Evaluation of a polyvinyl alcohol-alginate based hydrogel for precise 3D bioprinting

Elossaily G, Ansari MN, Ali N. An Insight on Microfluidic Organ-on-a-Chip Models for PM2.5-Induced Pulmonary Complications

Pulmonary diseases like asthma, chronic obstructive pulmonary disorder, lung fibrosis, and lung cancer pose a significant burden to global human health. Many of these complications arise as a result of exposure to particulate matter (PM), which has been examined in several preclinical and clinical trials for its effect on several respiratory diseases. Particulate matter of size less than 2.5 μm (PM2.5) has been known to inflict unforeseen repercussions, although data from epidemiological studies to back this are pending. Conventionally utilized two-dimensional (2D) cell culture and preclinical animal models have provided insufficient benefits in emulating the in vivo physiological and pathological pulmonary conditions. Three-dimensional (3D) structural models, including organ-on-a-chip models, have experienced a developmental upsurge in recent times. Lung-on-a-chip models have the potential to simulate the specific features of the lungs. With the advancement of technology, an emerging and advanced technique termed microfluidic organ-on-a-chip has been developed with the aim of identifying the complexity of the respiratory cellular microenvironment of the body. In the present Review, the role of lung-on-a-chip modeling in reproducing pulmonary complications has been explored, with a specific emphasis on PM2.5-induced pulmonary complications.

3D Printing Assisted Fabrication of Copper-Silver Mesoporous Bioactive Glass Nanoparticles Reinforced Sodium Alginate/Poly(vinyl alcohol) Based Composite Scaffolds: Designed for Skin Tissue Engineering

Additive manufacturing (also known as 3D printing) is a promising method for producing patient-specific implants. In the present study, sodium alginate (Na-ALG)/poly(vinyl alcohol) (PVA) polymer blends of varying ratios (1:0, 3:1, 1:1, and 1:3) were used to produce tailored-designed skin scaffolds using a 3D bioprinter. Samples of skin scaffolds were printed at 20 layers with a layer height of 0.15 mm using a needle with an inner diameter of 330 μm while maintaining the extrusion speed, extrusion width, and fill density at 10 mm/s, 0.2 mm, and 85%, respectively. The Na-ALG/PVA blend with a 3:1 ratio showed the best printability due to its good viscosity and minimal nozzle leakage, allowing for the fabrication of skin scaffolds with high fidelity and the desired morphological characteristics. Then, copper-silver doped mesoporous bioactive glass nanoparticles (Cu-Ag MBGNs) were incorporated into the Na-ALG/PVA blend (which had already been prepared by using a Na-ALG:PVA ratio of 3:1) in order to obtain therapeutic (angiogenic and antibacterial) effects. The fabricated Na-ALG/PVA/Cu-Ag MBGNs biocomposite scaffolds with dimensions of 20 mm× 20 × 3 mm3 and pore size of 400 ± 60 μm exhibited a promising fidelity. The presence of chemical bonds attributed to Na-ALG, PVA, and Cu-Ag MBGNs and the uniform distribution of Na, C, and O elements within the microstructure of the scaffolds were confirmed by EDX, SEM, and FTIR analyses. The scaffolds were hydrophilic and exhibited proper swelling and degradation behavior for skin tissue engineering. According to the inhibition halo test, the scaffolds exhibited strong antibacterial activity against Staphylococcus aureus and Escherichia coli. The cytocompatibility to human-derived fibroblast cells was confirmed by the WST-8 assay and in vivo Chorioallantoic Membrane Assay. In addition, Na-ALG/PVA/Cu-Ag MBGNs showed angiogenic potential, exhibiting favorable wound healing properties.

Classification, processing, and applications of bioink and 3D bioprinting: A detailed review

With the advancement in 3D bioprinting technology, cell culture methods can design 3D environments which are both, complex and physiologically relevant. The main component in 3D bioprinting, bioink, can be split into various categories depending on the criterion of categorization. Although the choice of bioink and bioprinting process will vary greatly depending on the application, general features such as material properties, biological interaction, gelation, and viscosity are always important to consider. The foundation of 3D bioprinting is the exact layer-by-layer implantation of biological elements, biochemicals, and living cells with the spatial control of the implantation of functional elements onto the biofabricated 3D structure. Three basic strategies underlie the 3D bioprinting process: autonomous self-assembly, micro tissue building blocks, and biomimicry or biomimetics. Tissue engineering can benefit from 3D bioprinting in many ways, but there are still numerous obstacles to overcome before functional tissues can be produced and used in clinical settings. A better comprehension of the physiological characteristics of bioink materials and a higher level of ability to reproduce the intricate biologically mimicked and physiologically relevant 3D structures would be a significant improvement for 3D bioprinting to overcome the limitations.

3D Bioprinted Hydroxyapatite or Graphene Oxide Containing Nanocellulose-Based Scaffolds for Bone Regeneration

Bone tissue is usually damaged after big traumas, tumors, and increasing aging-related diseases such as osteoporosis and osteoarthritis. Current treatments are based on implanting grafts, which are shown to have several inconveniences. In this regard, tissue engineering through the 3D bioprinting technique has arisen to manufacture structures that would be a feasible therapeutic option for bone regenerative medicine. In this study, nanocellulose-alginate (NC-Alg)-based bioink is improved by adding two different inorganic components such as hydroxyapatite (HAP) and graphene oxide (GO). First, ink rheological properties and biocompatibility are evaluated as well as the influence of the sterilization process on them. Then, scaffolds are characterized. Finally, biological studies of embedded murine D1 mesenchymal stem cells engineered to secrete erythropoietin are performed. Results show that the addition of both HAP and GO prevents NC-Alg ink from viscosity lost in the sterilization process. However, GO is reduced due to short cycle autoclave sterilization, making it incompatible with this ink. In addition, HAP and GO have different influences on scaffold architecture and surface as well as in swelling capacity. Scaffolds mechanics, as well as cell viability and functionality, are promoted by both elements addition. Additionally, GO demonstrates an enhanced bone differentiation capacity.

Printability of Double Network Alginate-Based Hydrogel for 3D Bio-Printed Complex Structures

Three-dimensional (3D) bio-printing has recently emerged as a crucial technology in tissue engineering, yet there are still challenges in selecting materials to obtain good print quality. Therefore, it is essential to study the influence of the chosen material (i.e., bio-ink) and the printing parameters on the final result. The “printability” of a bio-ink indicates its suitability for bio-printing. Hydrogels are a great choice because of their biocompatibility, but their printability is crucial for exploiting their properties and ensuring high printing accuracy. However, the printing settings are seldom addressed when printing hydrogels. In this context, this study explored the printability of double network (DN) hydrogels, from printing lines (1D structures) to lattices (2D structures) and 3D tubular structures, with a focus on printing accuracy. The DN hydrogel has two entangled cross-linked networks and a balanced mechanical performance combining high strength, toughness, and biocompatibility. The combination of poly (ethylene glycol)-diacrylate (PEDGA) and sodium alginate (SA) enables the qualities mentioned earlier to be met, as well as the use of UV to prevent filament collapse under gravity. Critical correlations between the printability and settings, such as velocity and viscosity of the ink, were identified. PEGDA/alginate-based double network hydrogels were explored and prepared, and printing conditions were improved to achieve 3D complex architectures, such as tubular structures. The DN solution ink was found to be unsuitable for extrudability; hence, glycerol was added to enhance the process. Different glycerol concentrations and flow rates were investigated. The solution containing 25% glycerol and a flow rate of 2 mm/s yielded the best printing accuracy. Thanks to these parameters, a line width of 1 mm and an angle printing inaccuracy of less than 1° were achieved, indicating good shape accuracy. Once the optimal parameters were identified, a tubular structure was achieved with a high printing accuracy. This study demonstrated a 3D printing hydrogel structure using a commercial 3D bio-printer (REGEMAT 3D BIO V1) by synchronizing all parameters, serving as a reference for future more complex 3D structures.

Surface Functionalities of Polymers for Biomaterial Applications

Changes of a material biointerface allow for specialized cell signaling and diverse biological responses. Biomaterials incorporating immobilized bioactive ligands have been widely introduced and used for tissue engineering and regenerative medicine applications in order to develop biomaterials with improved functionality. Furthermore, a variety of physical and chemical techniques have been utilized to improve biomaterial functionality, particularly at the material interface. At the interface level, the interactions between materials and cells are described. The importance of surface features in cell function is then examined, with new strategies for surface modification being highlighted in detail.

Current Advances in 3D Bioprinting for Cancer Modeling and Personalized Medicine

Tumor cells evolve in a complex and heterogeneous environment composed of different cell types and an extracellular matrix. Current 2D culture methods are very limited in their ability to mimic the cancer cell environment. In recent years, various 3D models of cancer cells have been developed, notably in the form of spheroids/organoids, using scaffold or cancer-on-chip devices. However, these models have the disadvantage of not being able to precisely control the organization of multiple cell types in complex architecture and are sometimes not very reproducible in their production, and this is especially true for spheroids. Three-dimensional bioprinting can produce complex, multi-cellular, and reproducible constructs in which the matrix composition and rigidity can be adapted locally or globally to the tumor model studied. For these reasons, 3D bioprinting seems to be the technique of choice to mimic the tumor microenvironment in vivo as closely as possible. In this review, we discuss different 3D-bioprinting technologies, including bioinks and crosslinkers that can be used for in vitro cancer models and the techniques used to study cells grown in hydrogels; finally, we provide some applications of bioprinted cancer models.

Physical Modification of Hybrid Hydrogels to Fabricate Full-Scale Construct Using Three-Dimensional Bio-Printing Process

Bioprinting for regenerative medicine has been gaining a lot of popularity in today's world. Despite being one of the rigorously studied fields, there are still several challenges yet to be solved. Geometric fidelity and mechanical complexities stand as roadblocks when it comes to the printability of the customized constructs. Exploring the rheological properties of the compositions helps us understand the physical and mechanical properties of the biomaterials which are closely tied to the printability of the filament and eventually, geometric fidelity of the constructs. To ensure the structural integrity of the constructs, viscosity enhancers such as carboxymethyl cellulose (CMC) and crosslinkers like CaCl₂ and CaSO₄ were used. These crosslinkers can be used before (precrosslinking) and after (postcrosslinking) the extrusion of considered compositions to investigate and compare the outcome. To do this, mixtures of CMC (viscosity enhancer), Alginate, and CaCl₂ and CaSO₄ (crosslinkers) were prepared at various concentrations maintaining minimum solid content (≤8%). Each composition was subjected to a set of rheological tests like flow curve for shear thinning behavior, three points thixotropic for recovery rate, and amplitude test for gelation point. Various geometric fidelity identification tests were conducted and correlated with their physical properties. Some compositions were used to fabricate large-scale constructs (in cm-scale) to demonstrate their capability. This research is a thorough investigation of compositions when they are introduced to crosslinkers and viscosity enhancers which can be crucial for the 3D printing world.

Chondroitin and Dermatan Sulfate Bioinks for 3D Bioprinting and Cartilage Regeneration

Cartilage is a connective tissue which a limited capacity for healing and repairing. In this context, osteoarthritis disease may be developed with high prevalence in which the use of scaffolds may be a promising treatment. In addition, three-dimensional (3D) bioprinting has become an emerging additive manufacturing technology because of its rapid prototyping capacity and the possibility of creating complex structures. This study was focused on the development of nanocellulose-alginate (NC-Alg) based bioinks for 3D bioprinting for cartilage regeneration to which it was added chondroitin sulfate (CS) and dermatan sulfate (DS). First, rheological properties were evaluated. Then, sterilisation effect, biocompatibility and printability on developed NC-Alg-CS and NC-Alg-DS inks were evaluated. Subsequently, printed scaffolds were characterized. Finally, NC-Alg-CS and NC-Alg-DS inks were loaded with murine D1-MSCs-EPO and cell viability and functionality, as well as the chondrogenic differentiation ability were assessed. Results showed that the addition of both CS and DS to the NC-Alg ink improved its characteristics in terms of rheology and cell viability and functionality. Moreover, differentiation to cartilage was promoted on NC-Alg-CS and NC-Alg-DS scaffolds. Therefore, the utilization of MSCs containing NC-Alg-CS and NC-Alg-DS scaffolds may become a feasible tissue engineering approach for cartilage regeneration. This article is protected by copyright. All rights reserved.

3D Bio-Printability of Hybrid Pre-Crosslinked Hydrogels

Maintaining shape fidelity of 3D bio-printed scaffolds with soft biomaterials is an ongoing challenge. Here, a rheological investigation focusing on identifying useful physical and mechanical properties directly related to the geometric fidelity of 3D bio-printed scaffolds is presented. To ensure during- and post-printing shape fidelity of the scaffolds, various percentages of Carboxymethyl Cellulose (CMC) (viscosity enhancer) and different calcium salts (CaCl₂ and CaSO₄, physical cross-linkers) were mixed into alginate before extrusion to realize shape fidelity. The overall solid content of Alginate-Carboxymethyl Cellulose (CMC) was limited to 6%. A set of rheological tests, e.g., flow curves, amplitude tests, and three interval thixotropic tests, were performed to identify and compare the shear-thinning capacity, gelation points, and recovery rate of various compositions. The geometrical fidelity of the fabricated scaffolds was defined by printability and collapse tests. The effect of using multiple cross-linkers simultaneously was assessed. Various large-scale scaffolds were fabricated (up to 5.0 cm) using a pre-crosslinked hybrid. Scaffolds were assessed for the ability to support the growth of Escherichia coli using the Most Probable Number technique to quantify bacteria immediately after inoculation and 24 h later. This pre-crosslinking-based rheological property controlling technique can open a new avenue for 3D bio-fabrication of scaffolds, ensuring proper geometry.

PVA-Based Hydrogels: Promising Candidates for Articular Cartilage Repair

The complex, gradient physiological structure of articular cartilage is a severe hindrance of its self-repair, leaving the clinical treatment of cartilage defects a demanding issue to be addressed. Currently applied tissue engineering treatments and traditional non-tissue engineering treatments have different limitations, for example, cell dedifferentiation, immune rejection, and prosthesis-related complications. Thus, studies have been focusing on seeking promising candidates for novel cartilage repair methods. Polyvinyl alcohol (PVA) hydrogels with excellent biocompatibility and tunable material properties have become the alternatives. For pure PVA hydrogels, the mechanical strength and lubricity are not capable of replacing articular cartilage until proper modifications are done. This paper summarizes the research progress in PVA hydrogels, including the preparation, modification, and cartilage-repair-aimed biomimetic improvements. Design guidance of PVA hydrogels is put forward as assistance to functional hydrogel preparation. Finally, the prospects and main obstacles of PVA hydrogels are discussed.

Development, characterization and sterilisation of Nanocellulose-alginate-(hyaluronic acid)- bioinks and 3D bioprinted scaffolds for tissue engineering

3D-bioprinting is an emerging technology of high potential in tissue engineering (TE), since it shows effective control over scaffold fabrication and cell distribution. Biopolymers such as alginate (Alg), nanofibrillated cellulose (NC) and hyaluronic acid (HA) offer excellent characteristics for use as bioinks due to their excellent biocompatibility and rheological properties. Cell incorporation into the bioink requires sterilisation assurance, and autoclave, β-radiation and γ-radiation are widely used sterilisation techniques in biomedicine; however, their use in 3D-bioprinting for bioinks sterilisation is still in their early stages. In this study, different sterilisation procedures were applied on NC-Alg and NC-Alg-HA bioinks and their effect on several parameters was evaluated. Results demonstrated that NC-Alg and NC-Alg-HA bioinks suffered relevant rheological and physicochemical modifications after sterilisation; yet, it can be concluded that the short cycle autoclave is the best option to sterilise both NC-Alg based cell-free bioinks, and that the incorporation of HA to the NC-Alg bioink improves its characteristics. Additionally, 3D scaffolds were bioprinted and specifically characterized as well as the D1 mesenchymal stromal cells (D1-MSCs) embedded for cell viability analysis. Notably, the addition of HA demonstrates better scaffold properties, together with higher biocompatibility and cell viability in comparison with the NC-Alg scaffolds. Thus, the use of MSCs containing NC-Alg based scaffolds may become a feasible tissue engineering approach for regenerative medicine.

Recent trends in natural polysaccharide based bioinks for multiscale 3D printing in tissue regeneration: A review

Biofabrication by three-dimensional (3D) printing has been an attractive technology in harnessing the possibility to print anatomical shaped native tissues with controlled architecture and resolution. 3D printing offers the possibility to reproduce complex microarchitecture of native tissues by printing live cells in a layer by layer deposition to provide a biomimetic structural environment for tissue formation and host tissue integration. Plant based biomaterials derived from green and sustainable sources have represented to emulate native physicochemical and biological cues in order to direct specific cellular response and formation of new tissues through biomolecular recognition patterns. This comprehensive review aims to analyze and identify the most commonly used plant based bioinks for 3D printing applications. An overview on the role of different plant based biomaterial of terrestrial origin (Starch, Nanocellulose and Pectin) and marine origin (Ulvan, Alginate, Fucoidan, Agarose and Carrageenan) used for 3D printing applications are discussed elaborately. Furthermore, this review will also emphasis in the functional aspects of different 3D printers, appropriate printing material, merits and demerits of numerous plant based bioinks in developing 3D printed tissue-like constructs. Additionally, the underlying potential benefits, limitations and future perspectives of plant based bioinks for tissue engineering (TE) applications are also discussed.

Enhanced Biomechanical Properties of Polyvinyl Alcohol-Based Hybrid Scaffolds for Cartilage Tissue Engineering

Articular cartilage damage is a primary feature of osteoarthritis and other inflammatory joint diseases (i.e., rheumatoid arthritis). Repairing articular cartilage is highly challenging due to its avascular/aneural nature and low cellularity. To induce functional neocartilage formation, the tissue substitute must have mechanical properties which can adapt well to the loading conditions of the joint. Among the various biomaterials which may function as cartilage replacements, polyvinyl alcohol (PVA) hydrogels stand out for their high biocompatibility and tunable mechanical features. This review article describes and discusses the enrichment of PVA with natural materials (i.e., collagen, hyaluronic acid, hydroxyapatite, chitosan, alginate, extracellular matrix) ± synthetic additives (i.e., polyacrylic acid, poly-lactic-co-glycolic acid, poly(ethylene glycol) diacrylate, graphene oxide, bioactive glass) to produce cartilage substitutes with enhanced mechanical performance. PVA-based hybrid scaffolds have been investigated mainly by compression, tensile, friction, stress relaxation and creep tests, demonstrating increased stiffness and friction properties, and with cartilage-like viscoelastic behavior. In vitro and in vivo biocompatibility studies revealed positive outcomes but also many gaps yet to be addressed. Thus, recommendations for future research are proposed in order to prompt further progress in the fabrication of PVA-based hybrid scaffolds which increasingly match the biological and mechanical properties of native cartilage.

Rational Design of Smart Hydrogels for Biomedical Applications

Hydrogels are polymeric three-dimensional network structures with high water content. Due to their superior biocompatibility and low toxicity, hydrogels play a significant role in the biomedical fields. Hydrogels are categorized by the composition from natural polymers to synthetic polymers. To meet the complicated situation in the biomedical applications, suitable host–guest supramolecular interactions are rationally selected. This review will have an introduction of hydrogel classification based on the formulation molecules, and then a discussion over the rational design of the intelligent hydrogel to the environmental stimuli such as temperature, irradiation, pH, and targeted biomolecules. Further, the applications of rationally designed smart hydrogels in the biomedical field will be presented, such as tissue repair, drug delivery, and cancer therapy. Finally, the perspectives and the challenges of smart hydrogels will be outlined.

The potential impact of polyethylenimine on biological behavior of 3D-printed alginate scaffolds

Three-dimensional (3D) printing using biocompatible materials is a novel technology having a great potential for fabricating precise 3D scaffolds for tissue engineering. Alginate hydrogel undergoes unstable swelling and degradation properties as well as suffers from poor cell adhesion due to the lack of cell binding domains. These limit its applications in tissue engineering. In this study, 3D-printed alginate scaffolds were coated by branch polyethylenimine (PEI) to overcome the limitation of alginate because the branch PEI is a cationic polymer with a large number of active N-H groups. The results indicated that surface modification of 3D-printed alginate scaffolds using an appropriate concentration of PEI potentially promoted the fibroblast cells functions in 3D-printed alginate scaffolds, increased cell adhesion, cell proliferation and cell spreading through providing a large amount of N-H groups and increasing hydrophilicity of the surface. The degradation rate of alginate was degraded by interaction between N-H groups in PEI and -COO- groups in alginate structure and followed by the formation strong barrier layer in the interface of alginate and PEI. Therefore, ALG-PEI scaffolds can be a good candidate for tissue engineering and wound dressing applications.

Radical photoinitiation with LEDs and applications in the 3D printing of composites

Radical initiation upon LED light irradiation is discussed herein as well as its application in additive manufacturing. The ability of manufacturing complex structures, freedom of design, low energy consumption, fast prototyping, and excellent spatial resolution are the main benefits of the 3D printing technology by photopolymerization. Therefore, the 3D printing of composites through photopolymerization processes is developing rapidly in the academia and industry, and has been a turning point of additive manufacturing (AM). In the present review, an overview of radical initiation with LEDs (i.e., the photopolymerization LED technology, the photoinitiating systems, and the polymerizable media) and of the main 3D printing methods by photopolymerization, materials, and their applications in different fields has been carried out. As a challenging topic, the issue of light penetration in a filled matrix for the access to composites is discussed, including the light transmittance of the composite, the mismatch of the refractive index between the filler and the monomer, the factors of the filler, and the adverse influence of low light penetration on the 3D printing process. In particular, the popular applications of 3D printing by photopolymerization in biomedical science, electronic industry, materials for adsorption, and 4D printing are discussed. Overall, this review gives an overview of the 3D printing of polymer matrix composites through photopolymerization processes as a benchmark for future research and development.

Robotic in situ 3D bio-printing technology for repairing large segmental bone defects

Introduction

The traditional clinical treatment of long segmental bone defects usually requires multiple operations and depends on donor availability. The 3D bio-printing technology constitutes a great potential therapeutic tool for such an injury. However, in situ 3D bio-printing remains a major challenge.

Objectives

In this study, we report the repair of long segmental bone defects by in situ 3D bio-printing using a robotic manipulator 3D printer in a swine model.

Methods

We systematically optimized bio-ink gelation under physiological conditions to achieve desirable mechanical properties suitable for bone regeneration, and a D-H kinematic model was used to improve printing accuracy to 0.5 mm.

Results

These technical improvements allowed the repair of long segmental defects generated on the right tibia of pigs using 3D bio-printing within 12 min. The 3D bio-printing group showed improved treatment effects after 3 months.

Conclusion

These findings indicated that robotic in situ 3D bio-printing is promising for direct clinical application.

Hydrogels for Bioprinting: A Systematic Review of Hydrogels Synthesis, Bioprinting Parameters, and Bioprinted Structures Behavior

Nowadays, bioprinting is rapidly evolving and hydrogels are a key component for its success. In this sense, synthesis of hydrogels, as well as bioprinting process, and cross-linking of bioinks represent different challenges for the scientific community. A set of unified criteria and a common framework are missing, so multidisciplinary research teams might not efficiently share the advances and limitations of bioprinting. Although multiple combinations of materials and proportions have been used for several applications, it is still unclear the relationship between good printability of hydrogels and better medical/clinical behavior of bioprinted structures. For this reason, a PRISMA methodology was conducted in this review. Thus, 1,774 papers were retrieved from PUBMED, WOS, and SCOPUS databases. After selection, 118 papers were analyzed to extract information about materials, hydrogel synthesis, bioprinting process, and tests performed on bioprinted structures. The aim of this systematic review is to analyze materials used and their influence on the bioprinting parameters that ultimately generate tridimensional structures. Furthermore, a comparison of mechanical and cellular behavior of those bioprinted structures is presented. Finally, some conclusions and recommendations are exposed to improve reproducibility and facilitate a fair comparison of results.

Reversible Mechanical Regulation and Splicing Ability of Alginate-Based Gel Based on Photo-Responsiveness of Molecular-Level Conformation

In this study, benefiting from the sensitive molecular conformation transversion in azobenzene, a new strategy for fabricating alginate gels with the abilities of splicing and photo-responsive mechanical adjustment is reported. Firstly, a 4,4’-azobis(benzoylhydrazide) (Azo-hydrazide) linker was used to crosslink alginate physically via the electrostatic interaction between hydrazide groups and carboxyl groups. It was then shaped and transferred in situ to a chemically crosslinked gel via 450 nm light irradiation. Under the irradiation, the molecular conformation change of azobenzene in the linker was able to form covalent bonds at the crosslinking points of the gels. Furthermore, the reversible conformation transformation of azobenzene was able to induce the increase and decrease of the storage modulus under irradiation with 365 nm light and 450 nm light, respectively, while also providing gel-like mechanical properties, depending upon the irradiation time and given wavelength. Meanwhile, the results also indicated that active groups could contribute to the splicing ability of the gel and construct a hollow cavity structure. It is believed that this work could provide a versatile strategy for preparing photo-responsive gels with reversibly tunable mechanical properties.

Pectin Methacrylate (PEMA) and Gelatin-Based Hydrogels for Cell Delivery: Converting Waste Materials into Biomaterials

The emergence of nontoxic, eco-friendly, and biocompatible polymers derived from natural sources has added a new and exciting dimension to the development of low-cost and scalable biomaterials for tissue engineering applications. Here, we have developed a mechanically strong and durable hydrogel composed of an eco-friendly biopolymer that exists within the cell walls of fruits and plants. Its trade name is pectin, and it bears many similarities with natural polysaccharides in the native extracellular matrix. Specifically, we have employed a new pathway to transform pectin into a ultraviolet (UV)-cross-linkable pectin methacrylate (PEMA) polymer. To endow this hydrogel matrix with cell differentiation and cell spreading properties, we have also incorporated thiolated gelatin into the system. Notably, we were able to fine-tune the compressive modulus of this hydrogel in the range ∼0.5 to ∼24 kPa: advantageously, our results demonstrated that the hydrogels can support growth and viability for a wide range of three-dimensionally (3D) encapsulated cells that include muscle progenitor (C2C12), neural progenitor (PC12), and human mesenchymal stem cells (hMSCs). Our results also indicate that PEMA-gelatin-encapsulated hMSCs can facilitate the formation of bonelike apatite after 5 weeks in culture. Finally, we have demonstrated that PEMA-gelatin can yield micropatterned cell-laden 3D constructs through UV light-assisted lithography. The simplicity, scalability, processability, tunability, bioactivity, and low-cost features of this new hydrogel system highlight its potential as a stem cell carrier that is capable of bridging the gap between clinic and laboratory.