closer scrutiny has uncovered a few shortcomings, especially pertaining to immunogenicity and pharmaceutical characteristics (drug loading, targeting, etc.) of PEG. On the other hand, researchers have also begun questioning the biological behavior of the phospholipid portion in PEG-PLs. Consequently, stealth lipopolymers consisting of non-phospholipids and PEG-alternatives are being developed. These novel lipopolymers offer the potential advantages of structural versatility, reduced complement activation, greater stability, flexible handling and storage procedures and low cost. In this article, we review the materials available as alternatives to PEG and PEG-lipopolymers for effective surface modification of liposomes.