Effects of branching and molecular weight of surface-bound poly(ethylene oxide) on protein rejection

Effect of multi arm-PEG-NHS (polyethylene glycol n-hydroxysuccinimide) branching on cell adhesion to modified decellularized bovine and porcine pericardium

Implanting physical barrier materials to separate wounds from their surroundings is a promising strategy for preventing postoperative adhesions. Herein, we develop a material that switches from an anti-adhesive surface to an adhesive surface, preventing adhesion in the early stage of transplantation and then promoting recellularization. In this study, 2-arm, 4-arm, and 8-arm poly(ethylene glycol) succinimidyl glutarate (2-, 4-, 8-arm PEG-NHS) were used to modify the surface of decellularized porcine and bovine pericardium. The number of free amines on the surface of each material significantly decreased following modification regardless of the reaction molar ratio of NH2 and NHS, the number of PEG molecule branches, and the animal species of the decellularized tissue. The structure and mechanical properties of the pericardium were maintained after modification with PEG molecules. The time taken for the PEG molecules to detach through hydrolysis of the ester bonds differed between the samples, which resulted in different cell repulsion periods. By adjusting the reaction molar ratio, the number of PEG molecule branches, and the animal species of the decellularized pericardium, the duration of cell repulsion can be controlled and is expected to provide an anti-adhesion material for a variety of surgical procedures.

4-Arm PEG-Functionalized Decellularized Pericardium for Effective Prevention of Postoperative Adhesion in Cardiac Surgery

Postoperative adhesions are a very common and serious complication in cardiac surgery, and the development of an effective anti-adhesion membrane showing resistance to the physical stimulus generated by the pulsation of the heart is desirable. In this study, an anti-adhesion material was developed through amine coupling between decellularized bovine pericardia (dBPCs) and 4-arm poly(ethylene glycol) succinimidyl glutarate (4-arm PEG-NHS) for the postoperative care of cardiac surgical patients. The efficacy of the 4-arm PEG-functionalized dBPCs in the prevention of adhesions after cardiac surgery was investigated in a rabbit heart adhesion model. The dBPCs meet the requirements for biocompatibility, flexibility, and sufficient suturable strength, and the 4-arm PEG moieties provide an anti-adhesion effect by the high excluded volume interactions of the PEG chains with proteins. The 4-arm PEG-functionalized dBPCs had a significantly greater anti-adhesion effect than the other materials tested and showed re-establishment of the mesothelial monolayer. These results suggested that the 4-arm PEG-functionalized dBPCs are a favorable material for an anti-adhesion membrane.

Toxicological profile of lipid-based nanostructures: are they considered as completely safe nanocarriers?

Nanoparticles are ubiquitous in the environment and are widely used in medical science (e.g. bioimaging, diagnosis, and drug therapy delivery). Due to unique physicochemical properties, they are able to cross many barriers, which is not possible for traditional drugs. Nevertheless, exposure to NPs and their following interactions with organelles and macromolecules can result in negative effects on cells, especially, they can induce cytotoxicity, epigenicity, genotoxicity, and cell death. Lipid-based nanomaterials (LNPs) are one of the most important achievements in drug delivery mainly due to their superior physicochemical and biological characteristics, particularly its safety. Although they are considered as the completely safe nanocarriers in biomedicine, the lipid composition, the surfactant, emulsifier, and stabilizer used in the LNP preparation, and surface electrical charge are important factors that might influence the toxicity of LNPs. According to the author's opinion, their toxicity profile should be evaluated case-by-case regarding the intended applications. Since there is a lack of all-inclusive review on the various aspects of LNPs with an emphasis on toxicological profiles including cyto-genotoxiciy, this comprehensive and critical review is outlined.

In Vitro and in Vivo Behavior of Liposomes Decorated with PEGs with Different Chemical Features

The colloidal stability, in vitro toxicity, cell association, and in vivo pharmacokinetic behavior of liposomes decorated with monomethoxy-poly(ethylene glycol)-lipids (mPEG-lipids) with different chemical features were comparatively investigated. Structural differences of the mPEG-lipids used in the study included: (a) surface-anchoring moiety [1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE), cholesterol (Chol), and cholane (Chln)]; (b) mPEG molecular weight (2 kDa mPEG₄₅ and 5 kDa mPEG₁₁₄); and (c) mPEG shape (linear and branched PEG). In vitro results demonstrated that branched (mPEG₁₁₄)₂-DSPE confers the highest stealth properties to liposomes (∼31-fold lower cell association than naked liposomes) with respect to all PEGylating agents tested. However, the pharmacokinetic studies showed that the use of cholesterol as anchoring group yields PEGylated liposomes with longer permeance in the circulation and higher systemic bioavailability among the tested formulations. Liposomes decorated with mPEG₁₁₄-Chol had 3.2- and ∼2.1-fold higher area under curve (AUC) than naked liposomes and branched (mPEG₁₁₄)₂-DSPE-coated liposomes, respectively, which reflects the high stability of this coating agent. By comparing the PEGylating agents with same size, namely, linear 5 kDa PEG derivatives, linear mPEG₁₁₄-DSPE yielded coated liposomes with the best in vitro stealth performance. Nevertheless, the in vivo AUC of liposomes decorated with linear mPEG₁₁₄-DSPE was lower than that obtained with liposomes decorated with linear mPEG₁₁₄-Chol. Computational molecular dynamics modeling provided additional insights that complement the experimental results.

Targeted Drug Delivery in Lipid-like Nanocages and Extracellular Vesicles

The possibility of targeted drug delivery to a specific tissue, organ, or cell has opened new promising avenues in treatment development. The technology of targeted delivery aims to create multifunctional carriers that are capable of long circulation in the patient's organism and possess low toxicity at the same time. The surface of modern synthetic carriers has high structural similarity to the cell membrane, which, when combined with additional modifications, also promotes the transfer of biological properties in order to penetrate physiological barriers effectively. Along with artificial nanocages, further efforts have recently been devoted to research into extracellular vesicles that could serve as natural drug delivery vehicles. This review provides a detailed description of targeted delivery systems that employ lipid and lipid-like nanocages, as well as extracellular vesicles with a high level of biocompatibility, highlighting genetically encoded drug delivery vehicles.

Polymer Lung Surfactants

Animal-derived lung surfactants annually save 40 000 infants with neonatal respiratory distress syndrome (NRDS) in the United States. Lung surfactants have further potential for treating about 190 000 adult patients with acute respiratory distress syndrome (ARDS) each year. To this end, the properties of current therapeutics need to be modified. Although the limitations of current therapeutics have been recognized since the 1990s, there has been little improvement. To address this gap, our laboratory has been exploring a radically different approach in which, instead of lipids, proteins, or peptides, synthetic polymers are used as the active ingredient. This endeavor has led to an identification of a promising polymer-based lung surfactant candidate, poly(styrene-b-ethylene glycol) (PS-PEG) polymer nanomicelles. PS-PEG micelles produce extremely low surface tension under high compression because PS-PEG micelles have a strong affinity to the air-water interface. NMR measurements support that PS-PEG micelles are less hydrated than ordinary polymer micelles. Studies using mouse models of acid aspiration confirm that PS-PEG lung surfactant is safe and efficacious.

Nanostructured Polymer Thin Films Fabricated with Brush-based Layer-by-Layer Self-assembly for Site-selective Construction and Drug release

Layer-by-Layer (LbL) self-assembly has been investigated for several decades. However, the conventional LbL method has performance problems on the chair-side caused by its cumbersome and time-consuming process. Thus, we investigate a new LbL self-assembly technique for the fast and high efficient preparation process based on the brush. The multilayer films fabricated by simple sequential brushing of polyelectrolyte solutions are compared to the classical dipping method. We characterize the multilayer films by characteristics such as their morphology and thickness, and compare them against those of the classic method by profilometry, atomic force microscopy. We prepare multilayer films with biocompatible polyelectrolytes, chitosan, and alginate incorporated with a hydrophobic drug carrier. For the drug carrier, a poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL) block copolymer is introduced to construct micelles containing dexamethasone, which is a well-known osteogenesis-inducing drug. The hydrogen bonding behavior between adjacent layers and micelles is investigated by Fourier transform infrared spectroscopy. Additionally, we analyze the release profiles, degradation profiles and toxicity of the multilayer films for biomedical applications. From these results, we can identify the brushing LbL method as a reliable and more efficient multilayer film-construction process compared to conventional dipping LbL, especially for practical applications in dental and clinical situations.

Biodistribution Analysis of NIR-Labeled Nanogels Using in Vivo FMT Imaging in Triple Negative Human Mammary Carcinoma Models

The purpose of this study is to evaluate the biodistribution properties of random-copolymer-based core-cross-linked nanogels of various sizes and surface poly(ethylene glycol) composition. Systematic variations of near-IR labeled nanogels, comprising varying particle sizes (28-135 nm), PEG corona quantity (0-50 mol %), and PEG length (PEG M_n 1000, 2000, and 5000), were prepared and injected in mice that had been subcutaneously implanted with MDA-MB-231-luc-D3H2LN human mammary carcinoma. In vivo biodistribution was obtained using fluorescence molecular tomography imaging at 0, 6, 24, 48, and 72 h postinjection. Retention of total body probe and percentages of total injected dose in the tumor, liver, spleen, lungs, heart, intestines, and kidneys were obtained. Smaller nanogels (∼30-40 nm) with a high PEG conjugation (∼43-46 mol %) of M_n 2000 on their coronas achieved the highest tumor specificity with peak maximum 27% ID/g, a statistically significant propensity toward accumulation with 16.5% ID/g increase from 0 to 72 h of imaging, which constitutes a 1.5-fold increase. Nanogels with greater tumor localization also had greater retention of total body probe over 72 h. Nanogels without extensive PEGylation were rapidly excreted, even at similar sizes to PEGylated nanogels exhibiting whole body retention. Of all tissues, the liver had the highest % ID, however, like other tissues, it displayed a monotonic decrease over time, suggesting nanogel clearance by hepatic metabolism. Ex vivo quantification of individual tissues from gross necropsy at 72 h postinjection generally correlated with the FMT analysis, providing confidence in tissue signal segmentation in vivo. The parameters determined to most significantly direct a nanogel to the desired tumor target can lead to improve effectiveness for nanogels as therapeutic delivery vehicles.

Lipid-Based Nanoparticles as a Potential Delivery Approach in the Treatment of Rheumatoid Arthritis

Rheumatoid arthritis (RA), a chronic and joint-related autoimmune disease, results in immune dysfunction and destruction of joints and cartilages. Small molecules and biological therapies have been applied in a wide variety of inflammatory disorders, but their utility as a therapeutic agent is limited by poor absorption, rapid metabolism, and serious side effects. To improve these limitations, nanoparticles, which are capable of encapsulating and protecting drugs from degradation before they reach the target site in vivo, may serve as drug delivery systems. The present research proposes a platform for different lipid nanoparticle approaches for RA therapy, taking advantage of the newly emerging field of lipid nanoparticles to develop a targeted theranostic system for application in the treatment of RA. This review aims to present the recent major application of lipid nanoparticles that provide a biocompatible and biodegradable delivery system to effectively improve RA targeting over free drugs via the presentation of tissue-specific targeting of ligand-controlled drug release by modulating nanoparticle composition.

Towards clinically translatable in vivo nanodiagnostics

Nanodiagnostics as a field makes use of fundamental advances in nanobiotechnology to diagnose, characterize and manage disease at the molecular scale. As these strategies move closer to routine clinical use, a proper understanding of different imaging modalities, relevant biological systems and physical properties governing nanoscale interactions is necessary to rationally engineer next-generation bionanomaterials. In this Review, we analyse the background physics of several clinically relevant imaging modalities and their associated sensitivity and specificity, provide an overview of the materials currently used for in vivo nanodiagnostics, and assess the progress made towards clinical translation. This work provides a framework for understanding both the impressive progress made thus far in the nanodiagnostics field as well as presenting challenges that must be overcome to obtain widespread clinical adoption.

Perspectives on: Materials Aspects for Retinal Prostheses

Retinitis pigmentosa and age-related macular degeneration are both incurable eye diseases that lead to blindness due to photoreceptor degeneration. Electrically stimulating the remaining intact nerve cells may generate some useful vision for patients afflicted with these diseases. Various types of retinal prostheses, sub- and epi-retinal electrode arrays, as well as subretinal microphotodiode arrays are considered from a materials and biocompatibility point of view. Other, more innovative approaches to restoring vision, such as microfluidic pumps and activated nanosystems that deliver neurotransmitters in a controlled way and photodynamic therapy are being developed. This article discusses materials aspects of retinal prostheses that are currently in use or under development.

Lipid-Based Drug Delivery Systems in Cancer Therapy: What Is Available and What Is Yet to Come

Cancer is a leading cause of death in many countries around the world. However, the efficacy of current standard treatments for a variety of cancers is suboptimal. First, most cancer treatments lack specificity, meaning that these treatments affect both cancer cells and their normal counterparts. Second, many anticancer agents are highly toxic, and thus, limit their use in treatment. Third, a number of cytotoxic chemotherapeutics are highly hydrophobic, which limits their utility in cancer therapy. Finally, many chemotherapeutic agents exhibit short half-lives that curtail their efficacy. As a result of these deficiencies, many current treatments lead to side effects, noncompliance, and patient inconvenience due to difficulties in administration. However, the application of nanotechnology has led to the development of effective nanosized drug delivery systems known commonly as nanoparticles. Among these delivery systems, lipid-based nanoparticles, particularly liposomes, have shown to be quite effective at exhibiting the ability to: 1) improve the selectivity of cancer chemotherapeutic agents; 2) lower the cytotoxicity of anticancer drugs to normal tissues, and thus, reduce their toxic side effects; 3) increase the solubility of hydrophobic drugs; and 4) offer a prolonged and controlled release of agents. This review will discuss the current state of lipid-based nanoparticle research, including the development of liposomes for cancer therapy, different strategies for tumor targeting, liposomal formulation of various anticancer drugs that are commercially available, recent progress in liposome technology for the treatment of cancer, and the next generation of lipid-based nanoparticles.

Photopatterning of hydrogel scaffolds coupled to filter materials using stereolithography for perfused 3D culture of hepatocytes

In vitro models that recapitulate the liver's structural and functional complexity could prolong hepatocellular viability and function to improve platforms for drug toxicity studies and understanding liver pathophysiology. Here, stereolithography (SLA) was employed to fabricate hydrogel scaffolds with open channels designed for post-seeding and perfused culture of primary hepatocytes that form 3D structures in a bioreactor. Photopolymerizable polyethylene glycol-based hydrogels were fabricated coupled to chemically activated, commercially available filters (polycarbonate and polyvinylidene fluoride) using a chemistry that permitted cell viability, and was robust enough to withstand perfused culture of up to 1 µL/s for at least 7 days. SLA energy dose, photoinitiator concentrations, and pretreatment conditions were screened to determine conditions that maximized cell viability and hydrogel bonding to the filter. Multiple open channel geometries were readily achieved, and included ellipses and rectangles. Rectangular open channels employed for subsequent studies had final dimensions on the order of 350 µm by 850 µm. Cell seeding densities and flow rates that promoted cell viability were determined. Perfused culture of primary hepatocytes in hydrogel scaffolds in the presence of soluble epidermal growth factor (EGF) prolonged the maintenance of albumin production throughout the 7-day culture relative to 2D controls. This technique of bonding hydrogel scaffolds can be employed to fabricate soft scaffolds for a number of bioreactor configurations and applications.

Stealth properties to improve therapeutic efficacy of drug nanocarriers

Over the last few decades, nanocarriers for drug delivery have emerged as powerful tools with unquestionable potential to improve the therapeutic efficacy of anticancer drugs. Many colloidal drug delivery systems are underdevelopment to ameliorate the site specificity of drug action and reduce the systemic side effects. By virtue of their small size they can be injected intravenously and disposed into the target tissues where they release the drug. Nanocarriers interact massively with the surrounding environment, namely, endothelium vessels as well as cells and blood proteins. Consequently, they are rapidly removed from the circulation mostly by the mononuclear phagocyte system. In order to endow nanosystems with long circulation properties, new technologies aimed at the surface modification of their physicochemical features have been developed. In particular, stealth nanocarriers can be obtained by polymeric coating. In this paper, the basic concept underlining the "stealth" properties of drug nanocarriers, the parameters influencing the polymer coating performance in terms of opsonins/macrophages interaction with the colloid surface, the most commonly used materials for the coating process and the outcomes of this peculiar procedure are thoroughly discussed.

Influence of polymer architecture on antigens camouflage, CD47 protection and complement mediated lysis of surface grafted red blood cells

Hyperbranched polyglycerol (HPG) and polyethylene glycol (PEG) polymers with similar hydrodynamic sizes in solution were grafted to red blood cells (RBCs) to investigate the impact of polymer architecture on the cell structure and function. The hydrodynamic sizes of polymers were calculated from the diffusion coefficients measured by pulsed field gradient NMR. The hydration of the HPG and PEG was determined by differential scanning calorimetry analyses. RBCs grafted with linear PEG had different properties compared to the compact HPG grafted RBCs. HPG grafted RBCs showed much higher electrophoretic mobility values than PEG grafted RBCs at similar grafting concentrations and hydrodynamic sizes indicating differences in the structure of the polymer exclusion layer on the cell surface. PEG grafting impacted the deformation properties of the membrane to a greater degree than HPG. The complement mediated lysis of the grafted RBCs was dependent on the type of polymer, grafting concentration and molecular size of grafted chains. At higher molecular weights and graft concentrations both HPG and PEG triggered complement activation. The magnitude of activation was higher with HPG possibly due to the presence of many hydroxyl groups per molecule. HPG grafted RBCs showed significantly higher levels of CD47 self-protein accessibility than PEG grafted RBCs at all grafting concentrations and molecular sizes. PEG grafted polymers provided, in general, a better shielding and protection to ABO and minor antigens from antibody recognition than HPG polymers, however, the compact HPGs provided greater protection of certain antigens on the RBC surface. Our data showed that HPG 20 kDa and HPG 60 kDa grafted RBCs exhibited properties that are more comparable to the native RBC than PEG 5 kDa and PEG 10 kDa grafted RBCs of comparable hydrodynamic sizes. The study shows that small compact polymers such as HPG 20 kDa have a greater potential in the generation of functional RBC for therapeutic delivery applications. The intermediate sized polymers (PEG or HPG) which showed greater antigen camouflage at lower grafting concentrations have significant potential in transfusion as universal red blood donor cells.

Targeting nanoparticles to cancer

Nanotechnology applications in medicine, termed as nanomedicine, have introduced a number of nanoparticles of variable chemistry and architecture for cancer imaging and treatment. Nanotechnology involves engineering multifunctional devices with dimensions at the nanoscale, similar dimensions as those of large biological vesicles or molecules in our body. These devices typically have features just tens to hundred nanometers across and they can carry one or two detection signals and/or therapeutic cargo(s). One unique class of nanoparticles is designed to do both, providing this way the theragnostic nanoparticles (therapy and diagnosis). Being inspired by physiologically existing nanomachines, nanoparticles are designed to safely reach their target and specifically release their cargo at the site of the disease, this way increasing the drug's tissue bioavailability. Nanoparticles have the advantage of targeting cancer by simply being accumulated and entrapped in tumours (passive targeting). The phenomenon is called the enhanced permeation and retention effect, caused by leaky angiogenetic vessels and poor lymphatic drainage and has been used to explain why macromolecules and nanoparticles are found at higher ratios in tumours compared to normal tissues. Although accumulation in tumours is observed cell uptake and intracellular drug release have been questioned. Polyethyleneglycol (PEG) is used to protect the nanoparticles from the Reticulo-Endothelial System (RES), however, it prevents cell uptake and the required intracellular drug release. Grafting biorecognition molecules (ligands) onto the nanoparticles refers to active targeting and aims to increase specific cell uptake. Nanoparticles bearing these ligands are recognised by cell surface receptors and this leads to receptor-mediated endocytosis. Several materials are suggested for the design of nanoparticles for cancer. Polymers, linear and dendrimers, are associated with the drug in a covalent or non-covalent way and have been used with or without a targeting ligand. Stealth liposomes are suggested to carry the drug in the aqueous core, and they are usually decorated by recognition molecules, being widely studied and applied. Inorganic nanoparticles such as gold and iron oxide are usually coupled to the drug, PEG and the targeting ligand. It appears that the PEG coating and ligand decoration are common constituents in most types of nanoparticles for cancer. There are several examples of successful cancer diagnostic and therapeutic nanoparticles and many of them have rapidly moved to clinical trials. Nevertheless there is still a room for optimisation in the area of the nanoparticle kinetics such as improving their plasma circulation and tumour bioavailability and understanding the effect of targeting ligands on their efficiency to treat cancer. The need to develop novel and efficient ligands has never been greater, and the use of proper conjugation chemistry is mandatory.

Chemical grafting of poly(ethylene glycol) methyl ether methacrylate onto polymer surfaces by atmospheric pressure plasma processing

This article reports the use of atmospheric pressure plasma processing to induce chemical grafting of poly(ethylene glycol) methyl ether methacrylate (PEGMA) onto polystyrene (PS) and poly(methyl methacrylate) (PMMA) surfaces with the aim of attaining an adlayer conformation which is resistant to protein adsorption. The plasma treatment was carried out using a dielectric barrier discharge (DBD) reactor with PEGMA of molecular weights (MW) 1000 and 2000, PEGMA(1000) and PEGMA(2000), being grafted in a two step procedure: (1) reactive groups are generated on the polymer surface followed by (2) radical addition reactions with the PEGMA. The surface chemistry, coherency, and topography of the resulting PEGMA grafted surfaces were characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and atomic force microscopy (AFM), respectively. The most coherently grafted PEGMA layers were observed for the 2000 MW PEGMA macromolecule, DBD processed at an energy dose of 105.0 J/cm(2) as indicated by ToF-SIMS images. The effect of the chemisorbed PEGMA layer on protein adsorption was assessed by evaluating the surface response to bovine serum albumin (BSA) using XPS. BSA was used as a model protein to determine the grafted macromolecular conformation of the PEGMA layer. Whereas the PEGMA(1000) surfaces showed some protein adsorption, the PEGMA(2000) surfaces appeared to absorb no measurable amount of protein, confirming the optimum surface conformation for a nonfouling surface.

Critical parameters in the pegylation of gold nanoshells for biomedical applications: an in vitro macrophage study

Pegylation of gold nanoshells provides an effective means to reduce their reticuloendothelial system (RES) clearance in body. In this study, we perform a parametric investigation on the factors that would affect the macrophage uptake of gold nanoshells with the aim to optimize their pegylation and minimize their macrophage uptake. We synthesized and pegylated the gold nanoshells using methoxy-poly(ethylene glycol)-thiol and employed an in vitro macrophage assay to examine the effect of surface density of poly(ethylene glycol) (PEG), chain length of the PEG, and size of the gold nanoshells on their macrophage uptake. We have shown that a saturated surface density would minimize macrophage uptake, which could be obtained by experimental titration-based Ellman's reagent. Our results suggest that the chain length of PEG and size of gold nanoshells influence the surface density of PEG. We have also shown that PEG with molecular weight of around 2000Da and a size range larger than 186nm would be appropriate for facilitating a high surface density. Our in vitro macrophage system thus provides a good model to accurately predict the RES response to different pegylation parameters.

Biocompatible Nanocomplexes for Molecular Targeted MRI Contrast Agent

Accurate diagnosis in early stage is vital for the treatment of Hepatocellular carcinoma. The aim of this study was to investigate the potential of poly lactic acid-polyethylene glycol/gadolinium-diethylenetriamine-pentaacetic acid (PLA-PEG/Gd-DTPA) nanocomplexes using as biocompatible molecular magnetic resonance imaging (MRI) contrast agent. The PLA-PEG/Gd-DTPA nanocomplexes were obtained using self-assembly nanotechnology by incubation of PLA-PEG nanoparticles and the commercial contrast agent, Gd-DTPA. The physicochemical properties of nanocomplexes were measured by atomic force microscopy and photon correlation spectroscopy. The T(1)-weighted MR images of the nanocomplexes were obtained in a 3.0 T clinical MR imager. The stability study was carried out in human plasma and the distribution in vivo was investigated in rats. The mean size of the PLA-PEG/Gd-DTPA nanocomplexes was 187.9 +/- 2.30 nm, and the polydispersity index was 0.108, and the zeta potential was -12.36 +/- 3.58 mV. The results of MRI test confirmed that the PLA-PEG/Gd-DTPA nanocomplexes possessed the ability of MRI, and the direct correlation between the MRI imaging intensities and the nano-complex concentrations was observed (r = 0.987). The signal intensity was still stable within 2 h after incubation of the nanocomplexes in human plasma. The nanocomplexes gave much better image contrast effects and longer stagnation time than that of commercial contrast agent in rat liver. A dose of 0.04 mmol of gadolinium per kilogram of body weight was sufficient to increase the MRI imaging intensities in rat livers by five-fold compared with the commercial Gd-DTPA. PLA-PEG/Gd-DTPA nanocomplexes could be prepared easily with small particle sizes. The nanocomplexes had high plasma stability, better image contrast effect, and liver targeting property. These results indicated that the PLA-PEG/Gd-DTPA nanocomplexes might be potential as molecular targeted imaging contrast agent.

Recent developments in nanoparticle-based drug delivery and targeting systems with emphasis on protein-based nanoparticles

BACKGROUND

Drug delivery systems with nm dimensions (nanoparticles [NPs]) are attracting increasing attention because they can sequester drugs in systemic circulation, prevent non-specific biodistribution, and target to specific tissues.

OBJECTIVE

We reviewed the recent literature pertinent to NP-based drug delivery, primarily emphasizing NPs fabricated from proteins.

METHODS

A summary of common NP fabrication techniques is provided along with the range of sizes and functional properties obtained. The NP properties critical for injectable drug delivery are reviewed, as well as the attempts to design 'tissue-specific' NPs.

RESULTS/CONCLUSIONS

It has been possible to design > 100 nm NPs from different biomaterials, and further understanding of in vivo stability and interactions with physiologic systems will lead to improved drug delivery systems.

Addressing thrombogenicity in vascular graft construction

Thrombosis is a major cause of poor patency in synthetic vascular grafts for small diameter vessel (< 6 mm) bypass. Arteries have a host of structural mechanisms by which they prevent triggering of platelet activation and the clotting cascade. Many of these are present in vascular endothelial cells. These mechanisms act together with perpetual feedback at different levels, providing a constantly fine-tuned non-thrombogenic environment. The arterial wall anatomy also serves to promote thrombosis as a healing mechanism when it has been severely injured. Surface modification of synthetic graft surfaces to attenuate the coagulation cascade has reduced thrombosis levels and improved patency in vitro and in animal models. Success in this endeavor is critically dependent on the methods used to modify the surface. Platelets adhere to positively charged surfaces due to their own negative charge. They also preferentially attach to hydrophobic surfaces. Therefore synthetic graft development is concerned with hydrophilic materials with negative surface charge. However, fibrinogen has both hydrophilic and hydrophobic binding sites-amphiphilic materials reduce its adhesion and subsequent platelet activation. The self-endothelializing synthetic graft is an attractive proposition as a confluent endothelial layer incorporates many of the anti-thrombogenic properties of arteries. Surface modification to promote this has shown good results in animal models. The difficulties experienced in achieving spontaneous endothelialisation in humans have lead to the investigation of pre-implantation in vitro endothelial cell seeding. These approaches ultimately aim to result in novel synthetic grafts which are anti-thrombogenic and hence suitable for coronary and distal infrainguinal bypass.

Density control of poly(ethylene glycol) layer to regulate cellular attachment

A wide variety of cells usually integrate and respond to the microscale environment, such as soluble protein factors, extracellular matrix proteins, and contacts with neighboring cells. To gain insight into cellular microenvironment design, we investigated two-dimensional microarray formation of endothelial cells on a micropatterned poly(ethylene glycol) (PEG)-brushed surface, based on the relationship between PEG chain density and cellular attachment. The patterned substrates consisted of two regions: the PEG surface that acts as a cell-resistant layer and the exposed substrate surface that promotes protein or cell adsorption. A PEG-brushed layer was constructed on a gold substrate using PEG with a mercapto group at the end of the chain. The density of the PEG-brushed layer increased substantially with repetitive adsorption/rinse cycles of PEG on the gold substrate, allowing marked reduction of nonspecific protein adsorption. These repeated adsorption/rinse cycles were further regulated by using longer (5 kDa) and shorter (2 kDa) PEG to construct PEG layers with different chain density, and subsequent micropatterning was achieved by plasma etching through a micropatterned metal mask. The effects of PEG chain density on pattern formation of cell attachment were determined on micropatterning of endothelial cells. The results indicated that cell pattern formation was strongly dependent on the PEG chain density and on the extent of protein adsorption. Notably, a PEG chain density high enough to inhibit outgrowth of endothelial cells from the cell-adhering region in the horizontal direction could be obtained only by employing formation of a short filler layer of PEG in the preconstructed longer PEG-brushed layer, which prevented nonspecific protein adsorption almost completely. In this way, a completely micropatterned array of endothelial cells with long-term viability was obtained. This clearly indicated the importance of a short underbrushed PEG layer in minimizing nonspecific protein adsorption for long-term maintenance of the active cell pattern. The strategy for cell patterning presented here can be employed in tissue engineering to study cell-cell and cell-surface interactions. It is also applicable for high-throughput screening and clinical diagnostics, as well as interfacing cellular and microfabricated components of biomedical microsystems.

Modulating bone cells response onto starch-based biomaterials by surface plasma treatment and protein adsorption

The effect of oxygen-based radio frequency glow discharge (rfGD) on the surface of different starch-based biomaterials (SBB) and the influence of proteins adsorption on modulating bone-cells behavior was studied. Bovine serum albumin, fibronectin and vitronectin were used in single and complex protein systems. RfGD-treated surfaces showed to increase in hydrophilicity and surface energy when compared to non-modified SBB. Biodegradable polymeric blends of cornstarch with cellulose acetate (SCA; 50/50wt%), ethylene vinyl alcohol (SEVA-C; 50/50wt%) and polycaprolactone (SPCL; 30/70wt%) were studied. SCA and SCA reinforced with 10% hydroxyapatite (HA) showed the highest degree of modification as result of the rfGD treatment. Protein and control solutions were used to incubate with the characterized SBB and, following this, MG63 osteoblast-like osteosarcoma cells were seeded over the surfaces. Cell adhesion and proliferation onto SCA was found to be enhanced for non-treated surfaces and on SCA+10%HA no alteration was brought up by the plasma modification. Onto SCA surfaces, BSA, FN and VN single solutions improved cell adhesion, and this same effect was found upscaled for ternary systems. In addition, plasma treated SEVA-C directed an increase in both adhesion and proliferation comparing to non-treated surfaces. Even though adhesion onto treated and untreated SPCL was quite similar, plasma modification clearly promoted MG63 cells proliferation. Regarding MG63 cells morphology it was shown that onto SEVA-C surfaces the variation of cell shape was primarily defined by the protein system, while onto SPCL it was mainly affected by the plasma treatment.

Parameters influencing the stealthiness of colloidal drug delivery systems

Over the last few decades, colloidal drug delivery systems (CDDS) such as nano-structures have been developed in order to improve the efficiency and the specificity of drug action. Their small size permits them to be injected intravenously in order to reach target tissues. However, it is known that they can be rapidly removed from blood circulation by the immune system. CDDS are removed via the complement system and via the cells of the mononuclear phagocyte system (MPS), after their recognition by opsonins and/or receptors present at the cell surface. This recognition is dependent on the physicochemical characteristics of the CDDS. In this study, we will focus on parameters influencing the interactions of opsonins and the macrophage plasma membrane with the surface of CDDS, whereby parameters of the polymer coating become necessary to provide good protection.

Glycocalyx-mimetic dextran-modified poly(vinyl amine) surfactant coating reduces platelet adhesion on medical-grade polycarbonate surface

A dextran-modified poly(vinyl amine) comb-like surfactant polymer, poly(N-vinyl dextran aldonamide-co-N-vinyl hexanamide), that can surface-adsorb on hydrophobic polymeric substrates, was designed to improve the interfacial blood-compatibility of polymeric biomaterials. Medical-grade polycarbonate was selected as a model substrate because of its extensive use in blood-contacting biomedical devices like hemodialyzers, blood pumps and oxygenators. The surfactant polymer was physisorbed from aqueous solution onto the polycarbonate substrate. The surfactant coating was stable under dynamic shear conditions in whole blood, as confirmed by fluorescence microscopy and total internal reflection fluorescence (TIRF) experiments with fluorescein-labeled surfactant polymer. The coated disks and uncoated control disks were exposed to platelet-rich plasma (PRP) and whole human blood in a rotating disk system (RDS) to study platelet-adhesion under dynamic shear stress environments. Adhered platelets were stained with fluorescein isothiocyante (FITC)-tagged anti-CD41a monoclonal antibody and imaged by epifluorescence microscopy. Complimentary images were obtained by phase-contrast microscopy. Platelet adhesion on the surfactant-coated disks was reduced by approximately 90%, compared with uncoated disks. The images also showed a concomitant reduction in platelet-derived microparticles on surfactant-coated disks, compared with uncoated disks. The results suggest potential application of carbohydrate-modified surfactant polymers as a glycocalyx-mimetic non-thrombogenic interfacial coating for blood-contacting biomaterials.

Student Research Award in the Undergraduate Degree Candidate category, 30th Annual Meeting of the Society for Biomaterials, Memphis, Tennessee, April 27-30, 2005. Monocyte/lymphocyte interactions and the foreign body response: in vitro effects of biomaterial surface chemistry

To determine the effect of biomaterial surface chemistry on leukocyte interaction and activity at the material/tissue interface, human peripheral blood monocytes and lymphocytes were cultured on a series of poly(ethylene terephthalate) (PET)-based biomaterials. Both monocytes and lymphocytes were isolated from whole human blood and separated by a nonadherent density centrifugation method before being plated on PET disks, surface modified by photograft copolymerization to yield hydrophobic, hydrophilic, anionic, and cationic surface properties. Monocytes and lymphocytes were cultured separately, to elicit baseline levels of activity, in direct coculture, to promote direct cell surface interactions, or in an indirect coculture system with both cell types separated by a -0.02-microm Transwell apparatus, to promote indirect paracrine interactions. Monocyte adhesion, macrophage fusion, and lymphocyte proliferation were measured on days 3, 7, 10, and 14 of culture. Results demonstrated that the presence of monocytes increased the activity of cocultured lymphocytes at the biomaterial/tissue interface, while the corresponding presence of lymphocytes increased the activation and fusion of indirectly cocultured monocytes. Biomaterial surface chemistry was also found to have a significant effect on monocyte adhesion and activation, and lymphocyte activity. Hydrophilic surfaces significantly inhibited both initial and longterm monocyte adhesion, and inhibited lymphocyte proliferation at longer time points. Anionic and cationic surfaces both exhibited mild inhibition of monocyte adhesion at prolonged time points and increased levels of macrophage fusion, while cationic surfaces decreased levels of lymphocyte proliferation and inhibited monocyte activity. These results elucidate the complex role of juxtacrine and paracrine interactions between monocytes and lymphocytes in the foreign body response, as well as promote the consideration of hydrophilic surfaces in future designs of implantable biomedical devices and prostheses.

In situ fabrication of self-transformable and hydrophilic poly(ethylene glycol) derivative-modified polysulfone membranes

A self-transformable sulfonated poly(ethylene glycol) acrylate diblock copolymer (PEG-SO3A/OA) entrapped into polysulfone membrane was studied. The asymmetric membrane structure was prepared by a phase inversion process. The induced hydrophilicity by reorientation of diblock copolymer at the interface was evaluated by contact angle measurement, platelet adhesion test, and electron spectroscopy for chemical analysis (ESCA) depth profiling with ion sputtering. Molecular dynamic (MD) simulations as a function of copolymer density were also performed to obtain optimum interfacial structure information. The dependency of water clustering behavior as a hydrophilicity parameter was described in terms of an atom-atom radial distribution function (RDF). The results showed that the sulfonated diblock copolymer enhanced the hydrophilicity and long-term stability more than the copolymer having no hydrophobic block. Also, according to the ESCA, oxygen composition significantly began to decrease along the membrane depth, indicating the reorientation of diblock chains. The copolymer-entrapped surfaces significantly induced the degree of water clustering, and the resulting equilibrium rearrangement of interfacial structure was distinctly dependent upon the density of the copolymer.

Synthesis and characterization of tri(ethylene oxide)-attached poly(amidoamine) dendrimer layers on gold

This paper describes the synthesis of a tri(ethylene oxide)-attached fourth-generation poly(amidoamine) dendrimer (EO3-dendrimer) and the characterization of its layers on gold. NMR analysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed that about 61 amine groups of a G4 PAMAM dendrimer were covalently conjugated with tri(ethylene oxide) units, accounting for a 95% modification level. Layers of the EO3-dendrimer were formed on gold, and the resulting surface was characterized by infrared reflection absorption spectroscopy, ellipsometry, and contact angle goniometry. The EO3-dendrimer resulted in more hydrophilic and less compact layers with no substantial deformation of the molecule during layer formation by virtue of the EO3 units, compared to a PAMAM dendrimer. Interestingly, the specific binding of avidin to the biotinylated layers of the EO3-dendrimer approached a surface density of 5.2 +/- 0.2 ngmm-2, showing about 92% of full surface coverage. The layers of the EO3-dendrimer were found to be more resistant to nonspecific adsorption of proteins than PAMAM dendrimer layers when bovine serum albumin and serum proteins were tested.

Adsorption studies of human serum albumin, human gamma-globulins, and human fibrinogen on the surface of p(S/PGL) microspheres

Adsorption of human serum albumin (HSA), human gamma-globulins (gammaG), and human fibrinogen (Fb) onto the surface of poly(styrene/alpha-t-butoxy-omega-vinylbenzyl-polyglycidol) microspheres (P(S/PGL)) with controlled fraction of polyglycidol in the interfacial layer was investigated. The microspheres were synthesized by the emulsifier-free radical copolymerization of styrene and alpha-t-butoxy-omega-vinylbenzyl-polyglycidol macromonomer (PGL). Macromonomers with number average molecular weights Mn = 950 and 2,700 were used in the syntheses. Fraction of polyglycidol in the microsphere surface layer was varied from 0.22 to 0.44, depending on the composition of the monomer feed. It was found that the maximal surface concentration of adsorbed proteins and the equilibrium constant of protein adsorption decreased with increased fraction of polyglycidol in the microsphere surface layer. For microspheres with the highest fraction of polyglycidol at the surface the maximal surface protein concentration was c. ten times lower and the adsorption equilibrium constant was c. one hundred times lower than for the reference polystyrene microspheres. The dependence of maximal surface concentration of adsorbed proteins on the fraction of polyglycidol in the particle interfacial layer indicated random distribution of polyglycidol chains without formation of polyglycidol and polystyrene patches at the microspheres surface.

PEGylated nanoparticles for biological and pharmaceutical applications

The utility of polymeric micelles formed through the multimolecular assembly of block copolymer was comprehensively described as novel core-shell typed colloidal carriers for drug and gene targeting. Particularly, novel approaches for the formation of functionalized poly(ethylene glycol) (PEG) layers as hydrophilic outer shell were focused to attain receptor-mediated drug and gene delivery through PEG-conjugated ligands with a minimal non-specific interaction with other proteins. Surface organization of block copolymer micelles with cross-linking core was also described from a standpoint of the preparation of a new functional surface-coating with a unique macromolecular architecture. The micelle-attached surface and the thin hydrogel layer made by layered micelles exhibited nonfouling properties and worked as the reservoir for hydrophobic reagents. Furthermore, the potential utility of multimolecular assembly derived from heterobifunctional PEGs and block copolymers were explored to systematically modify the properties of metal and semiconductor nanostructures by controlling their structure and their surface properties, making them extremely attractive for use in biological and biomedical applications.

Shear-induced platelet activation and adhesion on human pulmonary artery endothelial cells seeded onto hydrophilic polymers

We evaluated platelet activation and adhesion on two plasma polymerized surfaces, N-vinyl pyrrolidone (NVP) and gamma-butyro lactone (GBL), which have been shown previously to promote endothelial cell growth and adhesion as well as fibronectin-coated glass (1 microg/cm(2)) coverslips. Human pulmonary artery endothelial cells were seeded onto coverslips at a low density ( approximately 20,000 cells/cm(2)) and grown to confluence (3-5 days). The materials, both with and without ECs, were then exposed to a shear rate of 400 s(-1) in a closed loop recirculating flow system containing human platelet-rich plasma. Plasma samples were taken at 0, 5, 15, 30, and 60 min and analyzed for platelet and coagulation activation. The coverslips were examined for EC coverage and platelet adherence. EC retention over a 1-h period was approximately 75% for all three materials. All three materials without ECs were highly platelet activating having similar P-selectin expression, platelet factor 4 (PF4) release, mepacrine uptake, and microparticle production. Both microparticle production and platelet adhesion were significantly lower in EC-seeded materials. Dense granule and PF4 release were both slightly diminished in all three materials seeded with ECs. P-selectin expression was reduced slightly for GBL, but remained the same for the other two materials. The EC-seeded materials displayed favorable characteristics with respect to platelet activation and adhesion; however, they still demonstrated some thrombogenic tendencies due to EC loss and exposure of the underlying substrate. Therefore, both EC coverage and EC hemostatic function are important factors in determining the thromboresistance of an EC-seeded surface.

Protein characterisation of salivary and plasma biofilms formed in vitro on non-corroded and corroded dental ceramic materials

Dental ceramics are generally regarded as low-adhesive materials. Different ceramics may, however, differ in composition and physico-chemical surface properties, which may be changed after corrosion. The aim of this study was to examine the adsorption of proteins onto specimens of different ceramic materials after the incubation in saliva and plasma before and after in vitro corrosion. In addition, the topography of the biofilm was examined by AFM. Surface-bound proteins were desorbed and analysed by polyacrylamide gel electrophoresis (PAGE) and immunoblotting using antibodies to saliva and plasma proteins. Silver-stained gels indicated differences in the adsorption of proteins. Differences in surface roughness at the nanometer level did not, however, seem to be correlated to the protein adsorption. After corrosion, unchanged or increased protein staining was generally seen in the gels and Western blots. The reactions for salivary amylase and proline-rich proteins varied between the different materials. Albumin and fibrinogen were identified in samples from all materials tested. Fibronectin and in specific IgA were more sparsely seen. No saliva but all plasma proteins were identified in the alumina and yttria-stabilised zirconia samples and reduced protein reactions were obtained after corrosion.