In recent years, it has been observed that the incidence of peri-implant mucositis and peri-implantitis has gradually increased due to the increasing popularity of dental implants. Dixon et al. reported that the rates of peri-mucositis and peri-implantitis may be up to 40%-65% and 20%-47%, respectively [1]. Although osseointegration between the implant and new surrounding bone tissues has made great strides in the last few years, the soft tissue integration around the implant remains weak. Owing to the absence of laminin 5 (laminin 332, LM332) and hemidesmosomes (HDs) at the upper-middle portion of the implant and peri-implant epithelium (PIE) interface, the biological seal between implants and soft tissue is more susceptible to damage compared to the natural tooth and junctional epithelium (JE) [2]. Despite the plethora of available strategies such as coating titanium surfaces with laminin 332-derived peptides or other proteins used to establish a strong soft tissue attachment around dental implants remain inefficient and limited due to fast protein degradation, the potential for rapid loss of bioactive properties, risk of host immune response, and high cost of treatment [3], [4], [5], [6], [7], [8], [9], [10], [11]. Despite continuous advances in enhancing soft tissue integration around implants, establishing a robust permanent biological seal between implants and PIE remains a major challenge.

To date, tissue engineering has emerged as a promising strategy for bone, cartilage, blood vessel, nerve, skin, cornea, muscle, heart, liver, kidney, and periodontal tissue reconstruction [12], [13], [14], [15]. Stem cell therapy as an important component of tissue engineering has received widespread attention because of its self-renewal, multilineage differentiation, and immunomodulatory capacities [16, 17]. Compared with other sources of MSCs, gingival tissue-derived MSCs (GMSCs) are easy to obtain from discarded dental tissue samples [18, 19]. They are readily isolated and can be massively expanded in vitro. In particular, GMSCs have multipotential differentiation and exhibit profound immunomodulatory capacities and anti-inflammatory activation of the immune system in vitro and in vivo [20], [21], [22], [23]. More importantly, Kanazawa et al. suggested that systemic MSC injection can enhance PIE formation and Ln-332-positive staining at the implant interface [24]. Although direct injection of MSCs has displayed promising results, it suffers from certain limitations, such as massive cell death following injection and inefficient targeting [25, 26]. Hence, the development of a suitable scaffold biomaterial as a cell delivery vehicle is essential for providing a suitable microenvironment to extend cell viability and improve stem cell survival [27].

The use of various naturally derived hydrogel-based biomaterials has been investigated as potential delivery vehicles for cell encapsulation. silk fibroin (SF) has been known for biomedical and tissue engineering applications owing to its ease of processability, high tensile strength, adjustable biodegradation, superior biocompatibility, minimal inflammatory response, and versatile functionalization [28, 29]. Furthermore, SF-based hydrogels have also been vastly applied for drug delivery, gene therapy, bone regeneration, cartilage regeneration, and wound healing [28, [30], [31], [32]]. It is crucial that SF plays a fundamental role in wound healing process by promoting cell migration, proliferation, angiogenesis, and re-epithelialization, which contributes to PIE formation [33], [34], [35]. Recently, SF-glycidyl methacrylate (SilMA) has become a popular hydrogel in the field of tissue engineering due to their rapid dissolution in water after modification and can photo-cross-link into hydrogels using lithium phenyl-2,4,6- trimethylbenzoyl phosphinate (LAP) as photo-initiator when using a 405 nm UV light [36, 37]. However, SilMA is not suitable for encapsulating stem cells directly since it lacks larger pores at the micro- or macro-scale [38].

A potential solution to this problem is gelatin methacryloyl (GelMA), which has tunable physical properties and degradation and can be extensively modified depending on the application [39, 40]. GelMA is a photo-cross-linkable hydrogel obtained by molecularly bonding gelatin with methacryloyl (MA). Moreover, GelMA has the ability to be easily fabricated in highly porous structures. Thus, incorporating SilMA and GelMA creates bicomponent polymer network hydrogels with improved biological properties, which can substantially increase the viability of encapsulated stem cells. To the best of our knowledge, GelMA/SilMA hydrogels encapsulating GMSCs have not been studied concerning gingival epithelial biological sealing around implants to date.

The present study aimed to develop a therapeutic strategy for desirable gingival epithelial biological sealing around implants using encapsulated GMSCs in Porous GelMA/SilMA hydrogels via an early implant placement model in rats. Furthermore, we aimed to demonstrate that GMSCs-laden Porous GelMA/SilMA hydrogels regulated the ability of M2 macrophage polarization (Fig. 1).