ONFH represents a prevalent and challenging orthopedic disorder. In its advanced stages, ONFH frequently precipitates femoral head collapse, concomitant with the onset of secondary osteoarthritis[1, 2]. The pathogenesis of osteonecrosis of the ONFH remains a topic of ongoing debate and controversy. In addition to traumatic factors, common etiological factors encompass the misuse of glucocorticoids, alcohol abuse, coagulation dysfunction, sickle cell anemia, other hemoglobinopathies, inflammation, and autoimmune disorders. Among these, steroid-induced femoral head osteonecrosis prevails as the most frequently observed condition[3]. The current diagnosis and treatment of ONFH primarily rely on the ARCO staging system and individual patient factors. For patients in stage I and II according to the ARCO classification, conservation treatments such as immobilization, appropriate traction, medication, core decompression, osteotomy, and vascularized or non-vascularized bone grafting are commonly employed. The primary objectives are to alleviate pain and slow down the progression of necrosis. On the other hand, for patients in stage III and IV, total hip arthroplasty (THA) is often required. THA involves the complete replacement of the hip joint[4–6]. However, none of these methods have demonstrated the ability to reverse and cure early-stage ONFH. Furthermore, each method has its own limitations. For instance, while immobilization and traction, as well as medication, carry a low risk of harm to patients, there is still debate regarding their effectiveness in alleviating long-term pain and slowing disease progression[7]. Various hip preservation surgeries may require patients to remain bedridden for an extended period after the procedure. Additionally, the low success rates and significant harm to patients associated with these surgeries have remained persistent concerns for many clinicians in the field. THA is the ultimate treatment option for patients with ONFH [8]. However, the lifespan of the artificial joint used in the replacement procedure is often limited. Additionally, the onset of ONFH has been occurring at a younger age in recent years. Consequently, an increasing number of scholars have turned their attention to early-stage treatments for ONFH, such as tissue engineering and regenerative medicine. This approach, which aims to facilitate self-repair of tissues and reverse early-stage osteonecrosis, has become a hot topic in current research[9, 10].
Bone marrow mesenchymal stem cells (BMSCs) therapy, as a regenerative approach, has been increasingly utilized in research for treating early-stage ONFH. These cells possess the potential for self-renewal, multi-lineage differentiation, and immunomodulation. Furthermore, BMSCs exhibit excellent proliferative capacity, preserving their chromosomal karyotype and telomerase activity even after multiple passages[11–13]. The treatment of ONFH with BMSCs typically involves intra-bone marrow core decompression injection. However, this simple approach of solely injecting BMSCs often falls short of expected outcomes. Several factors may contribute to the suboptimal effects of direct BMSCs injection therapy, including mechanical damage to cells during the injection process, extensive infiltration of cells into surrounding tissue gaps leading to low cell retention rate, and compromised cell functionality due to inadequate extracellular matrix accumulation after injection. Therefore, a straightforward method to enhance the effectiveness of cell injection therapy is through high-dose multiple injections. This strategy, theoretically, can address the issues of low cell retention and survival rates[11, 14]. However, the use of high-dose multiple cell injections increases treatment costs and reduces the practicality of cell therapy[15]. Furthermore, high-dose cell injections may lead to excessive cell expansion and uncontrollable aberrant mutations, particularly when using genetically modified cells, thereby further increasing the associated risks[14, 16]. Therefore, the exploration of an efficient and safe cell therapy has become a current research hotspot, with suitable cell carrier materials emerging as a promising choice. The objective is to achieve cell protection and minimize cell damage during the injection process, while increasing cell retention and survival rates, ultimately improving the efficacy of cell therapy [17, 18]. Common cell carrier materials are often in the form of hydrogels. However, hydrogels alone are not effective in promoting extracellular matrix accumulation or facilitating interactions between cells[16]. Therefore, we believe that ideal cell carrier materials should possess the following characteristics: 1) safety and non-toxicity with good cell compatibility; 2) injectability and biodegradability; 3) certain adsorption capacity to increase cell retention; 4) provide physical protection for cells; 5) create a physiologically relevant environment, such as a three-dimensional growth environment, to enhance the accumulation of extracellular mechanisms and interactions between cells. Ultimately, these properties improve cell utilization and prevent the need for high-dose repeated injections[19–22].
Therefore, our team has developed a 3D-TableTrix microcarrier material as a cell carrier. This microcarrier is stored in the form of tablets, which rapidly disperse into numerous microcarrier particles when dissolved in a neutral solution. Under a microscope, these microcarrier particles exhibit a three-dimensional structure with interconnected pores, providing a suitable environment for cell attachment and growth[23–25]. Our previous research has demonstrated that the microcarrier particles loaded with stem cells can enhance the therapeutic efficacy of cells. In a study using a rat model of knee osteoarthritis, we found that intra-articular injection of microcarrier-loaded low-dose stem cells produced similar therapeutic effects to the injection of high-dose stem cells alone[16, 23].
In this study, we for the first time utilized a 3D-TableTrix microcarriers loaded with low-dose bone marrow mesenchymal stem cells for the treatment of steroid-induced femoral head necrosis in a rat model. We also established an in vitro co-culture system of osteoblasts, hormone-induced osteoblasts, pure BMSCs, and BMSCs grown in 3D-TableTrix microcarriers for the analysis and identification of osteoblasts within the co-culture system. These findings confirm that the 3D-TableTrix microcarriers loaded with low-dose bone marrow mesenchymal stem cells may be a promising therapeutic strategy for early-stage steroid-induced femoral head necrosis.