Mechanically enhanced composite hydrogel scaffold for in situ bone repairs

Hydrogel loaded with thiolated chitosan modified taxifolin liposome promotes osteoblast proliferation and regulates Wnt signaling pathway to repair rat skull defects

To alleviate skull defects and enhance the biological activity of taxifolin, this study utilized the thin-film dispersion method to prepare paclitaxel liposomes (TL). Thiolated chitosan (CSSH)-modified TL (CTL) was synthesized through charge interactions. Injectable hydrogels (BLG) were then prepared as hydrogel scaffolds loaded with TAX (TG), TL (TLG), and CTL (CTLG) using a Schiff base reaction involving oxidized dextran and carboxymethyl chitosan. The study investigated the bone reparative properties of CTLG through molecular docking, western blot techniques, and transcriptome analysis. The particle sizes of CTL were measured at 248.90 ± 14.03 nm, respectively, with zeta potentials of +36.68 ± 5.43 mV, respectively. CTLG showed excellent antioxidant capacity in vitro. It also has a good inhibitory effect on Escherichia coli and Staphylococcus aureus, with inhibition rates of 93.88 ± 1.59 % and 88.56 ± 2.83 % respectively. The results of 5-ethynyl-2 '-deoxyuridine staining, alkaline phosphatase staining and alizarin red staining showed that CTLG also had the potential to promote the proliferation and differentiation of mouse embryonic osteoblasts (MC3T3-E1). The study revealed that CTLG enhances the expression of osteogenic proteins by regulating the Wnt signaling pathway, shedding light on the potential application of TAX and bone regeneration mechanisms.

High biocompatible bone screw enabled by a rapid and robust chitosan/silk fibroin composite material

Hydrogel has attracted tremendous attentions due to its excellent biocompatibility and adaptability in biomedical field. However, it is challenging by the conflicts between inadequate mechanical properties and service requirements. Herein, a rapid and robust hydrogel was developed by interpenetrating networks between chitosan and silk fibroin macromolecules. Thanks to these unique networks, the chitosan-based hydrogel exhibited superior mechanical performances. The maximum breaking strength, Young's modulus and swelling ratio of the hydrogel were 1187.8 kPa, 383.1 MPa and 4.5 % respectively. The hydrogel also supported the proliferation of human umbilical vein endothelial cells for 7 days. Notably, the hydrogel was easily molded into bone screw, and demonstrated compressive strengths of 45.7 MPa, Young's modulus of 675.6 MPa, respectively. After 49-day biodegradation, the residual rate of the screw in collagenase I solution was up to 89.6 % of the initial weight. In vitro, the screws not only had high resistance to biodegradation, but also had outstanding biocompatibility of osteoblast. This study provided a promising physical-chemical double crosslinking strategy to build orthopedic materials, holding a great potential in biomedical devices.

Injectable and In Situ Formed Dual-Network Hydrogel Reinforced by Mesoporous Silica Nanoparticles and Loaded with BMP-4 for the Closure and Repair of Skull Defects

Bone defects are a common and challenging orthopedic problem with poor self-healing ability and long treatment cycles. The difficult-to-heal bone defects cause a significant burden of medical expenses on patients. Currently, biomaterials with mechanical stability, long-lasting action, and osteogenic activity are considered as a suitable way to effectively heal bone defects. Here, an injectable double network (DN) hydrogel prepared using physical and chemical cross-linking methods is designed. The first rigid network is constructed using methylpropenylated hyaluronic acid (HAMA), while the addition of chitosan oligosaccharide (COS) forms a second flexible network by physical cross-linking. The mesoporous silica nanoparticles (MSN) loaded with bone morphogenetic protein-4 (BMP-4) were embedded into DN hydrogel, which not only enhanced the mechanical stability of the hydrogel, but also slowly released BMP-4 to achieve long-term skull repair. The designed composite hydrogel showed an excellent compression property and deformation resistance. In vitro studies confirmed that the HAMA/COS/MSN@BMP-4 hydrogel had good biocompatibility and showed great potential in supporting proliferation and osteogenic differentiation of mouse embryo osteoblast precursor (MC3T3-E1) cells. Furthermore, in vivo studies confirmed that the DN hydrogel successfully filled and closed irregular skull defect wounds, effectively promoted bone regeneration, and significantly promoted bone repair compared with the control group. In addition, HAMA/COS/MSN@BMP-4 hydrogel precursor solution can quickly form hydrogel in situ at the wound by ultraviolet light, which can be applied to the closure and repair of wounds of different shapes, which provides the new way for the treatment of bone defects.

Injecting hope: chitosan hydrogels as bone regeneration innovators

Spontaneous bone regeneration encounters substantial restrictions in cases of bone defects, demanding external intervention to improve the repair and regeneration procedure. The field of bone tissue engineering (BTE), which embraces a range of disciplines, offers compelling replacements for conventional strategies like autografts, allografts, and xenografts. Among the diverse scaffolding materials utilized in BTE applications, hydrogels have demonstrated great promise as templates for the regeneration of bone owing to their resemblance to the innate extracellular matrix. In spite of the advancement of several biomaterials, chitosan (CS), a natural biopolymer, has garnered significant attention in recent years as a beneficial graft material for producing injectable hydrogels. Injectable hydrogels based on CS formulations provide numerous advantages, including their capacity to absorb and preserve a significant amount of water, their minimally invasive character, the existence of porous structures, and their capability to adapt accurately to irregular defects. Moreover, combining CS with other naturally derived or synthetic polymers and bioactive materials has displayed its effectiveness as a feasible substitute for traditional grafts. We aim to spotlight the composition, production, and physicochemical characteristics and practical utilization of CS-based injectable hydrogels, explicitly focusing on their potential implementations in bone regeneration. We consider this review a fundamental resource and a source of inspiration for future research attempts to pioneer the next era of tissue-engineering scaffold materials.

Calcium Phosphate Biomaterials for 3D Bioprinting in Bone Tissue Engineering

Three-dimensional bioprinting is a promising technology for bone tissue engineering. However, most hydrogel bioinks lack the mechanical and post-printing fidelity properties suitable for such hard tissue regeneration. To overcome these weak properties, calcium phosphates can be employed in a bioink to compensate for the lack of certain characteristics. Further, the extracellular matrix of natural bone contains this mineral, resulting in its structural robustness. Thus, calcium phosphates are necessary components of bioink for bone tissue engineering. This review paper examines different recently explored calcium phosphates, as a component of potential bioinks, for the biological, mechanical and structural properties required of 3D bioprinted scaffolds, exploring their distinctive properties that render them favorable biomaterials for bone tissue engineering. The discussion encompasses recent applications and adaptations of 3D-printed scaffolds built with calcium phosphates, delving into the scientific reasons behind the prevalence of certain types of calcium phosphates over others. Additionally, this paper elucidates their interactions with polymer hydrogels for 3D bioprinting applications. Overall, the current status of calcium phosphate/hydrogel bioinks for 3D bioprinting in bone tissue engineering has been investigated.

Physiologically engineered porous titanium/brushite scaffolds for critical-size bone defects: A design and manufacturing study

Repairing critical-size bone defects still represents a critical clinical challenge in the field of trauma surgery. This study focuses on a physiological design and manufacturing of porous composite scaffold (titanium Ti with 10 % mole iron doped brushite DCPD-Fe3+) which can mimic the biomechanical properties of natural cortical bone, specifically for the purpose of repairing critical-size defects. To achieve this, the principle of design of experiments (DOE) was applied for investigating the impact of sintering temperature, mineral ratio, and volume fraction of porosity on the mechanical properties of the fabricated scaffolds. The fabricated scaffolds had open porosity up to 60 %, with pore size approximately between 100 μm and 850 μm. The stiffness of the porous composite scaffolds varied between 3.30 GPa and 20.50 GPa, while the compressive strength ranged from approximately 130 MPa-165 MPa at sintering temperatures equal to or exceeding 1000 °C. Scaffolds with higher porosity and mineral content demonstrated lower stiffness values, resembling natural bone. Numerical simulation was employed by Ansys Workbench to investigate the stress and strain distribution of a critical size defect in mid-shaft femur which was designed to be replaced with the fabricated scaffold. The fabricated scaffolds showed flexible biomechanical behaviour at the bone/scaffold interface, generating lower stress levels and indicating a better match with the femoral shaft stiffness. The experimental and numerical findings demonstrated promising applications for manufacturing a patient-specific bone scaffold for critical and potentially large defects for reducing stress shielding and minimizing non-union risk.

3D collagen porous scaffold carrying PLGA-PTX/SDF-1α recruits and promotes neural stem cell differentiation for spinal cord injury repair

Spinal Cord Injury (SCI), one of the major factors of disability, can cause irreversible motor and sensory impairment. There are no effective therapeutic drugs and technologies available in domestic or foreign countries currently. Neural stem cells (NSCs), with the potential for multidirectional differentiation, are a potential treatment for SCI. However, it has been demonstrated that NSCs primarily differentiated into astrocytes rather than neurons due to the inflammatory microenvironment, and the current challenge remains to direct the differentiation of NSCs into neurons in the lesion site. It was reported that the microtubule-stabilizing agent paclitaxel (PTX) was able to promote the differentiation of NSCs into neurons rather than astrocytes after SCI. SDF-1α can recruit NSCs and thus guide the migration of stem cells. In this study, we developed a functional collagen scaffold by loading SDF-1α and nanoparticle-encapsulated PLGA-PTX into a 3D collagen porous scaffold, allowing for slow release of PTX. When the functional scaffolds were implanted into the injury site, it provided a neural regeneration conduit channel for the migration of NSCs and neuronal differentiation. Neural regeneration promoted the recovery of motor function and reduced glial scar formation after SCI. In conclusion, a 3D collagen porous scaffold combined with PLGA-PTX and SDF-1α is a promising therapeutic strategy for SCI repair.

Multi-scale cellular PLA-based bionic scaffold to promote bone regrowth and repair

Large bone defects have presented a significant challenge in orthopedic treatments, and the emergence of tissue-engineered scaffolds has introduced new avenues for treatment. Nonetheless, the clinical application of such scaffolds has been hindered by drawbacks like inadequate mechanical properties, and deficient osteogenesis. Herein, a biocompatible polylactic acid (PLA) based composite was proposed to emulate cancellous bone's morphology by incorporating nano-hydroxyapatite (nHA). In addition, a quantity of Mg²⁺ and chitosan (CS) as active osteogenic factors were adopted to imitate the bone marrow mesenchymal components in vivo. Using a pre-evaporated solvent and sacrificial multi-template techniques, the cellular PLA-based tissue engineering scaffolds containing macropores larger than 100 μm and micropores smaller than 10 μm were developed. The scaffold's bionic structure, osteogenic active component, and multi-scale cellular make it comparable to cancellous bone, with favorable mechanical properties and hydrophilicity. Vitro tests using Sprague-Dawley (SD) rat bone marrow mesenchymal stem cells (rBMSCs) demonstrated the scaffold's excellent biocompatibility to induce high efficiency of osteogenic differentiation. The bionic porous scaffold with multi-scale cellular structure also can recruit rBMSCs, promote bone regrowth and osteogenic differentiation, and facilitate the regeneration of defective bone tissue for repair. This contribution presented a promising strategy for future advancements in bone tissue engineering.

Tissue engineering in growth plate cartilage regeneration: Mechanisms to therapeutic strategies

The repair of growth plate injuries is a highly complex process that involves precise spatiotemporal regulation of multiple cell types. While significant progress has been made in understanding the pathological mechanisms underlying growth plate injuries, effectively regulating this process to regenerate the injured growth plate cartilage remains a challenge. Tissue engineering technology has emerged as a promising therapeutic approach for achieving tissue regeneration through the use of functional biological materials, seed cells and biological factors, and it is now widely applied to the regeneration of bone and cartilage. However, due to the unique structure and function of growth plate cartilage, distinct strategies are required for effective regeneration. Thus, this review provides an overview of current research on the application of tissue engineering to promote growth plate regeneration. It aims to elucidates the underlying mechanisms by which tissue engineering promotes growth plate regeneration and to provide novel insights and therapeutic strategies for future research on the regeneration of growth plate.

Physiology-Inspired Multilayer Nanofibrous Membranes Modulating Endogenous Stem Cell Recruitment and Osteo-Differentiation for Staged Bone Regeneration

Bone regeneration involves a cascade of sophisticated, multiple-staged cellular and molecular events, where early-phase stem cell recruitment mediated by chemokines and late-phase osteo-differentiation induced by pro-osteogenic factors play the crucial roles. Herein, enlightened by a bone physiological and regenerative mechanism, the multilayer nanofibrous membranes (PLLA@SDF-1α@MT01) consisting of PLLA/MT01 micro-sol electrospun nanofibers as intima and PLLA/PEG/SDF-1α electrospun nanofibers as adventitia are fabricated through micro-sol electrospinning and manual multi-layer stacking technologies. In vitro releasing profiles show that PLLA@SDF-1α@MT01 represents the rapid release of stromal cell-derived SDF-1α (SDF-1α) in the outer layers, while with long-term sustained release of MT01 in the inner layer. Owing to interconnected porosity like the natural bone extracellular matrix and improved hydrophilia, PLLA@SDF-1α@MT01 manifests good biocompatibility both in vitro and in vivo. Furthermore, PLLA@SDF-1α@MT01 can promote bone marrow mesenchymal stem cells (BMSCs) migration by amplifying the SDF-1α/CXCR4 axis and stimulating BMSCs osteo-differentiation via activating the MAPK pathway in vitro. PLLA@SDF-1α@MT01, with a programmed dual-delivery system, exhibits the synergetic promotion of bone regeneration and vascularization by emulating key characteristics of the staged bone repair in vivo. Overall, PLLA@SDF-1α@MT01 that mimics the endogenous cascades of bone regeneration can enrich the physiology-mimetic staged regenerative strategy and represent a promising tissue-engineered scaffold for the bone defect.

Alendronate-functionalized double network hydrogel scaffolds for effective osteogenesis

Development of artificial bone substitutes mimicking the extracellular matrix is a promising strategy for bone repair and regeneration. In views of the actual requirement of biomechanics, biodegradability, and bioactivity, herein, a double-network (DN) hydrogel was constructed by interspersing a methacrylated gelatin (GelMA) network into alendronate (ALN)-modified oxidized alginate (OSA) network via Schiff base reaction and photo-crosslinking process to promote in situ bone regeneration. This GelMA@OSA-ALN DN hydrogel possessed favorable network and pores, good biocompatibility, and enhanced biomechanics. Notably, the introduction of Schiff base furnished the ND hydrogel scaffold with pH-responsive biodegradation and sustained ALN drug release delivery, which could provide effective bioactivity, upregulate osteogenesis-related genes, and promote the cell viability, growth, proliferation, and osteogenesis differentiation for bone regeneration. Therefore, we provide a new insight to develop functional DN hydrogel scaffold toward governing the on-demand drug release and achieving the stem cell therapy, which will be developed into the minimally invasive gelling system to prolong local delivery of bisphosphonates for the bone-related diseases.