Biomedical applications of stimuli-responsive "smart" interpenetrating polymer network hydrogels

In recent years, owing to the ongoing advancements in polymer materials, hydrogels have found increasing applications in the biomedical domain, notably in the realm of stimuli-responsive "smart" hydrogels. Nonetheless, conventional single-network stimuli-responsive "smart" hydrogels frequently exhibit deficiencies, including low mechanical strength, limited biocompatibility, and extended response times. In response, researchers have addressed these challenges by introducing a second network to create stimuli-responsive "smart" Interpenetrating Polymer Network (IPN) hydrogels. The mechanical strength of the material can be significantly improved due to the topological entanglement and physical interactions within the interpenetrating structure. Simultaneously, combining different network structures enhances the biocompatibility and stimulus responsiveness of the gel, endowing it with unique properties such as cell adhesion, conductivity, hemostasis/antioxidation, and color-changing capabilities. This article primarily aims to elucidate the stimulus-inducing factors in stimuli-responsive "smart" IPN hydrogels, the impact of the gels on cell behaviors and their biomedical application range. Additionally, we also offer an in-depth exposition of their categorization, mechanisms, performance characteristics, and related aspects. This review furnishes a comprehensive assessment and outlook for the advancement of stimuli-responsive "smart" IPN hydrogels within the biomedical arena. We believe that, as the biomedical field increasingly demands novel materials featuring improved mechanical properties, robust biocompatibility, and heightened stimulus responsiveness, stimuli-responsive "smart" IPN hydrogels will hold substantial promise for wide-ranging applications in this domain.

Injectable Thermoresponsive Hydrogels for Cancer Therapy: Challenges and Prospects

The enervating side effects of chemotherapeutic drugs have necessitated the use of targeted drug delivery in cancer therapy. To that end, thermoresponsive hydrogels have been employed to improve the accumulation and maintenance of drug release at the tumour site. Despite their efficiency, very few thermoresponsive hydrogel-based drugs have undergone clinical trials, and even fewer have received FDA approval for cancer treatment. This review discusses the challenges of designing thermoresponsive hydrogels for cancer treatment and offers suggestions for these challenges as available in the literature. Furthermore, the argument for drug accumulation is challenged by the revelation of structural and functional barriers in tumours that may not support targeted drug release from hydrogels. Other highlights involve the demanding preparation process of thermoresponsive hydrogels, which often involves poor drug loading and difficulties in controlling the lower critical solution temperature and gelation kinetics. Additionally, the shortcomings in the administration process of thermosensitive hydrogels are examined, and special insight into the injectable thermosensitive hydrogels that reached clinical trials for cancer treatment is provided.

Biobased polymer resources and essential oils: a green combination for antibacterial applications

To fight nosocomial infections, the excessive use of antibiotics has led to the emergence of multidrug-resistant microorganisms, which are now considered a relevant public health threat by the World Health Organization. To date, most antibacterial systems are based on the use of petro-sourced polymers, but the global supplies of these resources are depleting. Besides, silver NPs are widely accepted as the most active biocide against a wide range of bacterial strains but their toxicity is an issue. The growing interest in natural products has gained increasing interest in the last decade. Therefore, the design of functional antibacterial materials derived from biomass remains a significant challenge for the scientific community. Consequently, attention has shifted to naturally occurring substances such as essential oils (EOs), which are classified as Generally Recognized as Safe (GRAS). EOs can offer an alternative to the common antimicrobial agents as an inner solution or biocide agent to inhibit the resistance mechanism. Herein, this review not only aims at providing developments in the antibacterial modes of action of EOs against various bacterial strains and the recent advances in genomic and proteomic techniques for the elucidation of these mechanisms but also presents examples of biobased polymer resource-based EO materials and their antibacterial activities. Especially, we describe the antibacterial properties of biobased polymers, e.g. cellulose, starch, chitosan, PLA PHAs and proteins, associated with EOs (cinnamon (CEO), clove (CLEO), bergamot (BEO), ginger (GEO), lemongrass (LEO), caraway (CAEO), rosemary (REO), Eucalyptus globulus (EGEO), tea tree (TTEO), orange peel (OPEO) and apricot (Prunus armeniaca) kernel (AKEO) essential oils). Finally, we discuss the influence of EOs on the mechanical strength of bio-based materials.

In-situ forming hydrogel based on thiolated chitosan/carboxymethyl cellulose (CMC) containing borate bioactive glass for wound healing

Suitable wound dressings for accelerating wound healing are actively being designed and synthesised. In this study, thiolated chitosan (tCh)/oxidized carboxymethyl cellulose (OCMC) hydrogel containing Cu-doped borate bioglass (BG) was developed as a wound dressing to improve wound healing in a full-thickness skin defect of mouse animal model. Thiolation was used to incorporate thiol groups into chitosan (Ch) to enhance its water solubility and mucoadhesion characteristics. Here, the in situ forming hydrogel was successfully developed using the Schiff-based reaction, and its physio-chemical and antibacterial characteristics were examined. Borate BG was also incorporated in the generated hydrogel to promote angiogenesis and tissue regeneration at the wound site. Investigations of in vitro cytotoxicity assays demonstrated that the synthesised hydrogels showed good biocompatibility and promoted cell growth. These results inspired us to investigate the effectiveness of skin wound healing in a mouse model. On the backs of animals, two full-thickness wounds were created and treated utilising two different treatment conditions: (1) OCMC/tCh hydrogel, (2) OCMC/tCh/borate BG, and (3) control defect. The wound closure ratio, collagen deposition, and angiogenesis activity were measured after 14 days to determine the healing efficacy of the in situ hydrogels used as wound dressings. Overall, the hydrogel containing borate BG was maintained in the defect site, healing efficiency was replicable, and wound healing was apparent. In conclusion, we found consistent angiogenesis, remodelling, and accelerated wound healing, which we propose may have beneficial effects on the repair of skin defects.

Smart/stimuli-responsive hydrogels: Cutting-edge platforms for tissue engineering and other biomedical applications

Recently, biomedicine and tissue regeneration have emerged as great advances that impacted the spectrum of healthcare. This left the door open for further improvement of their applications to revitalize the impaired tissues. Hence, restoring their functions. The implementation of therapeutic protocols that merge biomimetic scaffolds, bioactive molecules, and cells plays a pivotal role in this track. Smart/stimuli-responsive hydrogels are remarkable three-dimensional (3D) bioscaffolds intended for tissue engineering and other biomedical purposes. They can simulate the physicochemical, mechanical, and biological characters of the innate tissues. Also, they provide the aqueous conditions for cell growth, support 3D conformation, provide mechanical stability for the cells, and serve as potent delivery matrices for bioactive molecules. Many natural and artificial polymers were broadly utilized to design these intelligent platforms with novel advanced characteristics and tailored functionalities that fit such applications. In the present review, we highlighted the different types of smart/stimuli-responsive hydrogels with emphasis on their synthesis scheme. Besides, the mechanisms of their responsiveness to different stimuli were elaborated. Their potential for tissue engineering applications was discussed. Furthermore, their exploitation in other biomedical applications as targeted drug delivery, smart biosensors, actuators, 3D and 4D printing, and 3D cell culture were outlined. In addition, we threw light on smart self-healing hydrogels and their applications in biomedicine. Eventually, we presented their future perceptions in biomedical and tissue regeneration applications. Conclusively, current progress in the design of smart/stimuli-responsive hydrogels enhances their prospective to function as intelligent, and sophisticated systems in different biomedical applications.

Exploring the role of chitosan in affecting the adhesive, rheological and antimicrobial properties of carboxymethyl cellulose composite hydrogels

Natural polysaccharide-based hydrogels are promising in food and pharmaceutical applications. In this study, the potential of composite hydrogels prepared by carboxymethyl cellulose (CMC) and chitosan as glue for cigar wrapping applications was firstly studied. The impacts of degree of carboxymethyl substitution (DS) and the ratio of CMC:chitosan on the adhesive performance and rheological behaviors of composite hydrogels have been investigated. And the results indicated that relatively low DS of CMC and relatively low ratio of chitosan might be favorable for the adhesive properties of composite hydrogels. But a higher ratio of chitosan may significantly improve the rheological properties of composite hydrogels and alter their thermal-sensitivity. The impacts of chitosan on the wet ability with tobacco leaf, the morphology and the XRD patterns of composite hydrogels were also observed. The CMC-chitosan composite hydrogel could significantly decrease the total molds on tobacco leaf brought by CMC, and therefore may show great potential to improve the quality of cigar during long-term storage. All the information in this study is new, which could be useful for exploring the application of CMC-chitosan composite hydrogel in food, pharmaceutical, even other fields.

Long-term pre-clinical evaluation of an injectable chitosan nanocellulose hydrogel with encapsulated adipose-derived stem cells in an ovine model for IVD regeneration

The potential therapeutic benefit of adipose-derived stem cells (ASCs) encapsulated in an injectable hydrogel for stimulating intervertebral disc (IVD) regeneration has been assessed by a number of translational and preclinical studies. However, previous work has been primarily limited to small animal models and short-term outcomes of only a few weeks. Long-term studies in representative large animal models are crucial for translation into clinical success, especially for permanent stabilization of major defects such as disc herniation. An injectable chitosan carboxymethyl cellulose hydrogel scaffold loaded with ASCs was evaluated regarding its intraoperative handling, crosslinking kinetics, cell viability, fully-crosslinked viscoelasticity, and long-term therapeutic effects in an ovine model. Three IVDs per animal were damaged in 10 sheep. Subcutaneous adipose tissue was the source for autologous ASCs. Six weeks after IVD damage, two of the damaged IVDs were treated via ASC-loaded hydrogel injection. After 12 months following the implantation, IVD disc height and histological and cellular changes were assessed. This system was reliable and easy to handle intraoperatively. Over 12 months, IVD height was stabilized and degeneration progression significantly mitigated compared to untreated, damaged IVDs. Here we show for the first time in a large animal model that an injectable chitosan carboxymethyl cellulose hydrogel system with encapsulated ASCs is able to affect long-term stabilization of an injured IVD and significantly decrease degeneration processes as compared to controls.

Assessment of properties, applications and limitations of scaffolds based on cellulose and its derivatives for cartilage tissue engineering: A review

Cartilage is a connective tissue, which is made up of ~80% of water. It is alymphatic, aneural and avascular with only one type of cells present, chondrocytes. They constitute about 1-5% of the entire cartilage tissue. It has a very limited capacity for spontaneous repair. Articular cartilage defects are quite common due to trauma, injury or aging and these defects eventually lead to osteoarthritis, affecting the daily activities. Tissue engineering (TE) is a promising strategy for the regeneration of articular cartilage when compared to the existing invasive treatment strategies. Cellulose is the most abundant natural polymer and has desirable properties for the development of a scaffold, which can be used for the regeneration of cartilage. This review discusses about (i) the basic science behind cartilage TE and the study of cellulose properties that can be exploited for the construction of the engineered scaffold with desired properties for cartilage tissue regeneration, (ii) about the requirement of scaffolds properties, fabrication mechanisms and assessment of cellulose based scaffolds, (iii) details about the modification of cellulose surface by employing various chemical approaches for the production of cellulose derivatives with enhanced characteristics and (iv) limitations and future research prospects of cartilage TE.

Photolithographically assembled polyelectrolyte complexes as shape-directing templates for thermoreversible gels

Preparation of soft materials with diverse, customized shapes has been a topic of intense research interest. To this end, we have recently demonstrated photolithographic directed assembly as a strategy for customizing polyelectrolyte complex (PEC) shape. This process uses in situ photopolymerization of an anionic monomer in the presence of a cationic polymer, which drives localized PEC formation at the irradiation sites. Here, we show how such photolithographically assembled PECs can serve as structure-directing templates for tailoring the shapes of other soft materials; namely, thermoreversible gels. These templated hydrogels are prepared by adding a thermogelling polymer (agarose) to the anionic monomer/cationic polymer/photoinitiator precursor solutions so that, upon irradiation, custom-shaped PECs form within agarose gel matrices. Once these PECs are formed, the surrounding agarose gels are melted (through heating) and washed away which, upon returning the samples to room temperature, produces interpenetrating PEC/agarose gel networks with photopatterned shapes and dimensions. Dissolution of these sacrificial PEC templates in concentrated NaCl solutions then generates photolithographically templated agarose gels, whose shapes and dimensions match those of their PEC templates. Besides tuning their shapes and sizes, the mechanical properties of these gels can be easily tailored by varying the initial agarose concentrations used. Moreover, this PEC-templated gel synthesis appears to not adversely affect hydrogel cytocompatibility, suggesting its potential suitability for biological and biomedical applications. Though the present study uses only agarose as the model gel system, this PEC-based strategy for customizing gel shape can likely also be applied to other thermoreversible gel networks (e.g., those based on methylcellulose, poloxamers or thermoresponsive chitosan derivatives) and could have many attractive applications, ranging from drug delivery and tissue engineering, to sensing and soft robotics.

Influence of chitosan oligosaccharide on the gelling and wound healing properties of injectable hydrogels based on carboxymethyl chitosan/alginate polyelectrolyte complexes

In situ injectable hydrogels for wound healing based on carboxymethyl chitosan (CMCS) and alginate were developed in this work. The liquid mixture of CMCS and alginate solutions formed a gel by polyelectrolyte complexation after addition of d-glucono-δ-lactone (GDL), which slowly hydrolyzed and donated protons. When chitosan oligosaccharide (COS) was added into the mixture, a two-stage gelling process occurred. The primary gelling process was similar to that of the hydrogel without COS, while the secondary gelling process appeared about 20 min later, and much stronger hydrogels with storage modulus G' about 1 MPa, 10⁴ times higher, were obtained. COS also significantly influenced the microstructure of hydrogels as well as their biological activities. The hydrogels with 0.5% of COS significantly promoted proliferation of human umbilical cord mesenchymal stem cells (HUMSCs). These injectable hydrogels, especially when COS was added, remarkably accelerated the wound healing process in a mouse skin defect model. Microscopic wound analysis showed an increase of the thickness and integrity of epidermal tissue, increased formation of collagen fibers, and enhanced expression of vascular endothelial growth factor as compared to the control group.

Cellulose-based hydrogel materials: chemistry, properties and their prospective applications

Hydrogels based on cellulose comprising many organic biopolymers including cellulose, chitin, and chitosan are the hydrophilic material, which can absorb and retain a huge proportion of water in the interstitial sites of their structures. These polymers feature many amazing properties such as responsiveness to pH, time, temperature, chemical species and biological conditions besides a very high-water absorption capacity. Biopolymer hydrogels can be manipulated and crafted for numerous applications leading to a tremendous boom in research during recent times in scientific communities. With the growing environmental concerns and an emergent demand, researchers throughout the globe are concentrating particularly on naturally derived hydrogels due to their biocompatibility, biodegradability and abundance. Cellulose-based hydrogels are considered as useful biocompatible materials to be used in medical devices to treat, augment or replace any tissue, organ, or help function of the body. These hydrogels also hold a great promise for applications in agricultural activity, as smart materials and some other useful industrial purposes. This review offers an overview of the recent and contemporary research regarding physiochemical properties of cellulose-based hydrogels along with their applications in multidisciplinary areas including biomedical fields such as drug delivery, tissue engineering and wound healing, healthcare and hygienic products as well as in agriculture, textiles and industrial applications as smart materials.

Biopolymer-based strategies in the design of smart medical devices and artificial organs

Advances in regenerative medicine and in modern biomedical therapies are fast evolving and set goals causing an upheaval in the field of materials science. This review discusses recent developments involving the use of biopolymers as smart materials, in terms of material properties and stimulus-responsive behavior, in the presence of environmental physico-chemical changes. An overview on the transformations that can be triggered in natural-based polymeric systems (sol-gel transition, polymer relaxation, cross-linking, and swelling) is presented, with specific focus on the benefits these materials can provide in biomedical applications.

Comparison of chitosan microsphere versus O-carboxymethyl chitosan microsphere for drug delivery systems

The development of controlled drug delivery systems for bone regeneration, especially microspheres, has become a research hotspot in recent years. Chitosan and its derivative O-carboxymethyl chitosan have been considered to be an effective way for controlled drug delivery due to their nontoxicity and biodegradability. Currently, most of the studies have researched on synthesizing and characterizing chitosan and O-carboxymethyl chitosan. However, few studies have focused on the differences between chitosan microspheres and O-carboxymethyl chitosan microspheres directly. In this study, chitosan and O-carboxymethyl chitosan microspheres were developed by water-in-oil emulsification cross-linking method using vanillin as the cross-linking agent, and then their physicochemical properties were evaluated by Fourier transform infrared spectroscopy, scanning electron microscopy, and in vitro release testing. The results showed that O-carboxymethyl chitosan was successfully modified by adding carboxymethyl group at the chitosan C6 position.The particle size of chitosan microspheres (50–90 µm) was significantly larger than that of O-carboxymethyl chitosan microspheres (10–50 µm), and the drug release profile of O-carboxymethyl chitosan microspheres showed larger initial burst release within the first day and sustained release at the fourth day, while chitosan microspheres showed sustained release at the seventh day. In addition, Cell Counting Kit-8 assay showed that MC3T3-E1 proliferated well and highly expressed the alkaline phosphatase marker protein on both chitosan and O-carboxymethyl chitosan microspheres. Overall, both chitosan and O-carboxymethyl chitosan microspheres showed good biocompatibility, and chitosan microspheres were superior to O-carboxymethyl chitosan microspheres. Moreover, the different drug release rates suggest that chitosan and O-carboxymethyl chitosan microspheres have the potential to be used for the repair of different bone defects.

A Review of Injectable Polymeric Hydrogel Systems for Application in Bone Tissue Engineering

Biodegradable, stimuli-responsive polymers are essential platforms in the field of drug delivery and injectable biomaterials for application of bone tissue engineering. Various thermo-responsive hydrogels display water-based homogenous properties to encapsulate, manipulate and transfer its contents to the surrounding tissue, in the least invasive manner. The success of bioengineered injectable tissue modified delivery systems depends significantly on their chemical, physical and biological properties. Irrespective of shape and defect geometry, injectable therapy has an unparalleled advantage in which intricate therapy sites can be effortlessly targeted with minimally invasive procedures. Using material testing, it was found that properties of stimuli-responsive hydrogel systems enhance cellular responses and cell distribution at any site prior to the transitional phase leading to gelation. The substantially hydrated nature allows significant simulation of the extracellular matrix (ECM), due to its similar structural properties. Significant current research strategies have been identified and reported to date by various institutions, with particular attention to thermo-responsive hydrogel delivery systems, and their pertinent focus for bone tissue engineering. Research on future perspective studies which have been proposed for evaluation, have also been reported in this review, directing considerable attention to the modification of delivering natural and synthetic polymers, to improve their biocompatibility and mechanical properties.

Preparation and Timed Release Properties of Self-Rupturing Gels

Swelling of polymeric hydrogels is sensitive to their cross-link densities. Here, we exploit this principle to prepare self-rupturing gels which are based on a commonly-used, nontoxic, and inexpensive polyelectrolyte, poly(acrylic acid), and are prepared through a simple and low-cost polymerization-based technique. The self-rupture of these covalently cross-linked gels is achieved by preparing them to have highly nonuniform cross-link densities. This heterogeneity in cross-linking leads to highly nonuniform swelling, which generates stresses that are high enough to induce gel rupture. The time required for this rupture to occur depends on the difference in the cross-link densities between the adjoining gel regions, gel size, order in which the variably cross-linked gel portions are synthesized, and on the ambient pH and ionic strength. Furthermore, when these self-rupturing gels are prepared to have liquid-filled (capsule-like) morphologies, they can act as timed/delayed release devices. The self-rupture of these capsules provides a burst payload release after a preprogrammed delay, which is on the timescale of days and can be easily tuned by varying the rupture time, i.e., by varying either the cross-link nonuniformity or the pH and ionic strength of the release media.

A molecular zipping/unzipping nano-vehicles sensitive to tumor extracellular pH

A new class of pH- responsive multivalent host–guest interactions to manipulate polypeptide-based nano-vehicles was developed. Poly(l-lysine) (poly(Lys)) grafted with β-cyclodextrin and 2,3-dimethylmaleic acid was coupled with oleic acid. This new polymer was utilized to fabricate pH-responsive nano-vehicles for antitumor drug doxorubicin delivery. The host–guest (zipping) interaction between β-cyclodextrin and 2,3-dimethylmaleic acid moieties and the hydrophobic interaction between the oleic acid molecules contributed to form self-assembled nano-vehicles. 2,3-Dimethylmaleic acid moieties were highly degradable at a slightly acidic pH (~pH 6.8). These nano-vehicles increased the release of the encapsulated doxorubicin content (by the unzipping interaction between β-cyclodextrin and degraded 2,3-dimethylmaleic acid moieties) when the pH of the solution decreased to 6.8. This event caused a significant increase in the efficiency of cellular doxorubicin uptake and in vitro tumor inhibition.

Polymers in cell encapsulation from an enveloped cell perspective

In the past two decades, many polymers have been proposed for producing immunoprotective capsules. Examples include the natural polymers alginate, agarose, chitosan, cellulose, collagen, and xanthan and synthetic polymers poly(ethylene glycol), polyvinyl alcohol, polyurethane, poly(ether-sulfone), polypropylene, sodium polystyrene sulfate, and polyacrylate poly(acrylonitrile-sodium methallylsulfonate). The biocompatibility of these polymers is discussed in terms of tissue responses in both the host and matrix to accommodate the functional survival of the cells. Cells should grow and function in the polymer network as adequately as in their natural environment. This is critical when therapeutic cells from scarce cadaveric donors are considered, such as pancreatic islets. Additionally, the cell mass in capsules is discussed from the perspective of emerging new insights into the release of so-called danger-associated molecular pattern molecules by clumps of necrotic therapeutic cells. We conclude that despite two decades of intensive research, drawing conclusions about which polymer is most adequate for clinical application is still difficult. This is because of the lack of documentation on critical information, such as the composition of the polymer, the presence or absence of confounding factors that induce immune responses, toxicity to enveloped cells, and the permeability of the polymer network. Only alginate has been studied extensively and currently qualifies for application. This review also discusses critical issues that are not directly related to polymers and are not discussed in the other reviews in this issue, such as the functional performance of encapsulated cells in vivo. Physiological endocrine responses may indeed not be expected because of the many barriers that the metabolites encounter when traveling from the blood stream to the enveloped cells and back to circulation. However, despite these diffusion barriers, many studies have shown optimal regulation, allowing us to conclude that encapsulated grafts do not always follow nature's course but are still a possible solution for many endocrine disorders for which the minute-to-minute regulation of metabolites is mandatory.

Sequential ionic and thermogelation of chitosan spherical hydrogels prepared using superhydrophobic surfaces to immobilize cells and drugs

Chitosan is soluble in acidic media, which makes it incompatible for the encapsulation of cells and pH-sensitive molecules. In this work, a mild chitosan-based system with two sequential gelation steps is proposed, where the model drug dexamethasone and L929 cells are immobilized inside hydrogel beads. Superhydrophobic surfaces were used to produce the spherical hydrogel particles that provided favorable conditions to encapsulate cells or bioactive agents. First, the chitosan acidic solution was neutralized with β-glycerophosphate at room temperature to pH 6.2. Suspended cells (or dexamethasone) in the formulation were dispensed in controlled volumes onto biomimetic polystyrene superhydrophobic surfaces, to form spherical shapes. The addition of sodium tripolyphosphate on the top of each sphere induced an ionic gelation process of the chitosan through electrostatic interactions. At 37°C, the hydrophobicity of the chitosan-based formulations increased and a second gelation step occurred, which increased the elastic modulus. In addition, the pH-responsive behavior characteristic of chitosan was maintained. The softness and flexibility of the system can potentially be utilized to implant cells and therapeutic molecules using less invasive procedures.

In vitro and in vivo evaluation of biodegradable embolic microspheres with tunable anticancer drug release

Natural polymer-derived materials have attracted increasing interest in the biomedical field. Polysaccharides have obvious advantages over other polymers employed for biomedical applications due to their exceptional biocompatibility and biodegradability. None of the spherical embolic agents used clinically is biodegradable. In the current study, microspheres prepared from chitosan and carboxymethyl cellulose (CMC) were investigated as a biodegradable embolic agent for arterial embolization applications. Aside from the enzymatic degradability of chitosan units, the cross-linking bonds in the matrix, Schiff bases, are susceptible to hydrolytic cleavage in aqueous conditions, which would overcome the possible shortage of enzymes inside the arteries. The size distribution, morphology, water retention capacity and degradability of the microspheres were found to be affected by the modification degree of CMC. An anticancer drug, doxorubicin, was successfully incorporated into these microspheres for local release and thus for killing cancerous cells. These microspheres demonstrated controllable degradation time, variable swelling and tunable drug release profiles. Co-culture with human umbilical vein endothelial cells revealed non-cytotoxic nature of these microspheres compared to monolayer control (P>0.95). In addition, a preliminary study on the in vivo degradation of the microspheres (100-300μm) was performed in a rabbit renal embolization model, which demonstrated that the microspheres were compatible with microcatheters for delivery, capable of occluding the arteries, and biodegradable inside arteries. These microspheres with biodegradability would be promising for embolization therapies.

Colloidal stability and “in vitro” antitumor targeting ability of lipid nanocapsules coated by folate–chitosan conjugates

In this study, the synthesis and characterization of lipid nanocapsules coated with folate–chitosan conjugates at varying folate concentrations are reported; these nanocapsules have a potential application as anticancer drug carriers. The main goal of this study was to evaluate (a) the colloidal stability of the particles and (b) their cell targeting. A classical colloidal characterization of the nanocapsules was carried out by analyzing size, electrokinetic charge, and stability in different saline solutions, including cell culture media. At neutral pH, the stability was improved by the presence of folate due to electrical interactions. In addition, folate modulated the hydrophilic/phobic nature of the surface, which became critical to keep the systems stable (or not) under physiological saline conditions due to the action of short-range repulsive hydration forces. The cellular uptake of our nanocapsules was evaluated by working with four tumor cell lines. Both fluorescent analyses with particles colored by Nile Red, and antitumor activity of our systems loaded with docetaxel, demonstrated that the folate-mediated internalization of the particles in the cancer cells was improved when the nanocapsules were coated by folate–chitosan conjugates.

Nanocomposite thermogel for controlled release of small proteins

A nanocomposite thermogel composed of Pluronic®-based multiblock copolymer and laponite nanoclay was developed to sustain delivery of low-molecular-weight proteins. The rapid release of low-molecular-weight proteins from multiblock copolymer thermogels has been a problem for sustained delivery but was solved by using nanocomposite thermogel. Lysozyme (Mw = 14,700), a relatively low-molecular-weight protein, was successfully loaded into and released from nanocomposite thermogel. In addition, interactions among multiblock copolymer, laponite, and lysozyme were studied in terms of gelation, micellization, particle size, and zeta potential. Critical micellization temperatures and sol–gel transition temperatures of multiblock copolymer solutions were lowered with laponite addition. Positively charged lysozyme was adsorbed onto anionic surface of laponite, which increased with an increase in the lysozyme concentration. Particle size and zeta potential of the laponite–lysozyme complex were also dependent on the lysozyme concentration. The nanocomposite thermogel sustained lysozyme release to 40 days, whereas lysozyme release from multiblock copolymer thermogel lasted for only 18 days. The structural stability of released lysozyme was confirmed by circular dichroism spectroscopy and differential scanning calorimetry.

Hydrogels based on dual curable chitosan-graft-polyethylene glycol-graft-methacrylate: application to layer-by-layer cell encapsulation

Ultraviolet (UV) photo-cross-linkable hydrogels have been commonly used for three-dimensional (3D) encapsulation of cells. Previous UV cross-linkable hydrogels have employed one-shot hardening of mixtures of hydrogels and cells. Here we propose an alternative method of making hydrogel-encapsulated cell constructs through layer by layer (LBL) buildup of alternating layers of cells and hydrogel. The LBL method potentially permits better spatial control of different cell types and control of cell orientation. Each hydrogel layer must be hardened before deposition of the next layer of cells. A UV-curable gel precursor that can also be gelled at physiological temperature is desirable to avoid repeated UV exposure of cells after deposition of each successive hydrogel layer. We designed, synthesized, and applied such a precursor, dual-curable-both thermoresponsive and UV-curable-chitosan-graft-polyethylene glycol-graft-methacrylate (CEGx-MA) copolymer (x is the PEG molecular weight in Daltons). We found that CEG350-MA copolymer solutions (5 wt % polymer) formed physical gels at approximately 37 degrees C and could be further photopolymerized to form thermally stable dual-cured hydrogels. This material was applied to the creation of a two-layer LBL smooth muscle cell (SMC)/hydrogel construct using temperature elevation to approximately 37 degrees C to gel each hydrogel layer. The physically gelled two-layered hydrogel/cell construct was finally exposed to a single UV shot to improve its mechanical properties and render it thermally stable. CEG350-MA solution and gel are nontoxic to SMCs. Cells remained mostly viable when they were encapsulated inside both physically gelled and dual-cured CEG350-MA and suffered little damage from the single brief UV exposure. The combination of LBL tissue engineering with a dual curable hydrogel precursor such as CEG350-MA permits the buildup of viable thick and complex tissues in a stable, biocompatible, and biodegradable matrix.

Salicylic Acid-grafted Chitosan Oligosaccharide Nanoparticle for Paclitaxel Delivery

A hydrotropic agent, salicylic acid (SA), was grafted to chitosan oligosaccharide (CSO) backbone to develop a CSO/SA conjugate. The CSO/SA self-assembled to form nanoparticles (NPs) in aqueous medium. The sizes of the NPs were smaller as more SA was grafted and when lower molecular weight CSO was used. The ζ-potentials of all CSO/SA NPs were above 40 mV. The critical aggregation concentrations of NPs decreased from 454.79 to 164.0 μg/mL by increasing the grafted SA content or the CSO Mw. Paclitaxel (PTX)-loaded NPs were prepared by a dialysis method; the particle sizes and ζ-potentials were smaller than the blank NPs. A series of PTX-loaded CSO28,000/SA50% NPs were prepared; as the size decreased or the drug content increased, the in vitro release rate increased. The in vitro cytotoxicity of blank CSO/SA NPs was determined using the MCF-7 cell line. The CSO/SA provides a new means of making a stable delivery for PTX.

Controllable aggregation and reversible pH sensitivity of AuNPs regulated by carboxymethyl cellulose

A pH-sensitive gold nanoparticle-cysteamine/carboxymethyl cellulose (Au-CA/CMC) dispersion system was prepared by a simple approach. Gold nanoparticles (AuNPs) were first synthesized by directly reducing chloroauric acid (HAuCl(4)) with sodium carboxymethyl cellulose (CMC). Then the AuNPs were decorated by an electrostatic compound of cysteamine hydrochloride (CA) and sodium carboxymethyl cellulose (CMC) through ligand exchange to get the assembly of Au-CA/CMC. The Au-CA/CMC dispersion system exhibits strongly reversible pH-responsive behavior with the aggregation of AuNPs caused by the combined action of the chain conformation change of CMC and electrostatic interactions between CA and CMC at different pH values. Finally, the reversible aggregation mechanism of AuNPs in the Au-CA/CMC dispersion system has been investigated by transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV-vis spectroscopy). This study provides a new method to fabricate a stimuli-responsive system free from complicated organic synthesis without using a toxic reducing agent.

Cyclotriphosphazene-Pt-DACH Conjugates with Dipeptide Spacers for Drug Delivery Systems

An intelligent drug delivery system that exhibits a thermosensitive phase transition from a soluble to insoluble state was developed to deliver drugs into a tumor. Cyclotriphosphazene-Pt-DACH ( trans(±)-1,2-diaminocyclohexane) conjugates with dipeptide spacers were synthesized by successive reaction steps. The conjugates exhibited a reversible and thermosensitive phase transition with lower critical solution temperature in aqueous media that was varied by the substitution of different hydrophilic/hydrophobic side groups. The conjugate had similar cytotoxicity as cisplatin, but much greater than carboplatin against various human cancer cell lines. The conjugate was much more potent than cisplatin against the cisplatin-resistant cell line, A2780/CP70. The biodistribution and pharmacokinetic studies indicate that the present thermosensitive conjugate exhibits locally controlled drug delivery feature that could circumvent surgery treatment and reduce toxic side effects due to systemic administration.

Electroresponsive Polyacrylamide-grafted-xanthan Hydrogels for Drug Delivery

An electroresponsive drug delivery system was developed using poly(acrylamide-grafted-xanthan gum) (PAAm-g-XG) hydrogel for transdermal delivery of ketoprofen. The electrically sensitive PAAm-g-XG copolymer was synthesized by free radical polymerization under nitrogen atmosphere followed by alkaline hydrolysis. When a swollen PAAm-g-XG hydrogel was placed in between a pair of electrodes, deswelling of the hydrogel was observed in the vicinity of electrodes carrying the electric stimulus. The membrane-controlled drug delivery systems were prepared using drug-loaded PAAm-g-XG hydrogel as the reservoir and crosslinked with poly(vinyl alcohol) to form films as rate controlling membranes (RCM). The in vitro drug permeation study from the formulations was performed through excised rat abdominal skin. Drug permeation across the skin was greatly enhanced in the presence of electric stimulus as compared to passive diffusion and was found to be dependent upon the applied electric current strength and crosslink density of RCM. A pulsated pattern of drug release was observed as the electric stimulus was switched `on' and `off.' The skin histopathology study demonstrated that, after the application of an electrical stimulus, there were changes in the structure of stratum corneum and cell structure. These PAAm-g-XG hydrogel could be useful as transdermal drug delivery systems actuated by an electric signal to provide on-demand release of drugs.

Biocompatibility Evaluation of Chitosan-based Injectable Hydrogels for the Culturing Mice Mesenchymal Stem Cells In Vitro

A thermosensitive polymer can be held liquid before being injected to deliver living cells or therapeutic agents and formed monolithic gels when injected in vivo. In this study, chitosan-based thermosensitive hydrogels were prepared, characterized and the biocompatibility for culturing mice bone mesenchymal stem cells (BMSC) on 2D films and within 3D hydrogel were investigated. The gelation temperature and biocompatibility could be modulated by addition hydroxyethyl cellulose (HEC) to chitosan—glycerophosphate (CH—GP) formulation. The CH—GP—HEC liquid solution can turn into gel at body temperature and has highly compatible with BMSC. Therefore, the CH—GP—HEC gel could be used as an attractive injected in-situ forming scaffold for future applications of delivering biologically active therapeutics for tissue engineering filed.

Biodegradable Cellulose-based Hydrogels: Design and Applications

Hydrogels are macromolecular networks able to absorb and release water solutions in a reversible manner, in response to specific environmental stimuli. Such stimuli-sensitive behaviour makes hydrogels appealing for the design of ‘smart’ devices, applicable in a variety of technological fields. In particular, in cases where either ecological or biocompatibility issues are concerned, the biodegradability of the hydrogel network, together with the control of the degradation rate, may provide additional value to the developed device. This review surveys the design and the applications of cellulose-based hydrogels, which are extensively investigated due to the large availability of cellulose in nature, the intrinsic degradability of cellulose and the smart behaviour displayed by some cellulose derivatives.