Hydrogels for bone organoid construction:From a materiobiological perspective

Bone organoids,which simulate and construct special organs in vitro with complex biological func-tions based on tissue engineering technology,provide dramatically realistic models for bone regenerative medicine development and lay the foundation for a new therapeutic strategy.The matrix microenviron-ment around tissues and cells plays a key role in the physiological functions and phenotypes of bone organoids.Traditionally,the commercially available Matrigel has been widely applied for organoid cul-tures.However,Matrigel is still facing challenges,including xenogenous origins and variable composi-tion.To address these issues,newly developed hydrogels become an appropriate candidate to alternate Matrigel for bone organoid culture.In this review,we summarized the development and limitations of ECM-based matrix(Matrigel)in the bone organoid cultures.Then we highlighted various hydrogel al-ternatives,including PEG,collagen,alginate,gelatin,chitosan,skin fibroin,and DNA derivative hydrogels,which have shown a promising application in bone tissue engineering and organoid cultures.Additionally,the effects of material properties(stiffness,viscoelasticity,charge,et al.)in hydrogels on cell culture and bone organoid culture were deeply investigated.Finally,we predicted that hydrogel-based biomaterials have a great potential for the construction and application of bone organoids.

A novel decellularized matrix of Wnt signaling-activated osteocytes accelerates the repair of critical-sized parietal bone defects with osteoclastogenesis, angiogenesis, and neurogenesis

Cell source is the key to decellularized matrix(DM)strategy.This study compared 3 cell types,osteocytes with/without dominant active Wnt/β-catenin signaling(daCO and WTO)and bone marrow stromal cells(BMSCs)for their DMs in bone repair.Decellularization removes all organelles and>95%DNA,and retained>74%collagen and>71%GAG,maintains the integrity of cell basement membrane with dense boundaries showing oval and honeycomb structure in osteocytic DM and smooth but irregular shape in the BMSC-DM.DM produced higher cell survival rate(90%)and higher proliferative activity.In vitro,daCO-DM induces more and longer stress fibers in BMSCs,conducive to cell adhesion,spreading,and osteogenic differentiation.8-wk after implantation of the critical-sized parietal bone defect model,daCO-DM formed tight structures,composed of a large number of densely-arranged type-I collagen under polarized light microscope,which is similar to and integrated with host bone.BV/TV(>54%)was 1.5,2.9,and 3.5 times of WTO-DM,BMSC-DM,and none-DM groups,and N.Ob/T.Ar(3.2×10^(2)/mm^(2))was 1.7,2.9,and 3.3 times.At 4-wk,daCO-DM induced osteoclastogenesis,2.3 times higher than WTO-DM;but BMSC-DM or none-DM didn't.daCO-DM increased the expression of RANKL and MCSF,Vegfa and Angpt1,and Ngf in BMSCs,which contributes to osteoclastogenesis,angiogenesis,and neurogenesis,respectively.daCO-DM promoted H-type vessel formation and nerve markersβ3-tubulin and NeuN expression.Conclusion:daCO-DM produces metabolic and neurovascularized organoid bone to accelerate the repair of bone defects.These features are expected to achieve the effect of autologous bone transplantation,suitable for transformation application.

Bioactive elements manipulate bone regeneration

While bone tissue is known for its inherent regenerative abilities,various pathological conditions and trauma can disrupt its meticulously regulated processes of bone formation and resorption.Bone tissue engineering aims to replicate the extracellular matrix of bone tissue as well as the sophisticated biochemical mechanisms crucial for effective regeneration.Traditionally,the field has relied on external agents like growth factors and pharmaceuticals to modulate these processes.Although efficacious in certain scenarios,this strategy is compromised by limitations such as safety issues and the transient nature of the compound release and half-life.Conversely,bioactive elements such as zinc(Zn),magnesium(Mg)and silicon(Si),have garnered increasing interest for their therapeutic benefits,superior stability,and reduced biotic risks.Moreover,these elements are often incorporated into biomaterials that function as multifaceted bioactive components,facilitating bone regeneration via release on-demand.By elucidating the mechanistic roles and therapeutic efficacy of the bioactive elements,this review aims to establish bioactive elements as a robust and clinically viable strategy for advanced bone regeneration.

The horizon of bone organoid: A perspective on constructionand application

Bone defects repair and regeneration by various causes such as tumor resection, trauma, degeneration, etc. havealways been a key issue in the clinics. As one of the few organs that can regenerate after adulthood, bone itselfhas a strong regenerative ability. In recent decades, bone tissue engineering technology provides various types offunctional scaffold materials and seed cells for bone regeneration and repair, which significantly accelerates thespeed and quality of bone regeneration, and many clinical problems are gradually solved. However, the bonemetabolism mechanism is complicated, the research duration is long and difficult, which significantly restrictsthe progress of bone regeneration and repair research. Organoids as a new concept, which is built in vitro withthe help of tissue engineering technology based on biological theory, can simulate the complex biologicalfunctions of organs in vivo. Once proposed, it shows broad application prospects in the research of organdevelopment, drug screening, mechanism study, and so on. As a complex and special organ, bone organoidconstruction itself is quite challenging. This review will introduce the characteristics of bone microenvironment,the concept of organoids, focus on the research progress of bone organoids, and propose the strategies for boneorganoid construction, study direction, and application prospects.

Ca_v3.3-mediated endochondral ossification in a three-dimensional bioprinted Gel MA hydrogel

The growth plate(GP)is a crucial tissue involved in skeleton development via endochondral ossification(EO).The bone organoid is a potential research model capable of simulating the physiological function,spatial structure,and intercellular communication of native GPs.However,mimicking the EO process remains a key challenge for bone organoid research.To simulate this orderly mineralization process,we designed an in vitro sh Ca_(v)3.3 ATDC5-loaded gelatin methacryloyl(Gel MA)hydrogel model and evaluated its bioprintability for future organoid construction.In this paper,we report the first demonstration that the T-type voltage-dependent calcium channel(T-VDCC)subtype Ca_(v)3.3 is dominantly expressed in chondrocytes and is negatively correlated with the hypertrophic differentiation of chondrocytes during the EO process.Furthermore,Ca_(v)3.3 knockdown chondrocytes loaded with the Gel MA hydrogel successfully captured the EO process and provide a bioink capable of constructing layered and orderly mineralized GP organoids in the future.The results of this study could therefore provide a potential target for regulating the EO process and a novel strategy for simulating it in bone organoids.