Ca:Mg:Zn:CO 3 and Ca:Mg:CO 3 —tri- and bi-elemental carbonate microparticles for novel injectable self-gelling hydrogel–microparticle composites for tissue regeneration

The influence of Ca/Mg ratio on autogelation of hydrogel biomaterials with bioceramic compounds

Hydrogels, which are versatile three-dimensional structures containing polymers and water, are very attractive for use in biomedical fields, but they suffer from rather weak mechanical properties. In this regard, biocompatible particles can be used to enhance their mechanical properties. The possibility of loading such particles with drugs (e.g. enzymes) makes them a particularly useful component in hydrogels. In this study, micro/nanoparticles containing various ratios of Ca²⁺/Mg²⁺ with sizes ranging from 1 to 8 μm were prepared and mixed with gellan gum (GG) solution to study the in-situ formation of hydrogel-particle composites. The particles provide multiple functionalities: 1) they efficiently crosslink GG to induce hydrogel formation through the release of the divalent cations (Ca²⁺/Mg²⁺) known to bind to GG polymer chains; 2) they enhance mechanical properties of the hydrogel from 2 up to 100 kPa; 3) the samples most efficiently promoting cell growth were found to contain two types of minerals: vaterite and hydroxymagnesite, which enhanced cells proliferation and hydroxyapatite formation. The results demonstrate that such composite materials are attractive candidates for applications in bone regeneration.

A novel magnesium ion-incorporating dual-crosslinked hydrogel to improve bone scaffold-mediated osteogenesis and angiogenesis

Osteogenesis is closely complemented by angiogenesis during the bone regeneration process. The development of functional hydrogel bone substitutes that mimic the extracellular matrix is a promising strategy for bone tissue engineering. However, the development of scaffold materials tailored to exhibit sufficient biomechanics, biodegradability, and favorable osteogenic and angiogenic activity continue to present a great challenge. Herein, we prepared a novel magnesium ion-incorporating dual-crosslinked hydrogel through the photocrosslinking of gelatin methacryloyl (GelMA), thiolated chitosan (TCS) and modified polyhedral oligomeric silsesquioxane (POSS) nanoparticles, and active Mg²⁺ ions were then introduced into system via coordination bonds of MgS, which can be tailored to possess superior mechanical strength, a stable network structure and more suitable pore size and degradation properties. The fabricated GelMA/TCS/POSS-Mg hydrogels effectively promoted cell adhesion, spreading, and proliferation, demonstrating that the introduction of POSS and Mg²⁺ not only stimulates the osteogenic differentiation of BMSCs but also promotes angiogenesis both in vitro and in vivo, thereby facilitating subsequent bone regeneration in calvarial defects of rats. Taken together, the results of this study indicate that the GelMA/TCS/POSS-Mg hydrogel has promising potential for repairing bone defects by promoting cell adhesion, osteogenesis and vascularization.

Identification and Analysis of Key Parameters for the Ossification on Particle Functionalized Composites Hydrogel Materials

Developing materials for tissue engineering and studying the mechanisms of cell adhesion is a complex and multifactor process that needs analysis using physical chemistry and biology. The major challenge is the labor-intensive data mining as well as requirements of the number of advanced techniques. For example, hydrogel-based biomaterials with cell-binding sites, tunable mechanical properties, and complex architectures have emerged as a powerful tool to control cell adhesion and proliferation for tissue engineering. Composite hydrogels could be used for bone tissue regeneration, but they exhibit poor ossification properties. In current work, we have designed new osteoinductive gellan gum hydrogels by a thermal annealing approach and consequently functionalized them with Ca/Mg carbonate submicron particles. Determination of key parameters, which influence a successful hydroxyapatite generation, was done via the principal component analysis of 18 parameters (Young's modulus of the hydrogel and particles, particle size, and mass) and cell behavior at various time points (like viability, numbers of the cells, rate of alkaline phosphatase production, and cells area) obtained by characterizing such composite hydrogel. It is determined that the particles size and concentration of calcium ions have a dominant effect on the hydroxyapatite formation, because of providing local areas with a high Young's modulus in a hydrogel, a desirable property for cell adhesion. The detailed analysis presented here allows identifying hydrogels for cell growth applications, while on the other hand, material properties can be predicted, and their overall number can be minimized leading to efficient optimization of bone reconstruction and other cell growth applications.

Marine-Inspired Enzymatic Mineralization of Dairy-Derived Whey Protein Isolate (WPI) Hydrogels for Bone Tissue Regeneration

Whey protein isolate (WPI) is a by-product from the production of cheese and Greek yoghurt comprising β-lactoglobulin (β-lg) (75%). Hydrogels can be produced from WPI solutions through heating; hydrogels can be sterilized by autoclaving. WPI hydrogels have shown cytocompatibility and ability to enhance proliferation and osteogenic differentiation of bone-forming cells. Hence, they have promise in the area of bone tissue regeneration. In contrast to commonly used ceramic minerals for bone regeneration, a major advantage of hydrogels is the ease of their modification by incorporating biologically active substances such as enzymes. Calcium carbonate (CaCO3) is the main inorganic component of the exoskeletons of marine invertebrates. Two polymorphs of CaCO3, calcite and aragonite, have shown the ability to promote bone regeneration. Other authors have reported that the addition of magnesium to inorganic phases has a beneficial effect on bone-forming cell growth. In this study, we employed a biomimetic, marine-inspired approach to mineralize WPI hydrogels with an inorganic phase consisting of CaCO3 (mainly calcite) and CaCO3 enriched with magnesium using the calcifying enzyme urease. The novelty of this study lies in both the enzymatic mineralization of WPI hydrogels and enrichment of the mineral with magnesium. Calcium was incorporated into the mineral formed to a greater extent than magnesium. Increasing the concentration of magnesium in the mineralization medium led to a reduction in the amount and crystallinity of the mineral formed. Biological studies revealed that mineralized and unmineralized hydrogels were not cytotoxic and promoted cell viability to comparable extents (approximately 74% of standard tissue culture polystyrene). The presence of magnesium in the mineral formed had no adverse effect on cell viability. In short, WPI hydrogels, both unmineralized and mineralized with CaCO3 and magnesium-enriched CaCO3, show potential as biomaterials for bone regeneration.

Inter-protein interactions govern protein loading into porous vaterite CaCO3 crystals

Loading of therapeutic proteins into mesoporous vaterite crystals is driven by inter-protein interactions in bulk solution and inside the crystals.

Porous Alginate Scaffolds Assembled Using Vaterite CaCO3 Crystals

Formulation of multifunctional biopolymer-based scaffolds is one of the major focuses in modern tissue engineering and regenerative medicine. Besides proper mechanical/chemical properties, an ideal scaffold should: (i) possess a well-tuned porous internal structure for cell seeding/growth and (ii) host bioactive molecules to be protected against biodegradation and presented to cells when required. Alginate hydrogels were extensively developed to serve as scaffolds, and recent advances in the hydrogel formulation demonstrate their applicability as "ideal" soft scaffolds. This review focuses on advanced porous alginate scaffolds (PAS) fabricated using hard templating on vaterite CaCO3 crystals. These novel tailor-made soft structures can be prepared at physiologically relevant conditions offering a high level of control over their internal structure and high performance for loading/release of bioactive macromolecules. The novel approach to assemble PAS is compared with traditional methods used for fabrication of porous alginate hydrogels. Finally, future perspectives and applications of PAS for advanced cell culture, tissue engineering, and drug testing are discussed.

Modulatory effect of simultaneously released magnesium, strontium, and silicon ions on injectable silk hydrogels for bone regeneration

Injectable silk hydrogels are ideal carriers of therapeutic agents due to their biocompatibility and low immunogenicity. Injectable silk hydrogels for bone regeneration have been previously developed but often utilize expensive biologics. In this study, we have developed an injectable silk composite incorporated with a triphasic ceramic called MSM-10 (54 Mg₂SiO₄, 36 Si₃Sr₅ and 10 MgO (wt%)) capable of simultaneously releasing magnesium, silicon, and strontium ions into its environment. These ions have been previously reported to possess therapeutic effects for bone regeneration. MSM-10 particles were incorporated into the silk hydrogels at various weight percentages [0.1 (SMH-0.1), 0.6 (SMH-0.6), 1 (SMH-1) and 2 (SMH-2)]. The effects of the released ions on the physicochemical and biological properties of the silk hydrogel were comprehensively evaluated. Increased MSM-10 loading was found to hinder the gelation kinetics of the silk hydrogel through the reduction of beta-sheet phase formation, which in turn affected the required sonication time for gelation, compressive strength, force of injection, microstructure and in vitro degradation rate. Primary human osteoblasts seeded on SMH-0.6 demonstrated increased proliferation and early alkaline phosphatase activity, as well as enhanced osteogenic gene expression compared to pure silk hydrogel and SMH-0.1. In vivo results in subcutaneous mouse models showed both decreased fibrous capsule formation and increased number of new blood vessels around the injected SMH-0.1 and SMH-0.6 implants compared to pure silk hydrogels. The results in this study indicate that the ions released from MSM-10 is able to influence the physicochemical and biological properties of silk hydrogels, and SMH-0.6 in particular shows promising properties for bone regeneration.