Recent Progress in Polyion Complex Nanoparticles with Enhanced Stability for Drug Delivery

Polyion complex (PIC) nanoparticles, including PIC micelles and PICsomes, are typically composed of poly(ethylene glycol) block copolymers coupled with oppositely charged polyelectrolytes or therapeutic agents via electrostatic interaction. Due to a simple and rapid preparation process with high drug-loading efficiency, PIC nanoparticles are beneficial to maintaining the chemical integrity and high biological activity of the loaded drugs. However, the stability of PIC nanoparticles can be disrupted in high-ionic-strength solutions because electrostatic interaction is the DRIVING force; these disruptions can thus impair drug delivery. Herein, we summarize the advances in the use of PIC nanoparticles for delivery of charged drugs, focusing on the different chemical and physical strategies employed to enhance their stability, including enhancing the charge density, crosslinking, increasing hydrophobic interactions, forming hydrogen bonds, and the development of PIC-based gels. In particular, we describe the use of PIC nanoparticles to load peptide antibiotics targeting antibiotic-resistant and biofilm-related diseases and the use of nanoparticles that load chemotherapeutics and gaseous donors for cancer treatment. Furthermore, the application of PIC nanoparticles as magnetic resonance imaging contrast agents is summarized for the first time. Therefore, this review is of great significance for advances in the use of polymeric nanoparticles for functional drug delivery.

A review on multifaceted biomedical applications of heparin nanocomposites: Progress and prospects

Advances in polymer-based nanocomposites have revolutionized biomedical applications over the last two decades. Heparin (HP), being a highly bioactive polymer of biological origin, provides strong biotic competence to the nanocomposites, broadening the horizon of their applicability. The efficiency, biocompatibility, and biodegradability properties of nanomaterials significantly improve upon the incorporation of heparin. Further, inclusion of structural/chemical derivatives, fractionates, and mimetics of heparin enable fabrication of versatile nanocomposites. Modern nanotechnological interventions have exploited the inherent biofunctionalities of heparin by formulating various nanomaterials, including inorganic/polymeric nanoparticles, nanofibers, quantum dots, micelles, liposomes, and nanogels ensuing novel functionalities targeting diverse clinical applications involving drug delivery, wound healing, tissue engineering, biocompatible coatings, nanosensors and so on. On this note, the present review explicitly summarises the recent HP-oriented nanotechnological developments, with a special emphasis on the reported successful engagement of HP and its derivatives/mimetics in nanocomposites for extensive applications in the laboratory and health-care facility. Further, the advantages and limitations/challenges specifically associated with HP in nanocomposites, undertaken in this current review are quintessential for future innovations/discoveries pertaining to HP-based nanocomposites.

Size-Controlled Ammonium-Based Homopolymers as Broad-Spectrum Antibacterials

Ammonium group containing polymers possess inherent antimicrobial properties, effectively eliminating or preventing infections caused by harmful microorganisms. Here, homopolymers based on monomers containing ammonium groups were synthesized via Reversible Addition Fragmentation Chain Transfer Polymerization (RAFT) and evaluated as potential antibacterial agents. The antimicrobial activity was evaluated against Gram-positive (M. luteus and B. subtilis) and Gram-negative bacteria (E. coli and S. typhimurium). Three polymers, poly(diallyl dimethyl ammonium chloride), poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), and poly(vinyl benzyl trimethylammonium chloride), were examined to explore the effect of molecular weight (10 kDa, 20 kDa, and 40 kDa) on their antimicrobial activity and toxicity to mammalian cells. The mechanisms of action of the polymers were investigated with dye-based assays, while Scanning Electron Microscopy (SEM) showed collapsed and fused bacterial morphologies due to the interactions between the polymers and components of the bacterial cell envelope, with some polymers proving to be bactericidal and others bacteriostatic, while being non-hemolytic. Among all the homopolymers, the most active, non-Gram-specific polymer was poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), with a molecular weight of 40 kDa, with minimum inhibitory concentrations between 16 and 64 µg/mL, showing a bactericidal mode of action mediated by disruption of the cytoplasmic membrane. This homopolymer could be useful in biomedical applications such as surface dressings and in areas such as eye infections.

Poly-ion complex (PIC) formation of heparin and polyamines: PIC with tetrakis (3-aminopropyl) ammonium allows sustained release of heparin

Physical mixtures of cationic polymers and heparin have been developed to overcome the limitations of unfractionated heparin. In this study, we found that heparin associates with natural polyamines in water, resulting in the generation of a poly-ion complex (PIC). PIC formation (or stability) was influenced by the concentration and ratio of heparin and polyamines, molecular weight of heparin, nature of polyamines, and pH conditions. Interestingly, the PIC obtained when heparin and tetrakis (3-aminopropyl) ammonium (Taa) were mixed exhibited stability and was sticky in nature. PIC formation was due to an electrostatic interaction between heparin and Taa. Heparin-Taa PIC was administered subcutaneously to mice, and the time to maximum heparin concentration within the therapeutic range of heparin was markedly increased compared to that after a single dose of heparin. These results suggest that the quaternary ammonium structure of Taa is critical for the preparation of a stable PIC, thereby allowing the sustained release of heparin into the blood.

On Complex Coacervate Core Micelles: Structure-Function Perspectives

The co-assembly of ionic-neutral block copolymers with oppositely charged species produces nanometric colloidal complexes, known, among other names, as complex coacervates core micelles (C3Ms). C3Ms are of widespread interest in nanomedicine for controlled delivery and release, whilst research activity into other application areas, such as gelation, catalysis, nanoparticle synthesis, and sensing, is increasing. In this review, we discuss recent studies on the functional roles that C3Ms can fulfil in these and other fields, focusing on emerging structure-function relations and remaining knowledge gaps.

Serum Albumin-Peptide Conjugates for Simultaneous Heparin Binding and Detection

Heparin is a polysaccharide-based anticoagulant agent, which is widely used in surgery and blood transfusion. However, overdosage of heparin may cause severe side effects such as bleeding and low blood platelet count. Currently, there is only one clinically licensed antidote for heparin: protamine sulfate, which is known to provoke adverse effects. In this work, we present a stable and biocompatible alternative for protamine sulfate that is based on serum albumin, which is conjugated with a variable number of heparin-binding peptides. The heparin-binding efficiency of the conjugates was evaluated with methylene blue displacement assay, dynamic light scattering, and anti-Xa assay. We found that multivalency of the peptides played a key role in the observed heparin-binding affinity and complex formation. The conjugates had low cytotoxicity and low hemolytic activity, indicating excellent biocompatibility. Furthermore, a sensitive DNA competition assay for heparin detection was developed. The detection limit of heparin was 0.1 IU/mL, which is well below its therapeutic range (0.2-0.4 IU/mL). Such biomolecule-based systems are urgently needed for next-generation biocompatible materials capable of simultaneous heparin binding and sensing.

Production of LMWH-conjugated core/shell hydrogels encapsulating paclitaxel for transdermal delivery: In vitro and in vivo assessment

Topical applications that reduce systemic toxic effects while increasing therapeutic efficacy are a promising alternative strategy. The aim of this study was to provide an enhanced transdermal delivery of low molecular weight heparin (LMWH) through the stratum corneum by using cationic carrier as a novel permeation enhancer. Recent studies have shown that heparin-conjugated biomaterials can be effective in inhibiting tumor growth during cancer treatment due to their high ability to bind growth factors. Paclitaxel (PCL) was co-encapsulated into the same cationic carrier for the purpose of improving of therapeutic efficacy for a combined cancer treatment with LMWH. In vitro and in vivo studies showed that the LMWH and PCL release was significantly affected by polymer molecular weight and block composition. Skin penetration tests have indicated that larger amounts of LMWH were absorbed from LMWH-gel conjugate through SC, than aqueous formula. However, it was found that the plasma transition of LMWH released from gel conjugate was lower compared to the plasma concentration of LMWH released from aqueous solution. It is recommended that PCL-loaded LMWH-conjugated core/shell hydrogels can be used as promising drug release systems for transdermal applications that can improve therapeutic efficacy and reduce side effects in a combined cancer treatment.

Evaluation of the Bactericidal and Fungicidal Activities of Poly([2-(methacryloyloxy)ethyl]trimethyl Ammonium Chloride)(Poly (METAC))-Based Materials

Poly([2-(methacryloyloxy)ethyl]trimethyl ammonium chloride) (METAC) and the gels were prepared and evaluated for their bactericidal and fungicidal activities. The antimicrobial properties of poly(METAC) were tested against Escherichia coli (E. coli), Bacillus subtilis (B. subtilis), Saccharomyces cerevisiae (Sa. cerevisiae), methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa (P. aeruginosa), and Candida albicans (C. albicans). Moreover, the structural forms of the linear and cross-linked poly(METAC) were investigated for their influences on bacterial aggregation, precipitation, and cell-death. To our knowledge, this is the first report on the comparison of the antimicrobial properties of poly(METAC) and poly(METAC)-gels. The bactericidal and fungicidal activities were evaluated by determining minimum inhibitory concentrations (MICs), UV⁻Vis spectroscopy, and fluorescence and confocal microscopies. The MICs were found to be 123 (MSSA), 123 (MRSA), 123 (P. aeruginosa), 370 (E. coli), 123 (B. subtilis), 370 (C. albicans), and 370 μg/mL (Sa. cerevisiae), as determined by broth dilution, and 370 (MSSA), 370 (MRSA), 370 (P. aeruginosa), 3300 (E. coli), 370 (B. subtilis), 1100 (C. albicans), and >10,000 μg/mL (Sa. cerevisiae), as determined by paper disc diffusion (on solid medium). The poly(METAC)-gels achieved rapid adsorption/precipitation of bacteria via the cationic surface charge. Thus, these poly(METAC)-based polymers can potentially be used as antibacterial materials.

Polyion Complex Micelles for Protein Delivery

Proteins are ubiquitous in life and next to water, they are the most abundant compounds found in human bodies. Proteins have very specific roles in the body and depending on their function, they are for example classified as enzymes, antibodies or transport proteins. Recently, therapeutic proteins have made an impact in the drug market. However, some proteins can be subject to quick hydrolytic degradation or denaturation depending on the environment and therefore require a protective layer. A range of strategies are available to encapsulate and deliver proteins, but techniques based on polyelectrolyte complex formation stand out owing to their ease of formulation. Depending on their isoelectric point, proteins are charged and can condense with oppositely charged polymers. Using block copolymers with a neutral block and a charged block results in the formation of polyion complex (PIC) micelles when mixed with the oppositely charged protein. The neutral block stabilises the charged protein–polymer core, leading to nanoparticles. The types of micelles are also known under the names interpolyelectrolyte complex, complex coacervate core micelles, and block ionomer complexes. In this article, we discuss the formation of PIC micelles and their stability. Strategies to enhance the stability such as supercharging the protein or crosslinking the PIC micelles are discussed.

Morphological control of self-assembled multivalent (SAMul) heparin binding in highly competitive media

Shape control – self-assembly of ligands into different morphologies directs their ability to bind heparin.

Drug-loading of poly(ethylene glycol methyl ether methacrylate) (PEGMEMA)-based micelles and mechanisms of uptake in colon carcinoma cells

In this study polymeric micelles formed from poly(poly(ethylene glycol) methyl ether methacrylate)-block-poly(methyl methacrylate) (P(PEGMEMA75)-b-PMMA80) block copolymer of approximately 25nm in diameter were used to encapsulate the model drug, Nile Red, with a loading efficiency of 0.08wt% and a chemotherapeutic drug, doxorubicin (DOX), with an efficiency of 2.75wt%. The release of DOX from the micelles was sufficient to be cytotoxic to human colon carcinoma cells, WiDr, while Nile Red and the unloaded micelles were found not to be cytotoxic when exposed to the cells at polymer concentrations up to 200μg/mL. Nile Red loaded micelles were used to analyze uptake of the micelles into the cells which were rapidly internalized within minutes of exposure. The three major endocytotic pathways were involved in the internalization of micelles; however other passive mechanisms were also at play as the addition of inhibitors to all three pathways did not completely inhibit the uptake of these nanoparticles. These data demonstrate the potential of the P(PEGMEMA)75-b-PMMA80 block copolymer micelles to be rapidly internalized by carcinoma cells and deliver low doses of drugs intracellularly for controlled drug release.

Curcumin-Loading-Dependent Stability of PEGMEMA-Based Micelles Affects Endocytosis and Exocytosis in Colon Carcinoma Cells

Polymeric micelles were formed from poly(poly(ethylene glycol) methyl ether methacrylate)-block-poly(styrene) (P(PEGMEMA)-b-PS) block copolymer of two different chain lengths. The micelles formed were approximately 16 and 46 nm in diameter and used to encapsulate curcumin. Upon loading of the curcumin into the micelles, their size increased to approximately 34 and 80 nm in diameter, respectively, with a loading efficiency of 58%. The unloaded micelles were not cytotoxic to human colon carcinoma cells, whereas only the smaller loaded micelles were cytotoxic after 72 h of exposure. The micelles were rapidly internalized by the cells within minutes of exposure, with the loaded micelles internalized to a greater extent owing to their enhanced stability compared to that of the unloaded micelles. The larger micelles were more rapidly internalized and exocytosed than the smaller micelles, demonstrating the effect of micelle size and drug loading on drug delivery and cytotoxicity.

An Oligonucleotide Transfection Vector Based on HSA and PDMAEMA Conjugation: Effect of Polymer Molecular Weight on Cell Proliferation and on Multicellular Tumor Spheroids

A novel gene transfection vector was fabricated based on the conjugation of human serum albumin (HSA) and maleimide end functionalized poly[(N,N-dimethylamino) ethyl methacrylate] (PDMAEMA). The bioconjugation was achieved in a site-specific manner to yield well-defined polymer-protein conjugates. The biohybrid was able to bind DNA with high affinity resulting in nanoparticles with a HSA shell. This paper mainly focuses on the influence of polymeric chain length on the particle properties and their drug-carrying ability to deliver oligonucleotides into breast cancer cells. The cytotoxic agent of interest, ISIS5132, is an oligonucleotide which disrupts DNA function within the cell. There was no evidence that the polymeric chain length had any effects on the conjugation efficiency and the subsequent condensation ability of the conjugates to oligonucleotide. However, the polymeric chain length had an obvious effect on the size of the complex micelles. Low molecular weights only led to loosely compacted complexes with the oligonucleotide, while large molecular weight led to well-defined nanoparticle structures. More importantly, it was found that the variation in the length of the PDMAEMA block resulted in a change in cytotoxicity of the drug loaded complex micelle. That is, the concentration of 50% inhibition (IC50 ) of the complex micelle on MDA-MB-231 and MCF-7 cells reached the lowest value at a chain length of around 21 000 g mol(-1) . The IC50 value increased when the polymeric chain length was shorter (8000 g mol(-1) and 10 000 g mol(-1) ) while it increased again when PDMAMEA of M¯n = 47 000 g mol(-1) , probably due to insufficient release of the drug. These result were reflected when investigating the performance of the polyplex using MCF-7 multicellular tumor spheroids, where again the medium PDMAEMA chain length led to the best delivery vehicle for ISIS5132.

Glycosaminoglycan functionalized nanoparticles exploit glycosaminoglycan functions

Nanoparticles are being explored for a variety of applications including medical imaging, drug delivery, and biochemical detection. Surface functionalization of nanoparticles with glycosaminoglycans (GAGs) is an attractive strategy that is only starting to be investigated to improve their properties for biological and therapeutic applications. Herein, we describe a method to functionalize the surface of cerium oxide nanoparticles (nanoceria) with organosilane linkers, such as 3-(aminopropyl)triethoxysilane (APTES) and 3-(mercaptopropyl)trimethoxysilane (MPTMS), and GAGs, such as unfractionated and low molecular weight heparin. Examples of how the activity of these heparin functionalized nanoparticles are governed by the pendant GAGs are detailed. The activity of heparin covalently attached to the nanoceria was found to be unchanged when compared to unfractionated heparin using the activated partial clotting time (APTT) assay.

Polyion complex micelle based on albumin-polymer conjugates: multifunctional oligonucleotide transfection vectors for anticancer chemotherapeutics

Novel biocompatible polyion complex micelles, containing bovine serum albumin (BSA), polymer, and oligonucleotide, were synthesized as a generation of vectors for the gene transfection. Maleimide-terminated poly((N,N-dimethyl amino) ethyl methacrylate) (PDMAEMA) was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequently deprotected. Precise one to one albumin-PDMAEMA bioconjugates have been achieved via 1,4-addition with the free thiol group on Cys34 on the BSA protein. SDS-PAGE and GPC (water) confirmed and quantified the successful conjugation. The conjugation efficiency was found to be independent of the molecular weight of PDMAEMA. After careful pH adjustment, the conjugate could efficiently condense anticancer oligonucleotide, ISIS 5132, which resulted in particles of 15-35 nm with a negative zeta-potential. The size was easily controlled by the polymer chain length. The albumin corona provides complete protection of the cationic polymer and genetic drug, which gave rise to lower potential toxicity from the polymer and higher gene transfection efficiency. Although a control experiment with a traditional PEG-based polyion complex micelle could deliver the drug just as effectively, if not more so, to the ovarian cancer cell line OVCAR-3, this carrier had no selectivity toward cancerous cells and proved just as toxic to HS27 (fibroblast) cell line. In contrast, the albumin-coated particles demonstrated desirable selectivity toward cancerous cells and have been shown to have outstanding performance in the cytotoxicity tests of several carcinoma monolayer cell models. In addition, the complex micelles were able to destroy pancreatic multicellular tumor spheroids, while free ISIS 5132 could not penetrate the spheroid at all. Hence, albumin-coated/oligonucleotide complex micelles are far more promising than the most classical gene delivery vectors.

HYDROGEL-BASED NANOCOMPOSITES OF THERAPEUTIC PROTEINS FOR TISSUE REPAIR

The ability to design artificial extracellular matrices as cell instructive scaffolds has opened the door to technologies capable of studying cell fates in vitro and to guide tissue repair in vivo. One main component of the design of artificial extracellular matrices is the incorporation of protein-based biochemical cues to guide cell phenotypes and multicellular organizations. However, promoting the long-term bioactivity, controlling the bioavailability and understanding how the physical presentations of these proteins impacts cellular fates are among the challenges of the field. Nanotechnolgy has advanced to meet the challenges of protein therapeutics. For example, the approaches to incorporating proteins into tissue repairing scaffolds have ranged from bulk encapsulations to smart nanodepots that protect proteins from degradations and allow opportunities for controlled release.

Heparin-functionalized polymeric biomaterials in tissue engineering and drug delivery applications

Heparin plays an important role in many biological processes via its interaction with various proteins, and hydrogels and nanoparticles comprising heparin exhibit attractive properties, such as anticoagulant activity, growth factor binding, and antiangiogenic and apoptotic effects, making them great candidates for emerging applications. Accordingly, this review summarizes recent efforts in the preparation of heparin-based hydrogels and formation of nanoparticles, as well as the characterization of their properties and applications. The challenges and future perspectives for heparin-based materials are also discussed. Prospects are promising for heparin-containing polymeric biomaterials in diverse applications ranging from cell carriers for promoting cell differentiation to nanoparticle therapeutics for cancer treatment.

Size effects of self-assembled block copolymer spherical micelles and vesicles on cellular uptake in human colon carcinoma cells

Block copolymers, poly(oligo ethylene glycol methyl ether methacrylate)-block-poly(styrene), POEGMEMA-b-PS, with various block lengths were prepared via RAFT polymerization and subsequently self-assembled into various aggregates to investigate their uptake ability into cancer cells.