Emerging concepts in bone repair and the premise of soft materials

Cartilage lacuna-biomimetic hydrogel microspheres endowed with integrated biological signal boost endogenous articular cartilage regeneration

Despite numerous studies on chondrogenesis, the repair of cartilage-particularly the reconstruction of cartilage lacunae through an all-in-one advanced drug delivery system remains limited. In this study, we developed a cartilage lacuna-like hydrogel microsphere system endowed with integrated biological signals, enabling sequential immunomodulation and endogenous articular cartilage regeneration. We first integrated the chondrogenic growth factor transforming growth factor-β3 (TGF-β3) into mesoporous silica nanoparticles (MSNs). Then, TGF-β3@MSNs and insulin-like growth factor 1 (IGF-1) were encapsulated within microspheres made of polydopamine (pDA). In the final step, growth factor-loaded MSN@pDA and a chitosan (CS) hydrogel containing platelet-derived growth factor-BB (PDGF-BB) were blended to produce growth factors loaded composite microspheres (GFs@μS) using microfluidic technology. The presence of pDA reduced the initial acute inflammatory response, and the early, robust release of PDGF-BB aided in attracting endogenous stem cells. Over the subsequent weeks, the continuous release of IGF-1 and TGF-β3 amplified chondrogenesis and matrix formation. μS were incorporated into an acellular cartilage extracellular matrix (ACECM) and combined with a polydopamine-modified polycaprolactone (PCL) structure to produce a tissue-engineered scaffold that mimicked the structure of the cartilage lacunae evenly distributed in the cartilage matrix, resulting in enhanced cartilage repair and patellar cartilage protection. This research provides a strategic pathway for optimizing growth factor delivery and ensuring prolonged microenvironmental remodeling, leading to efficient articular cartilage regeneration.

Gelatin Methacryloyl (GelMA) - 45S5 Bioactive Glass (BG) Composites for Bone Tissue Engineering: 3D Extrusion Printability and Cytocompatibility Assessment Using Human Osteoblasts

3D extrusion printing has been widely investigated for low-volume production of complex-shaped scaffolds for tissue regeneration. Gelatin methacryloyl (GelMA) is used as a baseline material for the synthesis of biomaterial inks, often with organic/inorganic fillers, to obtain a balance between good printability and biophysical properties. The present study demonstrates how 45S5 bioactive glass (BG) addition and GelMA concentrations can be tailored to develop GelMA composite scaffolds with good printability and buildability. The experimental results suggest that 45S5 BG addition consistently decreases the compression stiffness, irrespective of GelMA concentration, albeit within 20% of the baseline scaffold (without 45S5 BG). The optimal addition of 2 wt % 45S5 BG in 7.5 wt % GelMA was demonstrated to provide the best combination of printability and buildability in the 3D extrusion printing route. The degradation decreases and the swelling kinetics increases with 45S5 BG addition, irrespective of GelMA concentration. Importantly, the dissolution in simulated body fluid over 3 weeks clearly promoted the nucleation and growth of crystalline calcium phosphate particles, indicating the potential of GelMA-45S5 BG to promote biomineralization. The cytocompatibility assessment using human osteoblasts could demonstrate uncompromised cell proliferation or osteogenic marker expression over 21 days in culture for 3D printable 7.5 wt % GelMA -2 wt % 45S5 BG scaffolds when compared to 7.5 wt % GelMA. The results thus encourage further investigations of the GelMA/45S5 BG composite system for bone tissue engineering applications.

A Comprehensive Literature Review on Advancements and Challenges in 3D Bioprinting of Human Organs: Ear, Skin, and Bone

The field of 3D bioprinting is rapidly emerging within the realm of regenerative medicine, offering significant potential in dealing with the issue of organ shortages. Despite being in its early stages, it has the potential to replicate tissue structures accurately, providing new potential solutions for reconstructive surgery. This review explores the diverse applications of 3D bioprinting in regenerative medicine, pharmaceuticals, and the food industry, specifically focusing on ear, skin, and bone tissues due to their unique challenges and implications in the field. Significant progress has been made in cartilage and bone scaffold fabrication in ear reconstruction, yet challenges in functional maturation persist. Recent advancements highlight the potential for patient-specific ear substitutes, emphasizing the need for extensive clinical trials. In skin regeneration, 3D bioprinting addresses limitations in existing models, offering opportunities for improved wound healing and realistic skin models. While challenges exist, progress in biomaterials and in-situ bioprinting holds promise. In bone regeneration, 3D bioprinting presents personalized solutions for defects, but scaffold design refinement and addressing regulatory and ethical considerations are crucial. The transformative potential of 3D bioprinting in the field of medicine holds the promise of redefining therapeutic approaches and delivering personalized treatments and functional tissues. Interdisciplinary collaboration is essential for fully realizing the capabilities of 3D bioprinting. This review provides a detailed analysis of current methodologies, challenges, and prospects in 3D bioprinting for ear, skin, and bone tissue regeneration.

Nanocomposite Methacrylated Silk Fibroin-Based Scaffolds for Bone Tissue Engineering

The treatment of bone defects is a clinical challenge. Bone tissue engineering is gaining interest as an alternative to current treatments, with the development of 3D porous structures (scaffolds) helpful in promoting bone regeneration by ensuring temporary functional support. In this work, methacrylated silk fibroin (SilMA) sponges were investigated as scaffolds for bone tissue engineering by exploiting the combination of physical (induced by NaCl salt during particulate leaching) and chemical crosslinking (induced by UV-light exposure) techniques. A biomimetic approach was adopted to better simulate the extracellular matrix of the bone by introducing either natural (mussel shell-derived) or synthetic-origin hydroxyapatite nanoparticles into the SilMA sponges. The obtained materials were characterized in terms of pore size, water absorption capability and mechanical properties to understand both the effect of the inclusion of the two different types of nanoparticles and the effect of the photocrosslinking. Moreover, the SilMA sponges were tested for their bioactivity and suitability for bone tissue engineering purposes by using osteosarcoma cells, studying their metabolism by an AlamarBlue assay and their morphology by scanning electron microscopy. Results indicate that photocrosslinking helps in obtaining more regular structures with bimodal pore size distributions and in enhancing the stability of the constructs in water. Moreover, the addition of naturally derived hydroxyapatite was observed to be more effective at activating osteosarcoma cell metabolism than synthetic hydroxyapatite, showing a statistically significant difference in the AlamarBlue measurement on day 7 after seeding. The methacrylated silk fibroin/hydroxyapatite nanocomposite sponges developed in this work were found to be promising tools for targeting bone regeneration with a sustainable approach.

Suitability of Gelatin Methacrylate and Hydroxyapatite Hydrogels for 3D-Bioprinted Bone Tissue

BACKGROUND

Complex bone defects are challenging to treat. Autografting is the gold standard for regenerating bone defects; however, its limitations include donor-site morbidity and increased surgical complexity. Advancements in 3D bioprinting (3DBP) offer a promising alternative for viable bone grafts. In this experiment, gels composed of varying levels of gelatin methacrylate (GelMA) and hydroxyapatite (HA) and gelatin concentrations are explored. The objective was to increase the hydroxyapatite content and find the upper limit before the printability was compromised and determine its effect on the mechanical properties and cell viability.

METHODS

Design of Experiments (DoE) was used to design 13 hydrogel bioinks of various GelMA/HA concentrations. These bioinks were assessed in terms of their pipettability and equilibrium modulus. An optimal bioink was designed using the DoE data to produce the greatest stiffness while still being pipettable. Three bioinks, one with the DoE-designed maximal stiffness, one with the experimentally defined maximal stiffness, and a literature-based control, were then printed using a 3D bioprinter and assessed for print fidelity. The resulting hydrogels were combined with human bone-marrow-derived mesenchymal stromal cells (hMSCs) and evaluated for cell viability.

RESULTS

The DoE ANOVA analysis indicated that the augmented three-level factorial design model used was a good fit (p < 0.0001). Using the model, DoE correctly predicted that a composite hydrogel consisting of 12.3% GelMA, 15.7% HA, and 2% gelatin would produce the maximum equilibrium modulus while still being pipettable. The hydrogel with the most optimal print fidelity was 10% GelMA, 2% HA, and 5% gelatin. There were no significant differences in the cell viability within the hydrogels from day 2 to day 7 (p > 0.05). There was, however, a significantly lower cell viability in the gel composed of 12.3% GelMA, 15.7% HA, and 2% gelatin compared to the other gels with a lower HA concentration (p < 0.05), showing that a higher HA content or print pressure may be cytotoxic within hydrogels.

CONCLUSIONS

Extrusion-based 3DBP offers significant advantages for bone-tissue implants due to its high customizability. This study demonstrates that it is possible to create printable bone-like grafts from GelMA and HA with an increased HA content, favorable mechanical properties (145 kPa), and a greater than 80% cell viability.

Biomolecules based hydrogels and their potential biomedical applications: A comprehensive review

The need for biocompatible drug carriers has been significantly increased from the past few years. Researchers show great interest in the development of more versatile and sophisticated biomaterials based drug carriers. Hydrogels are beneficial drug carriers and easily release the controlled amount of drug at target site due to its tunable structure. The hydrogels made-up of potent biological macromolecules including collagen, gelatin, fibrin, elastin, fibroin, chitosan, starch, alginate, agarose and carrageenan have been proven as versatile biomaterials. These are three-dimensional polymeric networks, synthesized by crosslinking of hydrophilic polymers. The biological macromolecules based hydrogels containing therapeutic substances are used in a wide range of biomedical applications including wound healing, tissue engineering, cosmetics and contact lenses. However, many aspects related to hydrogels such as the mechanism of cross-linking and molecular entanglement are not clear. So, there is a need to do more research and exploration toward the extensive and cost-effective use of hydrogels. The present review article elaborately discusses the biomolecules based hydrogels and their possible biomedical applications in different fields.

Biomineralization-inspired mineralized hydrogel promotes the repair and regeneration of dentin/bone hard tissue

Maxillofacial hard tissue defects caused by trauma or infection often affect craniofacial function. Taking the natural hard tissue structure as a template, constructing an engineered tissue repair module is an important scheme to realize the functional regeneration and repair of maxillofacial hard tissue. Here, inspired by the biomineralization process, we constructed a composite mineral matrix hydrogel PAA-CMC-TDM containing amorphous calcium phosphates (ACPs), polyacrylic acid (PAA), carboxymethyl chitosan (CMC) and dentin matrix (TDM). The dynamic network composed of Ca²⁺·COO^- coordination and ACPs made the hydrogel loaded with TDM, and exhibited self-repairing ability and injectability. The mechanical properties of PAA-CMC-TDM can be regulated, but the functional activity of TDM remains unaffected. Cytological studies and animal models of hard tissue defects show that the hydrogel can promote the odontogenesis or osteogenic differentiation of mesenchymal stem cells, adapt to irregular hard tissue defects, and promote in situ regeneration of defective tooth and bone tissues. In summary, this paper shows that the injectable TDM hydrogel based on biomimetic mineralization theory can induce hard tissue formation and promote dentin/bone regeneration.

Biological Scaffolds Assembled with Magnetic Nanoparticles for Bone Tissue Engineering: A Review

Superparamagnetic iron oxide nanoparticles (SPION) are widely used in bone tissue engineering because of their unique physical and chemical properties and their excellent biocompatibility. Under the action of a magnetic field, SPIONs loaded in a biological scaffold can effectively promote osteoblast proliferation, differentiation, angiogenesis, and so on. SPIONs have very broad application prospects in bone repair, bone reconstruction, bone regeneration, and other fields. In this paper, several methods for forming biological scaffolds via the biological assembly of SPIONs are reviewed, and the specific applications of these biological scaffolds in bone tissue engineering are discussed.

A composite hydrogel scaffold based on collagen and carboxymethyl chitosan for cartilage regeneration through one-step chemical crosslinking

The number of cases of cartilage damage worldwide is increasing annually and this problem severely limits an individual's physical activities, subsequently contributing to additional medical problems. Hydrogels can repair cartilage defects and promote cartilage regeneration. In this study, a composite hydrogel scaffold was prepared with collagen (COL), carboxymethyl chitosan (CMC), and the Arg-Gly-Asp (RGD) peptide through one-step chemical crosslinking, in which the three compositions ratio was especially investigated. The hydrogel scaffold performed well in cell adhesion and biocompatibility experiments, mainly due to the favorable porosity (the aperture was concentrated at 100 μm and the porosity was >70 %) and RGD concentration (2 mM RGD was the optimal concentration, which could effectively improve the attachment of BMSCs to the stent). Moreover, bone marrow mesenchymal stem cells (BMSCs) filled in the hydrogel scaffold, together with transforming growth factor TGF-β3, which was applied to evaluate the feasibility on the repair of the injured cartilage of the rat. In vitro and in vivo study, according to the results of cell proliferation and cytotoxicity, the hydrogel material had no toxic effect on cells, and the COL2/CMC1 hydrogel scaffold had the most obvious role in promoting cell proliferation. The results of pathological section showed that the cell scaffold complex group provided good mechanical properties for the wound and supplemented the stem cells derived from chondrocytes and showed good cartilage defect repair effect; In the scaffold group, the surface fibrosis of the injured area was mainly filled with fibrocartilage and other collagen fibers The hydrogel/BMSCs complex based on COL and CMC can be beneficial for the regeneration of cartilage.

The role of the immune microenvironment in bone, cartilage, and soft tissue regeneration: from mechanism to therapeutic opportunity

Bone, cartilage, and soft tissue regeneration is a complex spatiotemporal process recruiting a variety of cell types, whose activity and interplay must be precisely mediated for effective healing post-injury. Although extensive strides have been made in the understanding of the immune microenvironment processes governing bone, cartilage, and soft tissue regeneration, effective clinical translation of these mechanisms remains a challenge. Regulation of the immune microenvironment is increasingly becoming a favorable target for bone, cartilage, and soft tissue regeneration; therefore, an in-depth understanding of the communication between immune cells and functional tissue cells would be valuable. Herein, we review the regulatory role of the immune microenvironment in the promotion and maintenance of stem cell states in the context of bone, cartilage, and soft tissue repair and regeneration. We discuss the roles of various immune cell subsets in bone, cartilage, and soft tissue repair and regeneration processes and introduce novel strategies, for example, biomaterial-targeting of immune cell activity, aimed at regulating healing. Understanding the mechanisms of the crosstalk between the immune microenvironment and regeneration pathways may shed light on new therapeutic opportunities for enhancing bone, cartilage, and soft tissue regeneration through regulation of the immune microenvironment.

Mechanical Characterization at the Microscale of Mineralized Bone Callus after Bone Lengthening

Distraction osteogenesis (DO) involves several processes to form an organized distracted callus. While bone regeneration during DO has been widely described, no study has yet focused on the evolution profile of mechanical properties of mineralized tissues in the distracted callus. The aim of this study was therefore to measure the elastic modulus and hardness of calcified cartilage and trabecular and cortical bone within the distracted callus during the consolidation phase. We used a microindentation assay to measure the mechanical properties of periosteal and endosteal calluses; each was subdivided into two regions. Histological sections were used to localize the tissues. The results revealed that the mechanical properties of calcified cartilage did not evolve over time. However, trabecular bone showed temporal variation. For elastic modulus, in three out of four regions, a similar evolution profile was observed with an increase and decrease over time. Concerning hardness, this evolves differently depending on the location in the distracted callus. We also observed spatial changes in between regions. A first duality was apparent between regions close to the native cortices and the central area, while latter differences were seen between periosteal and endosteal calluses. Data showed a heterogeneity of mechanical properties in the distracted callus with a specific mineralization profile.

A 3D-printed molybdenum-containing scaffold exerts dual pro-osteogenic and anti-osteoclastogenic effects to facilitate alveolar bone repair

The positive regulation of bone-forming osteoblast activity and the negative feedback regulation of osteoclastic activity are equally important in strategies to achieve successful alveolar bone regeneration. Here, a molybdenum (Mo)-containing bioactive glass ceramic scaffold with solid-strut-packed structures (Mo-scaffold) was printed, and its ability to regulate pro-osteogenic and anti-osteoclastogenic cellular responses was evaluated in vitro and in vivo. We found that extracts derived from Mo-scaffold (Mo-extracts) strongly stimulated osteogenic differentiation of bone marrow mesenchymal stem cells and inhibited differentiation of osteoclast progenitors. The identified comodulatory effect was further demonstrated to arise from Mo ions in the Mo-extract, wherein Mo ions suppressed osteoclastic differentiation by scavenging reactive oxygen species (ROS) and inhibiting mitochondrial biogenesis in osteoclasts. Consistent with the in vitro findings, the Mo-scaffold was found to significantly promote osteoblast-mediated bone formation and inhibit osteoclast-mediated bone resorption throughout the bone healing process, leading to enhanced bone regeneration. In combination with our previous finding that Mo ions participate in material-mediated immunomodulation, this study offers the new insight that Mo ions facilitate bone repair by comodulating the balance between bone formation and resorption. Our findings suggest that Mo ions are multifunctional cellular modulators that can potentially be used in biomaterial design and bone tissue engineering.

Coaxially Fabricated Dual-Drug Loading Electrospinning Fibrous Mat with Programmed Releasing Behavior to Boost Vascularized Bone Regeneration

In clinical treatment, the bone regeneration of critical-size defects is desiderated to be solved, and the regeneration of large bone segment defects depends on early vascularization. Therefore, overcoming insufficient vascularization in artificial bone grafts may be a promising strategy for critical-size bone regeneration. Herein, a novel dual-drug programmed releasing electrospinning fibrous mat (EFM) with a deferoxamine (DFO)-loaded shell layer and a dexamethasone (DEX)-loaded core layer is fabricated using coaxial electrospinning technology, considering the temporal sequence of vascularization and bone repair. DFO acts as an angiogenesis promoter and DEX is used as an osteogenesis inducer. The results demonstrate that the early and rapid release of DFO promotes angiogenesis in human umbilical vascular endothelial cells and the sustained release of DEX enhances the osteogenic differentiation of rat bone mesenchymal stem cells. DFO and DEX exert synergetic effects on osteogenic differentiation via the Wnt/β-catenin signaling pathway, and the dual-drug programmed releasing EFM acquired perfect vascularized bone regeneration ability in a rat calvarial defect model. Overall, the study suggests a low-cost strategy to enhance vascularized bone regeneration by adjusting the behavior of angiogenesis and osteogenesis in time dimension.

Biological Response to Bioinspired Microporous 3D-Printed Scaffolds for Bone Tissue Engineering

The scaffold is a key element in the field of tissue engineering, especially when large defects or substitutions of pathological tissues or organs need to be clinically addressed. The expected outcome is strongly dependent on the cell–scaffold interaction and the integration with the surrounding biological tissue. Indeed, mimicking the natural extracellular matrix (ECM) of the tissue to be healed represents a further optimization that can limit a possible morphological mismatch between the scaffold and the tissue itself. For this aim, and referring to bone tissue engineering, polylactic acid (PLA) scaffolds were 3D printed with a microstructure inspired by the trabecular architecture and biologically evaluated by means of human osteosarcoma SAOS-2 cells. The cells were seeded on two types of scaffolds differing for the designed pore size (i.e., 400 and 600 µm), showing the same growth exponential trend found in the control and no significant alterations in the actin distribution. The microporous structure of the two tested samples enhanced the protein adsorption capability and mRNA expression of markers related to protein synthesis, proliferation, and osteoblast differentiation. Our findings demonstrate that 3D-printed scaffolds support the adhesion, growth, and differentiation of osteoblast-like cells and the microporous architecture, mimicking the natural bone hierarchical structure, and favoring greater bioactivity. These bioinspired scaffolds represent an interesting new tool for bone tissue engineering and regenerative medicine applications.

Synthesis, Structural, and Mechanical Behavior of β-Ca3(PO4)2–ZrO2 Composites Induced by Elevated Thermal Treatments

Biocompatible β-Ca₃(PO₄)₂ and mechanically stable t-ZrO₂ composites are currently being combined to overcome the demerits of the individual components. A series of five composites were synthesized using an aqueous precipitation technique. Their structural and mechanical stability was examined through X-ray diffraction, Rietveld refinement, FTIR, Raman spectroscopy, high-resolution scanning electron microscopy, and nanoindentation. The characterization results confirmed the formation of β-Ca₃(PO₄)₂–t-ZrO₂ composites at 1100 °C. Heat treatment above 900 °C resulted in the degradation of the composites because of cationic interdiffusion between Ca²⁺ ions and O⁻² vacancy in Zr⁴⁺ ions. Sequential thermal treatments correspond to four different fractional phases: calcium-deficient apatite, β-Ca₃(PO₄)₂, t-ZrO₂, and m-ZrO₂. The morphological features confirm in situ synthesis, which reveals abnormal grain growth with voids caused by the upsurge in ZrO₂ content. The mechanical stability data indicate significant variation in Young’s modulus and hardness throughout the composite.