Evaluation of gelatin bloom strength on gelatin methacryloyl hydrogel properties

Gelatin methacryloyl (GelMA) hydrogels are widely used for a variety of tissue engineering applications. The properties of gelatin can affect the mechanical properties of gelatin gels; however, the role of gelatin properties such as bloom strength on GelMA hydrogels has not yet been explored. Bloom strength is a food industry standard for describing the quality of gelatin, where higher bloom strength is associated with higher gelatin molecular weight. Here, we evaluate the role of bloom strength on GelMA hydrogel mechanical properties. We determined that both bloom strength of gelatin and weight percent of GelMA influenced both stiffness and viscoelastic ratio; however, only bloom strength affected diffusivity, permeability, and pore size. With this library of GelMA hydrogels of varying properties, we then encapsulated Swan71 trophoblast spheroids in these hydrogel variants to assess how bloom strength affects trophoblast spheroid morphology. Overall, we observed a decreasing trend of spheroid area and Feret diameter as bloom strength increased. In identifying clear relationships between bloom strength, hydrogel mechanical properties, and trophoblast spheroid morphology, we demonstrate that bloom strength should considered when designing tissue engineered constructs.

Multifunctional hyaluronic acid/gelatin methacryloyl core-shell microneedle for comprehensively treating oral mucosal ulcers

Oral ulceration is the most common oral mucosal disease. Oral mucosal ulcers are extremely painful, may interfere with eating and speaking, and potentially complicate systemic symptoms in severe cases. The humid and highly dynamic environment of the oral cavity makes local drug administration for treating oral mucosal ulcers challenging. To overcome these challenges, we designed and prepared a novel dissolving microneedle (MN) patch containing multiple drugs in a core-shell to promote oral ulcer healing. The MNs contained a methacrylate gelatin shell layer of basic fibroblast growth factor (bFGF), a hyaluronic acid (HA) core loaded with dexamethasone (DXMS), and zeolite imidazoline framework-8 (ZIF-8) encapsulated in the HA-based backplane. Progressive degradation of gelatin methacryloyl (GelMA) from the tip of the MN patch in the oral mucosa resulted in sustained bFGF release at the lesion site, significantly promoting cell migration, proliferation, and angiogenesis. Moreover, the rapid release of HA and, subsequently, DXMS inhibited inflammation, and the remaining MN backing after the tip dissolved behaved as a dressing, releasing ZIF-8 for its antimicrobial effects. This novel, multifunctional, transmucosal core-shell MN patch exhibited excellent anti-inflammatory, antimicrobial, and pro-healing effects in vivo and in vitro, suggesting that it can promote oral ulcer healing.

SLA-3d printed building and characteristics of GelMA/HAP biomaterials with gradient porous structure

Developing a gradient porous scaffold similar to bone structure is gaining increasing attention in bone tissue engineering. The GelMA/HAP hydrogel has demonstrated potential in bone repair. Although 3D printing can build GelMA/HAP with porous structure, fabricating porous GelMA/HAP with gradient porosity and pore size in one step remains challenging. In this paper, a gradient porous structure with controllable pore size, based on gelatin methacryloyl (GelMA) and hydxroxyapatite (HAP), was engineered and printed using stereolithography. Firstly, the GelMA and HAP were mixed to prepare a hydrogel with a solid content ranging from 10 wt% to 50 wt% for stereolithography. Taking advantage of the sol-gel characteristics of GelMA/HAP hydrogel, GelMA/HAP was fed on the workbench through a combination of extrusion and paving to form a thin layer. During the curing of each layer, the hydrogel exposed to the curing of a single UV beam immediately solidified, forming a highly interconnected porous structure. Additionally, the hydrogel outside the scanning range could be further polymerized to form a relatively dense structure due to the residual laser energy. Finally, without gradient structural design or changing printing parameters, the gradient porous structure of bone-like could be printed in a single-step process. By adjusting the curing parameters of the single UV beam and the concentration and size of ceramic in the hydrogel, the printed pore diameter of the spongy structure could be controlled within the range of 50-260 μm, while the thickness of the compact area could be adjusted within 130-670 μm.

Hydrophobic association: A facile approach to prepare physical cross-linked gelatin hydrogel with desirable thermal stability, flexibility and self-healing ability

Methacrylic anhydride was added to 20 % gelatin solution to prepare gelatin methacryloyl (GelMA) but an unexpected gelation process was observed within several minutes. The experimental data revealed that the methacryloyl substitution can increase the hydrophobicity of gelatin and the micellar diameter in solution. Therefore, we speculated that the methacryloyl substitution caused the formation of micellar cross-links based on the hydrophobic residues of gelatin and the methacryloyl groups, thus obtaining the hydrophobic association hydrogels. The thixotropic and tensile experiments confirmed that GelMA hydrogel possessed the features of hydrophobic association hydrogels like self-healing and stretchable abilities. The rheological experiments revealed that the gelation rate and the mechanical strength of the GelMA hydrogels were in direct proportion to the concentration of GelMA and the degree of methacryloyl substitution. GelMA hydrogels possessed desirable thermal stability that it didn't melt after being heated to 90 °C. Furthermore, the MTT assays and calcein AM/PI staining revealed that GelMA hydrogel was biocompatible. These results collectively confirm that the hydrophobic association is a prospective and facile approach to prepare gelatin hydrogel with desirable properties for further application.

Guiding bone cell network formation in 3D via photosensitized two-photon ablation

A long-standing challenge in skeletal tissue engineering is to reconstruct a three-dimensionally (3D) interconnected bone cell network in vitro that mimics the native bone microarchitecture. While conventional hydrogels are extensively used in studying bone cell behavior in vitro, current techniques lack the precision to manipulate the complex pericellular environment found in bone. The goal of this study is to guide single bone cells to form a 3D network in vitro via photosensitized two-photon ablation of microchannels in gelatin methacryloyl (GelMA) hydrogels. A water-soluble two-photon photosensitizer (P2CK) was added to soft GelMA hydrogels to enhance the ablation efficiency. Remarkably, adding 0.5 mM P2CK reduced the energy dosage threshold five-fold compared to untreated controls, enabling more cell-compatible ablation. By employing low-energy ablation (100 J/cm2) with a grid pattern of 1 µm wide and 30 µm deep microchannels, we induced dendritic outgrowth in human mesenchymal stem cells (hMSC). After 7 days, the cells successfully utilized the microchannels and formed a 3D network. Our findings reveal that cellular viability after low-energy ablation was comparable to unablated controls, whereas high-energy ablation (500 J/cm2) resulted in 42 % cell death. Low-energy grid ablation significantly promoted network formation and >40 µm long protrusion outgrowth. While the broad-spectrum matrix metalloproteinase inhibitor (GM6001) reduced cell spreading by inhibiting matrix degradation, cells invaded the microchannel grid with long protrusions. Collectively, these results emphasize the potential of photosensitized two-photon hydrogel ablation as a high-precision tool for laser-guided biofabrication of 3D cellular networks in vitro. STATEMENT OF SIGNIFICANCE: The inaccessible nature of osteocyte networks in bones renders fundamental research on skeletal biology a major challenge. This limit is partly due to the lack of high-resolution tools that can manipulate the pericellular environment in 3D cultures in vitro. To create bone-like cellular networks, we employ a two-photon laser in combination with a two-photon sensitizer to erode microchannels with low laser dosages into GelMA hydrogels. By providing a grid of microchannels, the cells self-organized into a 3D interconnected network within days. Laser-guided formation of 3D networks from single cells at micron-scale resolution is demonstrated for the first time. In future, we envisage in vitro generation of bone cell networks with user-dictated morphologies for both fundamental and translational bone research.

GelMA/TCP nanocomposite scaffold for vital pulp therapy

Pulp capping is a necessary procedure for preserving the vitality and health of the dental pulp, playing a crucial role in preventing the need for root canal treatment or tooth extraction. Here, we developed an electrospun gelatin methacryloyl (GelMA) fibrous scaffold incorporating beta-tricalcium phosphate (TCP) particles for pulp capping. A comprehensive morphological, physical-chemical, and mechanical characterization of the engineered fibrous scaffolds was performed. In vitro bioactivity, cell compatibility, and odontogenic differentiation potential of the scaffolds in dental pulp stem cells (DPSCs) were also evaluated. A pre-clinical in vivo model was used to determine the therapeutic role of the GelMA/TCP scaffolds in promoting hard tissue formation. Morphological, chemical, and thermal analyses confirmed effective TCP incorporation in the GelMA nanofibers. The GelMA+20%TCP nanofibrous scaffold exhibited bead-free morphology and suitable mechanical and degradation properties. In vitro, GelMA+20%TCP scaffolds supported apatite-like formation, improved cell spreading, and increased deposition of mineralization nodules. Gene expression analysis revealed upregulation of ALPL, RUNX2, COL1A1, and DMP1 in the presence of TCP-laden scaffolds. In vivo, analyses showed mild inflammatory reaction upon scaffolds' contact while supporting mineralized tissue formation. Although the levels of Nestin and DMP1 proteins did not exceed those associated with the clinical reference treatment (i.e., mineral trioxide aggregate), the GelMA+20%TCP scaffold exhibited comparable levels, thus suggesting the emergence of differentiated odontoblast-like cells capable of dentin matrix secretion. Our innovative GelMA/TCP scaffold represents a simplified and efficient alternative to conventional pulp-capping biomaterials. STATEMENT OF SIGNIFICANCE: Vital pulp therapy (VPT) aims to preserve dental pulp vitality and avoid root canal treatment. Biomaterials that bolster mineralized tissue regeneration with ease of use are still lacking. We successfully engineered gelatin methacryloyl (GelMA) electrospun scaffolds incorporated with beta-tricalcium phosphate (TCP) for VPT. Notably, electrospun GelMA-based scaffolds containing 20% (w/v) of TCP exhibited favorable mechanical properties and degradation, cytocompatibility, and mineralization potential indicated by apatite-like structures in vitro and mineralized tissue deposition in vivo, although not surpassing those associated with the standard of care. Collectively, our innovative GelMA/TCP scaffold represents a simplified alternative to conventional pulp capping materials such as MTA and Biodentine™ since it is a ready-to-use biomaterial, requires no setting time, and is therapeutically effective.

Bilayer osteochondral graft in rabbit xenogeneic transplantation model comprising sintered 3D-printed bioceramic and human adipose-derived stem cells laden biohydrogel

Reconstruction of severe osteochondral defects in articular cartilage and subchondral trabecular bone remains a challenging problem. The well-integrated bilayer osteochondral graft design expects to be guided the chondrogenic and osteogenic differentiation for stem cells and provides a promising solution for osteochondral tissue repair in this study. The subchondral bone scaffold approach is based on the developed finer and denser 3D β-tricalcium phosphate (β-TCP) bioceramic scaffold process, which is made using a digital light processing (DLP) technology and the novel photocurable negative thermo-responsive (NTR) bioceramic slurry. Then, the concave-top disc sintered 3D-printed bioceramic incorporates the human adipose-derived stem cells (hADSCs) laden photo-cured hybrid biohydrogel (HG + 0.5AFnSi) comprised of hyaluronic acid methacryloyl (HAMA), gelatin methacryloyl (GelMA), and 0.5% (w/v) acrylate-functionalized nano-silica (AFnSi) crosslinker. The 3D β-TCP bioceramic compartment is used to provide essential mechanical support for cartilage regeneration in the long term and slow biodegradation. However, the apparent density and compressive strength of the 3D β-TCP bioceramics can be obtained for ~ 94.8% theoretical density and 11.38 ± 1.72 MPa, respectively. In addition, the in vivo results demonstrated that the hADSC + HG + 0.5AFnSi/3D β-TCP of the bilayer osteochondral graft showed a much better osteochondral defect repair outcome in a rabbit model. The other word, the subchondral bone scaffold of 3D β-TCP bioceramic could accelerate the bone formation and integration with the adjacent host cancellous tissue at 12 weeks after surgery. And then, a thicker cartilage layer with a smooth surface and uniformly aligned chondrocytes were observed by providing enough steady mechanical support of the 3D β-TCP bioceramic scaffold.

[Nilotinib-loaded gelatin methacryloyl microneedles patch for the treatment of cardiac dysfunction after myocardial infarction]

The study aimed to evaluate the therapeutic effect of nilotinib-loaded biocompatible gelatin methacryloyl (GelMA) microneedles patch on cardiac dysfunction after myocardial infarction(MI), and provide a new clinical perspective of myocardial fibrosis therapies. The GelMA microneedles patches were attached to the epicardial surface of the infarct and peri-infarct zone in order to deliver the anti-fibrosis drug nilotinib on the 10th day after MI, when the scar had matured. Cardiac function and left ventricular remodeling were assessed by such as echocardiography, BNP (brain natriuretic peptide) and the heart weight/body weight ratio (HW/BW). Myocardial hypertrophy and fibrosis were examined by WGA (wheat germ agglutinin) staining, HE (hematoxylin-eosin staining) staining and Sirius Red staining. The results showed that the nilotinib-loaded microneedles patch could effectively attenuate fibrosis expansion in the peri-infarct zone and myocardial hypertrophy, prevent adverse ventricular remodeling and finally improve cardiac function. This treatment strategy is a beneficial attempt to correct the cardiac dysfunction after myocardial infarction, which is expected to become a new strategy to correct the cardiac dysfunction after MI. This is of great clinical significance for improving the long-term prognosis of MI patients.

Photo-crosslinked gelatin methacryloyl hydrogel strengthened with calcium phosphate-based nanoparticles for early healing of rabbit calvarial defects

PURPOSE

The aim of this study was to investigate the efficacy of photo-crosslinked gelatin methacryloyl (GelMa) hydrogel containing calcium phosphate nanoparticles (CNp) when applying different fabrication methods for bone regeneration.

METHODS

Four circular defects were created in the calvaria of 10 rabbits. Each defect was randomly allocated to the following study groups: 1) the sham control group, 2) the GelMa group (defect filled with crosslinked GelMa hydrogel), 3) the CNp-GelMa group (GelMa hydrogel crosslinked with nanoparticles), and 4) the CNp+GelMa group (crosslinked GelMa loaded with nanoparticles). At 2, 4, and 8 weeks, samples were harvested, and histological and micro-computed tomography analyses were performed.

RESULTS

Histomorphometric analysis showed that the CNp-GelMa and CNp+GelMa groups at 2 weeks had significantly greater total augmented areas than the control group (P<0.05). The greatest new bone area was observed in the CNp-GelMa group, but without statistical significance (P>0.05). Crosslinked GelMa hydrogel with nanoparticles exhibited good biocompatibility with a minimal inflammatory reaction.

CONCLUSIONS

There was no difference in the efficacy of bone regeneration according to the synthesized method of photo-crosslinked GelMa hydrogel with nanoparticles. However, these materials could remain within a bone defect up to 2 weeks and showed good biocompatibility with little inflammatory response. Further improvement in mechanical properties and resistance to enzymatic degradation would be needed for the clinical application.

Load-induced fluid pressurisation in hydrogel systems before and after reinforcement by melt-electrowritten fibrous meshes

Fluid pressure develops transiently within mechanically-loaded, cell-embedding hydrogels, but its magnitude depends on the intrinsic material properties of the hydrogel and cannot be easily altered. The recently developed melt-electrowriting (MEW) technique enables three-dimensional printing of structured fibrous mesh with small fibre diameter (20 μm). The MEW mesh with 20 μm fibre diameter can synergistically increase the instantaneous mechanical stiffness of soft hydrogels. However, the reinforcing mechanism of the MEW meshes is not well understood, and may involve load-induced fluid pressurisation. Here, we examined the reinforcing effect of MEW meshes in three hydrogels: gelatin methacryloyl (GelMA), agarose and alginate, and the role of load-induced fluid pressurisation in the MEW reinforcement. We tested the hydrogels with and without MEW mesh (i.e., hydrogel alone, and MEW-hydrogel composite) using micro-indentation and unconfined compression, and analysed the mechanical data using biphasic Hertz and mixture models. We found that the MEW mesh altered the tension-to-compression modulus ratio differently for hydrogels that are cross-linked differently, which led to a variable change to their load-induced fluid pressurisation. MEW meshes only enhanced the fluid pressurisation for GelMA, but not for agarose or alginate. We speculate that only covalently cross-linked hydrogels (GelMA) can effectively tense the MEW meshes, thereby enhancing the fluid pressure developed during compressive loading. In conclusion, load-induced fluid pressurisation in selected hydrogels was enhanced by MEW fibrous mesh, and may be controlled by MEW mesh of different designs in the future, thereby making fluid pressure a tunable cell growth stimulus for tissue engineering involving mechanical stimulation.

3D bioprinting of corneal decellularized extracellular matrix: GelMA composite hydrogel for corneal stroma engineering

Millions of individuals across the world suffer from corneal stromal diseases that impair vision. Fortunately, three-dimensional (3D) bioprinting technology which has revolutionized the field of regenerative tissue engineering makes it feasible to create personalized corneas. In this study, an artificial cornea with a high degree of precision, smoothness, and programmable curvature was prepared by using digital light processing (DLP) 3D bioprinting in one piece with no support structure, and the construct was then confirmed by optical coherence tomography (OCT). On the basis of this approach, we developed a novel corneal decellularized extracellular matrix/gelatin methacryloyl (CECM-GelMA) bioink that can produce complex microenvironments with highly tunable mechanical properties while retaining high optical transmittance. Furthermore, the composite hydrogel was loaded with human corneal fibroblasts (hCFs), and in vitro experiments showed that the hydrogel maintained high cell viability and expressed core proteins. In vivo tests revealed that the hydrogel might promote epithelial regeneration, keep the matrix aligned, and restore clarity. This demonstrates how crucial a role CECM plays in establishing a favorable environment that encourages the transformation of cell function. Therefore, artificial corneas that can be rapidly customized have a huge potential in the development of in vitro corneal matrix analogs.

Minimally invasive injection of biomimetic Nano@Microgel for in situ ovarian cancer treatment through enhanced photodynamic reactions and photothermal combined therapy

Photodynamic therapy (PDT) induces immunogenic cell death (ICD) by producing reactive oxygen species (ROS), making it an ideal method for cancer treatment. However, the extremely lower level of oxygen, short half-life of produced ROS, and limited photosensitizers accumulating in the tumor site via intravenous administration are the main reasons that limit the further application of PDT. To address these issues, we loaded the photosensitizer porphine (THPP) into biomimetic gold nanorod-mesoporous silica core-shell nanoparticles (Au-MSN NPs) to prepare Au@MSN/THPP@CM NPs. We then seeded the NPs together with catalase (CAT) into a gelatin methacryloyl (GelMA) microgel matrix to form Au@MSN-Ter/THPP@CM@GelMA/CAT microspheres consisting of biomimetic nano@microgel. The NPs and biomimetic nano@microgel exhibited enhanced photodynamic (PD) reaction and excellent photothermal conversion ability. Moreover, we further conjugated an endoplasmic reticulum (ER) targeting ligand Tosyl Ethylenediamine (Ter) on the surface of Au-MSN NPs. The results showed that both Au@MSN-Ter/THPP@CM NPs and the finally formed Au@MSN-Ter/THPP@CM@GelMA/CAT biomimetic nano@microgel induced precise and prolonged ER stress through photodynamic reactions, which stimulated the exposure of the proapoptotic calreticulin (CRT) on the cell membrane and increased the release of high mobility group box 1 (HMGB1) form the nucleus in SKOV3 cells under near-infrared (NIR) laser irradiation. Additionally, a single dose of the nano@microgel delivered through minimally invasive injection generated a significant anti-tumor effect in the SKOV3 cell line-derived orthotopic ovarian cancer mouse model through a PD and PT combination therapy. This study offers a new strategy for enhanced PDT and provides a PD/PT synergistic treatment method for ovarian cancer.

Development of a biomimetic arch-like 3D bioprinted construct for cartilage regeneration using gelatin methacryloyl and silk fibroin-gelatin bioinks

In recent years, engineering biomimetic cellular microenvironments have been a top priority for regenerative medicine. Collagen II, which is arranged in arches, forms the predominant fiber network in articular cartilage. Due to the shortage of suitable microfabrication techniques capable of producing 3D fibrous structures, in vitro replication of the arch-like cartilaginous tissue constitutes one of the major challenges. Hence, in the present study, we report a 3D bioprinting approach for fabricating arch-like constructs using two types of bioinks, gelatin methacryloyl(GelMa) and silk fibroin-gelatin(SF-G). The bioprinted SF-G constructs displayed increased proliferation of the encapsulated human bone marrow-derived mesenchymal stem cells compared to the GelMA constructs. Biochemical assays, gene, and protein expression exhibited the superior role of SF-G in forming the fibrous collagen network and chondrogenesis. Protein-protein interaction study using Metascape evaluated the function of the proteins involved. Further GeneMANIA and STRING analysis using Col2A1, SOX9, ACAN, and the genes upregulated on day 21 in RT-PCR, i.e., β-catenin, TGFβR1, Col1A1 in SF-G and PRG4, Col10A1, MMP13 in GelMA validated our in vitro results. These findings emphasized the role of SF-G in regulating the Wnt/β-catenin and TGF-β signaling pathways. Hence, the 3D bioprinted arch-like constructs possess a substantial potential for cartilage regeneration.&#xD;&#xD.

A vertical additive-lathe printing system for the fabrication of tubular constructs using gelatin methacryloyl hydrogel

Reproducing both the mechanical and biological performance of native blood vessels remains an ongoing challenge in vascular tissue engineering. Additive-lathe printing offers an attractive method of fabricating long tubular constructs as a potential vascular graft for the treatment of cardiovascular diseases. Printing hydrogels onto rotating horizontal mandrels often leads to sagging, resulting in poor and variable mechanical properties. In this study, an additive-lathe printing system with a vertical mandrel to fabricate tubular constructs is presented. Various concentrations of gelatin methacryloyl (gelMA) hydrogel were used to print grafts on the rotating mandrel in a helical pattern. The printing parameters were selected to achieve the bonding of consecutive gelMA filaments to improve the quality of the printed graft. The hydrogel filaments were fused properly under the action of gravity on the vertical mandrel. Thus, the vertical additive-lathe printing system was used to print uniform wall thickness grafts, eliminating the hydrogel sagging problem. Tensile testing performed in both circumferential and longitudinal direction revealed that the anisotropic properties of printed gelMA constructs were similar to those observed in the native blood vessels. In addition, no leakage was detected through the walls of the gelMA grafts during burst pressure measurement. Therefore, the current printing setup could be utilized to print vascular grafts for the treatment of cardiovascular diseases.

Dual drug-loaded hydrogels with pH-responsive and antibacterial activity for skin wound dressing

Antibacterial and hemostatic properties are essential for wound healing dressing. In this study, a new type of hydrogel composed of gelatin methacryloyl (GelMA) and hyaluronic acid-aldehyde (HA-CHO) is fabricated by photo-crosslinking and respectively loaded with a single drug gentamicin sulfate (GS), and two drugs of GS and lysozyme (LZM). The composite hydrogel of GelMA and HA-CHO is successfully synthesized by the aldehyde and Schiff base reactions. The structures and compositions of the hydrogels with and without drug loaded are characterized by FT-IR, ¹H NMR, and XPS. Furthermore, the microstructure and swelling behaviour of hydrogels prove that the content of HA-CHO has a significant role in the formation of hydrogels with dense porous structures and super absorbent. pH 7.4 and pH 5.0 conditions are used to evaluate the drug release behaviour of the obtained hydrogels. The released amount of GS of the drug-loaded hydrogels in the acidic buffer is more than that of the physiological environment because of the cleaved Schiff base bonds and the electrostatic interaction. Especially for the dual drug-loaded hydrogel GelMA/HA-CHO/GS/LZM, the released ratio of GS is elevated from 59 % in pH 7.4 buffer to about 78 % in pH 5.0 buffer within the first 6 h, which verifies the excellent pH-stimulus responsiveness. These endow the GS-LZM dual drug-loaded hydrogels with superior antibacterial efficiencies to that of the single GS drug-loaded hydrogels, no drug-loaded hydrogels, and SEBS control, especially in inhibiting S. aureus in a lower concentration of 10⁶ CFU mL^-1, which can be attributed to the synergistic effect of LZM and GS. For S. aureus at 10⁶ CFU mL^-1, the bacterial survival of GelMA/HA-CHO/GS/LZM is 1.1 %, which shows outstanding antibacterial effect. Hence, the drug-loaded hydrogels, especially the dual drug-loaded hydrogels with pH-responsive, antibacterial, and hemostatic properties have great potential as wound healing materials.

Endotoxin contamination alters macrophage-cancer cell interaction and therapeutic efficacy in pre-clinical 3D in vitro models

The rapid developments in biofabrication, in particular 3D bioprinting, in the recent years have facilitated the need for novel biomaterials that aim to replicate the target tissue in great detail. The presence of endotoxins in these biomaterials is often an overlooked problem. In pre-clinical 3D in vitro models, endotoxins can have significant influence on cell behavior and credibility of the model. In this study we demonstrate the effects of high levels of endotoxins in commercially-available gelatin on the macrophage-cancer cell crosstalk in a 3D bioprinted co-culture model. First, it is demonstrated that, while presenting the same mechanical and structural stimuli, high levels of endotoxin can have significant influence on the metabolic activity of macrophages and cancer cells. Furthermore, this study shows that high endotoxin contamination causes a strong inflammatory reaction in macrophages and significantly inhibits the effects of a paracrine macrophage-cancer cell co-culture. At last, it is demonstrated that the differences in endotoxin levels can drastically alter the efficacy of novel macrophage modulating immunotherapies, AS1517499 and 3-methyladenine. Altogether, this study shows that endotoxin contamination in biomaterials can significantly alter intra- and intercellular communication and thereby drug efficacy, which might lead to misinterpretation of the potency and safety of the tested compounds.

Bacterial nanocellulose-reinforced gelatin methacryloyl hydrogel enhances biomechanical property and glycosaminoglycan content of 3D-bioprinted cartilage

Tissue-engineered ear cartilage scaffold based on three-dimensional (3D) bioprinting technology presents a new strategy for ear reconstruction in individuals with microtia. Natural hydrogel is a promising material due to its excellent biocompatibility and low immunogenicity. However, insufficient mechanical property required for cartilage is one of the major issues pending to be solved. In this study, the gelatin methacryloyl (GelMA) hydrogel reinforced with bacterial nanocellulose (BNC) was developed to enhance the biomechanical properties and printability of the hydrogel. The results revealed that the addition of 0.375% BNC significantly increased the mechanical properties of the hydrogel and promoted cell migration in the BNC-reinforced hydrogel. Constructs bioprinted with chondrocyte-laden BNC/GelMA hydrogel bio-ink formed mature cartilage in nude mice with higher Young's modulus and glycosaminoglycan content. Finally, an auricle equivalent with a precise shape, high mechanics, and abundant cartilage-specific matrix was developed in vivo. In this study, we developed a potentially useful hydrogel for the manufacture of auricular cartilage grafts for microtia patients.

Effect of gelatin methacryloyl hydrogel on healing of the guinea pig vaginal wall with or without mesh augmentation

INTRODUCTION AND HYPOTHESIS

The aims of this study were to evaluate the effectiveness of gelatin methacryloyl as an adjunct to anterior vaginal wall injury with or without vaginal mesh compared with traditional repair with suture.

METHODS

Virginal cycling Hartley strain guinea pigs (n = 60) were randomized to undergo surgical injury and repair using either polyglactin 910 suture or gelatin methacryloyl for epithelium re-approximation or anterior colporrhaphy with mesh augmentation using either polyglactin 910 suture or gelatin methacryloyl for mesh fixation and epithelium re-approximation. Noninjured controls (n = 5) were also evaluated. After 4 days, 4 weeks, or 3 months, tissues were analyzed by hematoxylin & eosin in addition to immunolabeling for macrophages, leukocytes, smooth muscle, and fibroblasts.

RESULTS

Surgical injury repaired with suture was associated with increased inflammation and vessel density compared with gelatin methacryloyl. Vimentin and α-smooth muscle actin expression were increased with gelatin methacryloyl at 4 days (p = 0.0026, p = 0.0272). There were no differences in changes in smooth muscle or overall histomorphology after 3 months between the two closure techniques. Mesh repair with suture was also associated with increased inflammation and vessel density relative to gelatin methacryloyl. Quantification of collagen content by picrosirius red staining revealed increased thick collagen fibers throughout the implanted mesh with gelatin methacryloyl compared with suture at 4 weeks (0.62 ± 0.01 μm2 vs 0.55 ± 0.01, p = 0.018). Even at the long-term time point of 3 months, mesh repair with suture resulted in a profibrotic encapsulation of the mesh fibers, which was minimal with gelatin methacryloyl. Smooth muscle density was suppressed after mesh implantation returning to baseline levels at 3 months regardless of fixation with suture or gelatin methacryloyl.

CONCLUSIONS

These results suggest that gelatin methacryloyl might be a safe alternative to suture for epithelium re-approximation and anchoring of prolapse meshes to the vagina and may improve chronic inflammation in the vaginal wall associated with mesh complications.

Novel biohybrid spongy scaffolds for fabrication of suturable intraoral graft substitutes

Despite the fact that classic autograft is the gold standard material for periodontal plastic surgery, it has some drawbacks, including the need for a second surgical site and the scarcity of palatal donor tissue. However, only a few research works on the manufacturing of bioengineered intraoral connective tissue grafts have been conducted. In this work, porous bovine serum albumin methacryloyl/gelatin methacryloyl (BG) biohybrid scaffolds were developed for super-elasticity, shape recovery, suturability for persistent stability, sufficient scaffolding function, and convenient manipulating characteristics to fabricate an intraoral graft substitute with superb stability to resist frequent dynamic forces caused by functional movement (speaking, masticating, and swallowing). Furthermore, in a 3D cell culture assay, BG scaffolds demonstrated excellent cell adhesion and proliferation of L929 cells. In addition, the BG scaffolds were able to release Ibuprofen in a controlled manner for postoperative recovery. The use of a low-cost, optimized cryogelation technique for functional biomacromolecules offers up new possibilities to develop promising scaffolds for dental clinical settings.

Comparison of globular albumin methacryloyl and random-coil gelatin methacryloyl: Preparation, hydrogel properties, cell behaviors, and mineralization

Bovine serum albumin methacryloyl (BSAMA) is a newly emerging photocurable globular protein-based material whereas gelatin methacryloyl (GelMA) is one of the most popular photocurable fibrous protein-based materials. So far, the influence of their different structural conformations as building blocks on hydrogel properties and mineral deposition has not been investigated. Here, we compared their differences in structures, gelation kinetics, hydrogel properties, mineralization, and cell behaviors. BSAMA maintained a stable globular structure while GelMA exhibited temperature-sensitive conformations (4 - 37 °C). BSAMA displayed slower gelation kinetics and much more retarded enzymatic degradation compared to GelMA. Photocurable BSAMA (6.41 - 390.95 kPa) and GelMA hydrogels (36.09 - 199.70 kPa) exhibited tunable mechanical properties depending on their concentrations (10 - 20%). Interestingly, BSAMA hydrogels mineralized needle-like apatite (Ca/P: 1.409) with higher crystallinity compared to GelMA hydrogels (Ca/P: 1.344). BSAMA and GelMA supported satisfactory cell (MC3T3-L1) viability of 99.43 ± 0.57% and 97.14 ± 0.69%, respectively. However, BSAMA gels were less favorable to cell proliferation and migration than GelMA gels. In serum-free environments, cells on GelMA displayed a higher amount of attachment, a more elongated shape, and a longer protrusion compared to those on BSAMA (p < 0.01) during the early adhesion.

Effects of mechanical properties of gelatin methacryloyl hydrogels on encapsulated stem cell spheroids for 3D tissue engineering

Cell spheroids are three-dimensional cell aggregates that have been widely employed in tissue engineering. Spheroid encapsulation has been explored as a method to enhance cell-cell interactions. However, the effect of hydrogel mechanical properties on spheroids, specifically soft hydrogels (<1 kPa), has not yet been studied. In this study, we determined the effect of encapsulation of stem cell spheroids by hydrogels crosslinked with different concentrations of gelatin methacryloyl (GelMA) on the functions of the stem cells. To this end, human adipose-derived stem cell (ADSC) spheroids with a defined size were prepared, and spheroid-laden hydrogels with various concentrations (5, 10, 15%) were fabricated. The apoptotic index of cells from spheroids encapsulated in the 15% hydrogel was high. The migration distance was five-fold higher in cells encapsulated in the 5% hydrogel than the 10% hydrogel. After 14 days of culture, cells from spheroids in the 5% hydrogel were observed to have spread and proliferated. Osteogenic factor and pro-angiogenic factor production in the 15% hydrogel was high. Collectively, our results indicate that the functionality of spheroids can be regulated by the mechanical properties of hydrogel, even under 1 kPa. These results indicate that spheroid-laden hydrogels are suitable for use in 3D tissue construction.

Microfluidic Coaxial Bioprinting of Hollow, Standalone, and Perfusable Vascular Conduits

Three-dimensional bioprinting represents promising approach for fabricating standalone and perfusable vascular conduits using biocompatible materials. Here we describe a step-by-step method by using a multichannel coaxial extrusion system (MCCES) and a blend bioink constituting gelatin methacryloyl, sodium alginate, and eight-arm poly(ethylene glycol)-acrylate with a tripentaerythritol core for the fabrication of standalone circumferentially multilayered hollow tubes. This microfluidic bioprinting method allows the fabrication of perfusable vascular conduits with a core lumen, an inner endothelial layer resembling the tunica intima, and an outer smooth muscle cell layer resembling the tunica media of the blood vessel. Biocompatible and perfusable blood vessels with a widely tunable size range in terms of luminal diameters and wall thicknesses can be successfully fabricated using the MCCES.

A tuned gelatin methacryloyl (GelMA) hydrogel facilitates myelination of dorsal root ganglia neurons in vitro

Investigating axonal myelination by Schwann cells (SCs) is crucial for understanding mechanisms underlying demyelination and remyelination, which may help gain insights into incurable disorders like neurodegenerative diseases. In this study, a gelatin-based hydrogel, gelatin methacryloyl (GelMA), was optimized to achieve the biocompatibility, porosity, mechanical stability, and degradability needed to provide high cell viability for dorsal root ganglia (DRG) neurons and SCs, and to enable their long-term coculture needed for myelination studies. The results of cell viability, neurite elongation, SC function and maturation, SC-axon interaction, and myelination were compared with two other commonly used substrates, namely collagen and Poly-d Lysine (PDL). The tuned GelMA constructs (Young's modulus of 32.6 ± 1.9 kPa and the median value of pore size of 10.3 μm) enhanced single axon generation (unlike collagen) and promoted the interaction of DRG neurons and SCs (unlike PDL). While DRG cells exhibited relatively higher viability on PDL after 48 h, i.e., 83.8%, the cells had similar survival rate on GelMA and collagen substrates, 66.7% and 61.5%, respectively. Further adjusting the hydrogel properties to achieve two distinct ranges of relatively small and large pores supported SCs to extend their processes freely and enabled physical contact with and wrapping around their corresponding axons. Staining the cells with myelin basic protein (MBA) and myelin-associated glycoprotein (MAG) revealed enhanced myelination on GelMA hydrogel compared to PDL and collagen. Moreover, the engineered porosity enhanced DRGs and SCs attachments and flexibility of movement across the substrate. This engineered hydrogel structure can now be further explored to model demyelination in neurodegenerative diseases, as well as to study the effects of various compounds on myelin regeneration.

Quantification of fractional and absolute functionalization of gelatin hydrogels by optimized ninhydrin assay and 1H NMR

3D cell culture in protein-based hydrogels often begins with chemical functionalization of proteins with cross-linking agents such as methacryloyl or norbornene. An important and variable characteristic of these materials is the degree of functionalization (DoF), which controls the reactivity of the protein for cross-linking and therefore impacts the mechanical properties and stability of the hydrogel. Although ¹H NMR has emerged as the most accurate technique for quantifying absolute DoF of chemically modified proteins, colorimetric techniques still dominate in actual use and may be more useful for quantifying fractional or percent DoF. In this work, we sought to develop an optimized colorimetric assay for DoF of common gelatin-based biomaterials and validate it versus NMR; along the way, we developed a set of best practices for both methods and considerations for their most appropriate use. First, the amine-reactive ninhydrin assay was optimized in terms of solvent properties, temperature, ninhydrin concentration, and range of gelatin standards. The optimized assay produced a linear response to protein concentration in a convenient, 96-well plate format and yielded a fractional DoF similar to NMR in most cases. In comparing with NMR, we identified that DoF can be expressed as fractional or absolute, and that fractional DoF can be inaccurate if the amino acid content of the parent protein is not properly accounted for. In summary, the fractional DoF of methacryloyl- and norbornene-functionalized gelatins was quantified by an optimized colorimetric ninhydrin assay and orthogonally by ¹H NMR. These methods will be valuable for quality control analysis of protein-based hydrogels and 3D cell culture biomaterials. Graphical abstract.

Optimization of 3D bioprinting of periodontal ligament cells

Three-dimensional (3D) bioprinting of cells is an emerging area of research but has been not explored yet in the context of periodontal tissue engineering.

OBJECTIVE

This study reports on the optimisation of the 3D bioprinting of periodontal ligament cells for potential application in periodontal regeneration.

METHODS

We systematically investigated the printability of various concentrations of gelatin methacryloyl (GelMA) hydrogel precursor using a microextrusion based three-dimensional (3D) printer. The influence of different printing parameters such as photoinitiator concentration, UV exposure, pressure and dispensing needle diameter on the viability of periodontal ligament cells encapsulated within the 3D bioprinted construct were subsequently assessed.

RESULTS

This systematic evaluation enabled the selection of the most suited printing conditions for achieving high printing resolution, dimensional stability and cell viability for 3D bioprinting of periodontal ligament cells.

SIGNIFICANCE

The optimised bioprinting system is the first step towards to the reproducible manufacturing of cell laden, space maintaining scaffolds for the treatment of periodontal lesions.

The Influence of Astaxanthin on the Proliferation of Adipose-derived Mesenchymal Stem Cells in Gelatin-Methacryloyl (GelMA) Hydrogels

Recently, astaxanthin, a red lipophilic pigment belonging to the xanthophyllic family of carotenoids, has shown the feasibility of its uses in tissue engineering and regenerative medicine, due to its excellent antioxidant activities and its abilities to enhance the self-renewal potency of stem cells. In this study, we demonstrate the influence of astaxanthin on the proliferation of adipose-derived mesenchymal stem cells in tissue-engineered constructs. The tissue engineered scaffolds were fabricated using photopolymerizable gelatin methacryloyl (GelMA) with different concentrations of astaxanthin. The effects of astaxanthin on cellular proliferation in two-dimensional environments were assessed using alamar blue assay and reverse transcription polymerase chain reaction (RT-PCR). Then, rheological properties, chemical structures and the water absorption of the fabricated astaxanthin-incorporated GelMA hydrogels were characterized using NMR analysis, rheological analysis and a swelling ratio test. Finally, the influence in three-dimensional environments of astaxanthin-incorporated GelMA hydrogels on the proliferative potentials of adipose-derived stem cells was assessed using alamar blue assay and the confocal imaging with Live/dead staining. The experimental results of the study indicate that an addition of astaxanthin promises to induce stem cell potency via proliferation, and that it can be a useful tool for a three-dimensional culture system and various tissue engineering applications.

Modular microporous hydrogels formed from microgel beads with orthogonal thermo-chemical responsivity: Microfluidic fabrication and characterization

Despite the significant advances in designing injectable bulk hydrogels, the inability to control the pore interconnectivity and decoupling it from the matrix stiffness has tremendously limited the applicability of stiff, flowable hydrogels for 3D cellular engineering, e.g., in hard tissue engineering. To overcome this persistent challenge, here, we introduce a universal method to convert thermosensitive macromolecules with chemically-crosslinkable moieties into annealable building blocks, forming 3D microporous beaded scaffolds in a bottom-up approach. In particular, we show gelatin methacryloyl (GelMA), a widely used biomaterial in tissue engineering, may be converted into physically-crosslinked microbeads using a facile microfluidic approach, followed by flow of the microbead suspension and chemical crosslinking in situ to fabricate microporous beaded GelMA (B-GelMA) scaffolds with interconnected pores, promoting cell functionality and rapid (within minutes) 3D seeding in stiff scaffolds, which are otherwise impossible in the bulk gel counterparts. This novel approach may set the stage for the next generation modular hydrogels with orthogonal porosity and stiffness made up of a broad range of natural and synthetic biomaterials.

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This method combines well-known flow focusing microfluidic devices with facile post-processing steps to fabricate microporous scaffolds.

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Temperature-driven physical crosslinking of the microbeads enables the facile purification of gel building blocks without further chemical reactions.

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This method provides a simple approach to fabricate microporous scaffolds, which overcomes some of the challenges of newly emerging beaded scaffolds, including oxygen-mediated impaired crosslinking.

Photocrosslinkable Gelatin Hydrogels Modulate the Production of the Major Pro-inflammatory Cytokine, TNF-α, by Human Mononuclear Cells

Hydrogels are an attractive class of biomaterials in tissue engineering due to their inherently compatible properties for cell culture. Gelatin methacryloyl (GelMA) has shown significant promise in the fields of tissue engineering and drug delivery, as its physical properties can be precisely tuned depending on the specific application. There is a growing appreciation for the interaction between biomaterials and cells of the immune system with the increasing usage of biomaterials for in vivo applications. Here, we addressed the current lack of information regarding the immune-modulatory properties of photocrosslinked GelMA. We investigated the ability of human mononuclear cells to mount inflammatory responses in the context of a GelMA hydrogel platform. Using lipopolysaccharide to stimulate a pro-inflammatory immune response, we found tumor necrosis factor-α (TNF-α) expression was suppressed in GelMA culture conditions. Our findings have important implications on the future use of GelMA, and potentially similar hydrogels, and highlight the significance of investigating the potential immune-modulatory properties of biomaterials.

Cell infiltrative hydrogel fibrous scaffolds for accelerated wound healing

Development of natural protein-based fibrous scaffolds with tunable physical properties and biocompatibility is highly desirable to construct three-dimensional (3D), fully cellularized scaffolds for wound healing. Herein, we demonstrated a simple and effective technique to construct electrospun 3D fibrous scaffolds for accelerated wound healing using a photocrosslinkable hydrogel based on gelatin methacryloyl (GelMA). We found that the physical properties of the photocrosslinkable hydrogel including water retention, stiffness, strength, elasticity and degradation can be tailored by changing the light exposure time. We further observed that the optimized hydrogel fibrous scaffolds which were soft and elastic could support cell adhesion, proliferation and migration into the whole scaffolds, facilitating regeneration and formation of cutaneous tissues within two weeks. Such tunable characteristics of the fibrous GelMA scaffolds distinguished them from other reported substrates developed for reconstruction of wound defects including glutaraldehyde-crosslinked gelatin or poly (lactic-co-glycolic acid) (PLGA), whose physical and chemical properties were difficult to modify to allow cell infiltration into the 3D scaffolds for tissue regeneration. We anticipate that the ability to become fully cellularized will make the engineered GelMA fibrous scaffolds suitable for widespread applications as skin substitutes or wound dressings.

STATEMENT OF SIGNIFICANCE

In present study, we generate three-dimensional photocrosslinkable gelatin (GelMA)-based fibrous scaffolds with tunable physical and biological properties by using a combined photocrosslinking/electrospinning approach. The developed GelMA fibrous scaffolds can not only support cell viability and cell adhesion, but also facilitate cell migration and proliferation, accelerating regeneration and formation of cutaneous tissues. In addition, the physical properties of the engineered fibrous GelMA hydrogel including water retention capability, mechanical properties and biodegradability can be tuned to accommodate different patients' needs, making it a promising candidate for skin tissue engineering.