Cell adhesion is a fundamental function of biomaterials, typically mediated by CAPs, which interact with designated cell receptors membrane, such as integrins and fibronectin-binding proteins. Several CAPs target integrins, with the fibronectin-derived RGD peptide being widely utilized due to its effectiveness in promoting cell attachment (Huettner et al., 2018). RGD can bind to multiple integrins, thereby activating additional processes like osteogenesis, angiogenesis, and neurogenesis. RGD peptides coupled with their products, for instance RGDS, PRGDSGYRGDS (PRG), and DGRGDSVAYG (DGR), Undergo tailoring into different types of supramolecular peptides to create bioactive hydrophobic hydrogels (Hao et al., 2022; Matsugami et al., 2021; Liu et al., 2012; Luo et al., 2019). A peptide inspired by fibronectin, designed to enhance cell attachment Pro-His-Ser-Arg-Asn (PHSRN)PHSAA recent findings indicate that synergistically improve cell attachment and cell multiplication when combined with RGD in supramolecular peptides (Aye et al., 2018).

The mechanical features of SPNHs play a crucial role in promoting cell attachment, spreading, along with differentiation. Such stiffness and elasticity of SPNHs directly affect cellular behavior, as materials that are too soft or rigid may impair cell attachment and function (Hao et al., 2022; Wang S. et al., 2021). By adjusting the mechanical properties to align with the target tissue, such as bone, it is possible to enhance integrin engagement, which in turn promotes stronger cell adhesion and proliferation. When combined with biochemical signals, such as the RGD sequence in CAPs, this mechanical stimulation creates a synergistic effect that promotes tissue regeneration (Abioye et al., 2024). Balancing both mechanical and biochemical properties makes SPNHs an ideal platform for bone repair and regeneration.

Cell recruitment involves the ability of biomaterials to attract endogenous repair cells from niches like the bone marrow, promoting their migration into the material. This reduces reliance on exogenous seed cells, thereby lowering costs and enhancing the body’s natural healing response. SPNHs offer a porous, ECM-mimetic microenvironment that promotes cell recruitment, a process that can be further augmented by integrating bioactive elements. Whereas these substances mimic such porous architecture of the extracellular matrix (ECM) to promote endogenous cell migration, current limitations lie in the precise control of bioactive motif release kinetics. Future designs could focus on spatiotemporal modulation of signaling molecules to optimize recruitment efficiency. Bone marrow homing peptides (BMHPs), containing high levels of K, P, F, S, along with T, can be identified through phage display as effective in promoting MSC migration. Incorporating BMHPs into SPNHs can optimize regenerative outcomes by leveraging the body’s intrinsic repair mechanism (Restu et al., 2020). Lu et al. (2018) developed composite nanoscaffolds Via the integration of decellularized cartilage matrix (DCM) with RADA 16 water-based gel otherwise RADA 16/RADA 16-GG-PFSSTKT hydrogel. Their findings demonstrated that both RADA 16/RADA 16-GG-PFSSTKT and RADA 16/RADA 16-GG-SKPPGTSS hydrogels effectively promoted subchondral bone regeneration within the DCM. Although these studies primarily focused on osteogenic differentiation and gene expression, they also highlighted the potential of these hydrogels for directing MSCs to the injury area, as evidenced by increased cellular infiltration in the defect area. Additionally, the concurrent application of BMHP1 with crosslinked RADA 16 significantly amplified alkaline phosphatase levels and upregulated expression of bone-related genes in MSCs (Figure 2). Existed experimental results further confirmed that RADA 16/RADA 16-GG-PFSSTKT scaffold accelerates regeneration in rodent skull lesions (Cui et al., 2022). Additionally, Substance P (SP), a neuropeptide with the sequence RPKPQQFFGLM, plays a role in neurological functions known for its ability to recruit MSCs (Zhang K. et al., 2024). Upon subcutaneously implanting poly (lactic acid) (PLA) scaffolds containing KLD 12-/KLD 12-SP hydrogels in nude mice, it was observed that the PLA hydrogels exhibited the highest homing activity, recruiting the most labeled MSCs. Furthermore, several active biomolecules, like stromal cell-derived factor 1β (SDF-1β) (Raftery et al., 2024)along with interleukin-8 (IL-8) (Lin et al., 2019))demonstrated cell migration properties and can be physically encapsulated within SPNHs for enhanced bone regeneration (Table 1).

Hydrogel matrices should provide niches that facilitate the infiltration of endogenous cells, ensuring that the scaffold can effectively degrade during the bone defect repair process. Moreover, the speed of decomposition in the matrix should be carefully balanced in accordance with tissue development speed regeneration into optimize healing outcomes (Kou et al., 2021). One strategy involves using diverse sequences that exhibit varying response rates to matrix metalloproteinases (MMPs), potentially resulting in distinct physical performance of the SPNHs. Giano et al. (2011) implemented various MMP-13-cleavable sequences into β-hairpin peptides following the PTGXKV pattern, substituting different residues at the X position: phenylalanine for Decapeptide 1 (DP1), leucine to Decapeptide 2 (DP2), isoleucine to Decapeptide 3 (DP3), along with alanine in Decapeptide 4 (DP4) (Hao et al., 2022). This data indicated a degradation rate order of the different hairpin structure peptides in the following manner: DP 1 > DP 2 > DP 3 > DP 4 (Giano et al., 2011). A possible cause of this is that DP one exhibits the lowest mechanical properties, potentially facilitating MMP-13’s penetration and degradation of the matrix. Another approach involves linking MMP-cleavable sequences through distinct spacer regions characterized by unique secondary structures. The MMP-1-cleavable sequence (GPQGIWGQ) was connected to hydrophobic alkyl chains via different spacer regions: Peptide Assembly 1(PA1), Peptide Assembly 3(PA3), and Peptide Assembly 4(PA4) (well-known folding sequences), and Peptide Assembly 2(PA2) (exhibiting 20% helical structure). Results indicated degradation did not appear in PA three along with PA 4 nano-scale filaments over 70 h, while PA one nanofibers exhibited detectable degradation (0.21%) within 24 h (Shi et al., 2019). In the case of PA 2, a degradation rate of 3.22% was observed after 24 h. These results suggest that the secondary structure of the spacer can influence degradability by affecting the availability of the active sites (Shi et al., 2019). (Figure 3) This expands the possibilities for selecting SPNHs.

In bone tissue engineering, SPNHs can enhance osteogenesis by incorporating bone-inducing factors or peptides. Among the most widely used bioactive proteins are recombinant BMPs, including BMP-2, BMP-3, BMP-4, BMP-6, BMP-7, BMP-9, and BMP-12, which exhibit osteoinductive activity. Studies have shown that when BMPs are encapsulated within peptide amphiphiles (PAs), they promote healing in rabbit cranial defects (Fichman and Schneider, 2020). However, BMPs face challenges such as purification difficulties, high costs, supraphysiological dosing, and rapid release rates. To address these issues, enhancing the affinity between SPNHs and bioactive factors is an effective strategy. Heparan sulfate (HS), a glycosaminoglycan component of the ECM, is able to non-covalently bind to bioactive proteins, improving signal transduction in osteogenesis by stabilizing receptors and protecting proteins from hydrolysis, ultimately enhancing bone formation and mineralization (Huang et al., 2019; Rabenstein, 2002). This interaction can enhance signal transduction, stabilize receptors, and protect proteins from hydrolysis (Figure 4). Lee et al. (2013) developed the functionalized PA with heparin-binding peptides (LRKKLGKA) engineered to mimic these interactions, demonstrating collagen-based hydrogel composites containing BMP-2 along with HS reduce BMP-2 dosage by tenfold while promoting bone regeneration compared to collagen/BMP-2 composites. However, animal-sourced HS in clinical settings is constrained by poor bioavailability and potential side effects. To overcome this, sulfated monosaccharides have been employed to simulate natural polysaccharides and conjugated to PA (Lee et al., 2017). ECM-derived peptides, such as RGD, DGEA (Amirahmadi et al., 2023), GFOGER (Ha et al., 2023), P-15 (GTPGPQGIAGQRGVV) (Atieh et al., 2021),and KRSR (lysine-arginine-serine-arginine) (Gentile et al., 2017), can also selectively bind to osteoblasts, promoting biomineralization. Additionally, extracellular vesicles (EVs), rich in bioactive components, have emerged as promising materials for promoting osteogenesis and angiogenesis (Dee et al., 1998; Wang et al., 2022). Nevertheless, their clinical utility in bone tissue engineering is constrained by rapid degradation and systemic clearance. The integration of CAPs into peptide hydrogels significantly strengthens EV-matrix interactions, thereby optimizing their therapeutic potential for bone repair applications (Firoozi et al., 2020; Wan et al., 2024). Clinically, SPNHs serve as excellent drug carriers, holding promise for the delivery of osteoinductive drugs, thus emerging as potential materials for bone tissue engineering.

Taking into account that bone has a dense vascular network and innervated structure, both blood vessels and nerves play crucial roles in bone metabolism, remodeling, cellular function, and nutrient exchange. This intricate network not only supports the mechanical integrity of bone but also regulates various biological processes essential for maintaining bone health and facilitating repair mechanisms (Fan et al., 2014). When passive diffusion of oxygen and nutrients is insufficient to promote bone regeneration, angiogenesis and neurogenesis become crucial for the repair of injured bone. New blood vessel formation is critical for supplying nutrients and oxygen, while nerve regeneration supports cellular signaling and metabolic regulation necessary for effective healing (Wang B. et al., 2021). Therefore, incorporating angiogenic signals into biomaterials enhances bone regeneration. Various bioactive proteins play pivotal roles in angiogenesis, including VEGF (Lin et al., 2012), bFGF (Hosseinkhani et al., 2006) along with IGFs, all critical for cellular growth and repair (Kang et al., 2012). VEGF is widely recognized for its role in inducing the formation of new blood vessels (Hao et al., 2022). To illustrate, linking VEGF to BMP-2 and tangibly encapsulating it in PA hydrogels loaded into collagen demonstrated enhanced bone regeneration in a rat model of extensive skull damage. This underscores the significant influence of angiogenesis in bone regeneration (Bakshi et al., 2021).

NGF and BDNF are vital bioactive molecules involved in the formation and regeneration of neural tissue, both of which influence bone formation either directly or indirectly (Sun et al., 2020; Liu et al., 2021; Liu et al., 2018). The combination of neurotrophic molecules and osteogenic agents within SPNHs has the potential to stimulate bone repair, as these hydrogels are widely explored for use in neural along with neurotissue engineering (Koss et al., 2016). Neurodevelopmental sequences extracted through neurotrophic factors comprise peptides that mimic BDNF (e.g., RGIDKRHWNSQ, cyclic RKKADP) (Lu et al., 2019) coupled with emanating from neural cell anchoring factors sequences (e.g., EVYVVAENQQGKSKA (Wang et al., 2015) and SIDRVEPYSSTAQ (Zou et al., 2014)), which are designed to promote neurogenesis. Neurogenic components obtained in the native extracellular matrix, such as Emanating from laminin sequences (e.g., IKVAV, YIGSR, and RNIAEIIKDI), are applied in the field of NTE. Notably, both IKVAV and YIGSR have proven capable of stimulating angiogenesis as well (Jain and Roy, 2020).

The importance of this immune system in regulating osteogenesis is crucial, particularly the involvement of several components of the immune response, like neutrophils, macrophages, and T lymphocytes. Macrophages, specifically, play a significant role; initially exhibiting an M1 phenotype that facilitates the uptake of apoptotic cells coupled with pathogens while promoting inflammation, they subsequently transition to an anti-inflammatory M2 phenotype, which stimulates osteogenesis (Jiang et al., 2021). Current research has prioritized dual modulation of macrophage phenotypes by suppressing M1 polarization and enhancing M2 activation. To achieve this, interleukin-4 (IL-4)—a potent M2-polarizing cytokine—was covalently conjugated with BMP-2 conjugated with graphene oxide (GO) to establish a controlled release platform. This IL-4/BMP-2 functionalized GO system was subsequently encapsulated within carboxymethyl chitosan/polyethylene glycol diacrylate (CMC/PEGDA) hybrid hydrogels. Experimental studies ex vivo showed that such dual-factor hydrogel synergistically encouraged M2 macrophage activation and bone regeneration, while in vivo evaluations demonstrated significant inflammation suppression coupled with enhanced bone formation (Zou et al., 2021). Additionally, certain immunomodulators can be incorporated as drug carriers into SPNHs for applications in bone tissue engineering.

Acute and chronic bone infections present significant treatment challenges due to bacterial colonization and acidic microenvironments (Fang et al., 2021). Osteomyelitis, typically caused by infections leading resulting in bone tissue response otherwise bone marrow, is typically managed with completely removing the affected tissue, followed by the implantation of antimicrobial materials. SPNHs serve as a perfect support system functioning in two ways, with scaffolding as one along with controlled release, providing both antibacterial and osteogenic properties. Yang et al. (2018) included positively charged antimicrobial peptides (Amps) within RADA 16 hydrogels, achieving controlled release of Amps in a rabbit osteomyelitis model. This approach effectively inhibited the multiplication of S. aureus as well as promoted bone repair. Additionally, encapsulating ciprofloxacin within RADA 16/calcium phosphate cement scaffolds demonstrated significant efficacy in preventing postoperative infections (Li et al., 2021).

Scaffolds with combined capabilities of tumor inhibition and bone regeneration offer a potential treatment for bone abnormalities resulting from tumors. Antitumor agents with osteogenic properties, such as metformin—a diabetes medication that inhibits tumors and promotes bone formation—were successfully incorporated into scaffolds, inducing multiple beneficial functions, including both antitumor effects and enhanced bone regeneration (Tan et al., 2021). Currently, there are few studies investigating SPNHs as controlled release scaffolds. Conjugating antitumor agents to SPNHs presents a promising strategy for enhancing their therapeutic efficacy in bone regeneration.