Synthetic Polymer Hydrogels Research Articles

Integrin α4 mediates ATDC5 cell adhesion to negatively charged synthetic polymer hydrogel leading to chondrogenic differentiation

Negatively charged synthetic hydrogels have been known to facilitate various cellular responses including cell adhesion, proliferation, and differentiation; however, the molecular mechanism of hydrogel-dependent control of cell behavior remains unclear. Recently, we reported that negatively charged poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel induces chondrogenic differentiation of ATDC5 cells via novel protein reservoir function. In this study, we identified the cell adhesion molecules binding to PAMPS gels that act as mechanoreceptors. First, we performed a pull-down assay by particle gels using cell membrane proteins of ATDC5, and found that multiple membrane proteins bound to the PAMPS gel, whereas the uncharged poly(N,N′-dimethylacrylamide) gel as control did not bind to any membrane proteins. Western blot analysis indicated differential binding of integrin (ITG) isoforms to the PAMPS gel, in which the α4 isoform, but not α5 and αv, efficiently bound to the PAMPS gel. ITG α4 knockdown decreased cell spreading of ATDC5 on PAMPS gels, whereas the enhanced expression increased the behavior. Furthermore, ITG α4 depletion suppressed PAMPS gel-induced expression of bone morphogenic protein (BMP) 4 contributing to chondrogenic differentiation, in concordance with the reduction of ERK activation. These results demonstrated that membrane protein binding to PAMPS gels occurred in a charge-dependent manner, and that ITG α4 plays a crucial role in cell spreading on PAMPS gels and acts as a mechanoreceptor triggering cellular signaling leads to chondrogenic differentiation.

Polymer Hydrogels to Guide Organotypic and Organoid Cultures

AbstractHuman organotypic and organoid cultures provide increasingly life‐like models of tissue/organ development and disease, enable more realistic drug screening, and may ultimately pave the way for new therapies. A broad variety of extracellular matrix‐based or inspired materials is instrumental in these approaches. In this review article, the foundations of the related materials design are summarized with an emphasis on the advantages and limitations of decellularized and reconstituted biopolymeric matrices as well as biohybrid and fully synthetic polymer hydrogel systems applied to enable specific organotypic and organoid cultures. Recent progress in the fabrication of defined hydrogel systems offering thoroughly tunable biochemical and biophysical properties is highlighted. Potentialities of hydrogel‐based approaches to address the persisting challenges of organoid technologies, namely scalability, connectivity/integration, reproducibility, parallelization, and in situ monitoring are discussed.

Hydrogels for Skeletal Muscle Regeneration

Skeletal muscle is made up of hundreds of multinucleated, aligned fibers that work together during contraction. While smaller injuries are typically able to be repaired by the body, large volumetric muscle loss (VML) typically results in loss of function. Tissue engineering (TE) applications that use cells seeded onto hydrogels are one potential option for regenerating the lost tissue. Hydrogels are described as soft crosslinked polymeric networks with high water content that simulates the body’s natural aqueous environment. They can be formulated from many different starting materials into biocompatible, biodegradable systems. Fabrication methods such as electrospinning, freeze-drying, molding, and 3D printing can be used with the hydrogel solution to form 3D structures. In this review, natural, semi-synthetic, synthetic, and composite hydrogels for skeletal muscle regeneration are discussed. It was ascertained that the majority of the current research focused on natural polymeric hydrogels including collagen, gelatin, agarose, alginate, fibrin, chitosan, keratin, and combinations of the aforementioned. This category was followed by a discussion of composite hydrogels, defined in this review as at least one synthetic and one natural polymer combined to form a hydrogel, and these are the next most favored materials. Synthetic polymer hydrogels came in third with semi-synthetic polymers, chemically modified natural polymers, being the least common. While many of the hydrogels show promise for skeletal muscle regeneration, continued investigation is needed in order to regenerate a functional muscle tissue replacement. Skeletal muscle tissue engineering focuses on regenerating large amounts of skeletal muscle tissue lost due to tumor removal, traumatic injuries, and/or disease. Neither natural repair processes by the body nor current medical interventions are able to completely restore function after volumetric muscle loss. Thus, scientists are investigating alternative approaches to regenerate the lost muscle, restore function, and increase patient quality of life. This review paper summarizes the research from 2013 to early 2018 using hydrogels, a soft material with a high water content, as a tool to regenerate muscle. The review is categorized into hydrogels made from natural materials, semi-synthetic materials, synthetic materials, and composite materials (at least one natural and one synthetic material combined).

Processing, Mechanical Properties and Bio-Applications of Silk Fibroin-Based High Strength Hydrogels

Hydrogels are an attractive class of materials that possess similar structural and functional characteristics to biological tissues, and demonstrate a diversity of applications in biomedical engineering. Silk fibroin (SF) is a unique natural polymer for its versatile formats, excellent processability, biocompatibility, tunable biodegradation and thus a good hydrogel candidate for bio-applications. Compared to synthetic polymer hydrogels, poor mechanical performance is still a fatal drawback that hinders the application of SF hydrogels. Researchers have attempted to develop strategies to construct silk fibroin-based high strength hydrogels (SF-HSHs). Herein, we review the processing approaches to prepare SF-HSHs with a focus on the gelation mechanisms. The mechanical properties of SF-HSHs are summarized under four categories according to the gelation mechanism, physical-crosslinked, dual-crosslinked, double network and composites. Furthermore, a brief description of the utility of SF-HSHs in biomedicine and devices is presented. Finally, the potential challenges and future development of SF-HSHs are briefly discussed. This review will enhance our understanding on the structure-property-function relationships of soft materials from natural polymers, and guide future biomedical applications of silk fibroin-based hydrogels.

Specific surface area of strongly swelling polymer hydrogels for agriculture

The study is the first attempt in soil physics to estimate the effective specific surface area of strongly swelling polymer hydrogels as soil conditioners of a new generation. Along with the standard assessment of water vapor desorption isotherms by the BET method, a new method for determining the specific surface area deduced from the slope of water retention curves was used. Water desorption isotherms and water retention curves were obtained by a dynamic sorption equilibrium method and by a new method of thermodesorption. The specific surface area values of synthetic polymer hydrogels ranged from 468 to 1029 m2/g. An innovative Russian product VM-P with amphiphilic filler in the form of dispersed peat had the maximum specific surface area among all studied types of hydrogels. Water absorption properties and dispersion of gels have a hysteresis caused, presumably, by the dynamics of dispersion in the cycles of wetting-drying.

Synthetic Extracellular Matrices with Nonlinear Elasticity Regulate Cellular Organization.

One of the promises of synthetic materials in cell culturing is that control over their molecular structures may ultimately be used to control their biological processes. Synthetic polymer hydrogels from polyisocyanides (PIC) are a new class of minimal synthetic biomaterials for three-dimensional cell culturing. The macromolecular lengths and densities of biofunctional groups that decorate the polymer can be readily manipulated while preserving the intrinsic nonlinear mechanics, a feature commonly displayed by fibrous biological networks. In this work, we propose the use of PIC gels as cell culture platforms with decoupled mechanical inputs and biological cues. For this purpose, different types of cells were encapsulated in PIC gels of tailored compositions that systematically vary in adhesive peptide (GRGDS) density, polymer length, and concentration; with the last two parameters controlling the gel mechanics. Both cancer and smooth muscle cells grew into multicellular spheroids with proliferation rates that depend on the adhesive GRGDS density, regardless of the polymer length, suggesting that for these cells, the biological input prevails over the mechanical cues. In contrast, human adipose-derived stem cells do not form spheroids but rather spread out. We find that the morphological changes strongly depend on the adhesive ligand density and the network mechanics; gels with the highest GRGDS densities and the strongest stiffening response to stress show the strongest spreading. Our results highlight the role of the nonlinear mechanics of the extracellular matrix and its synthetic mimics in the regulation of cell functions.

Sonochemically Synthesized Lignin Nanoparticles and its Application in the Development of Nanocomposite Hydrogel

Abstract The hydrophilic gels or hydrogels are chemically or physically crosslinked polymeric network which are capable in absorbing a large quantity of water in their three-dimensional polymeric network. In contrast with synthetic polymer hydrogels, biopolymeric hydrogels are biocompatible, flexible, biodegradable, and non-toxic, hence they have received a great attention in numerous biomedical, engineering, and industrial applications. Conventionally developed synthetic polymer [i.e., polyvinyl alcohol (PVA)] and biopolymer [i.e., chitosan (CS)] hydrogels have insignificant physical as well as chemical properties, which can be overcome by the development of these hydrogels in association with nanoparticles. The present study focuses on the synthesis of lignin nanoparticles derived from natural resources by using ultrasound and its application in the development of CS–PVA hydrogel. The nanoparticles were found to be in the range of 10–50 nm. Physical crosslinking method has been adopted for the development of hydrogel. Further to examine the thermal stability of hydrogel TGA was performed. Post addition of nanoparticles in CS–PVA hydrogel manifested a significant increase in the thermal stability. Considering numerous advantages of the proposed nanocomposite hydrogel, this could be possibly used in drug delivery, food packaging and wound dressing

Hydrogel Cryopreservation System: An Effective Method for Cell Storage.

At present, living cells are widely used in cell transplantation and tissue engineering. Many efforts have been made aiming towards the use of a large number of living cells with high activity and integrated functionality. Currently, cryopreservation has become well-established and is effective for the long-term storage of cells. However, it is still a major challenge to inhibit cell damage, such as from solution injury, ice injury, recrystallization and osmotic injury during the thawing process, and the cytotoxicity of cryoprotectants. Hence, this review focused on different novel gel cryopreservation systems. Natural polymer hydrogel cryopreservation, the synthetic polymer hydrogel cryopreservation system and the supramolecular hydrogel cryopreservation system were presented, respectively. Due to the unique three-dimensional network structure of the hydrogel, these hydrogel cryopreservation systems have the advantages of excellent biocompatibility for natural polymer hydrogel cryopreservation systems, designability for synthetic polymer hydrogel cryopreservation systems, and versatility for supramolecular hydrogel cryopreservation systems. To some extent, the different hydrogel cryopreservation methods can confine ice crystal growth and decrease the change rates of osmotic shock in cell encapsulation systems. It is notable that the cryopreservation of complex cells and tissues is demanded in future clinical research and therapy, and depends on the linkage of different methods.

Water absorption by decellularized dermis

Water absorption by decellularized dermis was investigated and compared with biopolymer and synthetic polymer hydrogels (glutaraldehyde-crosslinked gelatin and crosslinked poly(acrylamide) hydrogel, respectively). Porcine dermis was decellularized in an aqueous sodium dodecyl sulfate (SDS) solution. Histological evaluation revealed that the SDS-treated dermis has much larger gaps between collagen fibrils than non-treated dermis, and that water absorption depends on these gaps. Decellularized dermis has low water absorptivity and the absorption obeys Fick's second law. During absorption, the water diffusion rate decreases with time and occurs in two steps. The first is rapid absorption into the large gaps, followed by slow absorption by the collagen fiber layer. Because of the gaps, decellularized dermis can absorb more water than native dermis and shows different water absorption behavior to glutaraldehyde-crosslinked gelatin and crosslinked poly(acrylamide) hydrogels.

Synthetic polymeric biomaterials for wound healing: a review

Wounds are of a variety of types and each category has its own distinctive healing requirements. This realization has spurred the development of a myriad of wound dressings, each with specific characteristics. It is unrealistic to expect a singular dressing to embrace all characteristics that would fulfill generic needs for wound healing. However, each dressing may approach the ideal requirements by deviating from the ‘one size fits all approach’, if it conforms strictly to the specifications of the wound and the patient. Indeed, a functional wound dressing should achieve healing of the wound with minimal time and cost expenditures. This article offers an insight into several different types of polymeric materials clinically used in wound dressings and the events taking place at cellular level, which aid the process of healing, while the biomaterial dressing interacts with the body tissue. Hence, the significance of using synthetic polymer films, foam dressings, hydrocolloids, alginate dressings, and hydrogels has been reviewed, and the properties of these materials that conform to wound-healing requirements have been explored. A special section on bioactive dressings and bioengineered skin substitutes that play an active part in healing process has been re-examined in this work.

Molecular Engineering Mechanically Programmable Hydrogels with Orthogonal Functionalization

A unique orthogonally tunable synthetic polymer hydrogel with programmable elasticity is described herein. The temporal modulation of mechanical properties was achieved by an orthogonal sulfonium-containing synthon, acting both as crosslinkable motifs and as functionalizable handles for chemical modification of the gel. The kinetic formation of in-situ covalent cross-linked hydrogels with ionic features enabled time-dependent mechanical behavior over weeks, a critical parameter of biomimetic substrates for cell development. The elasticity of the dynamic hydrogel was approximately 2 orders of magnitude greater than that of the ionically cross-linked sample with constant stiffness. In addition, we achieved on-demand control of the elastic properties of the hydrogels by application of a thermal stimulus of 37 °C, which provides new avenues to regulate cell behavior and fate. Furthermore, sulfonium groups and styrenyl moieties within the network provided covalent attachment sites for molecules of interest via...

Decorating a Blank Slate Protein Hydrogel: A General and Robust Approach for Functionalizing Protein Hydrogels.

Protein hydrogels constructed from recombinant proteins have attracted increasing interests for fundamental biological studies as well as applications in biomedical engineering field. In such protein hydrogels, biochemical and physical properties of protein hydrogels are often coupled to each other, making it challenging to investigate the individual effect of chemical and physical cues on cells. Moreover, laborious engineering is often required to incorporate different protein ligands into such hydrogels. To address these challenges, functionalizing a blank slate protein hydrogel is an attractive approach. However, conjugating ligands to such a blank slate protein hydrogel is challenging, as existing bioconjugation methods developed in synthetic polymer hydrogels cannot be readily adapted for protein hydrogels, significantly impeding the use of this approach in the field. Here we report a facile, general, and robust method, which is based on the SpyCatcher-SpyTag chemistry, to covalently functionalize the "blank slate" of protein hydrogels using genetically encoded interacting partners. We demonstrate that this novel method enables covalent conjugation of a wide variety of ligands, including full-length intact folded proteins, to a blank slate protein hydrogel, and allows for the decoupling of biochemical and physical properties of hydrogels from each other and investigating the individual effect of biochemical and mechanical cues on cell behaviors. To our best knowledge, this is the first general approach enabling functionalization of protein hydrogels, and we anticipate that this novel approach will find a broad range of uses in protein-based biomaterials for applications in biomedical engineering.

Modulating Supramolecular Peptide Hydrogel Viscoelasticity Using Biomolecular Recognition.

Self-assembled peptide-based hydrogels are emerging materials that have been exploited for wound healing, drug delivery, tissue engineering, and other applications. In comparison to synthetic polymer hydrogels, supramolecular peptide-based gels have advantages in biocompatibility, biodegradability, and ease of synthesis and modification. Modification of the emergent viscoelasticity of peptide hydrogels in a stimulus responsive fashion is a longstanding goal in the development of next-generation materials. In an effort to selectively modulate hydrogel viscoelasticity, we report herein a method to enhance the elasticity of β-sheet peptide hydrogels using specific molecular recognition events between functionalized hydrogel fibrils and biomolecules. Two distinct biomolecular recognition strategies are demonstrated: oligonucleotide Watson-Crick duplex formation between peptide nucleic acid (PNA) modified fibrils with a bridging oligonucleotide and protein-ligand recognition between mannose modified fibrils with concanavalin A. These methods to modulate hydrogel elasticity should be broadly adaptable in the context of these materials to a wide variety of molecular recognition partners.

On-demand dissolution of modular, synthetic extracellular matrix reveals local epithelial-stromal communication networks.

Methods to parse paracrine epithelial-stromal communication networks are a vital need in drug development, as disruption of these networks underlies diseases ranging from cancer to endometriosis. Here, we describe a modular, synthetic, and dissolvable extracellular matrix (MSD-ECM) hydrogel that fosters functional 3D epithelial-stromal co-culture, and that can be dissolved on-demand to recover cells and paracrine signaling proteins intact for subsequent analysis. Specifically, synthetic polymer hydrogels, modified with cell-interacting adhesion motifs and crosslinked with peptides that include a substrate for cell-mediated proteolytic remodeling, can be rapidly dissolved by an engineered version of the microbial transpeptidase Sortase A (SrtA) if the crosslinking peptide includes a SrtA substrate motif and a soluble second substrate. SrtA-mediated dissolution affected only 1 of 31 cytokines and growth factors assayed, whereas standard protease degradation methods destroyed about half of these same molecules. Using co-encapsulated endometrial epithelial and stromal cells as one model system, we show that the dynamic cytokine and growth factor response of co-cultures to an inflammatory cue is richer and more nuanced when measured from SrtA-dissolved gel microenvironments than from the culture supernate. This system employs accessible, reproducible reagents and facile protocols; hence, has potential as a tool in identifying and validating therapeutic targets in complex diseases.

Stem Cell Delivery With Polymer Hydrogel for Treatment of Intervertebral Disc Degeneration: From 3D Culture to Design of the Delivery Device for Minimally Invasive Therapy.

Nucleus pulposus (NP) tissue damage can induce detrimental mechanical strain on the biomechanical performance of intervertebral discs (IVDs), causing subsequent disc degeneration. A novel, photocurable, injectable, synthetic polymer hydrogel (pHEMA-co-APMA grafted with PAA) has already demonstrated success in encapsulating and differentiating human mesenchymal stem cells (hMSCs) toward an NP phenotype during hypoxic conditions. After demonstration of promising results in our previous work, in this study we have further investigated the inclusion of mechanical stimulation and its impact on hMSC differentiation toward an NP phenotype through the characterization of matrix markers such as SOX-9, aggrecan, and collagen II. Furthermore, investigations were undertaken in order to approximate delivery parameters for an injection delivery device, which could be used to transport hMSCs suspended in hydrogel into the IVD. hMSC-laden hydrogel solutions were injected through various needle gauge sizes in order to determine its impact on postinjection cell viability and IVD tissue penetration. Interpretation of these data informed the design of a potential minimally invasive injection device, which could successfully inject hMSCs encapsulated in a UV-curable polymer into NP, prior to photo-cross-linking in situ.

Cross-Linked Hydrogels Formed through Diels-Alder Coupling of Furan- and Maleimide-Modified Poly(methyl vinyl ether-alt-maleic acid).

The Diels-Alder [4 + 2] cycloaddition between furan- and maleimide-functional polyanions was used to form cross-linked synthetic polymer hydrogels. Poly(methyl vinyl ether-alt-maleic anhydride) was reacted with furfurylamine or N-(2-aminoethyl)maleimide in acetonitrile to form pairs of furan- and maleimide-functionalized poly(methyl vinyl ether-alt-maleic acid)s. Mixtures of these mutually reactive polyanions in water gelled within 15 min to 18 h, depending on degree of functionalization and polymer concentrations. Solution and magic-angle spinning (1)H NMR were used to confirm the formation of the Diels-Alder adduct, to analyze competing hydrolytic side reactions, and demonstrate postgelation functionalization. The effect of the degree of furan and maleimide functionalization, polymer concentration, pH, and calcium ion concentration, on gelation time, gel mechanical properties, and equilibrium swelling, are described. Release of dextran as a model drug was studied using fluorescence spectroscopy, as a function of gel composition and calcium treatment.

Thermal-Responsive Behavior of a Cell Compatible Chitosan/Pectin Hydrogel.

Biopolymer hydrogels are important materials for wound healing and cell culture applications. While current synthetic polymer hydrogels have excellent biocompatibility and are nontoxic, they typically function as a passive matrix that does not supply any additional bioactivity. Chitosan (CS) and pectin (Pec) are natural polymers with active properties that are desirable for wound healing. Unfortunately, the synthesis of CS/Pec materials have previously been limited by harsh acidic synthesis conditions, which further restricted their use in biomedical applications. In this study, a zero-acid hydrogel has been synthesized from a mixture of chitosan and pectin at biologically compatible conditions. For the first time, we demonstrated that salt could be used to suppress long-range electrostatic interactions to generate a thermoreversible biopolymer hydrogel that has temperature-sensitive gelation. Both the hydrogel and the solution phases are highly elastic, with a power law index of close to -1. When dried hydrogels were placed into phosphate buffered saline solution, they rapidly rehydrated and swelled to incorporate 2.7× their weight. As a proof of concept, we removed the salt from our CS/Pec hydrogels, thus, creating thick and easy to cast polyelectrolyte complex hydrogels, which proved to be compatible with human marrow-derived stem cells. We suggest that our development of an acid-free CS/Pec hydrogel system that has excellent exudate uptake, holds potential for wound healing bandages.

Bioprinted Scaffolds for Cartilage Tissue Engineering.

Researchers are focusing on bioprinting technology as a viable option to overcome current difficulties in cartilage tissue engineering. Bioprinting enables a three-dimensional (3-D), free-form, computer-designed structure using biomaterials, biomolecules, and/or cells. The inner and outer shape of a scaffold can be controlled by this technology with great precision. Here, we introduce a hybrid bioprinting technology that is a co-printing process of multiple materials including high-strength synthetic polymer and cell-laden hydrogel. The synthetic polymer provides mechanical support for shape maintenance and load bearing, while the hydrogel provides the biological environment for artificial cartilage regeneration. This chapter introduces the procedures for printing of a 3-D scaffold using our hybrid bioprinting technology and includes the source materials for preparation of 3-D printing.

Three-dimensional hypoxic culture of human mesenchymal stem cells encapsulated in a photocurable, biodegradable polymer hydrogel: A potential injectable cellular product for nucleus pulposus regeneration

Nucleus pulposus (NP) tissue damage can induce detrimental mechanical stresses and strains on the intervertebral disc, leading to disc degeneration. This study demonstrates the potential of a novel, photo-curable, injectable, synthetic polymer hydrogel (pHEMA-co-APMA grafted with polyamidoamine (PAA)) to encapsulate and differentiate human mesenchymal stem cells (hMSC) towards a NP phenotype under hypoxic conditions which could be used to restore NP tissue function and mechanical properties. Encapsulated hMSC cultured in media (hMSC and chondrogenic) displayed good cell viability up to day 14. The genotoxicity effects of ultraviolet (UV) on hMSC activity confirmed the acceptability of 2.5min of UV light exposure to cells. Cytotoxicity investigations revealed that hMSC cultured in media containing p(HEMA-co-APMA) grafted with PAA degradation product (10% and 20%v/v concentration) for 14days significantly decreased the initial hMSC adhesion ability and proliferation rate from 24hrs to day 14. Successful differentiation of encapsulated hMSC within hydrogels towards chondrogenesis was observed with elevated expression levels of aggrecan and collagen II when cultured in chondrogenic media under hypoxic conditions, in comparison with culture in hMSC media for 14days. Characterization of the mechanical properties revealed a significant decrease in stiffness and modulus values of cellular hydrogels in comparison with acellular hydrogels at both day 7 and day 14. These results demonstrate the potential use of an in vivo photo-curable injectable, synthetic hydrogel with encapsulated hMSC for application in the repair and regeneration of NP tissue.

In vitro and in vivo evaluation of polymer hydrogels for hemorrhage control

In vitro and in vivo experimentation of various synthetic polymer hydrogels was conducted to establish some of the integral material properties that influence hemostasis. In vitro swelling experiments suggested that positive electrostatic charge was a key determinant of the ability of a polymer hydrogel to absorb physiological fluids, e.g. human plasma and blood. In vitro testing using unadulterated sheep blood suggested positive electrostatic charge and crosslink density were key determinants of the ability of a material to induce or enhance clot formation. Hydrogel formulations composed of higher amounts of positive electrostatic charge and lower crosslink density were able to effectively induce and enhance clot formation in the presence of a coagulation cascade activator. In vivo experimentation confirmed that hydrogels containing higher electrostatic charge and low crosslink density are more effective at fostering the formation of a robust hemostatic plug to control blood loss.