Physically crosslinked dextran hydrogels by stereocomplex formation of lactic acid oligomers: degradation and protein release behavior

Development of a bioactive hyaluronic acid hydrogel functionalised with antimicrobial peptides for the treatment of chronic wounds

Chronic wounds present significant clinical challenges due to delayed healing and high infection risk. This study presents the development and characterisation of acrylated hyaluronic acid (AcHyA) hydrogels functionalised with gelatin (G) and the antimicrobial peptide (AMP) PP4-3.1 to enhance cellular responses while providing antimicrobial activity. AcHyA-G and AcHyA-AMP hydrogels were formed via thiol-acrylate crosslinking, enabling in situ AcHyA hydrogel formation with stable mechanical properties across varying gelatin concentrations. Biophysical characterisation of AcHyA-G hydrogels showed rapid gelation, elastic behaviour, uniform mesh size, and consistent molecular diffusion across all formulations. Moreover, the presence of gelatin enhanced stability without affecting the hydrogel's degradation kinetics. AcHyA-G hydrogels supported the adhesion and spreading of key cell types involved in wound repair (dermal fibroblasts and endothelial cells), with 0.5% gelatin identified as the optimal effective concentration. Furthermore, the conjugation of the AMP conferred bactericidal activity against Staphylococcus aureus and Escherichia coli, two of the most prevalent bacterial species found in chronically infected wounds. These results highlight the dual function of AcHyA-AMP hydrogels in promoting cellular responses and antimicrobial activity, offering a promising strategy for chronic wound treatment. Further in vivo studies are needed to evaluate their efficacy, including in diabetic foot ulcers.

Poly(Lactic Acid): Recent Stereochemical Advances and New Materials Engineering

Poly(lactic acid) (PLA) is a representative biobased and biodegradable aliphatic polyester and a front-runner among sustainable materials. As a semicrystalline thermoplastic, PLA exhibits excellent mechanical and physical properties, attracting considerable attention in commodity and medical fields. Stereochemistry is a key factor affecting PLA's properties, and to this end, the engineering of PLA's microstructure for tailored material properties has been an active area of research over the decade. This Review first covers the basic structural variety of PLA. A perspective on the current states of stereocontrolled synthesis as well as the relationships between the structures and properties of PLA stereosequences are included, with an emphasis on record regularity and properties. At last, state-of-the-art examples of high-performance PLA-based materials within an array of applications are given, including packaging, fibers, and textiles, healthcare and electronic devices. Among various stereo-regular sequences of PLA, poly(L-lactic acid) (PLLA) is the most prominent category and has myriad unique properties and applications. In this regard, cutting-edge applications of PLLA are mainly overviewed in this review. At the same time, new materials developed based on other PLA stereosequences are highlighted, which holds the potential to a wide variety of PLA-based sustainable materials.

Trends in sustainable chitosan-based hydrogel technology for circular biomedical engineering: A review

Eco-friendly materials have emerged in biomedical engineering, driving major advances in chitosan-based hydrogels. These hydrogels offer a promising green alternative to conventional polymers due to their non-toxicity, biodegradability, biocompatibility, environmental friendliness, affordability, and easy accessibility. Known for their remarkable properties such as drug encapsulation, delivery capabilities, biosensing, functional scaffolding, and antimicrobial behavior, chitosan hydrogels are at the forefront of biomedical research. This paper explores the fabrication and modification methods of chitosan hydrogels for diverse applications, highlighting their role in advancing climate-neutral healthcare technologies. It reviews significant scientific advancements and trends chitosan hydrogels focusing on cancer diagnosis, drug delivery, and wound care. Additionally, it addresses current challenges and green synthesis practices that support a circular economy, enhancing biomedical sustainability. By providing an in-depth analysis of the latest evidence on climate-neutral management, this review aims to facilitate informed decision-making and foster the development of sustainable strategies leveraging chitosan hydrogel technology. The insights from this comprehensive examination are pivotal for steering future research and applications in sustainable biomedical solutions.

Bioactive Hydrogels Based on Tyramine and Maleimide Functionalized Dextran for Tissue Engineering Applications

Hydrogels are widely used in tissue engineering due to their ability to form three-dimensional (3D) structures that support cellular functions and mimic the extracellular matrix (ECM). Despite their advantages, dextran-based hydrogels lack intrinsic biological activity, limiting their use in this field. Here, we present a strategy for developing bioactive hydrogels through sequential thiol-maleimide bio-functionalization and enzyme-catalyzed crosslinking. The hydrogel network is formed through the reaction of tyramine moieties in the presence of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2), allowing for tunable gelation time and stiffness by adjusting H2O2 concentrations. Maleimide groups on the hydrogel backbone enable the coupling of thiol-containing bioactive molecules, such as arginylglycylaspartic acid (RGD) peptides, to enhance biological activity. We examined the effects of hydrogel stiffness and RGD concentration on human mesenchymal stem cells (hMSCs) during differentiation and found that hMSCs encapsulated within these hydrogels exhibited over 88% cell viability on day 1 across all conditions, with a slight reduction to 60-81% by day 14. Furthermore, the hydrogels facilitated adipogenic differentiation, as evidenced by positive Oil Red O staining. These findings demonstrate that DexTA-Mal hydrogels create a biocompatible environment that is conducive to cell viability and differentiation, offering a versatile platform for future tissue engineering applications.

A Comprehensive Review of Hydrogel-Based Drug Delivery Systems: Classification, Properties, Recent Trends, and Applications

As adaptable biomaterials, hydrogels have shown great promise in several industries, which include the delivery of drugs, engineering of tissues, biosensing, and regenerative medicine. These hydrophilic polymer three-dimensional networks have special qualities like increased content of water, soft, flexible nature, as well as biocompatibility, which makes it excellent candidates for simulating the extracellular matrix and promoting cell development and tissue regeneration. With an emphasis on their design concepts, synthesis processes, and characterization procedures, this review paper offers a thorough overview of hydrogels. It covers the various hydrogel material types, such as natural polymers, synthetic polymers, and hybrid hydrogels, as well as their unique characteristics and uses. The improvements in hydrogel-based platforms for controlled drug delivery are examined. It also looks at recent advances in bioprinting methods that use hydrogels to create intricate tissue constructions with exquisite spatial control. The performance of hydrogels is explored through several variables, including mechanical properties, degradation behaviour, and biological interactions, with a focus on the significance of customizing hydrogel qualities for particular applications. This review paper also offers insights into future directions in hydrogel research, including those that promise to advance the discipline, such as stimuli-responsive hydrogels, self-healing hydrogels, and bioactive hydrogels. Generally, the objective of this review paper is to provide readers with a detailed grasp of hydrogels and all of their potential uses, making it an invaluable tool for scientists and researchers studying biomaterials and tissue engineering.

Gelation upon the Mixing of Amphiphilic Graft and Triblock Copolymers Containing Enantiomeric Polylactide Segments through Stereocomplex Formation

Biodegradable injectable polymer (IP) systems that form hydrogels in situ when injected into the body have considerable potential as medical materials. In this paper, we report a new two-solution mixed biodegradable IP system that utilizes the stereocomplex (SC) formation of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA). We synthesized triblock copolymers of PLLA and poly(ethylene glycol), PLLA-b-PEG-b-PLLA (tri-L), and a graft copolymer of dextran (Dex) attached to a PDLA-b-PEG diblock copolymer, Dex-g-(PDLA-b-PEG) (gb-D). We found that a hydrogel can be obtained by mixing gb-D solution and tri-L solution via SC formation. Although it is already known that graft copolymers attached to enantiomeric PLLA and PDLA chains can form an SC hydrogel upon mixing, we revealed that hydrogels can also be formed by a combination of graft and triblock copolymers. In this system (graft vs. triblock), the gelation time was shorter, within 1 min, and the physical strength of the resulting hydrogel (G' > 100 Pa) was higher than when graft copolymers were mixed. Triblock copolymers form micelles (16 nm in diameter) in aqueous solutions and hydrophobic drugs can be easily encapsulated in micelles. In contrast, graft copolymers have the advantage that their molecular weight can be set high, contributing to improved mechanical strength of the obtained hydrogel. Various biologically active polymers can be used as the main chains of graft copolymers, and chemical modification using the remaining functional side chain groups is also easy. Therefore, the developed mixing system with a graft vs. triblock combination can be applied to medical materials as a highly convenient, physically cross-linked IP system.

Type I collagen concentration affects neurite outgrowth of adult rat DRG explants by altering mechanical properties of hydrogels

Type I collagen is a predominant fibrous protein that makes up the extracellular matrix. Collagen enhances cell attachment and is commonly used in three-dimensional culture systems, to mimic the native extracellular environment, for primary sensory neurons such as dorsal root ganglia (DRG). However, the effects of collagen concentration on adult rat DRG neurite growth have not been assessed in a physiologically relevant, three-dimensional culture. This study focuses on the effects of type I collagen used in a methacrylated hyaluronic acid (MAHA)-laminin-collagen gel (triple gel) on primary adult rat DRG explants in vitro. DRGs were cultured in triple gels, and the neurite lengths and number of support cells were quantified. Increased collagen concentration significantly reduced neurite length but did not affect support cell counts. Mechanical properties, fiber diameter, diffusivity, and mesh size of the triple gels with varying collagen concentration were characterized to further understand the effects of type I collagen on hydrogel property that may affect adult rat DRG explants. Gel stiffness significantly increased as collagen concentration increased and is correlated to DRG neurite length. Collagen concentration also significantly impacted fiber diameter but there was no correlation with DRG neurite length. Increasing collagen concentration had no significant effect on mesh size and diffusivity of the hydrogel. These data suggest that increasing type I collagen minimizes adult rat DRG explant growth in vitro while raising gel stiffness. This knowledge can help develop more robust 3D culture platforms to study sensory neuron growth and design biomaterials for nerve regeneration applications.

Fibrillar Hydrogel Based on Cellulose Nanocrystals Crosslinked via Diels-Alder Reaction: Preparation and pH-Sensitive Release of Benzocaine

A fibrillar hydrogel was obtained by covalent crosslinking via Diels-Alder reaction of two types of cellulose nanocrystals (CNCs) with furan and maleimide groups. Gelation has been studied at various ratios of components and temperatures in the range from 20 to 60 °C. It was shown that the rheological properties of the hydrogel can be optimized by varying the concentration and ratio of components. Due to the rigid structure of the CNCs, the hydrogel could be formed at a concentration of at least 5 wt%; however, it almost does not swell either in water with pH 5 or 7 or in the HBSS buffer. The introduction of aldehyde groups into the CNCs allows for the conjugation of physiologically active molecules containing primary amino groups due to the formation of imine bonds. Here, we used benzocaine as a model drug for conjugation with CNC hydrogel. The resulting drug-conjugated hydrogel demonstrated the stability of formulation at pH 7 and a pH-sensitive release of benzocaine due to the accelerated hydrolytic cleavage of the imine bond at pH < 7. The developed drug-conjugated hydrogel is promising as wound dressings for local anesthesia.

Natural polysaccharides and their derivatives as potential medical materials and drug delivery systems for the treatment of peripheral nerve injuries

Peripheral nerve repair following injury is one of the most serious problems in neurosurgery. Clinical outcomes are often unsatisfactory and associated with a huge socioeconomic burden. Several studies have revealed the great potential of biodegradable polysaccharides for improving nerve regeneration. We review here the promising therapeutic strategies involving different types of polysaccharides and their bio-active composites for promoting nerve regeneration. Within this context, polysaccharide materials widely used for nerve repair in different forms are highlighted, including nerve guidance conduits, hydrogels, nanofibers and films. While nerve guidance conduits and hydrogels were used as main structural scaffolds, the other forms including nanofibers and films were generally used as additional supporting materials. We also discuss the issues of ease of therapeutic implementation, drug release properties and therapeutic outcomes, together with potential future directions of research.

Peptide Stereocomplexation Orchestrates Supramolecular Assembly of Hydrogel Biomaterials

Stereocomplexation, or specific interactions among complementary stereoregular macromolecules, is burgeoning as an increasingly impactful design tool, exerting exquisite control of material structure and properties. Since stereocomplexation of polymers produces remarkable transformations in mechanics, morphology, and degradation, we sought to leverage stereocomplexation to tune these properties in peptide-based biomaterials. We found that blending the pentapeptides l- and d-KYFIL triggers dual mechanical and morphological transformations from stiff fibrous hydrogels into less stiff networks of plates, starkly contrasting prior reports that blending l- and d-peptides produces stiffer fibrous hydrogels than the individual constituents. The morphological transformation of KYFIL in phosphate-buffered saline from fibers that entangle into hydrogels to plates that cannot entangle explains the accompanying mechanical transformation. Moreover, the blends shield l-KYFIL from proteolytic degradation, producing materials with comparable proteolytic stability to d-KYFIL but with distinct 2D plate morphologies that in biomaterials may promote unique therapeutic release profiles and cell behavior. To confirm that these morphological, mechanical, and stability changes arise from differences in molecular packing as in polymer stereocomplexation, we acquired X-ray diffraction patterns, which showed l- and d-KYFIL to be amorphous and their blends to be crystalline. Stereocomplexation is particularly apparent in pure water, where l- and d-KYFIL are soluble random coils, and their blends form β-sheets and gel within minutes. Our results highlight the role of molecular details, such as peptide sequence, in determining the material properties resulting from stereocomplexation. Looking forward, the ability of stereocomplexation to orchestrate supramolecular assembly and tune application-critical properties champions stereochemistry as a compelling design consideration.

Aggregation and Gelation Behavior of Stereocomplexed Four-Arm PLA-PEG Copolymers Containing Neutral or Cationic Linkers

Poly(lactide) (PLA) and poly(ethylene glycol) (PEG)-based hydrogels were prepared by mixing phosphate buffer saline (PBS, pH 7.4) solutions of four-arm (PEG-PLA)₂-R-(PLA-PEG)₂ enantiomerically pure copolymers having the opposite chirality of the poly(lactide) blocks. Dynamic Light Scattering, rheology measurements, and fluorescence spectroscopy suggested that, depending on the nature of the linker R, the gelation process followed rather different mechanisms. In all cases, mixing of equimolar amounts of the enantiomeric copolymers led to micellar aggregates with a stereocomplexed PLA core and a hydrophilic PEG corona. Yet, when R was an aliphatic heptamethylene unit, temperature-dependent reversible gelation was mainly induced by entanglements of PEG chains at concentrations higher than 5 wt.%. When R was a linker containing cationic amine groups, thermo-irreversible hydrogels were promptly generated at concentrations higher than 20 wt.%. In the latter case, stereocomplexation of the PLA blocks randomly distributed in micellar aggregates is proposed as the major determinant of the gelation process.

Insights on Some Polysaccharide Gel Type Materials and Their Structural Peculiarities

Global resources have to be used in responsible ways to ensure the world's future need for advanced materials. Ecologically friendly functional materials based on biopolymers can be successfully obtained from renewable resources, and the most prominent example is cellulose, the well-known most abundant polysaccharide which is usually isolated from highly available biomass (wood and wooden waste, annual plants, cotton, etc.). Many other polysaccharides originating from various natural resources (plants, insects, algae, bacteria) proved to be valuable and versatile starting biopolymers for a wide array of materials with tunable properties, able to respond to different societal demands. Polysaccharides properties vary depending on various factors (origin, harvesting, storage and transportation, strategy of further modification), but they can be processed into materials with high added value, as in the case of gels. Modern approaches have been employed to prepare (e.g., the use of ionic liquids as "green solvents") and characterize (NMR and FTIR spectroscopy, X ray diffraction spectrometry, DSC, electronic and atomic force microscopy, optical rotation, circular dichroism, rheological investigations, computer modelling and optimization) polysaccharide gels. In the present paper, some of the most widely used polysaccharide gels will be briefly reviewed with emphasis on their structural peculiarities under various conditions.

4D Printing of Hydrogels: Innovation in Material Design and Emerging Smart Systems for Drug Delivery

Advancements in the material design of smart hydrogels have transformed the way therapeutic agents are encapsulated and released in biological environments. On the other hand, the expeditious development of 3D printing technologies has revolutionized the fabrication of hydrogel systems for biomedical applications. By combining these two aspects, 4D printing (i.e., 3D printing of smart hydrogels) has emerged as a new promising platform for the development of novel controlled drug delivery systems that can adapt and mimic natural physio-mechanical changes over time. This allows printed objects to transform from static to dynamic in response to various physiological and chemical interactions, meeting the needs of the healthcare industry. In this review, we provide an overview of innovation in material design for smart hydrogel systems, current technical approaches toward 4D printing, and emerging 4D printed novel structures for drug delivery applications. Finally, we discuss the existing challenges in 4D printing hydrogels for drug delivery and their prospects.

Consumer Acceptance and Production of In Vitro Meat: A Review

In vitro meat (IVM) is a recent development in the production of sustainable food. The consumer perception of IVM has a strong impact on the commercial success of IVM. Hence this review examines existing studies related to consumer concerns, acceptance and uncertainty of IVM. This will help create better marketing strategies for IVM-producing companies in the future. In addition, IVM production is described in terms of the types of cells and culture conditions employed. The applications of self-organising, scaffolding, and 3D printing techniques to produce IVM are also discussed. As the conditions for IVM production are controlled and can be manipulated, it will be feasible to produce a chemically safe and disease-free meat with improved consumer acceptance on a sustainable basis.

Tuning Net Charge in Aliphatic Polycarbonates Alters Solubility and Protein Complexation Behavior

A synthetic strategy yielded polyelectrolytes and polyampholytes with tunable net charge for complexation and protein binding. Organocatalytic ring-opening polymerizations yielded aliphatic polycarbonates that were functionalized with both carboxylate and ammonium side chains in a post-polymerization, radical-mediated thiol-ene reaction. Incorporating net charge into the polymer architecture altered the chain dimensions in phosphate buffered solution in a manner consistent with self-complexation and complexation behavior with model proteins. A net cationic polyampholyte with 5% of carboxylate side chains formed large clusters rather than small complexes with bovine serum albumin, while 50% carboxylate polyampholyte was insoluble. Overall, the aliphatic polycarbonates with varying net charge exhibited different macrophase solution behaviors when mixed with protein, where self-complexation appears to compete with protein binding and larger-scale complexation.

Stereocomplex Polylactide for Drug Delivery and Biomedical Applications: A Review

Polylactide (PLA) is among the most common biodegradable polymers, with applications in various fields, such as renewable and biomedical industries. PLA features poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) enantiomers, which form stereocomplex crystals through racemic blending. PLA emerged as a promising material owing to its sustainable, eco-friendly, and fully biodegradable properties. Nevertheless, PLA still has a low applicability for drug delivery as a carrier and scaffold. Stereocomplex PLA (sc-PLA) exhibits substantially improved mechanical and physical strength compared to the homopolymer, overcoming these limitations. Recently, numerous studies have reported the use of sc-PLA as a drug carrier through encapsulation of various drugs, proteins, and secondary molecules by various processes including micelle formation, self-assembly, emulsion, and inkjet printing. However, concerns such as low loading capacity, weak stability of hydrophilic contents, and non-sustainable release behavior remain. This review focuses on various strategies to overcome the current challenges of sc-PLA in drug delivery systems and biomedical applications in three critical fields, namely anti-cancer therapy, tissue engineering, and anti-microbial activity. Furthermore, the excellent potential of sc-PLA as a next-generation polymeric material is discussed.

Biodegradable polyelectrolyte complexes of chitosan and partially crosslinked dextran phosphate with potential for biomedical applications

Polyelectrolyte complexes (PECs) are spontaneously formed by mixing oppositely charged polyelectrolyte solutions without the use of organic solvents and chemical crosslinkers are great candidate carriers for drug delivery. Herein, biodegradable antimicrobial polyelectrolyte complexes of chitosan - dextran phosphate (DPCS) containing cefazolin were developed and characterized in order to assess their suitability for biomedical applications. For this purpose, the simultaneous partial crosslinking and functionalization of dextran with phosphoric acid in a urea melt under reduced pressure were studied. The functional group content and molecular weight of dextran phosphate were varied in order to establish their influence on gel fraction yield, thermal properties and morphologies of the hydrogels. The stoichiometric PECs of DPCS showed good in vitro biocompatibility, pH sensitivity and biodegradability depending on the hydrogel composition. The release of drug from cefazolin-loaded DPCS hydrogels was through non-Fickian diffusion and displayed long sustained-release time. The drug-loaded hydrogels showed antimicrobial activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. The tunable degradation behavior under physiological conditions in combination with biocompatibility of the pristine DPCS and high antibacterial efficacy drug-loaded hydrogels may render the presented materials interesting for biomedical applications.

The gamut of perspectives, challenges, and recent trends for in situ hydrogels: a smart ophthalmic drug delivery vehicle

Polymers have a major role in the controlled delivery of pharmaceutical compounds to a targeted portion of the body. In this quest, a high priority research area is the targeted delivery of ophthalmic drugs to the interior regions of the eyes. Due to their complex anatomical/biochemical nature. This necessitates an advanced drug delivery cargo that could administer a therapeutic agent to the targeted location by evading various obstacles. The ongoing focus is to design an ophthalmic formulation by coupling it with a smart in situ forming polymeric hydrogel. These smart macromolecules have an array of unique theranostic properties and can utilize the in vivo biological parameters as a stimulus to change their macromolecular state from liquid to gel. The fast gelling hydrogel improves the corneal contact time, facilitates sustained drug release, resists the burst-out effect, and assists drug permeability to anterior regions. This review summarizes the rationale, scientific objectives, properties, and classification of the biologically important in situ hydrogels in the niche of ophthalmic drug delivery. The current trends and prospectives of the array of stimulus-responsive polymers, copolymers, and nanomaterials are discussed broadly. The crucial biointerfacial attributes with pros and cons are reviewed by investigating the effect of the nature of polymers as well as the ratio/percentage of additives and copolymers that influence the overall performance.

Hyaluronic Acid Macromer Molecular Weight Dictates the Biophysical Properties and in Vitro Cellular Response to Semisynthetic Hydrogels

In situ-forming hydrogels present a promising approach for minimally invasive cell transplantation and tissue regeneration. Among prospective materials, hyaluronic acid (HyA) has displayed great potential, owing to its inherent biocompatibility, biodegradation, and ease of chemical modification. However, current studies in the literature use a broad range of HyA macromer molecular weights (MWs) from <100 kDa to 1 MDa with no consensus regarding an optimal MW for a specific application. We investigated the effects of different HyA macromer MWs on key biophysical properties of semisynthetic hydrogels, such as viscosity, gelation time, shear storage modulus, molecular diffusion, and degradation. Using higher-MW HyA macromers leads to quicker gelation times and stiffer, more stable hydrogels with smaller mesh sizes. Assessment of the potential for HyA hydrogels to support network formation by encapsulated vascular cells derived from human-induced pluripotent stem cells reveals key differences between HyA hydrogels dependent on macromer MW. These effects must be considered holistically to address the multifaceted, nonmonotonic nature of HyA MW on hydrogel behavior. Our study identified an intermediate HyA macromer MW of 500 kDa as providing optimal conditions for a readily injectable, in situ-forming hydrogel with appropriate biophysical properties to promote vascular cell spreading and sustain vascular network formation in vitro.

Dynamic covalent bonds in self-healing, shape memory, and controllable stiffness hydrogels

A review of hydrogels containing dynamic bonds that are shown to provide benefits for applications including self-healing and stimuli-induced stiffness changes.

Injectable hydrogels: a new paradigm for osteochondral tissue engineering

Osteochondral tissue engineering has become a promising strategy for repairing focal chondral lesions and early osteoarthritis (OA), which account for progressive joint pain and disability in millions of people worldwide. Towards improving osteochondral tissue repair, injectable hydrogels have emerged as promising matrices due to their wider range of properties such as their high water content and porous framework, similarity to the natural extracellular matrix (ECM), ability to encapsulate cells within the matrix and ability to provide biological cues for cellular differentiation. Further, their properties such as those that facilitate minimally invasive deployment or delivery, and their ability to repair geometrically complex irregular defects have been critical for their success. In this review, we provide an overview of innovative approaches to engineer injectable hydrogels towards improved osteochondral tissue repair. Herein, we focus on understanding the biology of osteochondral tissue and osteoarthritis along with the need for injectable hydrogels in osteochondral tissue engineering. Furthermore, we discuss in detail different biomaterials (natural and synthetic) and various advanced fabrication methods being employed for the development of injectable hydrogels in osteochondral repair. In addition, in vitro and in vivo applications of developed injectable hydrogels for osteochondral tissue engineering are also reviewed. Finally, conclusions and future perspectives of using injectable hydrogels in osteochondral tissue engineering are provided.

Chemically Modified Gellan Gum Hydrogels with Tunable Properties for Use as Tissue Engineering Scaffolds

Gellan gum is a naturally occurring polymer that can cross-link in the presence of divalent cations to form biocompatible hydrogels. However, physically cross-linked gellan gum hydrogels lose their stability under physiological conditions, thus restricting the applications of these hydrogels in vivo. To improve the mechanical strength of the gels, we incorporated methacrylate into the gellan gum and chemically cross-linked the hydrogel through three polymerization methods: step growth through thiol-ene photoclick chemistry, chain-growth via photopolymerization, and mixed model in which both mechanisms were employed. Methacrylation was confirmed and quantified by proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy. The mechanical properties and chemistry of the cross-linked gels were systematically altered by varying the reaction conditions. The compression moduli of the resulting hydrogels ranged between 6.4 and 17.2 kPa. The swelling ratios of the hydrogels were correlated with the compression moduli and affected by the addition of calcium. In vitro enzymatic degradation rate was found to depend on the degree of methacrylation. NIH/3T3 fibroblast cell proliferation and morphology were related to substrate stiffness, with a high stiffness leading generally to higher proliferation. The proliferation is further affected by the thiol-ene ratio. These results suggest that a hydrogel platform based on the gellan gum can offer versatile chemical modifications and tunable mechanical properties. The influence of these substrates on cell behavior suggests that the gellan gum hydrogels have the flexibility to be engineered for a variety of biomaterials applications.

On the parallelism between the mechanisms behind chromatography and drug delivery: the role of interactions with a stationary phase

A huge number of studies and work in the drug delivery literature are focused on understanding and modeling transport phenomena, the pivotal point for a good device design. The rationalization of all phenomena involved is fundamental, but several concerns arise leaving many issues unsolved. In order to change the point of view we decided to focus our attention on the parallelisms between two fields that seem to be very far from each other: chromatography and drug release. Taking advantages of the studies conducted by many researchers using chromatographic columns we decided to explain all the phenomena involved in drug delivery considering sodium ibuprofen (IP) molecules as analytes and hydrogel as a stationary phase. In particular, we considered not only diffusion, but also drug-polymer interactions as adsorption on the stationary phase and drug-drug interactions as aggregation of analytes. The hydrogel investigated is a promising formulation made of agarose and carbomer 974p (AC) loaded with IP, a non-steroidal common anti-inflammatory drug. The self-diffusion coefficient of IP in AC formulations was measured by using an innovative method based on a magic angle spinning NMR spectroscopic technique to produce high resolution (liquid-like) spectra. This method (HR-MAS NMR) is used in combination with pulsed field gradient spin echo (PGSE) liquid-state techniques. The model predictions satisfactorily match with the experimental data obtained in water and the gel environment, indicating that the model presented here, despite its simplicity, is able to describe the key phenomena governing the device behavior and could be used to rationalize the experimental activity.

Chitosan-based hydrogels: From preparation to biomedical applications

The advances in the field of biomaterials have led to several studies on alternative biocompatible devices and to their development focusing on their properties, benefits, limitations, and utilization of alternative resources. Due to their advantages like biocompatibility, biodegradability, and low cost, polysaccharides have been widely used in the development of hydrogels. Among the polysaccharides studied on hydrogels preparation, chitosan (pure or combined with natural/synthetic polymers) have been widely investigated for use in biomedical field. In view of potential applications of chitosan-based hydrogels, this review focuses on the most recent progress made with respect to preparation, properties, and their salient accomplishments for drug delivery and tissue engineering.

A microscopic view of graphene-oxide/poly(acrylic acid) physical hydrogels: effects of polymer charge and graphene oxide loading

In this work we have examined in detail by means of fully atomistic molecular dynamics simulations, physical hydrogels formed by a polymer electrolyte, poly(acrylic acid), and graphene oxide, at two different charging states of the polymer and two different graphene oxide concentrations. It was found that variations of these parameters incurred drastic changes in general morphological characteristics of the composite materials, the degree of physical adsorption of polyelectrolyte chains onto the graphene oxide surface, the polymer dynamic response at local and global length scales, in the charge distributions around the components, and in the mobility of the counterions. All these microscopic features are expected to significantly affect macroscopic physical properties of the hydrogels, such as their mechanical responses and their electrical behaviors.

Hydrogel-Based Materials for Delivery of Herbal Medicines

Herbal medicine, as an integral component of oriental medicine, has assimilated into the lives of Asian people for millennia. The therapeutic efficiency of herbal extracts and ingredients has, however, been limited by various factors, including the lack of targeting capacity and poor bioavailability. Hydrogels are hydrophilic polymer networks that can imbibe a substantial amount of fluids. They are biocompatible, and may enable sustained drug release. Hydrogels, therefore, have attracted widespread studies in pharmaceutical formulation. This article first reviews the latest progress in the development of hydrogel-based materials as carriers of herbal medicines, followed by a discussion of the relationships between hydrogel properties and carrier performance. Finally, the promising potential of using hydrogels to combine medicinal herbs with synthetic drugs in one single treatment will be highlighted as an avenue for future research.

Poly(lactic acid) based hydrogels

Polylactide (PLA) and its copolymers are hydrophobic polyesters used for biomedical applications. Hydrogel medicinal implants have been used as drug delivery vehicles and scaffolds for tissue engineering, tissue augmentation and more. Since lactides are non-functional, they are copolymerized with hydrophilic monomers or conjugated to a hydrophilic moiety to form hydrogels. Copolymers of lactic and glycolic acids with poly(ethylene glycol) (PEG) provide thermo-responsive hydrogels. Physical crosslinking mechanisms of PEG-PLA or PLA-polysaccharides include: lactic acid segment hydrophobic interactions, stereocomplexation of D and L-lactic acid segments, ionic interactions, and chemical bond formation by radical or photo crosslinking. These hydrogels may also be tailored as stimulus responsive (pH, photo, or redox). PLA and its copolymers have also been polymerized to include urethane bonds to fabricate shape memory hydrogels. This review focuses on the synthesis, characterization, and applications of PLA containing hydrogels.

Sulfamethazine-based pH-sensitive hydrogels with potential application for transcatheter arterial chemoembolization therapy

Transcatheter arterial chemoembolization (TACE) is the most common palliative therapy for unresectable hepatocellular carcinoma (HCC). The conventional TACE technique, which employs the Lipiodol® emulsion, has been widely used for human cancer treatments. However, this delivery system seems to be inconsistent and unstable in maintaining a high concentration of drugs at tumor sites. An alternative approach for TACE is loading drugs into a liquid embolic solution that exists as an injectable solution and can exhibit a sol-to-gel phase transition to form a solidified state once delivered to the tumor site. Here, we develop a novel sulfamethazine-based anionic pH-sensitive block copolymer with potential application as a radiopaque embolic material. The copolymer, named PCL-PEG-SM, and comprised of poly(ε-caprolactone), sulfamethazine, and poly(ethylene glycol), was fabricated by free radical polymerization. An aqueous solution of the developed copolymer underwent a sol-to-gel phase transition upon lowering the environmental pH to create a gel region that covered the physiological condition (pH 7.4, 37°C) and the low pH conditions at tumor sites (pH 6.5-7.0, 37°C). The release of doxorubicin (DOX) from DOX-loaded copolymer hydrogels could be sustained for more than 4weeks in vitro, and the released DOX retained its fully bioactivity via inhibition the proliferation of hepatic cancer cells. The radiopaque embolic formulations that were prepared by mixing copolymer solutions at pH 8.0 with Lipiodol®, a long-lasting X-ray contrast agent, could exhibit the gelation inside the tumor after intratumoral injection or intraarterial administration using a VX2 carcinoma hepatic tumor rabbit model. These results suggest that a novel anionic pH-sensitive copolymer has been developed with a potential application as a liquid radiopaque embolic solution for TACE of HCC.

STATE OF SIGNIFICANCE

Transcatheter arterial chemoembolization (TACE) has been widely used as a palliative treatment therapy for unresectable hepatocellular carcinoma (HCC). Conventional TACE technique, which usually employs emulsion of DOX-in-Lipiodol®, followed by an embolic agent, has significant limitation of inconsistency and lack of controlled release ability. To address these limitations of conventional TACE material system, we introduced a novel liquid radiopaque embolic material from our pH-sensitive hydrogel. The material has low viscosity that can be injected via a microcatheter, rather biocompatibility, and drug controlled release ability. Importantly, it can form gel in the tumor as well as tumoral vasculature in response to the lowered pH at the tumor site, which proved the potential for the use to treat HCC by TACE therapy.

A Novel Approach to Study Enzymatic Degradation of Ter-polymeric Beads for Gastrointestinal Drug Delivery: Synthesis and Characterization

The α-amylase induced enzymatic degradation of terpolymeric beads, composed of calcium alginate, starch and poly(ethylene) glycol, were studied for gastrointestinal drug delivery. The beads demonstrated faster degradation with increased enzyme activity in the range 0.64 to 2.24IU/mL. A linear relationship of the degradation rates and corresponding enzyme concentration indicate that degradation is governed by Michaelis-Menten kinetics. The degradation rate was enhanced with increases in starch content in the beads. The smaller value of KM (3.15 × 10−5 mol−1 dm−3) indicated higher enzyme-substrate affinity. The beads crosslinked with barium ions demonstrated slower degradation due to a higher degree of crosslinking in the beads. With increases in initial water content, the degradation was found to increase. In order to incorporate in vivo GI conditions, the degradation was also studied using a flow through diffusion cell (FTDC). The hydrogel beads exhibited slower degradation by FTDC compared to traditional in vitro methods and the degradation was dependent on the nature of the filler particles used in the diffusion cell.

Click reactive microgels as a strategy towards chemically injectable hydrogels

Doubly crosslinked microgels (DX microgels) are hydrogels constructed by covalently interlinked microgel particles, offering two levels of hierarchy within the network, the first one being the microgel and the second being the interlinked microgel network.

Zwitterionic cryogels for sustained release of proteins

The preparation of macroporous zwitterionic cryogels and their excellent protein encapsulation and sustained release properties are reported.