Osteogenic effects of covalently tethered rhBMP-2 and rhBMP-9 in an MMP-sensitive PEG hydrogel nanocomposite

Thermoresponsive dual-network chitosan-based hydrogels with demineralized bone matrix for controlled release of rhBMP9 in the treatment of femoral head osteonecrosis

In an effort to mitigate or reverse the pathological progression of early-stage osteonecrosis of the femoral head (ONFH), this study employed a promising strategy that involves the sustained delivery of osteogenic factors to augment core decompression, facilitated by the use of composite hydrogels. Specifically, a hydrogel was synthesized by blending chitosan, Pluronic F-127, and tripolyphosphate, utilizing both ionic bonding and copolymer micelle cross-linking techniques. This hydrogel demonstrated exceptional biocompatibility, temperature responsiveness, pH-dependent biodegradation, and controlled release properties. The average pore diameter of the optimal hydrogel expanded to 45 μm, accompanied by zeta potentials of +34.72 ± 4.13 mV. The loading efficiency notably surpassed 90 %, while the sustained release of recombinant human bone morphogenetic proteins 9 (rhBMP9) was observed to last over 25 days at pH = 6.0 and over 36 days at pH = 7.4. This chitosan-based hydrogel, which sustained rhBMP9 release, significantly enhanced the proliferation and migration of bone marrow mesenchymal stem cells and human umbilical vein endothelial cells and promoted osteogenesis and angiogenesis both in vitro and in vivo. Collectively, our study presents an rhBMP9-loaded chitosan-based composite hydrogel system that offers innovative avenues for the research and clinical application of advanced biomaterials in the treatment of early ONFH.

Bio-orthogonal tuning of matrix properties during 3D cell culture to induce morphological and phenotypic changes

Described herein is a protocol for producing a synthetic extracellular matrix that can be modified in situ during three-dimensional cell culture. The hydrogel platform is established using modular building blocks employing bio-orthogonal tetrazine (Tz) ligation with slow (norbornene, Nb) and fast (trans-cyclooctene, TCO) dienophiles. A cell-laden gel construct is created via the slow, off-stoichiometric Tz/Nb reaction. After a few days of culture, matrix properties can be altered by supplementing the cell culture media with TCO-tagged molecules through the rapid reaction with the remaining Tz groups in the network at the gel-liquid interface. As the Tz/TCO reaction is faster than molecular diffusion, matrix properties can be modified in a spatiotemporal fashion simply by altering the identity of the diffusive species and the diffusion time/path. Our strategy does not interfere with native biochemical processes nor does it require external triggers or a second, independent chemistry. The biomimetic three-dimensional cultures can be analyzed by standard molecular and cellular techniques and visualized by confocal microscopy. We have previously used this method to demonstrate how in situ modulation of matrix properties induces epithelial-to-mesenchymal transition, elicits fibroblast transition from mesenchymal stem cells and regulates myofibroblast differentiation. Following the detailed procedures, individuals with a bachelor's in science and engineering fields can successfully complete the protocol in 4-5 weeks. This protocol can be applied to model tissue morphogenesis and disease progression and it can also be used to establish engineered constructs with tissue-like anisotropy and tissue-specific functions.

Orthobiologic therapies delay the need for hip arthroplasty in patients with avascular necrosis of the femoral head: A systematic review and survival analysis

PURPOSE

The aim of this systematic review and survival analysis was to quantify the benefits of orthobiologic augmentation therapies for the treatment of avascular necrosis (AVN) of the femoral head and identify the most effective approach to delay the need for total hip arthroplasty (THA).

METHODS

A systematic review of the literature was performed on PubMed, Scopus, and Cochrane on clinical studies on orthobiologic therapies used alone or as an augmentation to core decompression or other procedures to address hip AVN. A qualitative analysis of the different biological therapies applied was performed. Afterward, the results of these procedures were quantitatively analysed to document their survivorship from THA compared to treatment groups without orthobiologics. Kaplan-Meier analysis was performed for all studies and then by categorising orthobiologics into treatment subgroups.

RESULTS

A total of 106 studies were included (4505 patients). Different orthobiologic approaches have been evaluated: cell-based therapies including bone marrow aspirate concentrate (BMAC) and bone marrow mesenchymal stromal cells (BM-MSCs), platelet-rich plasma (PRP), or other bioactive molecules applied in the osteonecrotic area or as intra-arterial injections. The survival analysis at 120 months documented a higher (p < 0.0005) cumulative survivorship with orthobiologics (69.4%) compared to controls (48.5%). The superiority was shown specifically for BMAC (p < 0.0005), BM-MSCs (p < 0.0005), intra-arterial (p < 0.0005) and PRP (p = 0.011) approaches, but the direct comparison of these approaches with their controls confirmed benefits only for BMAC (p < 0.0005).

CONCLUSION

This systematic review and survival analysis demonstrated that orthobiologics have the potential to improve survivorship in patients affected by hip AVN. In particular, the specific analysis of different orthobiologic products supported relevant benefits for BMAC augmentation in terms of survival from the need for THA, while no clear benefits were confirmed for other orthobiologics.

LEVEL OF EVIDENCE

Level III.

Hydrogels empowered mesenchymal stem cells and the derived exosomes for regenerative medicine in age-related musculoskeletal diseases

As the population ages, musculoskeletal diseases (MSK) have emerged as a significant burden for individuals, healthcare systems, and social care systems. Recently, regenerative medicine has exhibited vast potential in age-related MSK, with mesenchymal stromal cells (MSCs) and their derived exosomes (Exos) therapies showing distinct advantages. However, these therapies face several limitations, including issues related to ensuring stability and effective distribution within the body. Hydrogels, acting as an ideal carrier, can enhance the therapeutic effects and application range of MSCs and Exos derived from MSCs (MSC-Exos). Therefore, this review comprehensively summarizes the application progress of MSCs and MSC-Exos combined with hydrogels in age-related MSK disease research. It aims to provide a detailed perspective, showcasing the functional enhancement of MSCs and MSC-Exos when incorporated into hydrogels. Additionally, this review explores their potential and challenges in treating age-related MSK diseases, offering references for future research directions and potential innovative strategies.

Photocrosslinkable Biomaterials for 3D Bioprinting: Mechanisms, Recent Advances, and Future Prospects

Constructing scaffolds with the desired structures and functions is one of the main goals of tissue engineering. Three-dimensional (3D) bioprinting is a promising technology that enables the personalized fabrication of devices with regulated biological and mechanical characteristics similar to natural tissues/organs. To date, 3D bioprinting has been widely explored for biomedical applications like tissue engineering, drug delivery, drug screening, and in vitro disease model construction. Among different bioinks, photocrosslinkable bioinks have emerged as a powerful choice for the advanced fabrication of 3D devices, with fast crosslinking speed, high resolution, and great print fidelity. The photocrosslinkable biomaterials used for light-based 3D printing play a pivotal role in the fabrication of functional constructs. Herein, this review outlines the general 3D bioprinting approaches related to photocrosslinkable biomaterials, including extrusion-based printing, inkjet printing, stereolithography printing, and laser-assisted printing. Further, the mechanisms, advantages, and limitations of photopolymerization and photoinitiators are discussed. Next, recent advances in natural and synthetic photocrosslinkable biomaterials used for 3D bioprinting are highlighted. Finally, the challenges and future perspectives of photocrosslinkable bioinks and bioprinting approaches are envisaged.

Revolutionizing bone defect healing: the power of mesenchymal stem cells as seeds

Bone defects can arise from trauma or pathological factors, resulting in compromised bone integrity and the loss or absence of bone tissue. As we are all aware, repairing bone defects is a core problem in bone tissue engineering. While minor bone defects can self-repair if the periosteum remains intact and normal osteogenesis occurs, significant defects or conditions such as congenital osteogenesis imperfecta present substantial challenges to self-healing. As research on mesenchymal stem cell (MSC) advances, new fields of application have emerged; however, their application in orthopedics remains one of the most established and clinically valuable directions. This review aims to provide a comprehensive overview of the research progress regarding MSCs in the treatment of diverse bone defects. MSCs, as multipotent stem cells, offer significant advantages due to their immunomodulatory properties and ability to undergo osteogenic differentiation. The review will encompass the characteristics of MSCs within the osteogenic microenvironment and summarize the research progress of MSCs in different types of bone defects, ranging from their fundamental characteristics and animal studies to clinical applications.

A Rheological Study on the Effect of Tethering Pro- and Anti-Inflammatory Cytokines into Hydrogels on Human Mesenchymal Stem Cell Migration, Degradation, and Morphology

Polymer-peptide hydrogels are being designed as implantable materials that deliver human mesenchymal stem cells (hMSCs) to treat wounds. Most wounds can progress through the healing process without intervention. During the normal healing process, cytokines are released from the wound to create a concentration gradient, which causes directed cell migration from the native niche to the wound site. Our work takes inspiration from this process and uniformly tethers cytokines into the scaffold to measure changes in cell-mediated degradation and motility. This is the first step in designing cytokine concentration gradients into the material to direct cell migration. We measure changes in rheological properties, encapsulated cell-mediated pericellular degradation and migration in a hydrogel scaffold with covalently tethered cytokines, either tumor necrosis factor-α (TNF-α) or transforming growth factor-β (TGF-β). TNF-α is expressed in early stages of wound healing causing an inflammatory response. TGF-β is released in later stages of wound healing causing an anti-inflammatory response in the surrounding tissue. Both cytokines cause directed cell migration. We measure no statistically significant difference in modulus or the critical relaxation exponent when tethering either cytokine in the polymeric network without encapsulated hMSCs. This indicates that the scaffold structure and rheology is unchanged by the addition of tethered cytokines. Increases in hMSC motility, morphology and cell-mediated degradation are measured using a combination of multiple particle tracking microrheology (MPT) and live-cell imaging in hydrogels with tethered cytokines. We measure that tethering TNF-α into the hydrogel increases cellular remodeling on earlier days postencapsulation and tethering TGF-β into the scaffold increases cellular remodeling on later days. We measure tethering either TGF-β or TNF-α enhances cell stretching and, subsequently, migration. This work provides rheological characterization that can be used to design new materials that present chemical cues in the pericellular region to direct cell migration.

A composite hydrogel loaded with the processed pyritum promotes bone repair via stimulate the osteogenic differentiation of BMSCs

Tissue engineering shows promise in repairing extensive bone defects. The promotion of proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) by biological scaffolds has a significant impact on bone regeneration outcomes. In this study we used an injectable hydrogel, known as aminated mesoporous silica gel composite hydrogel (MSNs-NH2@GelMA), loaded with a natural drug, processed pyritum (PP), to promote healing of bone defects. The mechanical properties of the composite hydrogel were significantly superior to those of the blank hydrogel. In vitro experiments revealed that the composite hydrogel stimulated the osteogenic differentiation of BMSCs, and significantly increased the expression of type I collagen (Col 1), runt-related transcription factor 2 (Runx 2), alkaline phosphatase (ALP), osteocalcin (OCN). In vivo experiments showed that the composite hydrogel promoted the generation of new bones. These findings provide evidence that the composite hydrogel pyritum-loaded holds promise as a biomaterial for bone repair.