Spinal cord injury (SCI), an intractable neurological disorder, results in neurodegeneration and motor dysfunction, leading to lifelong disability [1], [2], [3]. A progressive cascade of pathophysiological events, including inflammation, neuronal necrosis, glial scar formation, and axonal rupture, poses a significant obstacle to neural regeneration and signaling following SCI [4], [5], [6]. Various therapeutic strategies focus on treating specific pathological events of SCI with the aim of preventing the deterioration at the injury site and expediting the treatment of spinal cord injury. These strategies encompass stem cell transplantation for neuronal differentiation [7], [8], [9], [10], [11], scaffold implantation to provide a regenerative environment for neural repair [12], [13], [14], [15], [16], [17], as well as delivery of neurotrophic factors to promote neurogenesis or axonogenesis [18], [19], [20], [21]. However, due to the intricate pathophysiological mechanisms after SCI, targeting a single pathological feature through therapeutic interventions fails to achieve satisfactory recovery outcomes for neural regeneration and signaling after SCI [22], [23], [24]. Therefore, identifying a multifaceted treatment strategy is urgently required, which can enhance neurogenesis and remyelination while facilitating motor functional recovery after SCI.

Stem cell therapy has been demonstrated as a promising strategy for the treatment of SCI due to its favorable safety profile and potential for multi-differentiation [25]. Specifically, mesenchymal stem cells (MSCs) have emerged as an attractive therapeutic option for repairing damaged spinal cords by exerting paracrine actions to attenuate inflammation and by enhancing neurogenesis via their differentiation into neural-like cells [26], [27], [28], [29]. However, several significant obstacles still impede the practical application of stem cells in nerve injury treatment, particularly the challenges associated with uncontrolled differentiation of transplanted stem cells into neurons or astrocytes, such as MSCs or neural stem cells (NSCs) [30,31]. One approach to enhance the directed differentiation ability of stem cells is to provide a differentiation-inducing factor that facilitates their differentiation into neural-like cells or neurons rather than astrocytes during SCI treatment [32]. Previous studies have demonstrated that decellularized extracellular matrix (dECM), which contains native extracellular matrix (ECM) or ECM-derived proteins, plays a crucial role in regulating cell fate and function, including cell proliferation, phenotype, and differentiation [33], [34], [35], [36], [37]. Particularly, decellularized spinal cord-derived ECM (dSECM), a promising therapeutic material for spinal cord injury treatment, has the potential to guide stem cells differentiation into neurons, reduce glial scar formation, and provide a supportive microenvironment for axon growth [38]. However, the limited effect of dSECM on axonal regeneration and remyelination is mainly attributed to insufficient neurotrophic factors [39], [40], [41], such as brain-derived neurotrophic factor (BDNF) [42] and glial cell-derived neurotrophic factor (GDNF) [43]. Therefore, it is necessary to enrich dSECM with neurotrophic factors to enhance the efficacy of SCI treatment. Recently, GDNF has been shown to effectively attract axonal regeneration and promote remyelination in central nervous system (CNS) injuries [44]. These findings provide inspiration for a multifunctional repair material for SCI that enhances neural signaling and improves motor function. Specifically, the combination of dSECM-induced differentiation of MSCs or NSCs into neural-like cells and neurotrophic factor mediated promotion of axonogenesis and remyelination represents a promising strategy for enhancing motor functional recovery in SCI patients. However, to date, the application of decellularized spinal cord ECM-based material combined with neurotrophic factor for motor functional improvement has been rarely reported.

Herein, we have developed a multifunctional platform, in which dSECM is crosslinked with GDNF (dSECM-GDNF), and dSECM-GDNF was encapsulated together with MSCs in gelatin methacrylate (GelMA) to form an in situ solidified hydrogel (dSECM-GDNF/MSC@GelMA) for SCI treatment (Scheme 1). With the degradation of GelMA, dSECM-GDNF was released to realize the multifunctional treatment for neurogenesis and remyelination. At 4 weeks post-surgery, neurogenesis was promoted by the dSECM induction to differentiate stem cells into neural-like cells. At 8 weeks post-surgery, axonogenesis and remyelination were enhanced by gradually releasing GDNF to activate PI3K/Akt and MEK/Erk signaling pathways. In this study, we evaluated the therapeutic effect of dSECM-GDNF on motor functional recovery and our multifunctional hydrogel offers insights for further improvement of clinical practice in SCI.