“Slow walk”mimetic tensile loading maintains human meniscus tissue resident progenitor cells homeostasis in photocrosslinked gelatin hydrogel

Meniscus,the cushion in knee joint,is a load-bearing tissue that transfers mechanical forces to extracellular matrix(ECM)and tissue resident cells.The mechanoresponse of human tissue resident stem/progenitor cells in meniscus(hMeSPCs)is significant to tissue homeostasis and regeneration but is not well understood.This study reports that a mild cyclic tensile loading regimen of~1800 loads/day on hMeSPCs seeded in 3-dimensional(3D)photocrosslinked gelatin methacryloyl(GelMA)hydrogel is critical in maintaining cellular homeostasis.Experimentally,a“slow walk”biomimetic cyclic loading regimen(10%tensile strain,0.5 Hz,1 h/day,up to 15 days)is applied to hMeSPCs encapsulated in GelMA hydrogel with a magnetic force-controlled loading actuator.The loading significantly increases cell differentiation and fibrocartilage-like ECM deposition without affecting cell viability.Transcriptomic analysis reveals 332 mechanoresponsive genes,clustered into cell senescence,mechanical sensitivity,and ECM dynamics,associated with interleukins,integrins,and collagens/matrix metalloproteinase pathways.The cell-GelMA constructs show active ECM remodeling,traced using a green fluorescence tagged(GFT)-GelMA hydrogel.Loading enhances nascent pericellular matrix production by the encapsulated hMeSPCs,which gradually compensates for the hydrogel loss in the cultures.These findings demonstrate the strong tissue-forming ability of hMeSPCs,and the importance of mechanical factors in maintaining meniscus homeostasis.

4D bioprinting of programmed dynamic tissues

Setting time as the fourth dimension,4D printing allows us to construct dynamic structures that can change their shape,property,or functionality over time under stimuli,leading to a wave of innovations in various fields.Recently,4D printing of smart biomaterials,biological components,and living cells into dynamic living 3D constructs with 4D effects has led to an exciting field of 4D bioprinting.4D bioprinting has gained increasing attention and is being applied to create programmed and dynamic cell-laden constructs such as bone,cartilage,and vasculature.This review presents an overview on 4D bioprinting for engineering dynamic tissues and organs,followed by a discussion on the approaches,bioprinting technologies,smart biomaterials and smart design,bioink requirements,and applications.While much progress has been achieved,4D bioprinting as a complex process is facing challenges that need to be addressed by transdisciplinary strategies to unleash the full potential of this advanced biofabrication technology.Finally,we present future perspectives on the rapidly evolving field of 4D bioprinting,in view of its potential,increasingly important roles in the development of advanced dynamic tissues for basic research,pharmaceutics,and regenerative medicine.

Engineering an extracellular matrix-functionalized,load-bearing tendon substitute for effective repair of large-to-massive tendon defects

A significant clinical challenge in large-to-massive rotator cuff tendon injuries is the need for sustaining high mechanical demands despite limited tissue regeneration,which often results in clinical repair failure with high retear rates and long-term functional deficiencies.To address this,an innovative tendon substitute named“BioTenoForce”is engineered,which uses(i)tendon extracellular matrix(tECM)’s rich biocomplexity for tendon-specific regeneration and(ii)a mechanically robust,slow degradation polyurethane elastomer to mimic native tendon’s physical attributes for sustaining long-term shoulder movement.Comprehensive assessments revealed outstanding performance of BioTenoForce,characterized by robust core-shell interfacial bonding,human rotator cuff tendon-like mechanical properties,excellent suture retention,biocompatibility,and tendon differentiation of human adipose-derived stem cells.Importantly,BioTenoForce,when used as an interpositional tendon substitute,demonstrated successful integration with regenerative tissue,exhibiting remarkable efficacy in repairing large-to-massive tendon injuries in two animal models.Noteworthy outcomes include durable repair and sustained functionality with no observed breakage/rupture,accelerated recovery of rat gait performance,and>1 cm rabbit tendon regeneration with native tendon-like biomechanical attributes.The regenerated tissues showed tendon-like,wavy,aligned matrix structure,which starkly contrasts with the typical disorganized scar tissue observed after tendon injury,and was strongly correlated with tissue stiffness.Our simple yet versatile approach offers a dual-pronged,broadly applicable strategy that overcomes the limitations of poor regeneration and stringent biomechanical requirements,particularly essential for substantial defects in tendon and other load-bearing tissues.

Engineering microparticles based on solidified stem cell secretome with an augmented pro-angiogenic factor portfolio for therapeutic angiogenesis

Tissue (re)vascularization strategies face various challenges, as therapeutic cells do not survive long enough in situ, while the administration of pro-angiogenic factors is hampered by fast clearance and insufficient ability to emulate complex spatiotemporal signaling. Here, we propose to address these limitations by engineering a functional biomaterial capable of capturing and concentrating the pro-angiogenic activities of mesenchymal stem cells (MSCs). In particular, dextran sulfate, a high molecular weight sulfated glucose polymer, supplemented to MSC cul-tures, interacts with MSC-derived extracellular matrix (ECM) components and facilitates their co-assembly and accumulation in the pericellular space. Upon decellularization, the resulting dextran sulfate-ECM hybrid material can be processed into MIcroparticles of SOlidified Secretome (MIPSOS). The insoluble format of MIPSOS protects protein components from degradation, while facilitating their sustained release. Proteomic analysis demonstrates that MIPSOS are highly enriched in pro-angiogenic factors, resulting in an enhanced pro-angiogenic bioactivity when compared to naïve MSC-derived ECM (cECM). Consequently, intravital microscopy of full-thickness skin wounds treated with MIPSOS demonstrates accelerated revascularization and healing, far superior to the ther-apeutic potential of cECM. Hence, the microparticle-based solidified stem cell secretome provides a promising platform to address major limitations of current therapeutic angiogenesis approaches.