Optimizing mesenchymal stem cell therapy for tendon-bone healing: Multifaceted approaches and future directions

Table 1 Summary of the effects of preconditioning methods on stem cells

Ref.	Pretreatment method	Cell type	Effects on stem cells	Mechanism	Animal model
Song et al[21], 2017	Mechanical stimulation	Rabbit BMSCs	Promote proliferation and differentiation	Increase collagen I, collagen III, ALP, OPN, tenascin C, and tenomodulin expression	Rabbit ACLR model
Wang et al[20], 2023	Mechanical stimulation	Mouse BMSCs	Promote chondrogenic differentiation	Stimulate macrophage polarization towards the M2 phenotype and secretion of TGF-β1	Mouse ACLR model
Li et al[17], 2015	Mechanical stimulation	Rat BMSCs	Inhibit adipogenic differentiation	Activate the TGFβ1/Smad2 signaling pathway	N/A
Kusuyama et al[26], 2014	LIPUS	Mouse MSCs line	Inhibit adipogenic differentiation, promote osteogenic differentiation	Regulate the ROCK-Cot/Tpl2-MEK-ERK signaling pathway and PPARγ2 activity	N/A
Chen et al[27], 2023	LIPUS	hUC-MSCs	Promote chondrogenic differentiation	Inhibit the TNF signaling pathway	Rat cartilage defect model
Wang et al[28], 2019	LIPUS	Rat BMSCs	Promote chondrogenic differentiation	Inhibit autophagy	N/A
Zhao et al[29], 2021	ESW	Human SCB-SPCs	Promote self-renewal	Activate the YAP/TAZ signaling pathway	Rabbit osteochondral defect model
Chen et al[31], 2017	ESW	Rat BMSCs	Promote proliferation and osteogenic differentiation	Increase Col1, OSX, Runx2, and ALP expression	Rat femoral shaft bone defect model
Hu et al[32], 2016	ESW	Human BMSCs, TDSCs, ADSCs	Promote osteogenic differentiation	Inhibit miR-138 to activate the FAK-ERK1/2-RUNX2 signaling pathway	Nude mouse bone induction model
Catalano et al[33], 2017	ESW	Human ADSCs	Promote osteogenic differentiation	Activate the ROS-ERK1/2-BMP2-Smad-RUNX2 signaling pathway	N/A
Wu et al[37], 2022	SLPI	Rat BMSCs	Promote migration and osteogenic differentiation	Upregulate Runx2, ALP, OCN, and OPN gene expression	Rat ACLR model
Han et al[38], 2024	TFRD	Mouse BMSCs	Promote vitality and osteogenic differentiation	Activate ERR1/2-Gga1-TGF-β/MAPK pathway	Rat ACLR model
Zhang et al[39], 2017	PVP-I	Rabbit BMSCs	Promote osteogenic differentiation	Increase the expression of BMP-2 and OPN	Rabbit ACLR model
Tian et al[40], 2018	Baicalein	Rat TDSCs	Promote osteogenic differentiation	Activate the Wnt/β-catenin signaling pathway	Rat calcaneus-Achilles tendon injury model
Wang et al[41], 2016	Icariin	Mouse MSCs	Promote osteogenic differentiation	Activate the Wnt/β-catenin signaling pathway	Mouse calvarial osteolysis model
Alipanah-Moghadam et al[42], 2023	Andrographolide	Rat BMSCs	Increase cell resistance to environmental stress	Induce the expression of HO-1	N/A
Tie et al[43], 2021	Dedifferentiated	Rabbit BMSCs	Promote osteogenic differentiation	Activate the Nanog/NFATc1/OSX signaling pathway	Rabbit ACLR model
Díaz-Tocados et al[44], 2017	Mg2+	Rat BMSCs	Promote proliferation and osteogenic differentiation	Activate the Notch1 signaling pathway	Rat femur decellularized scaffold
Kim et al[45], 2015	Static magnetic fields	Human BMSCs	Promote proliferation and osteogenic differentiation	Upregulate ALP, BSP-2, COL1A1, OCN, ON, OPN, OSX, and RUNX2 gene expression	N/A

BMSC: Bone marrow-derived stem cell; ALP: Alkaline phosphatase; OPN: Osteopontin; ACLR: Anterior cruciate ligament reconstruction; TGF: Transforming growth factor; LIPUS: Low-intensity pulsed ultrasound; MSC: Mesenchymal stem cell; ROCK: Rho-associated kinase; Cot/Tpl2: Cancer Osaka thyroid oncogene/tumor progression locus 2 kinase; MEK: Mitogen-activated protein kinase kinase 1; FAK: Focal adhesion kinase; ERK: Extracellular signal-regulated kinase; PPARγ2: Peroxisome proliferator-activated receptor gamma 2; hUC-MSC: Human umbilical cord-derived mesenchymal stem cell; TNF: Tumor necrosis factor; ESW: Extracorporeal shock wave; SCB-SPCs: Subchondral bone stem/progenitor cells; YAP: Yes-associated protein; TAZ: Transcriptional co-activator with PDZ-binding motif; Col1: Type I collagen; NFATc1: Nuclear factor of activated T-cells 1; OSX: Osterix; Runx2: Runt-related transcription factor 2; TDSC: Tendon-derived stem cell; ADSC: Adipose-derived stem cell; ROS: Reactive oxygen species; BMP2: Bone morphogenetic protein 2; OCN: Osteocalcin; SLPI: Secretory leukocyte protease inhibitor; TFRD: Total flavonoids of Rhizoma Drynariae; ERR1/2: Estrogen-related receptor 1 and 2; Gga1: Golgi-localized γ-ear containing ADP ribosylation factor-binding protein 1; MAPK: Mitogen-activated protein kinases; PVP-I: Polyvinylpyrrolidone iodine; HO-1: Heme oxygenase-1; BSP-2: Bone sialoprotein-2; COL1A1: Collagen type 1 alpha 1; ON: Osteonectin; N/A: Not available.

Table 2 Summary of biomaterial-enhanced stem cell therapy for tendon-bone healing

Ref.	Biomaterial	Material type	Cell type	Functions	Model
Chen et al[47], 2020	3D-printed PLGA scaffolds	Conventional biological scaffolds	Rabbit BMSCs	Support cell growth and differentiation	Rabbit RCT model
Yea et al[48], 2020	Hydroxyapatite-gradient scaffold	Conventional biological scaffolds	hUC-MSCs	Support cell adhesion, migration, and proliferation, promoting osteogenic and chondrogenic differentiation	Rat RCT model
Han et al[49], 2023	CS-FS	Conventional biological scaffolds	Rabbit BMSCs and TSPCs	Enhance cell differentiation and activity, maintaining the phenotype	Rat and rabbit RCT models
Zhang et al[50], 2024	Magnetically seeded biphasic scaffold	Conventional biological scaffolds	SPIO-BMSCs	Increase cell seeding efficiency, promote cell distribution and concentration, and enhance chondrogenic differentiation	Rat RCT model
Ji et al[53], 2023	Cocktail-like gradient gelatin/hyaluronic acid	Hydrogel-based materials	Rat BMSCs	Simulate natural gradient structure, support long-term cell culture and embedding, promote cell growth and differentiation	Rat RCT model
Rothrauff et al[54], 2019	Fibrin or GelMA	Hydrogel-based materials	Rat ADSC	Promote chondrogenic differentiation	Rat RCT model
McGoldrick et al[55], 2017	ECM hydrogel	Hydrogel-based materials	Rat ADSC	Better biocompatibility, enhance repair efficacy	Rat calcaneus-Achilles tendon injury model
Shekaran et al[58], 2016	ECM	Natural biomaterials	Human BMSCs	Promote cell proliferation and osteogenic differentiation	Mouse ectopic mineralization model
Deng et al[59], 2021	ECM	Natural biomaterials	Human BMSCs	Promote macrophage secretion of osteoinductive factors, enhance osteogenic differentiation	Mouse femoral defect model
Mifune et al[61], 2013	Cell sheets	Natural biomaterials	Human ACL-derived CD34+ cell	Increase proprioceptive recovery, graft maturation, and biomechanical strength	Rat ACLR model
Chang et al[62], 2012	Cell sheets	Natural biomaterials	Rabbit PPCs	Maintain cell differentiation capacity, promote fibrocartilage formation	Rabbit ACLR model
Tang et al[63], 2020	Cell sheets combined with acellular scaffolds	Natural biomaterials	Rabbit BMSCs	Promote cell differentiation, enhance new bone and fibrocartilage formation	Rabbit patella-patellar tendon injury model
Chen et al[64], 2020	Cell sheets	Natural biomaterials	Canine USCs	Promote fibrocartilage formation, increase trabecular thickness and biomechanical strength	Canine RCT model
Matsumoto et al[65], 2021	Cell sheets	Natural biomaterials	Human ADSCs	Bone tunnel narrowing, increased biomechanical strength	Rabbit ACLR model
Yao et al[66], 2023	Cell sheets	Natural biomaterials	Rat TDSCs	Enhance bone formation and angiogenesis, regulate macrophage polarization and MMP/TIMP expression	Rat ACLR model
Wei et al[67], 2023	Cell sheets	Natural biomaterials	LDSCs with BMP-2/TGF-β1 gene insertion	Promote osteogenic and tenogenic differentiation, improve biomechanical strength, enhance tissue maturation, inhibit bone tunnel widening	Mouse ACLR model

PLGA: Poly lactic-co-glycolic acid; BMSC: Bone marrow-derived stem cell; RCT: Rotator cuff tear; hUC-MSC: Human umbilical cord-derived mesenchymal stem cell; CS-FS: Chitosan-silk fibroin scaffold; TSPC: Tendon stem progenitor cell; SPIO: Superparamagnetic iron oxide; GelMA: Methacrylated gelatin; ADSC: Adipose-derived stem cell; ECM: Extracellular matrix; ACL: Anterior cruciate ligament; ACLR: Anterior cruciate ligament reconstruction; PPC: Periosteal progenitor cell; USC: Urine-derived stem cell; TDSC: Tendon-derived stem cell; MMP: Matrix metalloproteinase; TIMP: Tissue inhibitors of metalloproteinase; LDSC: Ligament-derived stem cell; BMP-2: Bone morphogenetic protein 2; TGF: Transforming growth factor.

Table 3 Limitations of mesenchymal stem cell therapy and main optimization strategies

Limitations	Strategies	Functions
Low delivery efficiency	Biomaterials	Sustained release of MSCs, reduced degradation, preventing cell leakage, and prolonging retention at the injury site
Limited direct differentiation potential	Preconditioning/gene modification	Enhancing MSC differentiation towards bone, cartilage, tendon, and other tissues
Limited cell functionality	Preconditioning/gene modification	Boosting MSC proliferation, migration, angiogenesis, and immune modulation capabilities
Immunogenicity	Exosomes	Acellular therapies that eliminate cellular immunogenicity

MSC: Mesenchymal stem cell.