Cell-encapsulating Hydrogels Research Articles

Novel nanocomposite scaffold based on gelatin/PLGA-PEG-PLGA hydrogels embedded with TGF-β1 for chondrogenic differentiation of human dental pulp stem cells in vitro

In the current study, a novel nanocomposite hydrogel scaffold comprising of natural-based gelatin and synthetic-based (poly D, L (lactide-co-glycolide) -b- poly (ethylene glycol)-b- poly D, L (lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymer was developed and loaded with transforming growth factor- β1 (TGF-β1).Synthesized scaffolds' chemical structure was examined by 1H NMR and ATR-FTIR. Scanning electron microscopy (SEM) confirmed particle size and morphology of the prepared nanoparticles as well as the scaffolds. The morphology analysis revealed a porous interconnected structure throughout the scaffold with a pore size dimension of about 202.05 µm. The swelling behavior, in vitro degradation, mechanical properties, density, and porosity were also evaluated. Phalloidin/DAPI staining was utilized for confirming the extended cytoskeleton of the chondrocytes. Alcian blue staining was conducted to determine cartilaginous matrix sulfated glycosaminoglycan (sGAG) synthesis. Eventually, over a period of 21 days, a real-time RT-PCR analysis was applied to measure the mRNA expression of chondrogenic marker genes, type-II collagen, SOX 9, and aggrecan, in hDPSCs cultured for up to 21 days to study the influence of gelatin/PLGA-PEG-PLGA-TGF-β1 hydrogels on hDPSCs. The findings of the cell-encapsulating hydrogels analysis suggested that the adhesion, viability, and chondrogenic differentiation of hDPSCs improved by gelatin/PLGA-PEG-PLGA-TGF-β1 nanocomposite hydrogels. These data supported the conclusion that gelatin/PLGA-PEG-PLGA-TGF-β1 nanocomposite hydrogels render the features that allow thein vitrofunctionality of encapsulated hDPSCs and hence can contribute the basis for new effective strategies for the treatment of cartilage injuries.

Induction of mesenchymal stem cell differentiation by co-culturing with mature cells in double-layered 2-methacryloyloxyethyl phosphorylcholine polymer hydrogel matrices.

The effects of differentiated cells on stem cell differentiation were analyzed via co-culturing using a cell-encapsulated double-layered hydrogel system. As a polymer hydrogel matrix, a water-soluble zwitterionic polymer having both a 2-methacryloyloxyethyl phosphorylcholine unit and a p-vinylphenylboronic acid unit (PMBV), was complexed spontaneously with poly(vinyl alcohol) (PVA) under mild cell culture conditions. The creep modulus of the hydrogel was controlled by changing the composition of the polymer in the solution. Mouse mesenchymal stem cells (MSCs), C3H10T1/2 cells, were encapsulated into PMBV/PVA hydrogels and cultured. In the PMBV/PVA hydrogel with a lower creep modulus (0.40 kPa), proliferation of C3H10T1/2 cells occurred, and the formation of cell aggregates was observed. On the other hand, a higher creep modulus (1.7 kPa) of the hydrogel matrix prevented cell proliferation. Culturing C3H10T1/2 cells encapsulated in the PMBV/PVA hydrogel in the presence of bone morphogenetic protein-2 increased the activity of intracellular alkaline phosphatase (ALP). This indicated that C3H10T1/2 cells differentiated into mature osteoblasts. When the C3H10T1/2 cells encapsulated in the PMBV/PVA hydrogel were cultured in combination with the mature osteoblasts in the hydrogel by a close contacting double-layered hydrogel structure, higher ALP activity was observed compared with the cells cultured separately. It was considered that the differentiation of C3H10T1/2 cells in the hydrogel layer was induced by cytokines diffused from mature osteoblasts encapsulated in another hydrogel layer. It could be concluded that the PMBV/PVA hydrogel system provides a good way to observe the effects of the surrounding cells on cell function in three-dimensional culture.

Rational formulation design of injectable thermosensitive chitosan-based hydrogels for cell encapsulation and delivery

This work reports a rational design of injectable thermosensitive chitosan systems for cell encapsulation and delivery. Using mixtures of two phosphate salts, beta-glycerophosphate and ammonium hydrogen phosphate, we demonstrate that the pH and the osmolarity can be adjusted separately by varying the molar ratios between the salts and the d-glucosamine monomers. We found the existence of a critical temperature above which gelation time decays following a power-law. This gelation kinetics can be finely tuned through the pH and salt-glucosamine ratios. Formulations having physiological pH and osmolarity were produced for chitosan concentrations ranging from 0.4 to 0.9 wt%. They remain liquid for more than 2 h at 20 °C and form a macroporous gel within 2 min at 37 °C. In vitro encapsulation of pre-osteoblastic cells and gingival fibroblasts showed homogeneous cell distribution and good cell viability up to 24 h. Such an approach provides a valuable platform to design thermosensitive cell-laden systems.

Injectable Acylhydrazone-Linked RAFT Polymer Hydrogels for Sustained Protein Release and Cell Encapsulation.

A new class of temperature responsive polymer, termed PADO, is synthesized by reversible addition-fragmentation chain-transfer polymerization. Synthesized from copolymerization of diacetone acrylamide (DAAM), di(ethylene glycol) ethyl ether acrylate, and oligo(ethylene glycol) methyl ether acrylate, PADO polymer phase separates at temperature above its lower critical solution temperature (36-42°C) due to enhanced hydrophobic interactions between the short ethylene glycol side chains. Solution of PADO polymers exhibit injectable shear-thinning properties and reach sol-gel transition rapidly (<5min) at 37°C.Whenthe ketone moieties on DAAM are linked by adipic acid dihydrazdie, PADO polymers form crosslinked and injectable acylhydrazone hydrogels, which are hydrolytically degradable at a mild acidic environment owing to the pH sensitive acylhydrazone bonds. The pH-responsive degradation kinetics can be controlled by tuning polymer contents and ketone/hydrazide ratio. Importantly, the injectable PADO hydrogels are highly cytocompatible and can be easily formulated for pH-responsive sustained protein delivery.

Cell-Incorporated Bioactive Tissue Engineering Scaffolds made by Concurrent Cell Electrospinning and Emulsion Electrospinning

Electrospun fibrous scaffolds attract great attention in tissue engineering owing to their high similarity in architecture to the extracellular matrix (ECM) that support cell attachment and growth in human bodies. Although they have shown superiority in promoting cell attachment and proliferation on their surfaces and hence, hold great promise for the regeneration of body tissues, the research still faces a great challenge of three-dimensional (3D) cell incorporation in electrospun scaffolds to form thick and cell-dense constructs because deep cell infiltration is hard to achieve in conventional electrospun scaffolds that normally have very small diameters of interconnected pores. Such hindrance has severely limited the clinical application of electrospun fibrous scaffolds to repair/regenerate various body tissues, particularly those with complex anatomies. To address this challenge, we have developed a concurrent cell electrospinning and emulsion electrospinning technique for fabricating bioactive bio-hybrid scaffolds with 3D and high-density cell incorporation. Through concurrent electrospinning, cell-encapsulated hydrogel fibers (“cell fibers”) and growth factor-containing ultrafine fibers are simultaneously deposited to form two-component scaffolds (i.e., scaffolds composed of two types of fibers) according to the design. With the breakup of cell fibers, live cells with well-preserved cell viability are released in situ inside the scaffolds, resulting in the creation of cell-incorporated bioactive scaffolds with ECM-mimicking fibrous architectures and 3D and high-density incorporation of cells. The growth and functions of incorporated cells in the scaffolds can be enhanced by the released growth factor from the emulsion electrospun fibrous component. The bioactive bio-hybrid scaffolds fabricated via concurrent electrospinning mimic the cell-matrix organization of body tissues and therefore have great potential for regenerating body tissues such as tendon and ligament.

Lighting the Path: Light Delivery Strategies to Activate Photoresponsive Biomaterials In Vivo

AbstractPhotoresponsive biomaterials are experiencing a transition from in vitro models to in vivo demonstrations that point toward clinical translation. Dynamic hydrogels for cell encapsulation, light‐responsive carriers for controlled drug delivery, and nanomaterials containing photosensitizers for photodynamic therapy are relevant examples. Nonetheless, the step to the clinic largely depends on their combination with technologies to bring light into the body. This review highlights the challenge of photoactivation in vivo, and presents strategies for light management that can be adopted for this purpose. The authors’ focus is on technologies that are materials‐driven, particularly upconversion nanoparticles that assist in “direct path” light delivery through tissue, and optical waveguides that “clear the path” between external light source and in vivo target. The authors’ intention is to assist the photoresponsive biomaterials community transition toward medical technologies by presenting light delivery concepts that can be integrated with the photoresponsive targets. The authors also aim to stimulate further innovation in materials‐based light delivery platforms by highlighting needs and opportunities for in vivo photoactivation of biomaterials.

Degradable alginate hydrogel microfiber for cell-encapsulation based on alginate lyase loaded nanoparticles

Cell-encapsulation in hydrogels is a promising strategy for tissue engineering and cell therapy, particularly alginate hydrogels as they immobilize the cells in porous matrices, which allows an exchange of nutrients and oxygen and protects the cells from immune clearance. However, alginate hydrogels have one key limitation that they are degraded gradually in the physiological environment providing undesirable character for cell-cell interaction and tissue formation. In this work, we produced cells encapsulated in hydrogel microfibers with accelerated degradation to promote cell proliferation by simultaneously integrating alginate lyase loaded poly(lactide-co-glycolide) (PLGA) nanoparticles into the cell-laden alginate. The microfluidic laminar flow method was employed to fabricates the cell encapsulated microfibers via an aqueous two-phase system (ATPS). The structure of the microfiber scaffold was observed, and the degree of swelling and degradation rate was investigated. This paper presented that the degradation of the alginate microfibers was controllable and tunable, while promoted cell proliferation. The degradable cells encapsulated alginate microfibers in this study were anticipated for further development of novel therapies for tissue regeneration.

Thiol-Methylsulfone-Based Hydrogels for Cell Encapsulation: Reactivity Optimization of Aryl-Methylsulfone Substrate for Fine-Tunable Gelation Rate and Improved Stability.

Hydrogels are widely used as hydrated matrices for cell encapsulation in a number of applications, spanning from advanced 3D cultures and tissue models to cell-based therapeutics and tissue engineering. Hydrogel formation in the presence of living cells requires cross-linking reactions that proceed efficiently under close to physiological conditions. Recently, the nucleophilic aromatic substitution of phenyl-oxadiazole (Ox) methylsulfones (MS) by thiols was introduced as a new cross-linking reaction for cell encapsulation. Reported poly(ethylene glycol) (PEG)-based hydrogels featured tunable gelation times within seconds to a few minutes within pH 8.0 to 6.6 and allowed reasonably good mixing with cells. However, their rapid degradation prevented cell cultures to be maintained beyond 1 week. In this Article, we present the reactivity optimization of the heteroaromatic ring of the MS partner to slow down the cross-linking kinetics and the degradability of the derived hydrogels. New MS substrates based on phenyl-tetrazole (Tz) and benzothiazole (Bt) rings, with lower electrophilicity than Ox, were synthesized by simple pathways. When mixed with PEG-thiol, the novel PEG-MS extended the working time of precursor mixtures and allowed longer term cell culture. The Tz-based MS substrate was identified as the best candidate, as it is accessible by simple chemical reactions from cost-effective reactants, hydrogel precursors show good stability in aqueous solution and keep high chemoselectivity for thiols, and the derived Tz gels support cell cultures for >2 weeks. The Tz system also shows tunable gelation kinetics within seconds to hours and allows comfortable manipulation and cell encapsulation. Our findings expand the toolkit of thiol-mediated chemistry for the synthesis of hydrogels with improved properties for laboratory handling and future automatization.

Holographic Display-Based Control for High-Accuracy Photolithography of Cellular Micro-Scaffold With Heterogeneous Architecture

Engineered three-dimensional (3D) tissues that replicate composite in-vivo architectures have shown great potential for use in biomedical research. Cell-encapsulated hydrogel micro-scaffolds have been applied widely as basic building blocks to construct these artificial tissues. However, accurate reproduction of heterogeneous hierarchical structures and different regional mechanical properties inside a single integrated micro-scaffold that mimics physiologically relevant complex tissues presents a major challenge. Here, we propose a novel fabrication control algorithm to achieve high-accuracy photolithography of micro-scaffolds that recapitulate the high fidelity of native tissues by adjusting a 3D digital mask using holographic imaging feedback. By performing digital holographic reconstruction to express the hydrogel photocuring process in a matrix form and presetting the curing duration for each discrete point, the 3D digital mask was predefined to represent the required customized micro-scaffold. During fabrication, the UV exposure area was divided into microscaled grids with relatively uniform irradiance to control the photocuring process discretely for every local region in the entire architecture. The holographic imaging feedback allowed the curing duration of each grid to be adjusted in real-time, which enabled accurate reproduction of a 3D construct integrated with different microstructural morphologies and mechanical properties. Finally, PEGDA and GelMA, as typical biomaterials, were used to fabricate the heterogeneous hierarchical micro-scaffold. The structural accuracy was improved from 65 m to 12 m and the Youngs modulus was controlled flexibly in the 27.93.5 to 91.23.5 kPa range. With different local mechanical properties, cell migration in the micro-scaffold from soft to stiff areas is observed successfully.

Bilayered, peptide-biofunctionalized hydrogels for in vivo osteochondral tissue repair

Osteochondral defects present a unique clinical challenge due to their combination of phenotypically distinct cartilage and bone, which require specific, stratified biochemical cues for tissue regeneration. Furthermore, the articular cartilage exhibits significantly worse regeneration than bone due to its largely acellular and avascular nature, prompting significant demand for regenerative therapies. To address these clinical challenges, we have developed a bilayered, modular hydrogel system that enables the click functionalization of cartilage- and bone-specific biochemical cues to each layer. In this system, the crosslinker poly(glycolic acid)-poly(ethylene glycol)-poly(glycolic acid)-di(but-2-yne-1,4-dithiol) (PdBT) was click conjugated with either a cartilage- or bone-specific peptide sequence of interest, and then mixed with a suspension of thermoresponsive polymer and mesenchymal stem cells (MSCs) to generate tissue-specific, cell-encapsulated hydrogel layers targeting the cartilage or bone. We implanted bilayered hydrogels in rabbit femoral condyle defects and investigated the effects of tissue-specific peptide presentation and cell encapsulation on osteochondral tissue repair. After 12 weeks implantation, hydrogels with a chondrogenic peptide sequence produced higher histological measures of overall defect filling, cartilage surface regularity, glycosaminoglycan (GAG)/cell content of neocartilage and adjacent cartilage, and bone filling and bonding compared to non-chondrogenic hydrogels. Furthermore, MSC encapsulation promoted greater histological measures of overall defect filling, cartilage thickness, GAG/cell content of neocartilage, and bone filling. Our results establish the utility of this click functionalized hydrogel system for in vivo repair of the osteochondral unit. Statement of significanceOsteochondral repair requires mimicry of both cartilage- and bone-specific biochemical cues, which are highly distinct. While traditional constructs for osteochondral repair have mimicked gross compositional differences between the cartilage and bone in mineral content, mechanical properties, proteins, or cell types, few constructs have recapitulated the specific biochemical cues responsible for the differential development of cartilage and bone.In this study, click biofunctionalized, bilayered hydrogels produced stratified presentation of developmentally inspired peptide sequences for chondrogenesis and osteogenesis. This work represents, to the authors’ knowledge, the first application of bioconjugation chemistry for the simultaneous repair of bone and cartilage tissue. The conjugation of tissue-specific peptide sequences successfully promoted development of both cartilage and bone tissues in vivo.

Injectable Supramolecular Polymer-Nanoparticle Hydrogels for Cell and Drug Delivery Applications

These methods describe how to formulate injectable, supramolecular polymer-nanoparticle (PNP) hydrogels for use as biomaterials. PNP hydrogels are composed of two components: hydrophobically modified cellulose as the network polymer and self-assembled core-shell nanoparticles that act as non-covalent cross linkers through dynamic, multivalent interactions. These methods describe both the formation of these self-assembled nanoparticles through nanoprecipitation as well as the formulation and mixing of the two components to form hydrogels with tunable mechanical properties. The use of dynamic light scattering (DLS) and rheology to characterize the quality of the synthesized materials is also detailed. Finally, the utility of these hydrogels for drug delivery, biopharmaceutical stabilization, and cell encapsulation and delivery is demonstrated through in vitro experiments to characterize drug release, thermal stability, and cell settling and viability. Due to its biocompatibility, injectability, and mild gel formation conditions, this hydrogel system is a readily tunable platform suitable for a range of biomedical applications.

Injectable Supramolecular Polymer-Nanoparticle Hydrogels for Cell and Drug Delivery Applications.

These methods describe how to formulate injectable, supramolecular polymer-nanoparticle (PNP) hydrogels for use as biomaterials. PNP hydrogels are composed of two components: hydrophobically modified cellulose as the network polymer and self-assembled core-shell nanoparticles that act as non-covalent cross linkers through dynamic, multivalent interactions. These methods describe both the formation of these self-assembled nanoparticles through nanoprecipitation as well as the formulation and mixing of the two components to form hydrogels with tunable mechanical properties. The use of dynamic light scattering (DLS) and rheology to characterize the quality of the synthesized materials is also detailed. Finally, the utility of these hydrogels for drug delivery, biopharmaceutical stabilization, and cell encapsulation and delivery is demonstrated through in vitro experiments to characterize drug release, thermal stability, and cell settling and viability. Due to its biocompatibility, injectability, and mild gel formation conditions, this hydrogel system is a readily tunable platform suitable for a range of biomedical applications.

Hydrogel Encapsulation of Mesenchymal Stem Cells and Their Derived Exosomes for Tissue Engineering.

Tissue engineering has been an inveterate area in the field of regenerative medicine for several decades. However, there remains limitations to engineer and regenerate tissues. Targeted therapies using cell-encapsulated hydrogels, such as mesenchymal stem cells (MSCs), are capable of reducing inflammation and increasing the regenerative potential in several tissues. In addition, the use of MSC-derived nano-scale secretions (i.e., exosomes) has been promising. Exosomes originate from the multivesicular division of cells and have high therapeutic potential, yet neither self-replicate nor cause auto-immune reactions to the host. To maintain their biological activity and allow a controlled release, these paracrine factors can be encapsulated in biomaterials. Among the different types of biomaterials in which exosome infusion is exploited, hydrogels have proven to be the most user-friendly, economical, and accessible material. In this paper, we highlight the importance of MSCs and MSC-derived exosomes in tissue engineering and the different biomaterial strategies used in fabricating exosome-based biomaterials, to facilitate hard and soft tissue engineering.

Bilayered, Peptide Biofunctionalized Hydrogels for in Vivo Osteochondral Tissue Repair

Osteochondral defects present a unique clinical challenge due to their combination of phenotypically distinct cartilage and bone, which require specific, stratified biochemical cues for tissue regeneration. Furthermore, the articular cartilage exhibits significantly worse regeneration than bone due to its largely acellular and avascular nature, prompting significant demand for regenerative therapies. To address these clinical challenges, we have developed a bilayered, modular hydrogel system that enables the click functionalization of cartilage- and bone-specific biochemical cues to each layer. In this system, the crosslinker poly(glycolic acid)-poly(ethylene glycol)-poly(glycolic acid)-di(but-2-yne-1,4-dithiol) (PdBT) was click conjugated with either a cartilage- or bone-specific peptide sequence of interest, and then mixed with a suspension of thermoresponsive polymer and mesenchymal stem cells (MSCs) to generate tissue-specific, cell-encapsulated hydrogel layers targeting the cartilage or bone. We implanted bilayered hydrogels in rabbit femoral condyle defects and investigated the effects of tissue-specific peptide presentation and cell encapsulation on osteochondral tissue repair. After 12 weeks implantation, hydrogels with a chondrogenic peptide sequence produced higher histological measures of overall defect filling, cartilage surface regularity, glycosaminoglycan (GAG)/cell content of neocartilage and adjacent cartilage, and bone filling and bonding compared to non-chondrogenic hydrogels. Furthermore, MSC encapsulation promoted greater histological measures of overall defect filling, cartilage thickness, GAG/cell content of neocartilage, and bone filling. Our results establish the utility of this click functionalized hydrogel system for in vivo repair of the osteochondral unit.

Challenges and solutions for fabrication of three-dimensional cocultures of neural cell-loaded biomimetic constructs

Fabrication of three-dimensional (3D) constructs to model body tissues and organs can contribute to research into tissue development and models for studying disease, as well as supporting preclinical drug screening in vitro. Furthermore, 3D constructs can also be used for diagnosis and therapy of disease conditions via lab on a chip and microarrays for diagnosis and engineered products for tissue repair, replacement, and regeneration. While cell culture approaches for studying tissue development and disease in two dimensions are long-established, the translation of this knowledge into 3D environments remains a fertile field of research. In this Tutorial, we specifically focus on the application of biosynthetic hydrogels for neural cell encapsulation. The Tutorial briefly covers background on using biosynthetic hydrogels for cell encapsulation, as well as common fabrication techniques. The Methods section focuses on the hydrogel design and characterization, highlighting key elements and tips for more effective approaches. Coencapsulation of different cell types, and the challenges associated with different growth and maintenance requirements, is the main focus of this Tutorial. Much care is needed to blend different cell types, and this Tutorial provides tips and insights that have proven successful for 3D coculture in biosynthetic hydrogels.

Preparation of Microporous Hydrogel Sponges for 3D Perfusion Culture of Mammalian Cells

Three-dimensional (3D) perfusable organ models, primarily composed of liver cells, are expected as an efficient tool for in vitro cell-based drug screening and development. Various types of hydrogel-based 3D cell culture systems have been developed, but the lack in proper techniques to form vasculature networks in the hydrogel matrices results in inefficient supply of oxygen and nutrition to the cells. Here we propose a facile strategy to creating a perfusable hydrogel-based liver cell culture system. We utilized a bicontinuous dispersion of an aqueous two-phase system, which was composed of polyethylene glycol (PEG)-rich and gelatin methacrylate (GelMA)-rich phases, to produce cell-encapsulating microporous GelMA-based hydrogels. We successfully encapsulated HepG2 cells in the hydrogel matrix with a high cell viability, and confirmed that the spongious hydrogel was superior to homogeneous hydrogels for 3D cell culture. We performed perfusion culture for the cells encapsulated in the hydrogel sponge, to verify the usability and versatility of the presented hydrogel material for perfusion culture. The presented approach would be useful as a unique tool for developing organs-on-a-chip systems.

Natural Multimerization Rules the Performance of Affinity-Based Physical Hydrogels for Stem Cell Encapsulation and Differentiation.

Tissue engineering and stem cell research greatly benefit from cell encapsulation within hydrogels as it promotes cell expansion and differentiation. Affinity-triggered hydrogels, an appealing solution for mild cell encapsulation, rely on selective interactions between the ligand and target and also on the multivalent presentation of these two components. Although these hydrogels represent a versatile option to generate dynamic, tunable, and highly functional materials, the design of hydrogel properties based on affinity and multivalency remains challenging and unstudied. Here, the avidin-biotin affinity pair, with the highest reported affinity constant, is used to address this challenge. It is demonstrated that the binding between the affinity hydrogel components is influenced by the multivalent display selected. In addition, the natural multivalency of the interaction must be obeyed to yield robust multicomponent synthetic protein hydrogels. The hydrogel's resistance to erosion depends on the right stoichiometric match between the hydrogel components. The developed affinity-triggered hydrogels are biocompatible and support encapsulation of induced pluripotent stem cells and their successful differentiation into a neural cell line. This principle can be generalized to other affinity pairs using multimeric proteins, yielding biomaterials with controlled performance.

Investigating materials and orientation parameters for the creation of a 3D musculoskeletal interface co-culture model.

Musculoskeletal tissue interfaces are a common site of injury in the young, active populations. In particular, the interface between the musculoskeletal tissues of tendon and bone is often injured and to date, no single treatment has been able to restore the form and function of damaged tissue at the bone–tendon interface. Tissue engineering and regeneration hold great promise for the manufacture of bespoke in vitro models or implants to be used to advance repair and so this study investigated the material, orientation and culture choices for manufacturing a reproducible 3D model of a musculoskeletal interface between tendon and bone cell populations. Such models are essential for future studies focussing on the regeneration of musculoskeletal interfaces in vitro. Cell-encapsulated fibrin hydrogels, arranged in a horizontal orientation though a simple moulding procedure, were shown to best support cellular growth and migration of cells to form an in vitro tendon–bone interface. This study highlights the importance of acknowledging the material and technical challenges in establishing co-cultures and suggests a reproducible methodology to form 3D co-cultures between tendon and bone, or other musculoskeletal cell types, in vitro.

Injectable Cucurbit[8]uril-Based Supramolecular Gelatin Hydrogels for Cell Encapsulation.

Recent efforts to develop hydrogel biomaterials have focused on better recapitulating the dynamic properties of the native extracellular matrix. In hydrogel biomaterials, binding thermodynamics and cross-link kinetics directly affect numerous bulk dynamic properties such as strength, stress relaxation, and material clearance. However, despite the broad range of bulk dynamic properties observed in biological tissues, present strategies to incorporate dynamic linkages in cell-encapsulating hydrogels rely on a relatively small number of dynamic covalent chemical reactions and host-guest interactions. To expand this toolkit, we report the preparation of supramolecular gelatin hydrogels with cucurbit[8]uril (CB[8])-based cross-links that form on demand via thiol-ene reactions between preassembled CB[8]·FGGC peptide ternary complexes and grafted norbornenes. Human fibroblast cells encapsulated within these optically transparent, shear thinning, injectable hydrogels remained highly viable and exhibited a well-spread morphology in culture. These CB[8]-based gelatin hydrogels are anticipated to be useful in applications ranging from bioprinting to cell and drug delivery.

Oxime Cross-Linked Alginate Hydrogels with Tunable Stress Relaxation.

Stress relaxation is an important design parameter of biomaterials that can provide an artificial microenvironment mimicking natural extracellular matrix (ECM). Here, we report a novel hydrogel platform based on sodium alginate (NaAlg) with tunable stress relaxation. We first developed a new synthesis route to introduce alkoxyamine functional groups into the alginate polymer backbone. By mixing the resulting polymer (NaAlg-AA) with aldehyde-containing oxidized alginate (NaAlg-Ald), oxime cross-linked alginate hydrogels were prepared. We demonstrate that highly tunable stress relaxation and mechanical properties can be achieved by systematically varying the composition (concentration, polymer mixing ratios, degree of oxidation of NaAlg-Ald) or environmental factors (pH, temperature, and use of catalyst). Combined with the natural capability of the alginate to be cross-linked by divalent cations, the developed hydrogel formations possess the unique capability of dual cross-linking mechanisms with different gelation kinetics. We demonstrated that this dual cross-linking capability can (i) be utilized for the creation of hydrogels in microbead or microthread geometries and (ii) be useful for biomedical applications that require both the fast encapsulation of cells in hydrogels (fast calcium cross-linking) and the provision of controlled viscoelastic environments to cultured cells for an extended period (durable oxime cross-linking). With biocompatibility confirmed by the culture of a B-cell line encapsulated within the developed hydrogel, this novel hydrogel platform provides a good prospect in various applications where stress relaxation plays a key role in cell-matrix interactions.