Complex Coacervates between a Lactose-Modified Chitosan and Hyaluronic Acid as Radical-Scavenging Drug Carriers

Macromolecular Crowding Effect on Chitosan-Hyaluronic Acid Complexation and the Activity of Encapsulated Catalase

The associative phase separation of charged biomacromolecules plays a key role in many biophysical events that take place in crowded intracellular environments. Such natural polyelectrolyte complexation and phase separation often occur at nonstoichiometric charge ratios with the incorporation of bioactive proteins, which is not studied as extensively as those complexations at stoichiometric ratios. In this work, we investigated how the addition of a crowding agent (polyethylene glycol, PEG) affected the complexation between chitosan (CS) and hyaluronic acid (HA), especially at nonstoichiometric ratios, and the encapsulation of enzyme (catalase, CAT) by the colloidal complexes. The crowded environment promoted colloidal phase separation at low charge ratios, forming complexes with increased colloidal and dissolution stability, which resulted in a smaller size and polydispersity (PDI). The binding isotherms revealed that the addition of PEG greatly enhanced the ion-pairing strength (with increased ion-pairing equilibrium constant Ka from 4.92 × 104 without PEG to 1.08 × 106 with 200 g/L PEG) and switched the coacervation from endothermic to exothermic, which explained the promoted complexation and phase separation. At the stoichiometric charge ratio, the enhanced CS-HA interaction in crowded media generated a more solid-like coacervate phase with a denser network, slower chain relaxation, and higher modulus. Moreover, both crowding and complex encapsulation enhanced the activity and catalytic efficiency of CAT, represented by a 2-fold increase in catalytic efficiency (Kcat/Km) under 100 g/L PEG crowding and CS-HA complex encapsulation. This is likely due to the lower polarity in the microenvironment surrounding the enzyme molecules. By a systematic investigation of both nonstoichiometric and stoichiometric charge ratios under macromolecular crowding, this work provided new insights into the complexation between natural polyelectrolytes in a scenario closer to an intracellular environment.

Drug Encapsulation via Peptide-Based Polyelectrolyte Complexes

Peptide-based polyelectrolyte complexes are biocompatible materials that can encapsulate molecules with different polarities due to their ability to be precisely designed. Here we use UV-Vis spectroscopy, fluorescence microscopy, and infrared spectroscopy to investigate the encapsulation of model drugs, doxorubicin (DOX) and methylene blue (MB) using a series of rationally designed polypeptides. For both drugs, we find an overall higher encapsulation efficiency with sequences that have higher charge density, highlighting the importance of ionic interactions between the small molecules and the peptides. However, comparing molecules with the same charge density, illustrated that the most hydrophobic sequence pairs had the highest encapsulation of both DOX and MB molecules. The phase behavior and stability of DOX-containing complexes did not change compared to the complexes without drugs. However, MB encapsulation caused changes in the stabilities of the complexes. The sequence pair with the highest charge density and hydrophobicity had the most dramatic increase in stability, which coincided with a phase change from liquid to solid. This study illustrates how multiple types of molecular interactions are required for efficient encapsulation of poorly soluble drugs and provides insights into the molecular design of delivery carriers.

Understanding the Impacts of Molecular and Macromolecular Crowding Agents on Protein-Polymer Complex Coacervates

Complex coacervation refers to the liquid-liquid phase separation (LLPS) process occurring between charged macromolecules. The study of complex coacervation is of great interest due to its implications in the formation of membraneless organelles (MLOs) in living cells. However, the impacts of the crowded intracellular environment on the behavior and interactions of biomolecules involved in MLO formation are not fully understood. To address this knowledge gap, we investigated the effects of crowding on a model protein-polymer complex coacervate system. Specifically, we examined the influence of sucrose as a molecular crowder and polyethylene glycol (PEG) as a macromolecular crowder. Our results reveal that the presence of crowders led to the formation of larger coacervate droplets that remained stable over a 25-day period. While sucrose had a minimal effect on the physical properties of the coacervates, PEG led to the formation of coacervates with distinct characteristics, including higher density, increased protein and polymer content, and a more compact internal structure. These differences in coacervate properties can be attributed to the effects of crowders on individual macromolecules, such as the conformation of model polymers, and nonspecific interactions among model protein molecules. Moreover, our results show that sucrose and PEG have different partition behaviors: sucrose was present in both the coacervate and dilute phases, while PEG was observed to be excluded from the coacervate phase. Collectively, our findings provide insights into the understanding of crowding effects on complex coacervation, shedding light on the formation and properties of coacervates in the context of MLOs.

Current and emerging applications of saccharide-modified chitosan: a critical review

Chitin, as the main component of the exoskeleton of Arthropoda, is a highly available natural polymer that can be processed into various value-added products. Its most important derivative, i.e., chitosan, comprising β-1,4-linked 2-amino-2-deoxy-β-d-glucose (deacetylated d-glucosamine) and N-acetyl-d-glucosamine units, can be prepared via alkaline deacetylation process. Chitosan has been used as a biodegradable, biocompatible, non-antigenic, and nontoxic polymer in some in-vitro applications, but the recently found potentials of chitosan for in-vivo applications based on its biological activities, especially antimicrobial, antioxidant, and anticancer activities, have upgraded the chitosan roles in biomaterials. Chitosan approval, generally recognized as a safe compound by the United States Food and Drug Administration, has attracted much attention toward its possible applications in diverse fields, especially biomedicine and agriculture. Even with some favorable characteristics, the chitosan's structure should be customized for advanced applications, especially due to its drawbacks, such as low drug-load capacity, low solubility, high viscosity, lack of elastic properties, and pH sensitivity. In this context, derivatization with relatively inexpensive and highly available mono- and di-saccharides to soluble branched chitosan has been considered a "game changer". This review critically reviews the emerging technologies based on the synthesis and application of lactose- and galactose-modified chitosan as two important chitosan derivatives. Some characteristics of chitosan derivatives and biological activities have been detailed first to understand the value of these natural polymers. Second, the saccharide modification of chitosan has been discussed briefly. Finally, the applications of lactose- and galactose-modified chitosan have been scrutinized and compared to native chitosan to provide an insight into the current state-of-the research for stimulating new ideas with the potential of filling research gaps.

Colloidal Polyelectrolyte Complexes from Hyaluronic Acid: Preparation and Biomedical Applications

Hyaluronic acid (HA) is a naturally occurring polysaccharide which has been extensively exploited in biomedical fields owing to its outstanding biocompatibility. Self-assembly of HA and polycations through electrostatic interactions can generate colloidal polyelectrolyte complexes (PECs), which can offer a wide range of applications while being relatively simple to prepare with rapid and "green" processes. The advantages of colloidal HA-based PECs stem from the combined benefits of nanomedicine, green chemistry, and the inherent properties of HA, namely high biocompatibility, biodegradability, and biological targeting capability. Accordingly, colloidal PECs from HA have received increasing attention in the recent years as high-performance materials for biomedical applications. Considering their potential, this review is aimed to provide a comprehensive understanding of colloidal PECs from HA in complex with polycations, from the most fundamental aspects of the preparation process to their various biomedical applications, notably as nanocarriers for delivering small molecule drugs, nucleic acids, peptides, proteins, and bioimaging agents or the construction of multifunctional platforms.

Ionic group-dependent structure of complex coacervate hydrogels formed by ABA triblock copolymers

This study investigates the nanostructure of complex coacervate core hydrogels (C3Gs) with varying compositions of cationic charged groups (i.e., ammonium and guanidinium) using small-angle X-ray/neutron scattering (SAX/NS). C3Gs were prepared by stoichiometric mixing of two oppositely charged ABA triblock copolymers in aqueous solvents, in which A end-blocks were functionalized with either sulfonate groups or a mixture of ammonium and guanidinium groups. Comprehensive small-angle X-ray/neutron scattering (SAX/NS) analysis elucidated the dependence of C3Gs structures on the fraction of guanidinium groups in the cationic end-block (x) and salt concentration (c_s). As x increases, the polymer volume fraction in the cores, and interfacial tension (γ_core) and salt resistance (c*) of the coacervate cores increase, which is attributed to the greater hydrophobicity and non-electrostatic association. Furthermore, we observed that the salt dependence of the interfacial tension follows γ_core ∼ (1 - c_s/c*)^3/2 in all series of x. The results show that the variation of the ionic group provides a powerful method to control the salt-responsiveness of C3Gs as stimuli-responsive materials.

Contributions of Women in Recent Research on Biopolymer Science

Nowadays, biopolymers are playing a fundamental role in our society because of the environmental issues and concerns associated with synthetic polymers. The aim of this Special Issue entitled ‘Women in Polymer Science and Technology: Biopolymers’ is highlighting the work designed and developed by women on biopolymer science and technology. In this context, this short review aims to provide an introduction to this Special Issue by highlighting some recent contributions of women around the world on the particular topic of biopolymer science and technology during the last 20 years. In the first place, it highlights a selection of important works performed on a number of well-studied natural polymers, namely, agar, chitin, chitosan, cellulose, and collagen. Secondly, it gives an insight into the discovery of new polysaccharides and enzymes that have a role in their synthesis and in their degradation. These contributions will be paving the way for the next generation of female and male scientists on this topic.

Coacervate microdroplet protocell-mediated gene transfection for nitric oxide production and induction of cell apoptosis

Liquid coacervate microdroplets have been widely explored as membrane-free compartment protocells for cargo delivery in therapeutic applications. In this study, coacervate protocells were developed as gene carriers for transfection of nitric oxide synthase (NOS) and overproduction of nitric oxide (NO) for killing of cancer cells. The coacervate microdroplet protocells were formed via the liquid-liquid phase separation of oppositely charged diethylaminoethyl-dextran/polyacrylic acids. The coacervate microdroplet protocells were found to facilitate gene transfection, which was demonstrated by cell imaging of the internalized coacervate microdroplets containing plasmids of enhanced green fluorescent protein. Due to their high transfection capability, the coacervate protocells were subsequently utilized for the delivery of NOS plasmids (pNOS). The cellular internalization of pNOS-containing coacervate carriers was found to result in high NOS expression coupled with NO overproduction, which then induced cell apoptosis and decreased cell viability. The cell apoptosis is associated with NO-mediated mitochondrial damage. The enhanced gene transfection was attributed to coacervate microdroplets' unique high sequestration capability and liquid-like fluidity. Overall, the incorporation of genes in coacervate microdroplets was demonstrated as a viable and novel strategy for the development of cargo biocarriers for biomedical applications.

Heterogeneous Charged Complexes of Random Copolymers for the Segregation of Organic Molecules

Nature harnesses the disorder of intrinsically disordered proteins to organize enzymes and biopolymers into membraneless organelles. The heterogeneous nature of synthetic random copolymers with charged, polar, and hydrophobic groups has been exploited to mimic intrinsically disordered proteins, forming complexes with enzymatically active proteins and delivering them into nonbiological environments. Here, the properties of polyelectrolyte complexes composed of two random copolymer polyelectrolytes are studied experimentally and via simulation with the aim of exploiting such complexes for segregating organic molecules from water. The anionic polyelectrolyte contains hydrophilic and hydrophobic side chains and forms self-assembled hydrophobic domains. The cationic polymer is a high-molecular-weight copolymer of hydrophilic and charged side groups and acts as a flocculant. We find that the polyelectrolyte complexes obtained with this anionic and cationic random copolymer system are capable of absorbing small cationic, anionic, and hydrophobic organic molecules, including perfluorooctanoic acid, a compound of great environmental and toxicologic concern. Importantly, these macroscopic complexes can be easily removed from water, thereby providing a simple approach for organic contaminant removal in aqueous media. MARTINI and coarse-grained molecular dynamics simulations explore how the microscale heterogeneity of these random copolymer complexes relates to their segregation functionality.

Polysaccharide-Based Materials Created by Physical Processes: From Preparation to Biomedical Applications

Polysaccharide-based materials created by physical processes have received considerable attention for biomedical applications. These structures are often made by associating charged polyelectrolytes in aqueous solutions, avoiding toxic chemistries (crosslinking agents). We review the principal polysaccharides (glycosaminoglycans, marine polysaccharides, and derivatives) containing ionizable groups in their structures and cellulose (neutral polysaccharide). Physical materials with high stability in aqueous media can be developed depending on the selected strategy. We review strategies, including coacervation, ionotropic gelation, electrospinning, layer-by-layer coating, gelation of polymer blends, solvent evaporation, and freezing-thawing methods, that create polysaccharide-based assemblies via in situ (one-step) methods for biomedical applications. We focus on materials used for growth factor (GFs) delivery, scaffolds, antimicrobial coatings, and wound dressings.

Antibacterial Electrospun Polycaprolactone Membranes Coated with Polysaccharides and Silver Nanoparticles for Guided Bone and Tissue Regeneration

Electrospun polycaprolactone (PCL) membranes have been widely explored in the literature as a solution for several applications in tissue engineering and regenerative medicine. PCL hydrophobicity and its lack of bioactivity drastically limit its use in the medical field. To overcome these drawbacks, many promising strategies have been developed and proposed in the literature. In order to increase the bioactivity of electrospun PCL membranes designed for guided bone and tissue regeneration purposes, in the present work, the membranes were functionalized with a coating of bioactive lactose-modified chitosan (CTL). Since CTL can be used for the synthesis and stabilization of silver nanoparticles, a coating of this compound was employed here to provide antibacterial properties to the membranes. Scanning electron microscopy imaging revealed that the electrospinning process adopted here allowed us to obtain membranes with homogeneous fibers and without defects. Also, PCL membranes retained their mechanical properties after several weeks of aging in simulated body fluid, representing a valid support for cell growth and tissue development. CTL adsorption on membranes was investigated by fluorescence microscopy using fluorescein-labeled CTL, resulting in a homogeneous and slow release over time. Inductively coupled plasma-mass spectrometry was used to analyze the release of silver, which was shown to be stably bonded to the CTL coating and to be slowly released over time. The CTL coating improved MG63 osteoblast adhesion and proliferation on membranes. On the other hand, the presence of silver nanoparticles discouraged biofilm formation by Pseudomonas aeruginosa and Staphylococcus aureus without being cytotoxic. Overall, the stability and the biological and antibacterial properties make these membranes a valid and versatile material for applications in guided tissue regeneration and in other biomedical fields like wound healing.

Polysaccharide nanoparticles: from fabrication to applications

The present review highlights the developments in polysaccharide nanoparticles with a particular focus on applications in biomedicine, cosmetics and food.

Efficient Synthesis of Stable Polyelectrolyte Complex Nanoparticles by Electrostatic Assembly Directed Polymerization

Polyelectrolyte complex nanoparticles with integrated advances of coacervate complexes and nanomaterials have attracted considerable attention as soft templates and functional nano-carriers. Herein, a facile and robust strategy, namely electrostatic assembly directed polymerization (EADP), for efficient and scalable preparation of stable coacervate nanoparticles is presented. With homo-polyelectrolyte PAA (polyacrylic acid) as template and out of charge stoichiometry, the cationic monomers are polymerized together with cross-linkers, which creates coacervate nanoparticles featuring high stability against salt through one-pot synthesis. The particle size can be tuned by varying the cross-linker amount and salt concentrations during the polymerization and the composition of nanoparticles, as well as the corresponding properties can be regulated by combining different charged blocks from both strong and weak ionic monomers. The strategy can tolerate both high monomer concentrations and increased volume of up to l L, which is favorable for scaled-up preparations. Moreover, the coacervate nanoparticles can be freeze-dried to produce a product in powder form, which can be redispersed without any effect on the particle size and size distribution. Finally, the obtained nanoparticles loaded with enzyme and Au nanoparticles exhibit enhanced catalytic performance, demonstrating a great potential for exploring various applications of coacervate particles as soft and functional nano-carriers.

Mechanisms for Tuning Engineered Nanomaterials to Enhance Radiation Therapy of Cancer

Engineered nanomaterials that produce reactive oxygen species on exposure to X- and gamma-rays used in radiation therapy offer promise of novel cancer treatment strategies. Similar to photodynamic therapy but suitable for large and deep tumors, this new approach where nanomaterials acting as sensitizing agents are combined with clinical radiation can be effective at well-tolerated low radiation doses. Suitably engineered nanomaterials can enhance cancer radiotherapy by increasing the tumor selectivity and decreasing side effects. Additionally, the nanomaterial platform offers therapeutically valuable functionalities, including molecular targeting, drug/gene delivery, and adaptive responses to trigger drug release. The potential of such nanomaterials to be combined with radiotherapy is widely recognized. In order for further breakthroughs to be made, and to facilitate clinical translation, the applicable principles and fundamentals should be articulated. This review focuses on mechanisms underpinning rational nanomaterial design to enhance radiation therapy, the understanding of which will enable novel ways to optimize its therapeutic efficacy. A roadmap for designing nanomaterials with optimized anticancer performance is also shown and the potential clinical significance and future translation are discussed.

Binary Solutions of Hyaluronan and Lactose-Modified Chitosan: The Influence of Experimental Variables in Assembling Complex Coacervates

A miscibility study between oppositely charged polyelectrolytes, namely hyaluronic acid and a lactose-modified chitosan, is here reported. Experimental variables such as polymers' weight ratios, pH values, ionic strengths and hyaluronic acid molecular weights were considered. Transmittance analyses demonstrated the mutual solubility of the two biopolymers at a neutral pH. The onset of the liquid-liquid phase separation due to electrostatic interactions between the two polymers was detected at pH 4.5, and it was found to be affected by the overall ionic strength, the modality of mixing and the polymers' weight ratio. Thorough Dynamic Light Scattering (DLS) measurements were performed to check the quality of the formed coacervates by investigating their dimensions, homogeneity and surface charge. The whole DLS results highlighted the influence of the hyaluronic acid molecular weight in affecting coacervates' dispersity and size.

Glycosylated-Chitosan Derivatives: A Systematic Review

Chitosan derivatives, and more specifically, glycosylated derivatives, are nowadays attracting much attention within the scientific community due to the fact that this set of engineered polysaccharides finds application in different sectors, spanning from food to the biomedical field. Overcoming chitosan (physical) limitations or grafting biological relevant molecules, to mention a few, represent two cardinal strategies to modify parent biopolymer; thereby, synthetizing high added value polysaccharides. The present review is focused on the introduction of oligosaccharide side chains on the backbone of chitosan. The synthetic aspects and the effect on physical-chemical properties of such modifications are discussed. Finally, examples of potential applications in biomaterials design and drug delivery of these novel modified chitosans are disclosed.

Characterization of Chitosan/Hyaluronan Complex Coacervates Assembled by Varying Polymers Weight Ratio and Chitosan Physical-Chemical Composition

Herein, we synthetized and characterized polysaccharide-based complex coacervates starting from two water-soluble biopolymers, i.e., hydrochloride chitosans and sodium hyaluronan. We used chitosans encompassing a range of molecular weights from 30,000 to 400,000 and showing different fraction of acetylated units (i.e., FA = 0.16, 0.46, and 0.63). This set of chitosans was mixed with a low molecular weight hyaluronan to promote electrostatic interactions. Resulting colloids were analyzed in terms of size, polydispersity and surface charge by Dynamic Light Scattering. The weight ratio between the two polyelectrolytes was studied as additional parameter influencing the liquid-liquid phase separation. Main results include the following: the polymers weight ratio was fundamental in dictating the colloids surface charge, whereas chitosan physical-chemical features influenced the dimension and homogeneity of colloids. This contribution presents additional understanding of the complex coacervation between these two oppositely charged polysaccharides, with the potential translation of present system in food and biomedical sectors.

On the Formation and Stability of Chitosan/Hyaluronan-Based Complex Coacervates

This contribution is aimed at extending our previous findings on the formation and stability of chitosan/hyaluronan-based complex coacervates. Colloids are herewith formed by harnessing electrostatic interactions between the two polyelectrolytes. The presence of tiny amounts of the multivalent anion tripolyphosphate (TPP) in the protocol synthesis serves as an adjuvant “point-like” cross-linker for chitosan. Hydrochloride chitosans at different viscosity average molar mass, Mv¯, in the range 10,000–400,000 g/mol, and fraction of acetylated units, F_A, (0.16, 0.46 and 0.63) were selected to fabricate a large library of formulations. Concepts such as coacervate size, surface charge and homogeneity in relation to chitosan variables are herein disclosed. The stability of coacervates in Phosphate Buffered Saline (PBS) was verified by means of scattering techniques, i.e., Dynamic Light Scattering (DLS) and Small-Angle X-ray Scattering (SAXS). The conclusions from this set of experiments are the following: (i) a subtle equilibrium between chitosan F_A and Mv¯ does exist in ensuring colloidal stability; (ii) once diluted in PBS, osmotic swelling-driven forces trigger the enlargement of the polymeric mesh with an ensuing increase of coacervate size and porosity.

Facile design of autogenous stimuli-responsive chitosan/hyaluronic acid nanoparticles for efficient small molecules to protein delivery

Chitosan is functionalized with oxidative stress-sensitive thioketal entities in a one-pot methodology, and self-assembled into drugs or protein loaded dual stimuli responsive nanoparticles, which kill glioblastoma cells and increase nerve outgrowth.

Aqueous self-assembly of arginine and K8SiW11O39: fine-tuning the formation of a coacervate intended for sprayable anticorrosive coatings

Coacervates are commonly thought to be formed from the liquid-liquid phase separation of macromolecules, such as oppositely charged polyelectrolytes, proteins or peptides. Unlike conventional systems, we here show an entirely novel coacervate obtained from the self-assembly of arginine (Arg) and K₈[α-SiW₁₁O₃₉] (SiW₁₁) in water. The formation of the coacervate Arg/SiW₁₁ is confirmed by combined techniques, including turbidity, rheology, optical microscopy, and scanning and transmission electron microscopy. Assessment of the rheological response reveals that the complex coacervate exhibits shear thinning behaviour. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, elemental analysis and thermogravimetric analysis are used to characterize the coacervate. The thermodynamic parameters of the coacervation are monitored by isothermal titration calorimetry (ITC), which identifies that the formation of the coacervate by mixing of Arg and SiW₁₁ is driven by a combination of entropic and enthalpic effects. The resultant coacervate shows a typical upper critical solution temperature (UCST) phenomenon, which is strongly dependent on the concentration of the species. Furthermore, we demonstrate that the coacervation could be tuned by stoichiometry and pH. A phase diagram for the complexation of Arg and SiW₁₁ thus has been constructed using turbidity measurements. Such a phase diagram is a very useful tool for the preparation of coacervates from a specific combination of Arg and SiW₁₁. Finally, the acid induced gelation of the coacervate has been explored to fabricate an anticorrosive coating to protect a copper plate from exposure to acid vapour.

Toward Regeneration of the Heart: Bioengineering Strategies for Immunomodulation

Myocardial Infarction (MI) is the most common cardiovascular disease. An average-sized MI causes the loss of up to 1 billion cardiomyocytes and the adult heart lacks the capacity to replace them. Although post-MI treatment has dramatically improved survival rates over the last few decades, more than 20% of patients affected by MI will subsequently develop heart failure (HF), an incurable condition where the contracting myocardium is transformed into an akinetic, fibrotic scar, unable to meet the body's need for blood supply. Excessive inflammation and persistent immune auto-reactivity have been suggested to contribute to post-MI tissue damage and exacerbate HF development. Two newly emerging fields of biomedical research, immunomodulatory therapies and cardiac bioengineering, provide potential options to target the causative mechanisms underlying HF development. Combining these two fields to develop biomaterials for delivery of immunomodulatory bioactive molecules holds great promise for HF therapy. Specifically, minimally invasive delivery of injectable hydrogels, loaded with bioactive factors with angiogenic, proliferative, anti-apoptotic and immunomodulatory functions, is a promising route for influencing the cascade of immune events post-MI, preventing adverse left ventricular remodeling, and offering protection from early inflammation to fibrosis. Here we provide an updated overview on the main injectable hydrogel systems and bioactive factors that have been tested in animal models with promising results and discuss the challenges to be addressed for accelerating the development of these novel therapeutic strategies.

Engineering Peptide-Based Polyelectrolyte Complexes with Increased Hydrophobicity

Polyelectrolyte complexation is a versatile platform for the design of self-assembled materials. Here we use rational design to create ionic hydrophobically-patterned peptides that allow us to precisely explore the role of hydrophobicity on electrostatic self-assembly. Polycations and polyanions were designed and synthesized with an alternating sequence of d- and l-chiral patterns of lysine or glutamic acid with either glycine, alanine or leucine due to their increasing hydrophobicity index, respectively. Two motifs were considered for the oppositely charged patterned peptides; one with equal residues of charged and uncharged amino acids and the other with increased charge density. Mass spectroscopy, circular dichroism, H- and F-NMR spectroscopy were used to characterize the polypeptides. Polyelectrolyte complexes (PECs) formed using the sequences were characterized using turbidity measurements, optical microscopy and infrared spectroscopy. Our results show that the critical salt concentration, a key measure of PEC stability, increased with both increasing charge density as well as hydrophobicity. Furthermore, by increasing the hydrophobicity, the amount of PEC formed increased with temperature, contrary to purely ionic PECs. Lastly, we assessed the encapsulation behavior of these materials using a hydrophobic dye. Concluding that encapsulation efficiency increased with hydrophobic content of the complexes providing insight for future work on the application of these materials for drug delivery.

Chitosan-Based Nanomaterials for Drug Delivery

This review discusses different forms of nanomaterials generated from chitosan and its derivatives for controlled drug delivery. Nanomaterials are drug carriers with multiple features, including target delivery triggered by environmental, pH, thermal responses, enhanced biocompatibility, and the ability to cross the blood-brain barrier. Chitosan (CS), a natural polysaccharide largely obtained from marine crustaceans, is a promising drug delivery vector for therapeutics and diagnostics, owing to its biocompatibility, biodegradability, low toxicity, and structural variability. This review describes various approaches to obtain novel CS derivatives, including their distinct advantages, as well as different forms of nanomaterials recently developed from CS. The advanced applications of CS-based nanomaterials are presented here in terms of their specific functions. Recent studies have proven that nanotechnology combined with CS and its derivatives could potentially circumvent obstacles in the transport of drugs thereby improving the drug efficacy. CS-based nanomaterials have been shown to be highly effective in targeted drug therapy.

Concepts for Developing Physical Gels of Chitosan and of Chitosan Derivatives

Chitosan macro- and micro/nano-gels have gained increasing attention in recent years, especially in the biomedical field, given the well-documented low toxicity, degradability, and non-immunogenicity of this unique biopolymer. In this review we aim at recapitulating the recent gelling concepts for developing chitosan-based physical gels. Specifically, we describe how nowadays it is relatively simple to prepare networks endowed with different sizes and shapes simply by exploiting physical interactions, namely (i) hydrophobic effects and hydrogen bonds-mostly governed by chitosan chemical composition-and (ii) electrostatic interactions, mainly ensured by physical/chemical chitosan features, such as the degree of acetylation and molecular weight, and external parameters, such as pH and ionic strength. Particular emphasis is dedicated to potential applications of this set of materials, especially in tissue engineering and drug delivery sectors. Lastly, we report on chitosan derivatives and their ability to form gels. Additionally, we discuss the recent findings on a lactose-modified chitosan named Chitlac, which has proved to form attractive gels both at the macro- and at the nano-scale.