The soft tissue around the implant protects the alveolar bone from bacterial invasion and infection, and is the basis for the long-term health and stability of the peri-implant tissue [1], [2], [3], [4], [5]. During the tooth eruption, the soft tissue around natural teeth gradually forms a closure, while peri-implant soft tissue begins to heal in the presence of biomaterials after local trauma [6]. The healing process of peri-implant soft tissues is similar to the healing of oral mucosa and involves three phases: coagulation, inflammation, and formative remodeling. This process includes inflammatory responses, angiogenesis, and new tissue formation with the help of various cells, including fibroblasts, epithelial cells, endothelial cells, and macrophages [7]. Endothelial cell-dominated angiogenic response is essential for tissue repair. Rapid reconstitution of the damaged vascular system can provide a good repair micro-environment for the injury site, necessary oxygen and nutrients for tissue regeneration, as well as deliver signaling molecules and cytokines [8], [9]. Therefore, biomaterials capable of delivering pro-angiogenic factors have been proposed to induce vascularization. Macrophages, as a heterogeneous population, can either participate in inflammation (M1 phenotype) or be converted to an anti-inflammatory phenotype (M2). M2-type macrophages can secrete anti-inflammatory and other factors such as TGF-β and PDGF to induce fibroblast proliferation and VEGF to promote capillary growth. These factors are essential for tissue repair [10]. Thus, inflammatory response and angiogenesis complement and influence each other to build a physiological micro-environment for tissue repair and regeneration [11], [12], [13].

SEMA4D is a member of the fourth group of the signaling family [14]. It has high- and low-affinity receptors, PlexinB1 and CD72, respectively. PlexinB1 is mostly expressed in non-lymphocytes, such as neuronal and endothelial cells [15], [16], [17], [18], [19], whereas CD72 is mostly expressed in lymphocytes, such as T-cells, B-cells, dendritic cells, and macrophages. SEMA4D crucially regulates angiogenesis and immune response [20]. Based on bimolecular, tissue, and cellular interactions [21], our team has successfully prepared SEMA4D-modified titanium surfaces using alkali heat treatment and self-assembly techniques. Our previous study indicated that these surfaces have indirect anti-inflammatory effects, as demonstrated by an indirect co-culture model of endothelial cells and macrophages [22]. However, further investigation is required to elucidate the intrinsic mechanism by which material interface induces cellular phenotypic changes.

Many studies have shown that the binding of SEMA4D with high-affinity receptor PlexinB1 activates downstream RhoA and its effector molecule ROCK [23]. A single-cell metabolic imaging study of endothelial cells showed that RhoA/ROCK1 regulates endothelial cell glycolysis and cytoskeletal remodeling [24]. Furthermore, endothelial cells have a unique metabolic profile[25] as even under resting conditions, these cells can convert glucose to lactate and generate most of the energy through glycolysis, thereby promoting migration and proliferation during angiogenesis [26]. In immunology, lactate is considered an important metabolic feedback regulator and unique signaling molecule, with cell-, receptor-, mediator- and micro-environment-specific effects. Lactate affects macrophage phenotypic differentiation via a variety of signaling pathway activation mechanisms [27], [28]. This investigation hypothesized that SEMA4D-modified titanium surfaces activate RhoA/ROCK1 in endothelial cells, which regulates their motility and glycolysis. By releasing lactate, endothelial cells are involved in metabolic communication with other cells in their micro-environment, leading to the transformation of macrophages into the pro-regenerative M2-like phenotype.