Degradation of partially oxidized alginate and its potential application for tissue engineering

Immune-responsive biodegradable scaffolds for enhancing neutrophil regeneration

Neutrophils are essential effector cells for mediating rapid host defense and their insufficiency arising from therapy-induced side-effects, termed neutropenia, can lead to immunodeficiency-associated complications. In autologous hematopoietic stem cell transplantation (HSCT), neutropenia is a complication that limits therapeutic efficacy. Here, we report the development and in vivo evaluation of an injectable, biodegradable hyaluronic acid (HA)-based scaffold, termed HA cryogel, with myeloid responsive degradation behavior. In mouse models of immune deficiency, we show that the infiltration of functional myeloid-lineage cells, specifically neutrophils, is essential to mediate HA cryogel degradation. Post-HSCT neutropenia in recipient mice delayed degradation of HA cryogels by up to 3 weeks. We harnessed the neutrophil-responsive degradation to sustain the release of granulocyte colony stimulating factor (G-CSF) from HA cryogels. Sustained release of G-CSF from HA cryogels enhanced post-HSCT neutrophil recovery, comparable to pegylated G-CSF, which, in turn, accelerated cryogel degradation. HA cryogels are a potential approach for enhancing neutrophils and concurrently assessing immune recovery in neutropenic hosts.

Mesenchymal stromal cell spheroids in sulfated alginate enhance muscle regeneration

The therapeutic efficacy of mesenchymal stromal cells (MSCs) for tissue regeneration is critically linked to the potency of the complex mixture of growth factors, cytokines, exosomes, and other biological cues that they secrete. The duration of cell-based approaches is limited by rapid loss of cells upon implantation, motivating the need to prolong cell viability and extend the therapeutic influence of the secretome. We and others demonstrated that the secretome is upregulated when MSCs are formed into spheroids. Although the efficacy of the MSC secretome has been characterized in the literature, no studies have reported the therapeutic benefit of in situ sequestration of the secretome within a wound site using engineered biomaterials. We previously demonstrated the capacity of sulfated alginate hydrogels to sequester components of the MSC secretome for prolonged presentation in vitro, yet the efficacy of this platform has not been evaluated in vivo. In this study, we used sulfated alginate hydrogels loaded with MSC spheroids to aid in the regeneration of a rat muscle crush injury. We hypothesized that the use of sulfated alginate to bind therapeutically relevant growth factors from the MSC spheroid secretome would enhance muscle regeneration by recruiting host cells into the tissue site. The combination of sulfated alginate and MSC spheroids resulted in decreased collagen deposition, improved myogenic marker expression, and increased neuromuscular junctions 2 weeks after injury. These data indicate that MSC spheroids delivered in sulfated alginate represent a promising approach for decreased fibrosis and increased functional regeneration of muscle. STATEMENT OF SIGNIFICANCE: The therapeutic efficacy of mesenchymal stromal cells (MSCs) for tissue regeneration is attributed to the complex diversity of the secretome. Cell-based approaches are limited by rapid cell death, motivating the need to extend the availability of the secretome. We previously demonstrated that sulfated alginate hydrogels sequester components of the MSC secretome for prolonged presentation in vitro, yet no studies have reported the in situ sequestration of the secretome. Herein, we transplanted MSC spheroids in sulfated alginate hydrogels to promote muscle regeneration. MSC spheroids in sulfated alginate decreased collagen deposition, improved myogenic marker expression, and increased neuromuscular junctions. These data indicate that MSC spheroids delivered in sulfated alginate represent a promising approach for decreasing fibrosis and increasing functional muscle regeneration.

Development of chondrocyte-laden alginate hydrogels with modulated microstructure and properties for cartilage regeneration

Alginate hydrogel is an attractive biomaterial for cell microencapsulation. The microarchitecture of hydrogels can regulate cellular functions. This study aims to investigate the applicability of sodium citrate buffer (SCB) as a culture medium supplement for modulating the microstructure of alginate microbeads to provide a favorable microenvironment for chondrogenic induction. The chondrocyte-laden microbeads, with and without TGF-β3 incorporation, were produced through an encapsulator. The obtained small-sized microbeads (~300 μm) were exposed to a treatment medium containing SCB, composed of varied concentrations of sodium citrate (1.10-1.57 mM), sodium chloride (3.00-4.29 mM), and ethylenediaminetetraacetic acid (0.60-0.86 mM) to partially degrade their crosslinked structure for 3 days, followed by culture in a normal medium until day 21. Scanning electron microscope micrographs demonstrated a loose hydrogel network with an enhanced pore size in the SCB-treated microbeads. Increasing the concentration of SCB in the treatment medium reduced the calcium content of the microbeads via a Na⁺ /Ca²⁺ exchange process and improved the water absorption of the microbeads, resulting in a higher swelling ratio. All the tested SCB concentrations were non-cytotoxic. Increases in aggrecan and type II collagen gene expression and their corresponding extracellular matrix accumulation, glycosaminoglycans, and type II collagen were vividly detected in the TGF-β3-containing microbeads with increasing SCB concentrations in the treatment medium. Our findings highlighted that the combination of SCB treatment and TGF-β3 incorporation in the chondrocyte-laden microbeads is a promising strategy for enhancing cartilage regeneration, which may contribute to a versatile application in cell delivery and tissue engineering.

Tunable Physicomechanical and Drug Release Properties of In Situ Forming Thermoresponsive Elastin-like Polypeptide Hydrogels

With the continued advancement in the design and engineering of hydrogels for biomedical applications, there is a growing interest in imparting stimuli-responsiveness to the hydrogels in order to control their physicomechanical properties in a more programmable manner. In this study, an in situ forming hydrogel is developed by cross-linking alginate with an elastin-like polypeptide (ELP). Lysine-rich ELP synthesized by recombinant DNA technology is reacted with alginate presenting an aldehyde via Schiff base formation, resulting in facile hydrogel formation under physiological conditions. The physicomechanical properties of alginate-ELP hydrogels can be controlled in a wide range by the concentrations of alginate and ELP. Owing to the thermoresponsive properties of the ELP, the alginate-ELP hydrogels undergo swelling/deswelling near the physiological temperature. Taking advantage of these highly attractive properties of alginate-ELP, drug release kinetics were measured to evaluate their potential as a thermoresponsive drug delivery system. Furthermore, an ex vivo model was used to demonstrate the minimally invasive tissue injectability.

Oxidized sodium alginate crosslinked silk fibroin composite scaffold for skin tissue engineering

Engineering skin substitutes represent a prospective source of advanced therapy in repairing severe traumatic wounds. Sodium alginate (SA) and silk fibroin (SF) are natural biomaterials, which are widely used in tissue engineering and other fields because of their low price, high safety, and good biocompatibility. However, SA itself degrades slowly, its degradation mode is difficult to control, and the degradation products are difficult to remove from the body because of its high molecular weight. Therefore, the composite scaffolds were prepared by freeze-drying composite technology by using the Schiff base reaction between biocompatible SF and permeable oxidized sodium alginate (OSA). Sodium periodate was used as oxidant to modify SA. The results showed that higher oxidation degree of OSA could be obtained by increasing the proportion of oxidant, and the relative molecular weight of the oxidized products could also be reduced. The composite scaffolds were prepared by using sodium tetraborate as a crosslinking accelerator of the Schiff base reaction between OSA and SF. FT-IR confirmed that the Schiff base group appeared in the material. In vitro biodegradation experiments showed that the biodegradation of the composite scaffolds was controllable, and the cytocompatibility experiment showed that the composite scaffolds had good biocompatibility.

Construction of a Band-Aid Like Cardiac Patch for Myocardial Infarction with Controllable H2 S Release

Excessive or persistent inflammation incites cardiomyocytes necrosis by generating reactive oxygen species in myocardial infarction (MI). Hydrogen sulfide (H2 S), a gaseous signal molecule, can quickly permeate cells and tissues, growing concerned for its cardioprotective effects. However, short resident time and strong side effects greatly restrict its application. Herein, a complex scaffold (AAB) is first developed to slowly release H2 S for myocardial protection by integrating alginate modified with 2-aminopyridine-5-thiocarboxamide (H2 S donor) into albumin electrospun fibers. Next, a band-aid like patch is constructed based on AAB (center) and nanocomposite scaffold which comprises albumin scaffold and black phosphorus nanosheets (BPNSs). With near-infrared laser (808 nm), thermal energy generated by BPNSs can locally change the molecular structure of fibrous scaffold, thereby attaching patch to the myocardium. In this study, it is also demonstrated that AAB can enhance regenerative M2 macrophage and attenuate inflammatory polarization of macrophages via reduction in intracellular ROS. Eventually, this engineered cardiac patch can relieve inflammation and promote angiogenesis after MI, and thereby recover heart function, providing a promising therapeutic strategy for MI treatment.

Novel injectable calcium phosphate scaffold with human periodontal ligament stem cell encapsulation in microbeads for bone regeneration

Objectives: 1) Develop a novel construct of human periodontal ligament stem cells (hPDLSCs) encapsulated in degradable alginate microbeads (DAMB) with human platelet lysate (hPL) and injectable calcium phosphate cement (ICPC); 2) Investigate the proliferation and osteogenic differentiation of hPDLSCs in ICPC with hPL as a xeno-free supplement and animal serum replacement for bone tissue engineering applications.

Methods: hPDLSCs were encapsulated in alginate-fibrin microbeads (DAMB + fibrin), alginate-hPL degradable microbeads (DAMB + hPL), or alginate-fibrin-hPL microbeads (DAMB + fibrin + hPL). The proliferation and osteogenic differentiation of hPDLSCs were investigated in culturing with the ICPC scaffold.

Results: Flexural strength of ICPC was 8.4 ± 0.91 MPa, and elastic modulus was 1.56 ± 0.1 GPa, exceeding those of cancellous bone. hPDLSCs had higher viability in DAMB + fibrin + hPL group than in DAMB + fibrin. ALP was 69.97 ± 16.96 mU/mg for ICPC + DAMB + fibrin + hPL group, higher than 30.68 ± 2.86 mU/mg of ICPC + DAMB + fibrin (p < 0.05) and 4.12 ± 1.65 mU/mg of control (p < 0.01). At 7 days, osteogenic gene expressions (ALP, RUNX2, COL1, and OPN) in ICPC + DAMB + fibrin + hPL and ICPC + DAMB + fibrin were 4–11 folds that of control. At 21 days, the hPDLSC-synthesized bone mineral amounts in ICPC + DAMB + fibrin + hPL and ICPC + DAMB + fibrin were 13.2 folds and 11.1 folds that of control group, respectively.

Conclusion: The novel injectable CPC scaffold encapsulating hPDLSCs and hPL is promising to protect and deliver hPDLSCs. The hPL-based medium significantly enhanced the osteogenic differentiation of hPDLSCs in ICPC + DAMB + fibrin + hPL construct, suggesting a promising xeno-free approach for bone tissue regeneration applications.

M, Zarrintaj P, Formela K, Saeb MR, Bencherif SA. Clickable Polysaccharides for Biomedical Applications: A Comprehensive Review

Recent advances in materials science and engineering highlight the importance of designing sophisticated biomaterials with well-defined architectures and tunable properties for emerging biomedical applications. Click chemistry, a powerful method allowing specific and controllable bioorthogonal reactions, has revolutionized our ability to make complex molecular structures with a high level of specificity, selectivity, and yield under mild conditions. These features combined with minimal byproduct formation have enabled the design of a wide range of macromolecular architectures from quick and versatile click reactions. Furthermore, copper-free click chemistry has resulted in a change of paradigm, allowing researchers to perform highly selective chemical reactions in biological environments to further understand the structure and function of cells. In living systems, introducing clickable groups into biomolecules such as polysaccharides (PSA) has been explored as a general approach to conduct medicinal chemistry and potentially help solve healthcare needs. De novo biosynthetic pathways for chemical synthesis have also been exploited and optimized to perform PSA-based bioconjugation inside living cells without interfering with their native processes or functions. This strategy obviates the need for laborious and costly chemical reactions which normally require extensive and time-consuming purification steps. Using these approaches, various PSA-based macromolecules have been manufactured as building blocks for the design of novel biomaterials. Clickable PSA provides a powerful and versatile toolbox for biomaterials scientists and will increasingly play a crucial role in the biomedical field. Specifically, bioclick reactions with PSA have been leveraged for the design of advanced drug delivery systems and minimally invasive injectable hydrogels. In this review article, we have outlined the key aspects and breadth of PSA-derived bioclick reactions as a powerful and versatile toolbox to design advanced polymeric biomaterials for biomedical applications such as molecular imaging, drug delivery, and tissue engineering. Additionally, we have also discussed the past achievements, present developments, and recent trends of clickable PSA-based biomaterials such as 3D printing, as well as their challenges, clinical translatability, and future perspectives.

Dual Dynamic Covalently Crosslinked Alginate Hydrogels with Tunable Properties and Multiple Stimuli-Responsiveness

Alginate is a biopolymer that can be crosslinked with calcium ions to fabricate cytocompatible hydrogels. However, using calcium ions to crosslink alginate provides limited properties and functions to alginate hydrogels, restricting their biomedical applications. Here, phenylboronic acid-functionalized polyethyleneimine (PBA-PEI) was developed to introduce two orthogonal dynamic covalent crosslinks in the alginate hydrogels, where PBA-PEI was used to crosslink alginate dialdehyde (ADA) through imine bonds and boronate ester bonds. The grafting degree of PBA in the PEI structure was applied to fine-tune the properties of PBA-PEI/ADA hydrogels, including the rheological property, mechanical strength, swelling behavior, and antibacterial activity. In particular, the highly sensitive boronate ester bonds in the network enabled PBA-PEI/ADA hydrogels to be responsive to several stimuli, such as glucose, fructose, and hydrogen peroxide. Taken together, PBA-PEI/ADA hydrogels with tunable properties and multiple stimuli-responsiveness have been demonstrated as smart biomaterials for advanced biomedical applications.

Human periodontal ligament stem cell encapsulation in alginate-fibrin-platelet lysate microbeads for dental and craniofacial regeneration

OBJECTIVE

Tissue engineering is promising for dental and craniofacial regeneration. The objectives of this study were to develop a novel xeno-free alginate-fibrin-platelet lysate hydrogel with human periodontal ligament stem cells (hPDLSCs) for dental regeneration, and to investigate the proliferation and osteogenic differentiation of hPDLSCs using hPL as a cell culture nutrient supplement.

METHODS

hPDLSCs were cultured with Dulbecco's modified eagle medium (DMEM), DMEM + 10% fetal bovine serum (FBS), and DMEM + hPL (1%, 2.5%, and 5%). hPDLSCs were encapsulated in alginate-fibrin microbeads (Alg+Fib), alginate-hPL microbeads (Alg+hPL), or alginate-fibrin-hPL microbeads (Alg+Fib+hPL). hPDLSCs encapsulated in alginate microbeads were induced with an osteogenic medium containing hPL or FBS. Quantitative real-time polymerase chain reaction (qRT-PCR), alkaline phosphatase (ALP) activity, ALP staining, and alizarin red (ARS) staining was investigated.

RESULTS

hPDLSCs were released faster from Alg+Fib+hPL than from Alg+hPL. At 14 days, ALP activity was 44.1 ± 7.61 mU/mg for Alg+Fib+hPL group, higher than 28.07 ± 5.15 mU/mg of Alg+Fib (p<0.05) and 0.95 ± 0.2 mU/mg of control (p<0.01). At 7 days, osteogenic genes (ALP, RUNX2, COL1, and OPN) in Alg+Fib+hPL and Alg+Fib were 3-10 folds those of control. At 21 days, the hPDLSC-synthesized bone mineral amount in Alg+Fib+hPL and Alg+Fib was 7.5 folds and 4.3 folds that of control group, respectively.

CONCLUSIONS

The 2.5% hPL was determined to be optimal for hPDLSCs. Adding hPL into alginate hydrogel improved the viability of the hPDLSCs encapsulated in the microbeads. The hPL-based medium enhanced the osteogenic differentiation of hPDLSCs in Alg+Fib+hPL construct, showing a promising xeno-free approach for delivering hPDLSCs to enhance dental, craniofacial and orthopedic regenerations.

Chemical strategies to engineer hydrogels for cell culture

Two-dimensional and three-dimensional cell culture systems are widely used for biological studies, and are the basis of the organoid, tissue engineering and organ-on-chip research fields in applications such as disease modelling and drug screening. The natural extracellular matrix of tissues, a complex scaffold with varying chemical and mechanical properties, has a critical role in regulating important cellular functions such as spreading, migration, proliferation and differentiation, as well as tissue morphogenesis. Hydrogels are biomaterials that are used in cell culture systems to imitate critical features of a natural extracellular matrix. Chemical strategies to synthesize and tailor the properties of these hydrogels in a controlled manner, and manipulate their biological functions in situ, have been developed. In this Review, we provide the rational design criteria for predictably engineering hydrogels to mimic the properties of the natural extracellular matrix. We highlight the advances in using biocompatible strategies to engineer hydrogels for cell culture along with recent developments to dynamically control the cellular environment by exploiting stimuli-responsive chemistries. Finally, future opportunities to engineer hydrogels are discussed, in which the development of novel chemical methods will probably have an important role.

Alginate as a Promising Biopolymer in Drug Delivery and Wound Healing: A Review of the State-of-the-Art

Biopolymeric nanoparticulate systems hold favorable carrier properties for active delivery. The enhancement in the research interest in alginate formulations in biomedical and pharmaceutical research, owing to its biodegradable, biocompatible, and bioadhesive characteristics, reiterates its future use as an efficient drug delivery matrix. Alginates, obtained from natural sources, are the colloidal polysaccharide group, which are water-soluble, non-toxic, and non-irritant. These are linear copolymeric blocks of α-(1→4)-linked l-guluronic acid (G) and β-(1→4)-linked d-mannuronic acid (M) residues. Owing to the monosaccharide sequencing and the enzymatically governed reactions, alginates are well-known as an essential bio-polymer group for multifarious biomedical implementations. Additionally, alginate’s bio-adhesive property makes it significant in the pharmaceutical industry. Alginate has shown immense potential in wound healing and drug delivery applications to date because its gel-forming ability maintains the structural resemblance to the extracellular matrices in tissues and can be altered to perform numerous crucial functions. The initial section of this review will deliver a perception of the extraction source and alginate’s remarkable properties. Furthermore, we have aspired to discuss the current literature on alginate utilization as a biopolymeric carrier for drug delivery through numerous administration routes. Finally, the latest investigations on alginate composite utilization in wound healing are addressed.

Genipin-crosslinked fibrin seeded with oxidized alginate microbeads as a novel composite biomaterial strategy for intervertebral disc cell therapy

Discectomy procedures alleviate disability caused by intervertebral disc (IVD) herniation, but do not repair herniation-induced annulus fibrosus (AF) defects. Cell therapy shows promise for IVD repair, yet cell delivery biomaterials capable of sealing AF defects and restoring biomechanical function have poor biological performance. To balance the biomechanical and biological demands of IVD cell delivery biomaterials, we engineered an injectable composite biomaterial using cell-laden, degradable oxidized alginate (OxAlg) microbeads (MBs) to deliver AF cells within high-modulus genipin-crosslinked fibrin (FibGen) hydrogels (FibGen + MB composites). Conceptually, the high-modulus FibGen would immediately stabilize injured IVDs, while OxAlg MBs would protect and release cells required for long-term healing. We first showed that AF cells microencapsulated in OxAlg MBs maintained high viability and, upon release, displayed phenotypic AF cell morphology and gene expression. Next, we created cell-laden FibGen + MB composites and demonstrated that OxAlg MBs functionalized with RGD peptides (MB-RGD) minimized AF cell apoptosis and retained phenotypic gene expression. Further, we showed that cell-laden FibGen + MB composites are biomechanically stable and promote extracellular matrix (ECM) synthesis in long-term in vitro culture. Lastly, we evaluated cell-laden FibGen + MB-RGD composites in a long-term bovine caudal IVD organ culture bioreactor and found that composites had low herniation risk, provided superior biomechanical and biological repair to discectomy controls, and retained anabolic cells within the IVD injury space. This novel injectable composite hydrogel strategy shows promise as an IVD cell delivery sealant with potentially broad applications for its capacity to balance biomechanical and biological performance.

Tuning the Degradation Rate of Alginate-Based Bioinks for Bioprinting Functional Cartilage Tissue

Negative foreign body responses following the in vivo implantation of bioprinted implants motivate the development of novel bioinks which can rapidly degrade with the formation of functional tissue, whilst still maintaining desired shapes post-printing. Here, we investigated the oxidation of alginate as a means to modify the degradation rate of alginate-based bioinks for cartilage tissue engineering applications. Raw and partially oxidized alginate (OA) were combined at different ratios (Alginate:OA at 100:0; 75:25; 50:50; 25:75; 0:100) to provide finer control over the rate of bioink degradation. These alginate blends were then combined with a temporary viscosity modifier (gelatin) to produce a range of degradable bioinks with rheological properties suitable for extrusion bioprinting. The rate of degradation was found to be highly dependent on the OA content of the bioink. Despite this high mass loss, the initially printed geometry was maintained throughout a 4 week in vitro culture period for all bioink blends except the 0:100 group. All bioink blends also supported robust chondrogenic differentiation of mesenchymal stem/stromal cells (MSCs), resulting in the development of a hyaline-like tissue that was rich in type II collagen and negative for calcific deposits. Such tuneable inks offer numerous benefits to the field of 3D bioprinting, from providing space in a controllable manner for new extracellular matrix deposition, to alleviating concerns associated with a foreign body response to printed material inks in vivo.

Antibacterial peptide NZ2114-loaded hydrogel accelerates Staphylococcus aureus-infected wound healing

Wound infection caused by Staphylococcus aureus (S. aureus) is a great challenge which has caused significant burden and economic loss to the medical system. NZ2114, a plectasin-derived peptide, is an antibacterial agent for preventing and treating S. aureus infection, especially for methicillin-resistant S. aureus (MRSA) infection. Here, three-dimensional reticulated antimicrobial peptide (AMP) NZ2114 hydrogels were developed based on hydroxypropyl cellulose (HPC) and sodium alginate (SA); they displayed sustained and stable release properties (97.88 ± 1.79% and 91.1 ± 10.52% release rate in 72 h, respectively) and good short-term cytocompatibility and hemocompatibility. But the HPC-NZ2114 hydrogel had a smaller pore size (diameter 0.832 ± 0.420 μm vs. 3.912 ± 2.881 μm) and better mechanical properties than that of the SA-NZ2114 hydrogel. HPC/SA-NZ2114 hydrogels possess efficient antimicrobial activity in vitro and in vivo. In a full-thickness skin defect model, the wound closure of the 1.024 mg/g HPC-NZ2114 hydrogel group was superior to those of the SA-NZ2114 hydrogel and antibiotic groups on day 7. The HPC-NZ2114 hydrogel accelerated wound healing by reducing inflammation and promoting the production of vascular endothelial growth factor (VEGF), endothelial growth factor (EGF) and angiogenesis (CD31) through histological and immunohistochemistry evaluation. These data indicated that the HPC-NZ2114 hydrogel is an excellent candidate for S. aureus infection wound dressing. KEY POINTS: •NZ2114 hydrogels showed potential in vitro bactericidal activity against S. aureus •NZ2114 hydrogels could release continuously for 72 h and had good biocompatibility •NZ2114 hydrogels could effectively promote S. aureus-infected wound healing.

A review on alginate-based bioinks, combination with other natural biomaterials and characteristics

The advent of three-dimensional (3D) Bioprinting increased the need for a suitable bioink in which Cells can live, proliferate and generate specific tissue and organ. Therefore, bioinks must have several physical and chemical characteristics that depend on the bioprinting modality and the target tissue. Alginate is considered a promising biomaterial for bioprinting due to its distinct physicochemical properties and diverse biological functions. However, some characteristics, such as cell adherence and biodegradability, are lacking, which can compensate when combined with other biomaterials, for example, gelatin, gelatin methacryloyl (GelMa), cellulose, silk fibroin, and hyaluronic acid. The alginate-gelatin blend receives considerable attention since gelatin has Arginine, Glycine, and Aspartate, the tripeptide Arg-Gly-Asp (RGD) sequence that could sustain cell attachment. Some parameters assist the optimization of bioink features like temperature, biomaterials' concentration, and crosslinking time. For instance, the viscosity of alginate increases by enhancing its concentration, and while it exhibits shear thinning property, it will be printed correctly. This review interprets the alginate-based bioink, focusing on its composite with other natural biomaterials, especially gelatin. Also, it discusses the parameters that affect bioink functionality and cell viability.

Alginate: Enhancement Strategies for Advanced Applications

Alginate is an excellent biodegradable and renewable material that is already used for a broad range of industrial applications, including advanced fields, such as biomedicine and bioengineering, due to its excellent biodegradable and biocompatible properties. This biopolymer can be produced from brown algae or a microorganism culture. This review presents the principles, chemical structures, gelation properties, chemical interactions, production, sterilization, purification, types, and alginate-based hydrogels developed so far. We present all of the advanced strategies used to remarkably enhance this biopolymer's physicochemical and biological characteristics in various forms, such as injectable gels, fibers, films, hydrogels, and scaffolds. Thus, we present here all of the material engineering enhancement approaches achieved so far in this biopolymer in terms of mechanical reinforcement, thermal and electrical performance, wettability, water sorption and diffusion, antimicrobial activity, in vivo and in vitro biological behavior, including toxicity, cell adhesion, proliferation, and differentiation, immunological response, biodegradation, porosity, and its use as scaffolds for tissue engineering applications. These improvements to overcome the drawbacks of the alginate biopolymer could exponentially increase the significant number of alginate applications that go from the paper industry to the bioprinting of organs.

Ultrasound in cellulose-based hydrogel for biomedical use: From extraction to preparation

As the most abundant natural polymer on the pl anet, cellulose has a wide range of applications in the biomedical field. Cellulose-based hydrogels further expand the applications of this class of biomaterials. However, a number of publications and technical reports are mainly about traditional preparation methods. Sonochemistry offers a simple and green route to material synthesis with the biomedical application of ultrasound. The tiny acoustic bubbles, produced by the propagating sound wave, enclose an incredible facility where matter interact among at energy as high as 13 eV to spark extraordinary chemical reactions. Ultrasonication not only improves the efficiency of cellulose extraction from raw materials, but also influences the hydrogel preparation process. The primary objective of this article is to review the literature concerning the biomedical cellulose-based hydrogel prepared via sonochemistry and application of ultrasound for hydrogel. An innovated category of recent generations of hydrogel materials prepared via ultrasound was also presented in some details.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Bioprinting a thick and cell-laden partially oxidized alginate-gelatin scaffold with embedded micro-channels as future soft tissue platform

Despite all the advancements in tissue engineering, one of the unsolved challenges is the mass transfer limitation. Therefore, the subject of pre-vascularization in the engineered tissues gets more attention to avoid necrotic core formation. In this study, we considered a design for interconnected channels with a muscle tissue-like structure, in silico and in vitro. A sequence of simple steps make it possible for us to use the same material, gelatin, as both a sacrificial material and one of the main components of the scaffold simultaneously. We defined a new approach to quantify the repeatability of a new combination of hydrogels (Partially Oxidized Alginate + Gelatin) for extrusion-based bioprinting. Additionally, the mechanical properties, hydrogel porosity, degradation time, and swelling ratio were also evaluated. Based on all these test results, the scaffold with the optimum properties was chosen for the bioprinting of adipose derived mesenchymal stem cells (ADMSCs) in the scaffolds with and without the channels. This bioprinted scaffold with microchannels showed promising mimicry of the microenvironment, leading to higher survival and proliferation rates of the cells by up to 250%. Based on these results, it has the potential to serve as a platform for further research in vascularization, healthy/disease modelling, and stem cell differentiation.

Alginate-Based Smart Materials and Their Application: Recent Advances and Perspectives

Nature produces materials using available molecular building blocks following a bottom-up approach. These materials are formed with great precision and flexibility in a controlled manner. This approach offers the inspiration for manufacturing new artificial materials and devices. Synthetic artificial materials can find many important applications ranging from personalized therapeutics to solutions for environmental problems. Among these materials, responsive synthetic materials are capable of changing their structure and/or properties in response to external stimuli, and hence are termed "smart" materials. Herein, this review focuses on alginate-based smart materials and their stimuli-responsive preparation, fragmentation, and applications in diverse fields from drug delivery and tissue engineering to water purification and environmental remediation. In the first part of this report, we review stimuli-induced preparation of alginate-based materials. Stimuli-triggered decomposition of alginate materials in a controlled fashion is documented in the second part, followed by the application of smart alginate materials in diverse fields. Because of their biocompatibility, easy accessibility, and simple techniques of material formation, alginates can provide solutions for several present and future problems of humankind. However, new research is needed for novel alginate-based materials with new functionalities and well-defined properties for targeted applications.

Sulfated Alginate Hydrogels Prolong the Therapeutic Potential of MSC Spheroids by Sequestering the Secretome

Cell-based approaches to tissue repair suffer from rapid cell death upon implantation, limiting the window for therapeutic intervention. Despite robust lineage-specific differentiation potential in vitro, the function of transplanted mesenchymal stromal cells (MSCs) in vivo is largely attributed to their potent secretome comprising a variety of growth factors (GFs). Furthermore, GF secretion is markedly increased when MSCs are formed into spheroids. Native GFs are sequestered within the extracellular matrix (ECM) via sulfated glycosaminoglycans, increasing the potency of GF signaling compared to their unbound form. To address the critical need to prolong the efficacy of transplanted cells, alginate hydrogels are modified with sulfate groups to sequester endogenous heparin-binding GFs secreted by MSC spheroids. The influence of crosslinking method and alginate modification is assessed on mechanical properties, degradation rate, and degree of sulfate modification. Sulfated alginate hydrogels sequester a mixture of MSC-secreted endogenous biomolecules, thereby prolonging the therapeutic effect of MSC spheroids for tissue regeneration. GFs are sequestered for longer durations within sulfated hydrogels and retain their bioactivity to regulate endothelial cell tubulogenesis and myoblast infiltration. This platform has the potential to prolong the therapeutic benefit of the MSC secretome and serve as a valuable tool for investigating GF sequestration.

Isolating and characterizing lymphatic endothelial progenitor cells for potential therapeutic lymphangiogenic applications

Lymphatic dysfunction is associated with the progression of several vascular disorders, though currently, there are limited strategies to promote new lymphatic vasculature (i.e., lymphangiogenesis) to restore lost lymphatic function. One promising approach to stimulate lymphangiogenesis involves delivering endothelial progenitor cells (EPCs), which are naturally involved in de novo blood vessel formation and have recently been identified to include a lymphatic subpopulation. However, the contribution of lymphatic EPCs in lymphangiogenesis is not clear and challenges with maintaining the activity of transplanted EPCs remain. Thus, the objective of this study was to isolate lymphatic EPCs from human umbilical cord blood and characterize their role in the initial stages of blood or lymphatic vasculature formation. Furthermore, this study also tested the applicability of alginate hydrogels to deliver lymphatic EPCs for a possible therapeutic application. We postulated and confirmed that blood and lymphatic EPC colonies could be isolated from human umbilical cord blood. Additionally, EPC populations responded to either angiogenic or lymphangiogenic growth factors and could stimulate their respective mature endothelial cells in vasculature models in vitro. Finally, lymphatic EPCs maintained their ability to promote lymphatic sprouts after prolonged interactions with the alginate hydrogel microenvironment. These results suggest EPCs have both a blood and a lymphatic population that have specific roles in promoting revascularization and highlight the potential of alginate hydrogels for the delivery of lymphatic EPCs. STATEMENT OF SIGNIFICANCE: Despite the potential therapeutic benefit of promoting lymphatic vasculature, lymphangiogenesis remains understudied. One appealing strategy for promoting lymphangiogenesis involves delivering lymphatic endothelial progenitor cells (EPCs), which are a subpopulation of EPCs involved in de novo vessel formation. Here, we investigate the role of isolated blood and lymphatic EPC subpopulations in promoting the early stages of vascularization and the utility of alginate hydrogels to deliver lymphatic EPCs. We determined that EPCs had two populations that expressed either blood or lymphatic markers, could stimulate their respective mature vasculature in tissue constructs and that alginate hydrogels maintained the therapeutic potential of lymphatic EPCs. We anticipate this work could support promising biomaterial applications of EPCs to promote revascularization, which could have many therapeutic applications.

Single-Cell Microgels for Diagnostics and Therapeutics

Cell encapsulation within hydrogel droplets is transforming what is feasible in multiple fields of biomedical science such as tissue engineering and regenerative medicine, in vitro modeling, and cell-based therapies. Recent advances have allowed researchers to miniaturize material encapsulation complexes down to single-cell scales, where each complex, termed a single-cell microgel, contains only one cell surrounded by a hydrogel matrix while remaining <100 μm in size. With this achievement, studies requiring single-cell resolution are now possible, similar to those done using liquid droplet encapsulation. Of particular note, applications involving long-term in vitro cultures, modular bioinks, high-throughput screenings, and formation of 3D cellular microenvironments can be tuned independently to suit the needs of individual cells and experimental goals. In this progress report, an overview of established materials and techniques used to fabricate single-cell microgels, as well as insight into potential alternatives is provided. This focused review is concluded by discussing applications that have already benefited from single-cell microgel technologies, as well as prospective applications on the cusp of achieving important new capabilities.

Silk Fibroin: A Promising Tool for Wound Healing and Skin Regeneration

Silk is a functional protein biomaterial produced by a variety of insects like flies, silkworms, scorpions, spiders, and mites. Silk synthesized by silkworms is extensively studied for its applications in tissue engineering and wound healing. Silk is undoubtedly a natural biocompatible material with humans and has its role in medical treatments from ancient times. The silk worm protein comprises two types of proteins namely fibroin and sericin. Silk fibroin makes up approximately 70% of cocoon weight and has wide applications in textiles and in all biomedical applications owing to its biocompatible, nontoxic, biodegradable, less immunogenic, and noncarcinogenic nature. It possesses outstanding toughness and mechanical strength, while silk sericin possesses high defensive ability against ultraviolet light and oxidation. Silk fibroin has been known to induce wound healing by increasing cell proliferation and growth and migrating various types of cells which are involved in different stages of wound healing process. With several silk varieties like silk worm fibroin, silk sericin, recombinant silk materials, and native spider silk have been investigated for its wound healing applications over the last several decades. With an objective of harnessing the silk regenerative properties, plentiful strategies have been studied and applied to develop bioartificial skin grafts and bioactive wound dressings in recent times. This review gives a detailed insight into the structure, general properties, fibroin structure-properties relationship, and biomedical applications of silk fibroin.

Esterification of Alginate with Alkyl Bromides of Different Carbon Chain Lengths via the Bimolecular Nucleophilic Substitution Reaction: Synthesis, Characterization, and Controlled Release Performance

To extend the alginate applicability for the sustained release of hydrophobic medicine in drug delivery systems, the alkyl alginate ester derivative (AAD), including hexyl alginate ester derivative (HAD), octyl alginate ester derivative (OAD), decyl alginate ester derivative (DAD), and lauryl alginate ester derivative (LAD), were synthesized using the alkyl bromides with different lengths of carbon chain as the hydrophobic modifiers under homogeneous conditions via the bimolecular nucleophilic substitution (SN2) reaction. Experimental results revealed that the successful grafting of the hydrophobic alkyl groups onto the alginate molecular backbone via the SN2 reaction had weakened and destroyed the intramolecular hydrogen bonds, thus enhancing the molecular flexibility of the alginate, which endowed the AAD with a good amphiphilic property and a critical aggregation concentration (CAC) of 0.48~0.0068 g/L. Therefore, the resultant AAD could form stable spherical self-aggregated micelles with the average hydrodynamic diameter of 285.3~180.5 nm and zeta potential at approximately -44.8~-34.4 mV due to the intra or intermolecular hydrophobic associations. With the increase of the carbon chain length of the hydrophobic side groups, the AAD was more prone to self-aggregation, and therefore was able to achieve the loading and sustained release of hydrophobic ibuprofen. Additionally, the swelling and degradation of AAD microcapsules and the diffusion of the loaded drug jointly controlled the release rate of ibuprofen. Meanwhile, the AAD also displayed low cytotoxicity to the murine macrophage RAW264.7 cells. Thanks to the good amphiphilic property, colloidal interface activity, hydrophobic drug-loading performance, and cytocompatibility, the synthesized AAD exhibited a great potential for the development of hydrophobic pharmaceutical formulations.

The Molecular Structure and Self-Assembly Behavior of Reductive Amination of Oxidized Alginate Derivative for Hydrophobic Drug Delivery

On account of the rigid structure of alginate chains, the oxidation-reductive amination reaction was performed to synthesize the reductive amination of oxidized alginate derivative (RAOA) that was systematically characterized for the development of pharmaceutical formulations. The molecular structure and self-assembly behavior of the resultant RAOA was evaluated by an FT-IR spectrometer, a 1H NMR spectrometer, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), a fluorescence spectrophotometer, rheology, a transmission electron microscope (TEM) and dynamic light scattering (DLS). In addition, the loading and in vitro release of ibuprofen for the RAOA microcapsules prepared by the high-speed shearing method, and the cytotoxicity of the RAOA microcapsules against the murine macrophage RAW264.7 cell were also studied. The experimental results indicated that the hydrophobic octylamine was successfully grafted onto the alginate backbone through the oxidation-reductive amination reaction, which destroyed the intramolecular hydrogen bond of the raw sodium alginate (SA), thereby enhancing its molecular flexibility to achieve the self-assembly performance of RAOA. Consequently, the synthesized RAOA displayed good amphiphilic properties with a critical aggregation concentration (CAC) of 0.43 g/L in NaCl solution, which was significantly lower than that of SA, and formed regular self-assembled micelles with an average hydrodynamic diameter of 277 nm (PDI = 0.19) and a zeta potential of about -69.8 mV. Meanwhile, the drug-loaded RAOA microcapsules had a relatively high encapsulation efficiency (EE) of 87.6 % and good sustained-release properties in comparison to the drug-loaded SA aggregates, indicating the good affinity of RAOA to hydrophobic ibuprofen. The swelling and degradation of RAOA microcapsules and the diffusion of the loaded drug jointly controlled the release rate of ibuprofen. Moreover, it also displayed low cytotoxicity against the RAW264.7 cell, similar to the SA aggregates. In view of the excellent advantages of RAOA, it is expected to become the ideal candidate for hydrophobic drug delivery in the biomedical field.

A bi-layered scaffold of a poly(lactic-co-glycolic acid) nanofiber mat and an alginate-gelatin hydrogel for wound healing

A resveratrol-loaded bi-layered scaffold (RBS) that consists of a resveratrol-loaded poly(lactic-co-glycolic acid) (Res-PLGA) electrospinning nanofiber mat (upper layer) and an alginate di-aldehyde (ADA)-gelatin (GEL) crosslinking hydrogel (ADA-GEL) (lower layer) was fabricated as a wound dressing material. It was made through mimicking the epidermis and dermis of the skin. The RBS exhibited good hemostatic ability and proper swelling ability. Furthermore, HaCaT cells and human embryonic skin fibroblasts (ESFs) were also cultured in the nanofiber layer and hydrogel layer of RBS, and the results indicated that both HaCaT and ESFs could grow well in the materials. The in vivo experiment using a Sprague-Dawley (SD) rat skin wound as a model showed that the RBS could accelerate the wound healing rate compared with the Res-PLGA group and ADA4-GEL6 group. These results indicated that this resveratrol-loaded bi-layered scaffold can be a potential candidate in promoting wound healing.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

Advanced biomaterials for sustainable applications in the food industry: Updates and challenges

Maintaining the safety and quality of food are major concerns while developing biomaterial based food packaging. It offers a longer shelf-life as well as protection and quality control to the food based on international standards. Nano-biotechnology contributes to a far extent to make advanced packaging by developing multifunctional biomaterials for potential applications providing smarter materials to consumers. Applications of nano-biocomposites may thus help to deliver enhanced barrier, mechanical strength, antimicrobial and antioxidant properties to novel food packaging materials. Starch derived bioplastics, polylactic acid and polyhydroxybutyrate are examples of active bioplastics currently in the food packaging sector. This review discusses the various types of biomaterials that could be used to improve future smarter food packaging, as well as biomaterials' potential applications as food stabilizers, pathogen control agents, sensors, and edible packaging materials. The regulatory concerns related to the use of biomaterials in food packaging and commercially available biomaterials in different fields are also discussed. Development of novel biomaterials for different food packaging applications can therefore guarantee active food packaging in future.

Degradable RGD-Functionalized 3D-Printed Scaffold Promotes Osteogenesis

To establish an ideal microenvironment for regenerating maxillofacial defects, recent research interests have concentrated on developing scaffolds with intricate configurations and manipulating the stiffness of extracellular matrix toward osteogenesis. Herein, we propose to infuse a degradable RGD-functionalized alginate matrix (RAM) with osteoid-like stiffness, as an artificial extracellular matrix, to a rigid 3D-printed hydroxyapatite scaffold for maxillofacial regeneration. The 3D-printed hydroxyapatite scaffold was produced by microextrusion technology and showed good dimensional stability with consistent microporous detail. RAM was crosslinked by calcium sulfate to manipulate the stiffness, and its degradation was accelerated by partial oxidation using sodium periodate. The results revealed that viability of bone marrow stem cells was significantly improved on the RAM and was promoted on the oxidized RAM. In addition, the migration and osteogenic differentiation of bone marrow stem cells were promoted on the RAM with osteoid-like stiffness, specifically on the oxidized RAM. The in vivo evidence revealed that nonoxidized RAM with osteoid-like stiffness upregulated osteogenic genes but prevented ingrowth of newly formed bone, leading to limited regeneration. Oxidized RAM with osteoid-like stiffness facilitated collagen synthesis, angiogenesis, and osteogenesis and induced robust bone formation, thereby significantly promoting maxillofacial regeneration. Overall, this study supported that in the stabilized microenvironment, oxidized RAM with osteoid-like stiffness offered requisite mechanical cues for osteogenesis and an appropriate degradation profile to facilitate bone formation. Combining the 3D-printed hydroxyapatite scaffold and oxidized RAM with osteoid-like stiffness may be an advantageous approach for maxillofacial regeneration.

Tuning Viscoelasticity in Alginate Hydrogels for 3D Cell Culture Studies

Physical properties of the extracellular matrix (ECM) affect cell behaviors ranging from cell adhesion and migration to differentiation and gene expression, a process known as mechanotransduction. While most studies have focused on the impact of ECM stiffness, using linearly elastic materials such as polyacrylamide gels as cell culture substrates, biological tissues and ECMs are viscoelastic, which means they exhibit time-dependent mechanical responses and dissipate mechanical energy. Recent studies have revealed ECM viscoelasticity, independent of stiffness, as a critical physical parameter regulating cellular processes. These studies have used biomaterials with tunable viscoelasticity as cell-culture substrates, with alginate hydrogels being one of the most commonly used systems. Here, we detail the protocols for three approaches to modulating viscoelasticity in alginate hydrogels for 2D and 3D cell culture studies, as well as the testing of their mechanical properties. Viscoelasticity in alginate hydrogels can be tuned by varying the molecular weight of the alginate polymer, changing the type of crosslinker-ionic versus covalent-or by grafting short poly(ethylene-glycol) (PEG) chains to the alginate polymer. As these approaches are based on commercially available products and simple chemistries, these protocols should be accessible for scientists in the cell biology and bioengineering communities. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Tuning viscoelasticity by varying alginate molecular weight Basic Protocol 2: Tuning viscoelasticity with ionic versus covalent crosslinking Basic Protocol 3: Tuning viscoelasticity by adding PEG spacers to alginate chains Support Protocol 1: Testing mechanical properties of alginate hydrogels Support Protocol 2: Conjugating cell-adhesion peptide RGD to alginate.

Evaluation of the in vivo fate of ultrapure alginate in a BALB/c mouse model

The linear anionic polysaccharide alginate (ALG) has been comprehensively studied for biomedical applications, yet thus far the in vivo fate of this polymer has not been explored in detail. The current study therefore evaluates the biodistribution of ultrapure ALG (M/G ratio ≥ 0.67 with a measured M_w of 530 kg/mol and polydispersity index; PDI of 1.49) over a 14-day period in BALB/c mice. The biodistribution pattern over 2-days after sample administration using PET imaging with ⁶⁴Cu-labelled ALG showed liver and spleen uptake. This was confirmed by the 14-day biodistribution profile of cyanine 5-labelled ALG from in vivo and ex vivo fluorescence imaging. Using MacGreen mice confirmed the uptake of the ALG by macrophages in the spleen at the 2-day time point. This extended biodistribution study confirmed the clearance of only a portion of the administered ALG biopolymer, but also uptake by macrophage populations in the spleen over a 14-day period.

Engineering Hydrogel-Based Biomedical Photonics: Design, Fabrication, and Applications

Light guiding and manipulation in photonics have become ubiquitous in events ranging from everyday communications to complex robotics and nanomedicine. The speed and sensitivity of light-matter interactions offer unprecedented advantages in biomedical optics, data transmission, photomedicine, and detection of multi-scale phenomena. Recently, hydrogels have emerged as a promising candidate for interfacing photonics and bioengineering by combining their light-guiding properties with live tissue compatibility in optical, chemical, physiological, and mechanical dimensions. Herein, the latest progress over hydrogel photonics and its applications in guidance and manipulation of light is reviewed. Physics of guiding light through hydrogels and living tissues, and existing technical challenges in translating these tools into biomedical settings are discussed. A comprehensive and thorough overview of materials, fabrication protocols, and design architectures used in hydrogel photonics is provided. Finally, recent examples of applying structures such as hydrogel optical fibers, living photonic constructs, and their use as light-driven hydrogel robots, photomedicine tools, and organ-on-a-chip models are described. By providing a critical and selective evaluation of the field's status, this work sets a foundation for the next generation of hydrogel photonic research.

Covalently Crosslinked Hydrogels via Step-Growth Reactions: Crosslinking Chemistries, Polymers, and Clinical Impact

Hydrogels are an important class of biomaterials with the unique property of high-water content in a crosslinked polymer network. In particular, chemically crosslinked hydrogels have made a great clinical impact in past years because of their desirable mechanical properties and tunability of structural and chemical properties. Various polymers and step-growth crosslinking chemistries are harnessed for fabricating such covalently crosslinked hydrogels for translational research. However, selecting appropriate crosslinking chemistries and polymers for the intended clinical application is time-consuming and challenging. It requires the integration of polymer chemistry knowledge with thoughtful crosslinking reaction design. This task becomes even more challenging when other factors such as the biological mechanisms of the pathology, practical administration routes, and regulatory requirements add additional constraints. In this review, key features of crosslinking chemistries and polymers commonly used for preparing translatable hydrogels are outlined and their performance in biological systems is summarized. The examples of effective polymer/crosslinking chemistry combinations that have yielded clinically approved hydrogel products are specifically highlighted. These hydrogel design parameters in the context of the regulatory process and clinical translation barriers, providing a guideline for the rational selection of polymer/crosslinking chemistry combinations to construct hydrogels with high translational potential are further considered.

Oxidation and RGD Modification Affect the Early Neural Differentiation of Murine Embryonic Stem Cells Cultured in Core-Shell Alginate Hydrogel Microcapsules

Directed neural differentiation of embryonic stem cells (ESCs) has been studied extensively to improve the treatment of neurodegenerative disorders. This can be done through stromal-cell derived inducing activity (SDIA), by culturing ESCs directly on top of a layer of feeder stromal cells. However, the stem cells usually become mixed with the feeder cells during the differentiation process, making it difficult to obtain a pure population of the differentiated cells for further use. To address this issue, a non-planar microfluidic device is used here to encapsulate murine ESCs (mESCs) in the 3D liquid core of microcapsules with an alginate hydrogel shell of different sizes for early neural differentiation through SDIA, by culturing mESC-laden microcapsules over a feeder layer of PA6 cells. Furthermore, the alginate hydrogel shell of the microcapsules is modified via oxidation or RGD peptide conjugation to examine the mechanical and chemical effects on neural differentiation of the encapsulated mESC aggregates. A higher expression of Nestin is observed in the aggregates encapsulated in small (∼300 μm) microcapsules and cultured over the PA6 cell feeder layer. Furthermore, the modification of the alginate with RGD facilitates early neurite extension within the microcapsules. This study demonstrates that the presence of the RGD peptide, the SDIA effect of the PA6 cells, and the absence of leukemia inhibition factor from the medium can lead to the early differentiation of mESCs with extensive neurites within the 3D microenvironment of the small microcapsules. This is the first study to investigate the effects of cell adhesion and degradation of the encapsulation materials for directed neural differentiation of mESCs. The simple modifications (i.e., oxidation and RGD incorporation) of the miniaturized 3D environment for improved early neural differentiation of mESCs may potentially enhance further downstream differentiation of the mESCs into more specialized neurons for therapeutic use and drug screening.

Tunable porosity of covalently crosslinked alginate-based hydrogels and its significance in drug release behavior

Task-specific drug release is essential in the development of hydrogels as drug delivery systems. The aim of the study is to report the effect of porosity on alginate hydrogels, which may be controlled by the design of crosslinkers, on drug release behavior. Two alginate-based hydrogels were prepared: alginate-norbornene (Alg-Nb) crosslinked by disulfide-tetrazine (S-Tz; hydrogel A) and alginate-furfuryl amine (Alg-FA) crosslinked by disulfide-maleimide (S-Ma; hydrogel B). Results showed the porosity of hydrogel A was controllable by adjusting the amount of S-Tz. Gel formation was facilitated by a "click" reaction between Alg-Nb and S-Tz, producing nitrogen gas, which, in turn, acted as an in-situ pore generator. Hydrogel B showed a non-porous morphology, as gelation was processed via addition reaction between Alg-FA and S-Ma, which produced no by-product. The study showed that crosslinker proportion and porosity were significant factors influencing drug release behavior of the alginate hydrogels. The presence of a porous structure increased the drug release while non-porous hydrogels led to a very slow release. In addition, the porous alginate hydrogels could sustainably release doxorubicin for 35 days.

Injectable hydrogel for co-delivery of 5-azacytidine in zein protein nanoparticles with stem cells for cardiac function restoration

Heart failure is major cause of mortality associated with mostly Myocardial infarction (MI). Transplanting mesenchymal stem cells (MSC) have exhibited potential role in myocardial regeneration. Secretion of immune-modulatory cytokines and various growth factors after transplantation plays significant role in remodelling process of MI region. However, low retention, higher shear stress during administration and rejection at host infarct environment hinders therapeutic efficacy. Myocardial regeneration demands for accurate spatio-temporal delivery of MSCs with supportive vascular network that leads to improvement of cardiac function. In this study, injectable alginate based microporous hydrogel has been used to deliver 5-Azacytidine (5-Aza) in zein protein nanoparticle with MSCs for attenuating adverse cardiac remodelling after MI. Zein nanoparticles loaded with 5-Aza were prepared by liquid-liquid dispersion, and it was found that 35% of drug was released in 7 days supported with mathematical modelling. The presence of 5-Aza and zein in developed hydrogel supported in vitro MSC proliferation, migration and angiogenesis. Significant increased expression of cardiac specific markers, GATA4, MEF2C, MLC, SERCA and NKX2.5 was observed in vitro. 5-Aza loaded protein nanoparticle with MSCs encapsulated hydrogels in rat MI model also exhibited substantial improvement of functional cardiac parameters such as cardiac output and ejection fraction. Histopathological analysis showed reduced fibrosis, attenuated infarct expansion and cardiac tissue restoration and angiogenesis. In brief, we developed nanocarrier-hydrogel system a promising strategy for co-delivering 5-Aza as cardiac differentiation cue with MSCs to achieve higher cell retention and enhanced improvement in myocardial regeneration after MI.

Alginate and alginate composites for biomedical applications

Alginate is an edible heteropolysaccharide that abundantly available in the brown seaweed and the capsule of bacteria such as Azotobacter sp. and Pseudomonas sp. Owing to alginate gel forming capability, it is widely used in food, textile and paper industries; and to a lesser extent in biomedical applications as biomaterial to promote wound healing and tissue regeneration. This is evident from the rising use of alginate-based dressing for heavily exuding wound and their mass availability in the market nowadays. However, alginate also has limitation. When in contact with physiological environment, alginate could gelate into softer structure, consequently limits its potential in the soft tissue regeneration and becomes inappropriate for the usage related to load bearing body parts. To cater this problem, wide range of materials have been added to alginate structure, producing sturdy composite materials. For instance, the incorporation of adhesive peptide and natural polymer or synthetic polymer to alginate moieties creates an improved composite material, which not only possesses better mechanical properties compared to native alginate, but also grants additional healing capability and promote better tissue regeneration. In addition, drug release kinetic and cell viability can be further improved when alginate composite is used as encapsulating agent. In this review, preparation of alginate and alginate composite in various forms (fibre, bead, hydrogel, and 3D-printed matrices) used for biomedical application is described first, followed by the discussion of latest trend related to alginate composite utilization in wound dressing, drug delivery, and tissue engineering applications.