Chitosan-catechol: A polymer with long-lasting mucoadhesive properties

Enhancement in Xerostomia Patient Salivary Lubrication Using a Mucoadhesive

Oral lubrication mediated by mucin and protein containing salivary conditioning films (SCFs) with strong water retainability can get impaired due to disease such as xerostomia, that is, a subjective dry mouth feel associated with the changed salivary composition and low salivary flow rate. Aberrant SCFs in xerostomia patient cause difficulties in speech, mastication, and dental erosion while the prescribed artificial saliva is inadequate to solve the complications on a lasting basis. With the growing aging population, it is urgently needed to propose a new strategy to restore oral lubrication. Existing saliva substitutes often overwhelm the aberrant SCFs, generating inadequate relief. Here we demonstrated that the function of aberrant SCFs in a patient with Sjögren syndrome can be boosted through mucin recruitment by a simple mucoadhesive, chitosan-catechol (Chi-C). Chi-C with different conjugation degrees (Chi-C7.6%, Chi-C14.5%, Chi-C22.4%) was obtained by carbodiimide chemistry, which induced a layered structure composed of a rigid bottom and a soft secondary SCF (S-SCF) after reflow of saliva. The higher conjugation degree of Chi-C generates a higher glycosylated S-SCF by mucin recruitment and a lower friction in vitro. The layered S-SCF extends the "relief period" for Sjögren patient saliva over 7-fold, measured on an ex vivo tongue-enamel friction system. Besides lubrication, Chi-C-treated S-SCF reduces dental erosion depths from 125 to 70 μm. Chi-C shows antimicrobial activity against Streptococcus mutans. This research provides a new key insight in restoring the functionality of conditioning film at articulating tissues in living systems.

Functionalized GO Nanovehicles with Nitric Oxide Release and Photothermal Activity-Based Hydrogels for Bacteria-Infected Wound Healing

Bacteria-infected wounds are attracting increasing attention, as antibiotic misuse and multidrug-resistant bacteria complicate their treatment. Herein, we reported a photothermal activity-based drug consisting of β-cyclodextrin (βCD)-functionalized graphene oxide (GO) near-infrared light-responsive nanovehicles combined with the nitric oxide donor BNN6, in a methacrylate-modified gelatin (GelMA)/hyaluronic acid graft dopamine (HA-DA) hydrogel. The synergistic effects of photothermal and gas therapies are expected to improve antibacterial efficiency and reduce drug resistance. The results revealed that GelMA/HA-DA/GO-βCD-BNN6 was an ideal antibacterial material that improved collagen deposition and angiogenesis and promoted wound healing in a mouse model of full-thickness skin repair, compared to the commercially available Aquacel Ag dressing. We developed a multifunctional nanocomposite hydrogel that exhibited antibacterial and angiogenic properties, adhesiveness, and mechanical properties that enhance the regeneration of bacteria-infected wounds.

pH-Triggered Adhesiveness and Cohesiveness of Chondroitin Sulfate-Catechol Biopolymer for Biomedical Applications

Nature provides biomaterials that tend to be effective to control both their adhesive and cohesive properties. A catecholamine motif found in the marine mussels, the mytilus edulis foot protein, can play adhesiveness and cohesiveness. Particularly, acidic pH drives catechol (Cat) to have adhesive function, resulting in surface coating, while basic pH allows to enhance its cohesive properties, resulting in the formation of hydrogels. In this work, we demonstrated the usefulness of Cat-conjugated chondroitin sulfate (CS) as a platform for mesenchymal stem cell culture, utilizing the adhesive property of CS-Cat as coating for different substrates and the cohesive properties as hydrogel for cells encapsulation. To prepare the CS-Cat biopolymer, dopamine (DP) was coupled to the CS by carbodiimide coupling reaction and the Cat content was determined by UV-Vis spectroscopy (4.8 ± 0.6%). To demonstrate the adhesive properties of the biopolymer, PLA, PCL, TiO₂, and SiO₂ substrates were immersed in CS-Cat solution (pH < 2). Following the coating, the surfaces became highly hydrophilic, exhibiting a contact angle less than 35°. Also, in the presence of an oxidizing agent at pH 8, CS-Cat solution immediately became a hydrogel, as shown by inverted-vial test. Finally, immortalized TERT human mesenchymal stem cells (Y201) confirmed the high cytocompatibility of the biopolymer. The CS-Cat coating significantly enabled the Y201 adhesion onto PLA substrates, while the prepared hydrogel demonstrated to be a suitable environment for the encapsulation of cells as suitable bioink for further bioprinting applications.

A bioinspired mucoadhesive restores lubrication of degraded cartilage through reestablishment of lamina splendens

Adsorbed lubricious films composed of biomacromolecules are natively present at all articulating interfaces in the human body where they provide ultralow friction and maintain normal physiological function. Biolubrication gets impaired due to diseases such as osteoarthritis, in which cartilage damage results from alterations in synovial fluid and lamina splendens composition. Osteoarthritis is treated with hyaluronic acid (HA) orally or via intra-articular injection, but due to the poor adsorption of HA on the cartilage surface in the absence of adhesive molecules, pain relief is temporary. Here, we describe how natural lubrication on degraded cartilage surface can be restored with the help of a bioinspired mucoadhesive biopolymer chitosan catechol (Chi-C). Quartz crystal microbalance was used to mimic the formation of lamina splendens in vitro, known as synovial fluid conditioning films (SyCF), and colloidal probe atomic force microscopy was used to measure their nanoscale frictional properties. Clear evidence of glycoprotein (PRG4) recruitment by Chi-C increased the softness of SyCF, which also improved nanoscale lubrication in vitro, decreasing the friction coefficient from 0.06 to 0.03. At the macroscale, cartilage damage induced by Chondroitinase ABC increased the coefficient of friction (COF) from 0.07 ± 0.04 (healthy tissue) to 0.15 ± 0.03 (after tissue damage) in the presence of synovial fluid after sliding for 50 min. After Chi-C treatment of damaged cartilage, the COF fell to 0.06 ± 0.03, which is comparable to healthy cartilage. Chi-C did not adversely affect the metabolic activity of human chondrocytes. This study provides new key insight into the potential for restoring biolubrication through the use of muco-adhesive molecules.

Okra-Thioglycolic Acid Conjugate—Synthesis, Characterization, and Evaluation as a Mucoadhesive Polymer

The success of mucoadhesive drug delivery systems relies on the type of polymer used, which becomes adhesive naturally upon hydration. Intended polymers should be able to maintain prolonged contact with biological membranes, and to protect or cater the drug to a prolonged period. Most of the hydro polymers form weak non-covalent bonds, that hinder localization of dosage forms at specific sites resulting in therapeutic inefficiency. This can be overcome by the thiol functionalization of natural polymers. In the present study, natural okra gum (OG) was extracted, followed by thiolation (TOG) and evaluated for mucoadhesion property and its role in enhancing the efficacy of repaglinide as a model drug (short-acting Type II antidiabetic drug). The thiol functionalization of OG (TOG) was confirmed by a Fourier-transform infrared spectroscopy (FTIR) study that showed a polyhedral to a spherical shape that had a rougher surface. Differential scanning calorimetry (DSC) and X-Ray Diffraction (XRD) studies of TOG indicated a decline in endothermic transition temperature and high crystallinity, respectively, in comparison to OG. CSFR (Crushing Strength: Friability Ratio), weight and thickness variations of repaglinidetablets formulated using TOG were >80% and <2.5% respectively. The highest swelling index (107.89 ± 1.99%) and strong mucoadhesion due to high disulfide bonds were observed for repaglinide TOG tablets in comparison to RG OG tablets. In-vitro release studies indicated a controlled drug release from thiolated formulations proportional to the concentration of thiomers that have a good correlation with in-vivo studies. Pharmacokinetic studies indicated higher AUC (area under the curve), longer t1/2 with thiomers. and Level A IVIV (in vitro in vivo) correlation was established from the bioavailability and dissolution data. Consequently, all the obtained results suggest that thiomers based formulations can be promising drug delivery systems, even in targeting onerous mucosal surfaces like nasal, ocular or vaginal.

Pires R, Botelho G, Reis RL, Alves NM. Spin-Coated Polysaccharide-Based Multilayered Freestanding Films with Adhesive and Bioactive Moieties

Freestanding films based on catechol functionalized chitosan (CHI), hyaluronic acid (HA), and bioglass nanoparticles (BGNPs) were developed by spin-coating layer-by-layer assembly (SA-LbL). The catechol groups of 3,4-dihydroxy-l-phenylalanine (DOPA) present in the marine mussels adhesive proteins (MAPs) are the main factors responsible for their characteristic strong wet adhesion. Then, the produced films were cross-linked with genipin to improve their stability in wet state. Overall, the incorporation of BGNPs resulted in thicker and bioactive films, hydrophilic and rougher surfaces, reduced swelling, higher weight loss, and lower stiffness. The incorporation of catechol groups onto the films showed a significant increase in the films' adhesion and stiffness, lower swelling, and weight loss. Interestingly, a synergetic effect on the stiffness increase was observed upon the combined incorporation of BGNPs with catechol-modified polymers, given that such films were the stiffest. Regarding the biological assays, the films exhibited no negative effects on cellular viability, adhesion, and proliferation, and the BGNPs seemed to promote higher cellular metabolic activity. These bioactive LbL freestanding films combine enhanced adhesion with improved mechanical properties and could find applications in the biomedical field, such as guided hard tissue regeneration membranes.

Adaptive control in lubrication, adhesion, and hemostasis by Chitosan-Catechol-pNIPAM

Bio-inspired wet adhesives attract considerable attention in the biomedical field. However, achieving reversible and controllable wet adhesion still remains a challenging issue. In this study, we report a new thermo-responsive polysaccharide wet adhesive conjugate named Chitosan-Catechol-poly(N-isopropyl acrylamide) (Chitosan-Catechol-pNIPAM), where catechol, the wet adhesive moiety, and pNIPAM, the thermal responsive group, are chemically tethered to a chitosan backbone. The as-synthesized Chitosan-Catechol-pNIPAM presents a reversible sol-gel transition behavior when the temperature is cycled below and above the lower critical solution temperature (LCST, 35 °C), along with dynamic switching between lubrication and wet adhesion on various materials. Based on these excellent features, Chitosan-Catechol-pNIPAM can realize controllable attachment/detachment behavior over the skin through heating/cooling processes. Due to its good biocompatibility, the Chitosan-Catechol-pNIPAM coated syringe needles exhibit instant hemostasis after removing the needles from the punctured sites of mouse veins. Overall, the as-synthesized Chitosan-Catechol-pNIPAM is expected to be used as a new intelligent adhesive in various biomedical settings.

Specialty Tough Hydrogels and Their Biomedical Applications

Hydrogels have long been explored as attractive materials for biomedical applications given their outstanding biocompatibility, high water content, and versatile fabrication platforms into materials with different physiochemical properties and geometries. Nonetheless, conventional hydrogels suffer from weak mechanical properties, restricting their use in persistent load-bearing applications often required of materials used in medical settings. Thus, the fabrication of mechanically robust hydrogels that can prolong the lifetime of clinically suitable materials under uncompromising in vivo conditions is of great interest. This review focuses on design considerations and strategies to construct such tough hydrogels. Several promising advances in the proposed use of specialty tough hydrogels for soft actuators, drug delivery vehicles, adhesives, coatings, and in tissue engineering settings are highlighted. While challenges remain before these specialty tough hydrogels will be deemed translationally acceptable for clinical applications, promising preliminary results undoubtedly spur great hope in the potential impact this embryonic research field can have on the biomedical community.

Mussel inspired bio-adhesive with multi-interactions for tissue repair

Bio-adhesives based on biopolymers have been widely researched for tissue repair. However, the adhesive properties are still insufficient to meet the practical applications. Introducing functional groups into the polymer chains that have multi-interactions among inter/intra-molecules and with substrates is an efficient way to increase cohesion force and further improve the adhesive properties. In this study, 3,4-dihydroxyphenyl propionic acid (DPA) and dopamine (DA) containing adhesion functional catechol groups were employed to modify chitosan (CS) and γ-polyglutamic acid (γPGA), respectively. The substituted degrees of the catechol groups were controlled by the catechol compositions. DPA modified chitosan/DA modified γPGA (CS-DPA/γPGA-DA) adhesives prepared by mixing CS-DPA and γPGA-DA. Effects of the substituted degrees and substrates on the adhesion strength were measured by tensile testing machine. The results showed good adhesion property of the CS-DPA/γPGA-DA adhesive on many surfaces of the substrates. Especially on the arthrodial cartilage, the adhesive strength reached around 150 kPa, much higher than commercially available tissue adhesives. The high adhesion property might be due to the adhesion interactions between the catechol groups and substrates and the high cohesion forces induced by the crosslinking interactions formation among the catechol groups and the electrostatic interactions between the CS and γPGA polymers. In vitro experiments demonstrated that the adhesive had good biocompatibility. These results suggested the catechol-based adhesive is a very suitable and promising biomaterial in the clinical medicine field.

Catechol-Functionalized Chitosan: Optimized Preparation Method and Its Interaction with Mucin

Chitosan is one of the most popular biopolymers used for biomedical applications with its unique properties of blood clotting and adhesion to tissues. Catechol-functionalized chitosan (CatChit) has shown a significant improvement of those properties of chitosan as biomaterials. However, some well-cited methods of CatChit preparation in existing literature, repeatedly followed by numerous research groups in the past decades, have not stressed the importance of the vulnerability of catechol to oxidation, which resulted in many priceless in vivo studies that used wrong materials, i.e., partially oxidized forms of CatChit. Since some key synthesis parameters were erroneous in those previous reports, it is a challenge to reproduce the published results. To avoid the loss of critical details with these repeated citations, it is essential that we re-establish the critical parameters in these methods. In this study, we examined the accuracy of existing protocols, and optimized one of the protocols to synthesize CatChit. We have confirmed that a notable degree of catechol oxidation is inevitable with the inaccurate synthetic protocols and the maintenance of pH < 5 throughout the preparation of CatChit is essential. We have also re-evaluated interaction between CatChit and mucin, which is widely present in the gastrointestinal (GI) tract, at different pH values using CatChit prepared via our optimized synthetic protocol. Turbidimetric titrations suggested that regardless of the reaction pH, the association between CatChit and mucin increased with increasing concentration of polymer with respect to mucin. The decrease in the average size of the aggregated particles observed by Dynamic Light Scattering (DLS) studies was attributed to the formation of a large number of aggregations with increasing polymer to mucin ratio. ζ potential (ZP) measurements suggested that at acidic reaction pH, the average particle size was dictated by electrostatic interactions, while at a physiological pH, consolidation of covalent and charge-based interactions contributed to the overall surface charge.

Hydrogels Based Drug Delivery Synthesis, Characterization and Administration

Hydrogels represent 3D polymeric networks specially designed for various medical applications. Due to their porous structure, they are able to swollen and to entrap large amounts of therapeutic agents and other molecules. In addition, their biocompatibility and biodegradability properties, together with a controlled release profile, make hydrogels a potential drug delivery system. In vivo studies have demonstrated their effectiveness as curing platforms for various diseases and affections. In addition, the results of the clinical trials are very encouraging and promising for the use of hydrogels as future target therapy strategies.

Catechol-Functionalized Succinyl Chitosan for Novel Mucoadhesive Drug Delivery

The objective of this research was to synthesized and evaluated a mucoadhesive catechol-bearing succinyl chitosan (Cat-SCS) as an innovative mucoadhesive substance for a mucoadhesive drug delivery system. Succinyl chitosan (SCS) was synthesized via ring-opening reactions with succinic anhydride. The Cat-SCS was then synthesized by reacting SCS with dopamine with the existence of N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDAC) and N-hydroxysulfosuccinimide (NHS). The successful functionalization of catechol onto chitosan backbone was verified using nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FT-IR). Mucoadhesion studies were performed using rheology measurement and ex-vivo mucoadhesion test. The findings exposed that the synthesized Cat-SCS exhibited excellent mucoadhesive properties which was better than the intact CS. Further indirect studies verified the occurrence of polymer-mucin glycoproteins interactions. The catechol content of catechol moiety on the Cat-SCS was determined to be 0.377 using the 1H NMR. The cytotoxicity test indicated the biocompatibility of the obtained polymer on human gingival fibroblast cells (HGF cells). Therefore, these results could advocate the capacity to use of Cat-SCS as an innovative mucoadhesive platform for mucoadhesive drug delivery.

Catechol-Bearing Hyaluronic Acid Coated Polyvinyl Pyrrolidone/Hydroxyl Propyl-β-Cyclodextrin/Clotrimazole Nanofibers for Oral Candidiasis Treatment

This research aimed to develop clotrimazole (CT)-loaded mucoadhesive nanofiber patches for oral candidiasis. The three-layered sandwich-like nanofiber patches were prepared by electrospinning technique. The spinning solution for the middle layer composed of 8 %wt polyvinylpyrrolidone (PVP), 90 mM hydroxy propyl-β-cyclodextrin (HPβCD) and 10 % (wt to polymer) of CT in a solvent mixture of ethanol:water:benzyl alcohol. The outer layers were fabricated from a mixture of 1 %wt hyaluronic acid (HA) or catechol bearing hyaluronic acid (HA-cat) and 10 %wt polyvinyl alcohol (PVA) at varied weight ratios. The thickness of the outer layers was varied by adjusting the volume of coating polymer solution ranging from 1 to 3 mL. Desirable smooth nanosized fibers were obtained from the electrospinning process. Increasing the thickness of the outer layer brought about a significant increase in the fiber strength and flexibility. The viscosity of HA-cat/mucin mixture showed good polymer-mucin interaction indicating higher mucoadhesive property of the nanofibers. The drug loading capacity (LC) displayed the potential of the nanofibers for drug encapsulation. The highest LC value of 123.80 ± 5.61 μg/mg was obtained from the nanofibers coated with 1 mL of the coating solution. CT was rapidly released from the nanofiber in the first hour followed by a steady release. The released amount reach above 80% in 2 h. The nanofibers provided superior antifungal activity against Candida albicans compared to CT powder. Moreover, they were found to be nontoxic to the human gingival fibroblast cells. Thus, the sandwich nanofibers may be further developed to be a potential candidate for oral candidiasis treatment in the near future.

Bioadhesive functional hydrogels: Controlled release of catechol species with antioxidant and antiinflammatory behavior

Chronic wounds are particularly difficult to heal and constitute an important global health care problem. Some key factors that make chronic wounds challenging to heal are attributed to the incessant release of free radicals, which activate the inflammatory system and impair the repair of the wound. Intrinsic characteristics of hydrogels are beneficial for wound healing, but the effective control of free radical levels in the wound and subsequent inflammation is still a challenge. Catechol, the key molecule responsible for the mechanism of adhesion of mussels, has been proven to be an excellent radical scavenger and anti-inflammatory agent. Our approach in this work lies in the preparation of a hybrid system combining the beneficial properties of hydrogels and catechol for its application as a bioactive wound dressing to assist in the treatment of chronic wounds. The hydrogel backbone is obtained through a self-covalent crosslinking between chitosan (Ch) and oxidized hyaluronic acid (HAox) in the presence of a synthetic catechol terpolymer, which is subsequently coordinated to Fe to obtain an interpenetrated polymer network (IPN). The structural analysis, catechol release profiles, in vitro biological behavior and in vivo performance of the IPN are analyzed and compared with the semi-IPN (without Fe) and the Ch/HAox crosslinked hydrogels as controls. Catechol-containing hydrogels present high tissue adhesion strength under wet conditions, support growth, migration and proliferation of hBMSCs, protect cells against oxidative stress damage induce by ROS, and promote down-regulation of the pro-inflammatory cytokine IL-1β. Furthermore, in vivo experiments reveal their biocompatibility and stability, and histological studies indicate normal inflammatory responses and faster vascularization, highlighting the performance of the IPN system. The novel IPN design also allows for the in situ controlled and sustained delivery of catechol. Therefore, the developed IPN is a suitable ECM-mimic platform with high cell affinity and bioactive functionalities that, together with the controlled catechol release, will enhance the tissue regeneration process and has a great potential for its application as wound dressing.

Construction of catechol-grafted chitosan alginate/barium sulfate microcapsules for computed tomography real-time imaging and gastroretentive drug delivery

Background: The gastroretentive drug delivery system is an effective administration route, which can improve the bioavailability of the drug and the therapeutic effect by prolonging the release time of the drug and controlling the release rate in the stomach. Methods: Inspired by the excellent adhesion properties of mussel protein, we prepared novel catechol-grafted chitosan alginate/barium sulfate microcapsules (Cat-CA/BS MCs) with mucoadhesive properties and computed tomography (CT) imaging function for gastric drug delivery. First, barium sulfate nanoclusters used as CT contrast agent were synthesized in situ in the Cat-CA/BS MCs through a one-step electronic spinning method. Next, catechol-grafted chitosan as the mucoadhesive moiety was coated on the surface of Cat-CA/BS MCs by polyelectrolyte molecule self-assembly. Results: The prepared Cat-CA/BS MCs could effectively retained in the stomach for 48 hours and successively released ranitidine hydrochloride, which could be used for the treatment of gastric ulcer. Cat-CA/BS MCs exhibited superior CT contrast imaging properties for real-time tracking in vivo after oral administration. Conclusion: These findings demonstrate that Cat-CA/BS MCs serving as multifunctional oral drug carriers possess huge potential in gastroretentive drug delivery and non-invasive visualization.

Progress and Current Trends in the Synthesis of Novel Polymers with Enhanced Mucoadhesive Properties

Mucoadhesion is defined as the adherence of a synthetic or natural polymer to a mucosal membrane via physical or chemical interactions. Mucoadhesive materials are widely used to develop dosage forms for transmucosal drug delivery via ocular, nasal, esophageal, oral, vaginal, rectal, and intravesical routes of administration. This review will discuss some of the most prominent and recent synthetic methodologies employed to modify polymeric materials in order to enhance their mucoadhesive properties. This includes chemical conjugation of polymers with molecules bearing thiol-, catechol-, boronate-, acrylate-, methacrylate-, maleimide-, and N-hydroxy(sulfo)succinimide ester- groups.

Hyaluronic acid-modified mesoporous silica-coated superparamagnetic Fe3O4 nanoparticles for targeted drug delivery

Introduction: The targeted delivery of anti-cancer drugs to tumor tissue has been recognized as a promising strategy to increase their therapeutic efficacy and reduce side effects. Mesoporous silica-coated superparamagnetic Fe3O4 nanoparticles (NH2-MSNs), a kind of nanocarrier, can passively enter tumor tissues to enhance the permeability and retention of drugs. However, NH2-MSNs do not specifically bind to cancer cells. This drawback encouraged us to develop a more efficient nanocarrier for cancer therapy.

Methods: Herein, we describe the development of an effective nanocarrier based on NH2-MSNs, which were modified with hyaluronic acid on their surface (HA-MSNs) and loaded with doxorubicin (DOX). We have successfully fabricated uniform spherical HA-MSNs nanocarriers. The targeting ability of this delivery system was evaluated through specific uptake by cells and IVIS imaging.

Results: DOX-HA-MSNs nanocarriers displayed more dramatic cytotoxic activity against 4T1 breast cancer cells compared to GES-1 gastric mucosa cells. In vivo results revealed that once DOX-HA-MSNs nanocarriers are exposed to an external magnetic field, they could be rapidly attracted to the magnet and effectively cross the cytoplasmic membrane via CD44 receptor-mediated transcytosis. This allows them to access the cancer cell cytoplasm and release DOX based on changes in the physiological environment. Both in vitro and in vivo results demonstrated that the HA-MSNs nanocarriers provided better therapeutic efficacy.

Conclusion: The HA-MSNs nanocarriers represent an effective new paradigm to treat cancers due to active targeting to the tumor cells. Moreover, the specific uptake by the tumor effectively protects normal tissues to reduce off-target side effects. The reported findings support further investigation of HA-MSNs for cancer therapy.

Chitosan as an emerging object for biological and biomedical applications

Natural polymers are being investigated with renewed exuberance as they have a tremendous unexploited potential. During the past few decades, much interest has developed in the biopolymer-based materials due to their biodegradable, nontoxic, biocompatible and non-allergic nature. Chitosan (CS) is the second most abundant naturally occurring amino polysaccharide after cellulose and is extracted from the shells of sea crustaceans. The primary amine group in CS is responsible for its various properties and it is derived from the deacetylated form of chitin. Its biocompatible, nontoxic, biodegradable and antimicrobial properties have led to significant research towards biomedical applications, such as tissue engineering, wound healing, drug delivery, obesity treatment, etc. This review summarizes the present work done by researchers in prospects of CS and its numerous applications in the biomedical field.

Mussel-Inspired Catechol-Functionalized Hydrogels and Their Medical Applications

Mussel adhesive proteins (MAPs) have a unique ability to firmly adhere to different surfaces in aqueous environments via the special amino acid, 3,4-dihydroxyphenylalanine (DOPA). The catechol groups in DOPA are a key group for adhesive proteins, which is highly informative for the biomedical domain. By simulating MAPs, medical products can be developed for tissue adhesion, drug delivery, and wound healing. Hydrogel is a common formulation that is highly adaptable to numerous medical applications. Based on a discussion of the adhesion mechanism of MAPs, this paper reviews the formation and adhesion mechanism of catechol-functionalized hydrogels, types of hydrogels and main factors affecting adhesion, and medical applications of hydrogels, and future the development of catechol-functionalized hydrogels.

Toxicity-Attenuated Glycol Chitosan Adhesive Inspired by Mussel Adhesion Mechanisms

Chitosan-catechol, inspired from mussel-adhesive-proteins, is characterized by the formation of an adhesive membrane complex through instant bonding with serum proteins not found in chitosan. Using this intrinsic property, chitosan-catechol is widely applied for hemostatic needles, general hemostatic materials, nanoparticle composites, and 3D printing. Despite its versatility, the practical use of chitosan-catechol in the clinic is limited due to its undesired immune responses. Herein, a catechol-conjugated glycol chitosan is proposed as an alternative hemostatic hydrogel with negligible immune responses enabling the replacement of chitosan-catechol. Comparative cellular toxicity and in vivo skin irritation between chitosan-catechol and glycol chitosan-catechol are evaluated. Their immune responses are also assessed using histological analysis after subcutaneous implantation into mice. The results show that glycol chitosan-catechol significantly attenuates the immune response compared with chitosan-catechol; this finding is likely due to the antibiofouling effect of ethylene glycol groups and the reduced adhesion of immune cells. Finally, the tissue adhesion and hemostatic ability of glycol chitosan-catechol hydrogels reveal that these ethylene glycol groups do not dramatically modify the adhesiveness and hemostatic ability compared with nonglycol chitosan-catechol. This study suggests that glycol chitosan-catechol can be a promising alternative to chitosan-catechol in various biomedical fields such as hemostatic agents.

Marine-Inspired Polymers in Medical Adhesion

Medical adhesives that are strong, easy to apply and biocompatible are promising alternatives to sutures and staples in a large variety of surgical and clinical procedures. Despite progress in the development and regulatory approval of adhesives for use in the clinic, adhesion to wet tissue remains challenging. Marine organisms have evolved a diverse set of highly effective wet adhesive approaches that have inspired the design of new medical adhesives. Here we provide an overview of selected marine animals and their chemical and physical adhesion strategies, the state of clinical translation of adhesives inspired by these organisms, and target applications where marine-inspired adhesives can have a significant impact. We will focus on medical adhesive polymers inspired by mussels, sandcastle worms, and cephalopods, emphasize the history of bioinspired medical adhesives from the peer reviewed and patent literature, and explore future directions including overlooked sources of bioinspiration and materials that exploit multiple bioinspired strategies.

Crossing biological barriers with nanogels to improve drug delivery performance

The current limitations in the use of nanocarriers to treat constantly evolving diseases call for the design of novel and smarter drug delivery systems (DDS). Nanogels (NGs) are three-dimensional crosslinked polymers with dimensions on the nanoscale and with a great potential for use in the biomedical field. Particular interest focuses on their application as DDS to minimize severe toxic effects and increase the therapeutic index of drugs. They have recently gained attention, since they can include responsive modalities within their structure, which enable them to excerpt a therapeutic function on demand. Their bigger sizes and controlled architecture and functionality, when compared to non-crosslinked polymers, make them particularly interesting to explore novel modalities to cross biological barriers. The present review summarizes the most significant developments of NGs as smart carriers, with focus on smart modalities to cross biological barriers such as cellular membrane, tumor stroma, mucose, skin, and blood brain barrier. We discuss the properties of each barrier and highlight the importance that the NG design has on their capability to overcome them and deliver the cargo at the site of action.

Challenges and Recent Progress in Oral Drug Delivery Systems for Biopharmaceuticals

Routes of drug administration and the corresponding physicochemical characteristics of a given route play significant roles in therapeutic efficacy and short term/long term biological effects. Each delivery method has favorable aspects and limitations, each requiring a specific delivery vehicles design. Among various routes, oral delivery has been recognized as the most attractive method, mainly due to its potential for solid formulations with long shelf life, sustained delivery, ease of administration and intensified immune response. At the same time, a few challenges exist in oral delivery, which have been the main research focus in the field in the past few years. The present work concisely reviews different administration routes as well as the advantages and disadvantages of each method, highlighting why oral delivery is currently the most promising approach. Subsequently, the present work discusses the main obstacles for oral systems and explains the most recent solutions proposed to deal with each issue.

Acrylated Eudragit® E PO as a novel polymeric excipient with enhanced mucoadhesive properties for application in nasal drug delivery

Eudragit® E PO (EPO) is a terpolymer based on N,N-dimethylaminoethyl methacrylate with methylmethacrylate and butylmethacrylate, produced by Evonik Industries AG as a pharmaceutical excipient. In this work, EPO was chemically modified through reaction with acryloyl chloride. The successful modification of EPO was confirmed by FTIR, NMR-spectroscopy, elemental and thermal analysis. The degree of acrylation was determined by permanganatometric titration. The slug mucosal irritation test was used to demonstrate non-irritant nature of EPO and its acrylated derivatives (AEPO). The mucoadhesive properties of EPO and AEPO were evaluated using freshly excised sheep nasal mucosa and it was demonstrated that acrylated polymers facilitated greater retention of sodium fluorescein on mucosal surfaces compared to solution mixture of this dye solution with EPO as well as free dye.

Urushiol-functionalized mesoporous silica nanoparticles and their self-assembly into a Janus membrane as a highly efficient hemostatic material

Quick hemostasis plays a very important role in preventing hemorrhagic shock and death by controlling blood loss from trauma in civil and military accidents. An ideal quick hemostat should have tissue-adhesive functional groups, clotting factor activating components, and a plasma non-permeable hydrophobic layer. Inspired by the adhesive behavior of mussels, a novel efficient hemostat of urushiol-functionalized mesoporous silica nanoparticles (MSN@U) with a core-shell structure was synthesized and their hemostatic performance was evaluated for the first time. MSN@U could form an amphipathic Janus membrane (a hydrophobic layer and a hydrophilic layer in one membrane) by interfacial self-assembly. The morphology and structure of MSN@U were characterized. The results showed that MSN@U possessed a large specific surface area of 448.91 m2 g-1 and a rich porous structure with an average pore diameter of 3.94 nm. The hydrophilic catechol groups and the long hydrophobic alkyl groups of urushiol allowed MSN@U to self-assemble at the blood/air interface. The former made MSN@U tightly adhere onto blood vessel tissue through covalent bonds, while the latter formed a hydrophobic barrier layer which hindered blood from oozing. Meanwhile, MSN@U would accelerate clotting cascade reactions. These three effects made MSN@U a very quick hemostat with a hemostatic time of 22 ± 2 s on a rat liver laceration. Both in vitro and in vivo tests showed that they had a better hemostatic effect and blood compatibility than MSN. Cell viability evaluations indicated that MSN@U had no cytotoxicity. MSN@U will be a safe and promising hemostatic agent for clinical applications.

pH-responsive injectable hydrogels with mucosal adhesiveness based on chitosan-grafted-dihydrocaffeic acid and oxidized pullulan for localized drug delivery

Injectable hydrogels with multifunctional properties, including tissue adhesiveness and pH-sensitivity are highly desired for localized drug delivery in disease treatment, and their design is still challenging. We developed a series of multifunctional injectable mucoadhesive and pH-responsive hydrogels based on chitosan-grafted-dihydrocaffeic acid (CS-DA) and oxidized pullulan (OP) via a Schiff base reaction. These hydrogels exhibited good injectability, suitable gelation time, in vitro pH-dependent equilibrated swelling ratios, morphologies, and rheological characteristics. The desirable in vitro pH-sensitive drug release behavior of these hydrogels was demonstrated by a drug release test with anti-cancer drug doxorubicin (DOX) loaded hydrogels at different pH values. The hydrogels showed good DOX release, effectively killing colon tumor cells (HCT116 cells) and good antibacterial properties against E. coli and S. aureus in vitro when the antibacterial model drug amoxicillin was encapsulated in the hydrogels. A lap-shear test was also carried out with these hydrogels. The hydrogels exhibited good mucosal adhesion, indicating their potential use in mucosa-localized drug delivery systems. All these results suggest that these injectable pH-responsive adhesive hydrogels are ideal candidates for development of colon cancer drug delivery carriers or mucoadhesive drug delivery systems.

In situ gelling and mucoadhesive polymers: why do they need each other?

INTRODUCTION

Mucosal drug delivery is an attractive route of administration, particularly in overcoming deficits of conventional dosage forms including high first-pass metabolism and poor bioavailability. Fast drainage from the target mucosa, however, represents a major limitation as it prevents sufficient drug absorption. In order to address these problems, mucoadhesive in situ gelling drug delivery systems have been investigated as they facilitate easy application in combination with a longer residence time at the administration site resulting in more desirable therapeutic effects.

AREAS COVERED

The present review evaluates the importance of the combination of mucoadhesive and in situ gelling polymers along with mechanisms of in situ gelation and mucoadhesion. In addition, an overview about recent applications in mucosal drug delivery is provided.

EXPERT OPINION

In situ gelling and mucoadhesive polymers proved to be essential excipients in order to prolong the mucosal residence time of drug delivery systems. Due to this prolonged residence time both local and systemic therapeutic efficacy of numerous drugs can be substantially improved. Depending on the site of administration and the incorporated drug, combinations of different polymers with in situ gelling and mucoadhesive properties are needed to keep the delivery system as long as feasible at the target site.

Mussel-Inspired Tissue-Adhesive Hydrogel Based on the Polydopamine-Chondroitin Sulfate Complex for Growth-Factor-Free Cartilage Regeneration

Glycosaminoglycan-based hydrogels are widely used for cartilage repair because glycosaminoglycans are the main component of the cartilage extracellular matrix and can maintain chondrocyte functions. However, most of the glycosaminoglycan-based hydrogels are negatively charged and cell-repellant, and they cannot host cells or favor tissue regeneration. Inspired by mussel chemistry, we designed a polydopamine-chondroitin sulfate-polyacrylamide (PDA-CS-PAM) hydrogel with tissue adhesiveness and super mechanical properties for growth-factor-free cartilage regeneration. Thanks to the abundant reactive catechol groups on the PDA, a cartilage-specific PDA-CS complex was formed by the self-assembly of PDA and CS, and then the PDA-CS complex was homogenously incorporated into an elastic hydrogel network. This catechol-group-enriched PDA-CS complex endowed the hydrogel with good cell affinity and tissue adhesiveness to facilitate cell adhesion and tissue integration. Compared with bare CS, the PDA-CS complex in the hydrogel was more effective in exerting its functions on adhered cells to upregulate chondrogenic differentiation. Because of the synergistic effects of noncovalent interactions caused by the PDA-CS complex and covalently cross-linked PAM network, the hydrogel exhibited super resilience and toughness, meeting the mechanical requirement of cartilage repair. Collectively, this tissue-adhesive and tough PDA-CS-PAM hydrogel with good cell affinity creates a growth-factor-free and biomimetic microenvironment for chondrocyte growth and cartilage regeneration and sheds light on the development of growth-factor-free biomaterials for cartilage repair.

Bioactive and Bioadhesive Catechol Conjugated Polymers for Tissue Regeneration

The effective treatment of chronic wounds constitutes one of the most common worldwide healthcare problem due to the presence of high levels of proteases, free radicals and exudates in the wound, which constantly activate the inflammatory system, avoiding tissue regeneration. In this study, we describe a multifunctional bioactive and resorbable membrane with in-built antioxidant agent catechol for the continuous quenching of free radicals as well as to control inflammatory response, helping to promote the wound-healing process. This natural polyphenol (catechol) is the key molecule responsible for the mechanism of adhesion of mussels providing also the functionalized polymer with bioadhesion in the moist environment of the human body. To reach that goal, synthesized statistical copolymers of N-vinylcaprolactam (V) and 2-hydroxyethyl methacrylate (H) have been conjugated with catechol bearing hydrocaffeic acid (HCA) molecules with high yields. The system has demonstrated good biocompatibility, a sustained antioxidant response, an anti-inflammatory effect, an ultraviolet (UV) screen, and bioadhesion to porcine skin, all of these been key features in the wound-healing process. Therefore, these novel mussel-inspired materials have an enormous potential for application and can act very positively, favoring and promoting the healing effect in chronic wounds.

Bioinspired Underwater Adhesives by Using the Supramolecular Toolbox

Nature has developed protein-based adhesives whose underwater performance has attracted much research attention over the last few decades. The adhesive proteins are rich in catechols combined with amphiphilic and ionic features. This combination of features constitutes a supramolecular toolbox, to provide stimuli-responsive processing of the adhesive, to secure strong adhesion to a variety of surfaces, and to control the cohesive properties of the material. Here, the versatile interactions used in adhesives secreted by sandcastle worms and mussels are explored. These biological principles are then put in a broader perspective, and synthetic adhesive systems that are based on different types of supramolecular interactions are summarized. The variety and combinations of interactions that can be used in the design of new adhesive systems are highlighted.

Chitosan and Its Derivatives for Application in Mucoadhesive Drug Delivery Systems

Mucoadhesive drug delivery systems are desirable as they can increase the residence time of drugs at the site of absorption/action, provide sustained drug release and minimize the degradation of drugs in various body sites. Chitosan is a cationic polysaccharide that exhibits mucoadhesive properties and it has been widely used in the design of mucoadhesive dosage forms. However, its limited mucoadhesive strength and limited water-solubility at neutral and basic pHs are considered as two major drawbacks of its use. Chemical modification of chitosan has been exploited to tackle these two issues. In this review, we highlight the up-to-date studies involving the synthetic approaches and description of mucoadhesive properties of chitosan and chitosan derivatives. These derivatives include trimethyl chitosan, carboxymethyl chitosan, thiolated chitosan, chitosan-enzyme inhibitors, chitosan-ethylenediaminetetraacetic acid (chitosan-EDTA), half-acetylated chitosan, acrylated chitosan, glycol chitosan, chitosan-catechol, methyl pyrrolidinone-chitosan, cyclodextrin-chitosan and oleoyl-quaternised chitosan. We have particularly focused on the effect of chemical derivatization on the mucoadhesive properties of chitosan. Additionally, other important properties including water-solubility, stability, controlled release, permeation enhancing effect, and in vivo performance are also described.