Calcium Phosphate Nanocluster-Loaded Injectable Hydrogel for Bone Regeneration

Injectable Hydrogels: A Paradigm Tailored with Design, Characterization, and Multifaceted Approaches

Biomaterials denoting self-healing and versatile structural integrity are highly curious in the biomedicine segment. The injectable and/or printable 3D printing technology is explored in a few decades back, which can alter their dimensions temporarily under shear stress, showing potential healing/recovery tendency with patient-specific intervention toward the development of personalized medicine. Thus, self-healing injectable hydrogels (IHs) are stunning toward developing a paradigm for tissue regeneration. This review comprises the designing of IHs, rheological characterization and stability, several benchmark consequences for self-healing IHs, their translation into tissue regeneration of specific types, applications of IHs in biomedical such as anticancer and immunomodulation, wound healing and tissue/bone regeneration, antimicrobial potentials, drugs, gene and vaccine delivery, ocular delivery, 3D printing, cosmeceuticals, and photothermal therapy as well as in other allied avenues like agriculture, aerospace, electronic/electrical industries, coating approaches, patents associated with therapeutic/nontherapeutic avenues, and numerous futuristic challenges and solutions.

A sodium alginate/carboxymethyl chitosan dual-crosslinked injectable hydrogel scaffold with tunable softness/hardness for bone regeneration

Recently, injectable dual-crosslinked (DC) hydrogel scaffolds have attracted many attentions as a class of excellent bone regeneration biomaterials with in-situ tunable functions. However, the design of injectable DC hydrogels with cell behavior-compatible network structure and mechanical property remains a bottleneck. Herein, based on the in-situ gelling method, we constructed an injectable CMCS/PEG+SA/CaCl2 (CPSC) chemical/physical DC hydrogel scaffold with tunable softness/hardness mechanical properties and good biocompatibility. The formation mechanism and properties of the CPSC hydrogel scaffold were investigated by FTIR, XRD, rheometry, and mechanical testing. It is found that proper softness/hardness mechanical properties can be obtained by adjusting the secondary network structure of the hydrogel. The CPSC hydrogel scaffold prepared under optimal conditions can effectively promote cell infiltration, nutrient transport, and the osteogenic differentiation of rat bone mesenchymal stem cells (rBMSCs). The in vivo experiments show that the rBMSCs-loaded injectable CPSC hydrogels with appropriate mechanical properties can effectively promote bone reconstruction. This study has provided important guidance for the construction of injectable DC hydrogels with adjustable softness/hardness to promote osteogenesis for bone defect repair.

Journey of Mineral Precursors in Bone Mineralization: Evolution and Inspiration for Biomimetic Design

Bone mineralization is a ubiquitous process among vertebrates that involves a dynamic physical/chemical interplay between the organic and inorganic components of bone tissues. It is now well documented that carbonated apatite, an inorganic component of bone, is proceeded through transient amorphous mineral precursors that transforms into the crystalline mineral phase. Here, the evolution on mineral precursors from their sources to the terminus in the bone mineralization process is reviewed. How organisms tightly control each step of mineralization to drive the formation, stabilization, and phase transformation of amorphous mineral precursors in the right place, at the right time, and rate are highlighted. The paradigm shifts in biomineralization and biomaterial design strategies are intertwined, which promotes breakthroughs in biomineralization-inspired material. The design principles and implementation methods of mineral precursor-based biomaterials in bone graft materials such as implant coatings, bone cements, hydrogels, and nanoparticles are detailed in the present manuscript. The biologically controlled mineralization mechanisms will hold promise for overcoming the barriers to the application of biomineralization-inspired biomaterials.

The osteogenic and angiogenic potential of microRNA-26a delivered via a non-viral delivery peptide for bone repair

Bone-related injuries and diseases are among the most common causes of morbidity worldwide. Current bone-regenerative strategies such as auto- and allografts are invasive by nature, with adverse effects such as pain, infection and donor site morbidity. MicroRNA (miRNA) gene therapy has emerged as a promising area of research, with miRNAs capable of regulating multiple gene pathways simultaneously through the repression of post-transcriptional mRNAs. miR-26a is a key regulator of osteogenesis and has been found to be upregulated following bone injury, where it induces osteodifferentiation of mesenchymal stem cells (MSCs) and facilitates bone formation. This study demonstrates, for the first time, that the amphipathic, cell-penetrating peptide RALA can efficiently deliver miR-26a to MSCs in vitro to regulate osteogenic signalling. Transfection with miR-26a significantly increased expression of osteogenic and angiogenic markers at both gene and protein level. Using a rat calvarial defect model with a critical size defect, RALA/miR-26a NPs were delivered via an injectable, thermo-responsive Cs-g-PNIPAAm hydrogel to assess the impact on both rate and quality of bone healing. Critical defects treated with the RALA/miR-26a nanoparticles (NPs) had significantly increased bone volume and bone mineral density at 8 weeks, with increased blood vessel formation and mechanical properties. This study highlights the utility of RALA to deliver miR-26a for the purpose of bone healing within an injectable biomaterial, warranting further investigation of dose-related efficacy of the therapeutic across a range of in vivo models.

Modulation of hydrogel networks by metal ions

Self-assembling hydrogels are receiving great attention for both biomedical and technological applications. Self-assembly of protein/peptides as well as organic molecules is commonly induced in response to external triggers such as changes of temperature, concentration, or pH. An interesting strategy to modulate the morphology and mechanical properties of the gels implies the use of metal ions, where coordination bonds regulate the dynamic cross-linking in the construction of hydrogels, and coordination geometries, catalytic, and redox properties of metal ions play crucial roles. This review aims to discuss recent insights into the supramolecular assembly of hydrogels involving metal ions, with a focus on self-assembling peptides, as well as applications of metallogels in biomedical fields including tissue engineering, sensing, wound healing, and drug delivery.

Self-Healing Injectable Hydrogels for Tissue Regeneration

Biomaterials with the ability to self-heal and recover their structural integrity offer many advantages for applications in biomedicine. The past decade has witnessed the rapid emergence of a new class of self-healing biomaterials commonly termed injectable, or printable in the context of 3D printing. These self-healing injectable biomaterials, mostly hydrogels and other soft condensed matter based on reversible chemistry, are able to temporarily fluidize under shear stress and subsequently recover their original mechanical properties. Self-healing injectable hydrogels offer distinct advantages compared to traditional biomaterials. Most notably, they can be administered in a locally targeted and minimally invasive manner through a narrow syringe without the need for invasive surgery. Their moldability allows for a patient-specific intervention and shows great prospects for personalized medicine. Injected hydrogels can facilitate tissue regeneration in multiple ways owing to their viscoelastic and diffusive nature, ranging from simple mechanical support, spatiotemporally controlled delivery of cells or therapeutics, to local recruitment and modulation of host cells to promote tissue regeneration. Consequently, self-healing injectable hydrogels have been at the forefront of many cutting-edge tissue regeneration strategies. This study provides a critical review of the current state of self-healing injectable hydrogels for tissue regeneration. As key challenges toward further maturation of this exciting research field, we identify (i) the trade-off between the self-healing and injectability of hydrogels vs their physical stability, (ii) the lack of consensus on rheological characterization and quantitative benchmarks for self-healing injectable hydrogels, particularly regarding the capillary flow in syringes, and (iii) practical limitations regarding translation toward therapeutically effective formulations for regeneration of specific tissues. Hence, here we (i) review chemical and physical design strategies for self-healing injectable hydrogels, (ii) provide a practical guide for their rheological analysis, and (iii) showcase their applicability for regeneration of various tissues and 3D printing of complex tissues and organoids.

Bioinspired Control of Calcium Phosphate Liesegang Patterns Using Anionic Polyelectrolytes

The Liesegang phenomenon is a spontaneous pattern formation, which is a periodic distribution of the precipitate discovered in diffusion-limited systems. Over the past century, it has been experimentally attempted to control the periodicity of patterns and structures of precipitates by varying the concentration of the hydrogel or electrolytes, adding organic or inorganic impurities, and applying an electric or pH field. In this work, the periodic patterns of calcium phosphate were manipulated with an anionic macromolecular additive inspired by bone mineralization in which various noncollagenous proteins are involved in the formation of a polymer-induced liquid precursor. The periodic patterns were systematically controlled by adjusting the amount of poly(acrylic acid), and they were numerically simulated by adjusting the threshold concentration of nucleation. The change of the pattern is explained by improved stability and directional diffusion of the intermediate.

Intraosseous Injection of Calcium Phosphate Polymer-Induced Liquid Precursor Increases Bone Density and Improves Early Implant Osseointegration in Ovariectomized Rats

PURPOSE

Osteoporosis, due to bone loss and structural deterioration, is a risk factor for dental implant failure, as it impedes initial stability and osseointegration. We aim to assess the effects of calcium phosphate polymer-induced liquid precursor (CaP-PILP) treatment, which significantly increases bone density and improves early implant osseointegration in ovariectomized rats.

METHODS

In this study, CaP-PILP was synthesized and characterized through TEM, FTIR and XRD. A rat model of osteoporosis was generated by ovariectomy. CaP-PILP or hydroxyapatite (HAP, negative control) was injected into the tibia, and the resulting changes in bone quality were determined. Further, implants were installed in the treated tibias, and implantation characteristics were assessed after 4 weeks.

RESULTS

The CaP-PILP group had superior bone repair. Importantly, CaP-PILP had excellent properties, similar to those of normal bone, in terms of implant osseointegration. In vivo experiment displayed that CaP-PILP group had better bone contact rate (65.97±3.176) than HAP and OVX groups. Meanwhile, a mound of mature and continuous new bone formed. Moreover, the values of BIC and BA showed no significant difference between the CaP-PILP group and the sham group.

CONCLUSION

In summary, CaP-PILP is a promising material for application in poor-quality bones to improve implant success rates in patients with osteoporosis. This research provides new perspectives on the application of nano-apatite materials in bone repair.

Rational design of hydrogels to enhance osteogenic potential

Bone tissue engineering (BTE) encompasses the field of biomaterials, cells, and bioactive molecules to successfully guide the growth and repair of bone tissue. Current BTE strategies rely on delivering osteogenic molecules or cells via scaffolding materials. However, growth factor- and stem cell-based treatments have several limitations, such as source restriction, low stability, difficulties in predicting long-term efficacy, and high costs, among others. These issues have promoted the development of material-based therapy with properties of accessibility, high stability, tunable efficacy, and low-cost production. Hydrogels are widely used in BTE applications because of their unique hydrophilic nature and tunable physicochemical properties to mimic the native bone environment. However, current hydrogel materials are not ideal candidates due to minimal osteogenic capability on their own. Therefore, recent studies of BTE hydrogels attempt to counterbalance these issues by modifying their biophysical properties. In this article, we review recent progress in the design of hydrogels to instruct osteogenic potential, and present strategies developed to precisely control its bone healing properties.

Enhanced Proliferation and Differentiation of Human Mesenchymal Stem Cell-laden Recycled Fish Gelatin/Strontium Substitution Calcium Silicate 3D Scaffolds

Cell-encapsulated bioscaffold is a promising and novel method to allow fabrication of live functional organs for tissue engineering and regenerative medicine. However, traditional fabrication methods of 3D scaffolds and cell-laden hydrogels still face many difficulties and challenges. This study uses a newer 3D fabrication technique and the concept of recycling of an unutilized resource to fabricate a novel scaffold for bone tissue engineering. In this study, fish-extracted gelatin was incorporated with bioactive ceramic for bone tissue engineering, and with this we successfully fabricated a novel fish gelatin methacrylate (FG) polymer hydrogel mixed with strontium-doped calcium silicate powder (FGSr) 3D scaffold via photo-crosslinking. Our results indicated that the tensile strength of FGSr was almost 2.5-fold higher as compared to FG thus making it a better candidate for future clinical applications. The in-vitro assays illustrated that the FGSr scaffolds showed good biocompatibility with human Wharton jelly-derived mesenchymal stem cells (WJMSC), as well as enhancing the osteogenesis differentiation of WJMSC. The WJMSC-laden FGSr 3D scaffolds expressed a higher degree of alkaline phosphatase activity than those on cell-laden FG 3D scaffolds and this result was further proven with the subsequent calcium deposition results. Therefore, these results showed that 3D-printed cell-laden FGSr scaffolds had enhanced mechanical property and osteogenic-related behavior that made for a more suitable candidate for future clinical applications.

Highly Porous Amorphous Calcium Phosphate for Drug Delivery and Bio-Medical Applications

Amorphous calcium phosphate (ACP) has shown significant effects on the biomineralization and promising applications in bio-medicine. However, the limited stability and porosity of ACP material restrict its practical applications. A storage stable highly porous ACP with Brunauer-Emmett-Teller surface area of over 400 m2/g was synthesized by introducing phosphoric acid to a methanol suspension containing amorphous calcium carbonate nanoparticles. Electron microscopy revealed that the porous ACP was constructed with aggregated ACP nanoparticles with dimensions of several nanometers. Large angle X-ray scattering revealed a short-range atomic order of <20 Å in the ACP nanoparticles. The synthesized ACP demonstrated long-term stability and did not crystallize even after storage for over 14 months in air. The stability of the ACP in water and an α-MEM cell culture medium were also examined. The stability of ACP could be tuned by adjusting its chemical composition. The ACP synthesized in this work was cytocompatible and acted as drug carriers for the bisphosphonate drug alendronate (AL) in vitro. AL-loaded ACP released ~25% of the loaded AL in the first 22 days. These properties make ACP a promising candidate material for potential application in biomedical fields such as drug delivery and bone healing.