Extensive research has demonstrated that S. aureus is capable of persisting within a diverse range of cellular environments, including macrophages, osteoblasts, osteoclasts, osteocytes, and fibroblasts, for prolonged durations (Masters et al., 2022). Macrophages harboring intracellular bacterial invasion are referred to as “Trojan horse” macrophages, facilitating the accumulation of small bacterial colony variants (Garzoni and Kelley, 2011). This intracellular residency of S. aureus accelerates osteoblast apoptosis and further augments osteoclast activity. Additionally, when pathogenic bacteria colonize bone cells, they trigger the secretion of inflammatory factors that induce osteoclasts, ultimately leading to pathological bone loss (Tong et al., 2022; Yoshimoto et al., 2022). Furthermore, S. aureus colonization within osteoblasts promotes their differentiation and maturation into osteocytes, serving as a vehicle for long-term immune evasion within the host (Alder et al., 2020; Watkins and Unnikrishnan, 2020).

The invasion of OLCN by S. aureus represents a novel mechanism of bacterial persistence and immune evasion in chronic osteomyelitis (Masters et al., 2021). Traditionally, S. aureus was considered a non-motile bacterium. However, recent advancements in research have established that S. aureus is capable of invading and residing within OLCN for extended durations (Yu et al., 2020). Notably, it has been demonstrated that the bacterium can successfully traverse the narrow spaces within the tubules by altering its shape (Jensen et al., 2023). In vitro investigations have revealed that the cell wall transpeptidase-penicillin-binding protein 4 (PBP4) and surface adhesin-S. aureus surface protein C (SasC) play pivotal roles in S. aureus’s ability to deform and replicate during its traversal through the tubules (Masters et al., 2021).

The intricate mechanism underlying biofilm formation during osteomyelitis has garnered significant attention in recent research. Biofilms, particularly those formed by S. aureus play a vital role. in persistent infections. Firstly, the biofilm matrix, composed of extracellular polymeric substances (EPS) including polysaccharides, proteins, and extracellular DNA secreted by bacteria during growth, serves as a protective barrier. This matrix not only hinders the diffusion of antibiotics to bacteria within the biofilm but also inhibits the penetration of immune cells, thereby contributing to bacterial persistence (Masters et al., 2022; Schilcher and Horswill, 2020). Secondly, the interaction between EPS and bacterial aggregates confers cohesion and viscoelasticity to the biofilm, enabling bacteria to adhere firmly to both biotic and abiotic surfaces and resist external mechanical forces (Peng et al., 2022). Thirdly, S. aureus exhibits altered metabolic phenotypes within biofilms, rendering it more resilient against the effects of antibiotics (Muthukrishnan et al., 2019). Additionally, the accessory gene regulator (Agr) quorum sensing system serves as a crucial regulator of S. aureus biofilm formation, which is intricately linked to imbalances in bone homeostasis and disease progression (Masters et al., 2022; Butrico and Cassat, 2020).

Abscess formation serves as an additional mechanism for the long-term survival and immune evasion of S. aureus. Initially, S. aureus overcomes the host’s innate immune defense mechanisms by expressing microbial surface components recognizing adhesive matrix molecules (MSCRAMMs). As S. aureus cells accumulate and establish colonies, a significant influx of neutrophils occurs in the affected area. These neutrophils undergo necrosis due to the effects of S. aureus, inadvertently creating a “protective barrier” that hinders the ability of newly recruited host immune cells to eliminate the bacteria within the abscess. Eventually, as the abscess ruptures, the bacteria disseminate to new anatomic locations, perpetuating the infection process (Masters et al., 2022; Muthukrishnan et al., 2019).

Furthermore, as inflammation ensues, the delicate balance between osteoblasts and osteoclasts within the local bone tissue is disrupted. Osteoclasts, the sole cell type responsible for bone resorption, exhibit excessive differentiation and proliferation, which are intricately linked to bone loss and ultimately give rise to infectious bone defects. S. aureus can directly bind to osteoclasts and promote bone resorption through its own virulence factors, such as Staphylococcal protein A (SpA), peptidoglycan, and lipoproteins. Additionally, it can indirectly stimulate osteoclasts to increase bone resorption by upregulating the synthesis of macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-κB ligand (RANKL) in osteoblasts. Notably, the activated immune system generates a copious amount of proinflammatory cytokines, which further promote osteoclast differentiation and exacerbate bone resorption (Tong et al., 2022; Mendoza et al., 2016; Kassem and Lindholm, 2016; Udagawa et al., 2021).

The involvement of bone as a secondary complication of DFIs is particularly severe, especially in cases of the most advanced soft tissue DFIs. Therefore, a high degree of vigilance is essential in the occurrence of DFO (Senneville et al., 2020).

DFIs are defined as infections involving soft tissue or bone located anywhere below the ankle in diabetic patients. These infections frequently originate from diabetic foot ulcers (DFUs) and are closely correlated with the eventual risk of lower limb amputation in affected patients (Noor et al., 2017; Mohseni et al., 2019). Multiple pathological factors elevate the risk of foot infections in individuals with diabetes, including neuropathy, vascular insufficiency, immune dysfunction, and alterations in foot biomechanics, all of which are contributing elements to the development of DFIs (Rubitschung et al., 2021; Noor et al., 2017). Neurological complications in diabetic patients encompass motor, sensory, and autonomic dysfunction. Motor neuropathy results in atrophy of foot muscles and associated deformities, leading to traumatic injuries. Impaired sensory function often leads to the body overlooking damage to the lower limbs, fostering a vicious cycle of injury. Autonomic neuropathy disrupts normal blood flow to the soles of the feet. When accompanied by a loss of sweat and sebaceous gland function, the skin becomes dry and keratinized, rendering it more susceptible to rupture and serving as a portal for initial infection (Pitocco et al., 2019). Concurrently, the presence of peripheral artery disease exacerbates tissue ischemia, impairs wound healing processes, and fosters an environment conducive to infection (Armstrong et al., 2023). Hyperglycemia-induced decreases in host defense capacity encompass deficiencies in neutrophil function, alterations in macrophage morphology, elevations in proinflammatory cytokines, and impairments in diabetic polymorphonuclear cell functions, including chemotaxis, phagocytosis, and bactericidal activity. Additionally, locally elevated blood glucose levels serve as an optimal medium for enhancing the virulence of pathogenic bacteria (Baroni and Russo, 2014).

Given that DFIs are the culmination of multiple factors, their treatment necessitates a multidisciplinary and coordinated comprehensive approach. Effective antibacterial interventions and necessary surgical procedures are pivotal. Local antimicrobial therapy and strategies to combat local drug resistance, encompassing antibiotic-impregnated biomaterials, novel antimicrobial peptides, nanomedicine, and photodynamic therapy, represent key considerations in the management of DFIs (Maity et al., 2024). Clinicians are continually focused on addressing how to facilitate the healing of locally damaged tissue, which involves revascularization, while rigorously managing blood glucose levels. Local growth factors, shockwave therapy, negative pressure wound therapy, and stem cell therapy have emerged as promising avenues for accelerating wound healing and reducing the incidence of DFUs as well as the amputation rate (Raja et al., 2023).

By incorporating biodegradable polymers, such as chitosan (CS), mannitol, hyaluronic acid, alginate, gelatin, collagen, hydroxypropyl methyl cellulose (HPMC), and poly (lactic-co-glycolic acid) (PLGA), into the drug-loaded matrix under specific conditions, it is possible to mitigate the initial burst release of drugs from the carriers. This modulation results in a more sustained and controlled drug release profile from the cement matrix (Vezenkova and Locs, 2022; Fosca et al., 2022; Mistry et al., 2016; Xu et al., 2017; Dorozhkin, 2019), thereby effectively fulfilling the objective of preventing and treating bone infection.

The influence of additives on the drug release rate within CPC manifests firstly through alterations in the drug’s affinity for the matrix, where a negative correlation exists between affinity and release rate. Secondly, the intrinsic properties of the additives themselves can modulate the rate of drug release. When polymers are employed as additives, they induce a spatial effect by swelling and filling the pores of the matrix, thereby inhibiting drug release. Subsequently, as the polymer undergoes degradation, the release rate augments due to the facilitated diffusion of drug molecules (Vezenkova and Locs, 2022; Fosca et al., 2022; Li et al., 2007; David Chen et al., 2011). When the local concentrations of antibiotics released by CPC remain subtherapeutic for an extended period following the initial burst release, the potential for bacterial resistance may arise (Thomes et al., 2002; Kendall et al., 1996). The incorporation of a polymer as an additive in the CPC matrix results in a reduction of the initial burst release of the drug and promotes a more sustained release profile of the drug over time (David Chen et al., 2011; Jin, 2015). This characteristic of the polymer is advantageous for modulating drug release within the therapeutic window in CPC, thereby mitigating the adverse effects of bacterial resistance and ensuring the antibacterial efficacy of the treated area within a safe concentration range. Furthermore, the rate of drug release in the CPC matrix can be controlled by adjusting the concentration of the polymer in the reaction solution (Tiğli et al., 2009).

Normal human bone comprises a complex combination of inorganic and organic materials. By incorporating polymeric organic polymers into CPC, we can better mimic the natural state of bone tissue, thereby enhancing the biocompatibility of CPC in vivo. Additionally, the inclusion of these polymers is advantageous in improving the injectability and mechanical strength of the bone cement matrix. Furthermore, it has been demonstrated that the antimicrobial properties of drug-loaded cement are also enhanced through the addition of polymers (Wu et al., 2021; Wu et al., 2020a; Bose et al., 2023).

CS is a polysaccharide compound derived from chitin through deacetylation (Bakshi et al., 2020). Its molecular structure harbors multiple functional groups, facilitating modifications and chemical reactions (Zhong et al., 2023). Apart from its biodegradability and biocompatibility, CS exhibits a strong affinity towards negatively charged bacterial membranes due to its cationic nature, thereby displaying moderate antibacterial activity (Tao et al., 2020; Negm et al., 2020). Yang et al. (2018) successfully fabricated a PLGA-HA scaffold grafted with CS using 3D printing technology. Both in vitro and animal experiments confirmed that the CS-PLGA-HA scaffold demonstrated remarkable antibacterial properties against S. aureus, along with bone conductivity, offering a novel approach to enhance the local therapeutic efficacy of CPCs in the treatment of infectious bone defects.

Antibiotics have long been extensively studied as a primary approach for preventing and treating bone infections. Surgical procedures such as wound contamination, fracture repair with or without internal fixation, joint prosthesis implantation, and spinal surgery can often lead to severe bone infections. Therefore, the successful osseointegration of CPCs during surgical procedures critically depends on the loading of antibacterial drugs, which effectively prevents bone infection at the surgical site (Ginebra et al., 2006). To prevent bone infection, it is essential that the antibiotics released from the bone cement carrier rapidly reach the minimum inhibitory concentration (MIC) of the corresponding pathogenic bacteria, while avoiding prolonged exposure to sub-inhibitory concentrations that may promote bacterial resistance. For the treatment of bone infection, it is necessary to achieve local long-term antibiotic release (Ginebra et al., 2012).

Currently, the antibiotics loaded into CPCs for the treatment of bone infections are primarily derived from a diverse range of antimicrobial agents. These include, but are not limited to, aminoglycosides such as gentamicin sulfate, tobramycin, and amikacin; β-lactams like meropenem and hydroxy benzylpenicillin; glycopeptides such as vancomycin and teicoplanin; quinolones like moxifloxacin and ciprofloxacin; and tetracyclines, such as doxycycline. These antibiotics, used singly or in combination, have demonstrated effectiveness in the prevention and treatment of bone infections (Ginebra et al., 2012; Mistry et al., 2016; Ribeiro et al., 2022; Nasser et al., 2022; Mabroum et al., 2023; Radwan et al., 2021; Liu et al., 2023; Mistry et al., 2022; Pradeep et al., 2023; Bhanwala and Kasaragod, 2022; Kumar Dewangan et al., 2023) (Table 1)

However, the emergence of antibiotic-resistant bacteria, including those that are refractory to almost all antibiotics and the challenges associated with the removal of biofilms, has garnered increasing attention. Consequently, the development of effective non-antibiotic alternatives has become a significant research focus in recent years (Aslam et al., 2018; Nir-Paz et al., 2019; Kalelkar et al., 2022). Additionally, the inclusion of antibiotics in bone cement matrices has been shown to compromise their mechanical stability, further emphasizing the need for alternative antimicrobial strategies (Arciola et al., 2018).

In the context of the escalating problem of antibiotic resistance in pathogenic bacteria, particularly caused by multidrug-resistant pathogens and biofilm formation (Peng et al., 2022; Muthukrishnan et al., 2019; van Staden and Heunis, 2011), the urgent need to identify reliable alternatives to antibiotics has become paramount. This is due to the difficulties in discovering new antibiotics that can effectively address this challenge in the near future (Volejníková et al., 2019; Sinha and Shukla, 2019; Costa et al., 2021).

Antimicrobial peptides (AMPs) represent a class of basic active peptides that exhibit broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria. These peptides demonstrate high antimicrobial efficacy even at low concentrations, possess anti-biofilm activity, and exert immunomodulatory effects (Costa et al., 2021; Melicherčík et al., 2018; Yazici et al., 2019; Luo and Song, 2021). Given that AMPs target multiple components within the plasma membrane and cytosol of bacteria, the likelihood of them inducing pathogen resistance is extremely low (Costa et al., 2021; Van Staden and Dicks, 2012). Currently, several AMPs have been approved by the U.S. Food and Drug Administration (FDA) for the treatment of severe bacterial infections, underscoring their potential as viable alternatives to traditional antibiotics (Dijksteel et al., 2021).

Notably, the application of drug-eluting coatings loaded with antimicrobial peptides onto porous calcium phosphate substrates represents a promising strategy for the prevention of orthopedic implant-related infections and the formation of biofilms on their surfaces:

Kazemzadeh-Narbat et al. (2010) selected the broad-spectrum AMP Tet213 and applied it to a titanium surface, creating coatings composed of microporous OCP as a drug carrier. These coatings, with a thickness of 7 μm and an AMP loading of 9 μg/cm², exhibited antimicrobial activity in vitro against both S. aureus (Gram-positive) and P. aeruginosa (Gram-negative). These results indicate that calcium phosphate-Tet213 coatings could potentially serve as an effective solution for the prevention of infections associated with orthopedic implants. Furthermore, the team demonstrated significantly lower in vitro cytotoxicity (200 μg/mL) of AMP HHC36 compared to AMP Tet213 (50 μg/mL) in calcium phosphate-HHC36 coatings applied to a titanium surface. Additionally, these coatings exhibited antimicrobial activity against both S. aureus and P. aeruginosa (Kazemzadeh-Narbat et al., 2012). Additionally, they also validated the ideal cytotoxicity and antibacterial efficiency of AMP HHC36 in vitro through antibacterial experiments utilizing titanium surface nanotubes coated with a palmitoyl oleoyl phosphatidyl-choline (POPC) film after loading AMP HHC36 into a supersaturated calcium phosphate coating matrix for sustained drug release (Kazemzadeh-Narbat et al., 2013).

Yazici et al. (2019) aimed to enhance the delivery efficiency of AMPs to localized regions and consequently developed bifunctional peptides by fabricating titanium surface nanotubes through HA deposition. The dual functionality of these peptides was achieved by conjugating hydroxyapatite binding peptide-1 (HABP1) with AMP using a flexible linker. The resulting HABP1-AMP conjugate demonstrated favorable affinity for HA and exhibited high antibacterial activity against S. mutans (Gram-positive) and E. coli (Gram-negative), thus presenting a promising approach for targeted delivery of AMPs to specific areas.

In the realm of biomaterial engineering stents, the integration of drug delivery functionality with therapeutic efficacy is a common strategy employed to augment stent performance. From a pharmaceutical standpoint, the manufacturing methodologies of stents must ensure compatibility with drug stability and sustained release profiles. In comparison to organic macromolecular drug molecules, TIIs exhibit several notable advantages, including reduced cost, superior stability, enhanced safety, and fewer constraints on the fabrication process of tissue-engineered scaffolds (Mouriño et al., 2012; Hoppe et al., 2013). Currently, in the ongoing research endeavors aimed at utilizing CPC as scaffolds for bone tissue engineering, researchers have selected specific metal ions as TIIs. These TIIs have been successfully validated for their notable efficacy in combating bacterial infections and enhancing the material matrix’s capacity to induce new bone formation (Gritsch et al., 2019; Feng et al., 2021).

Metals have been utilized as antibacterial agents and as materials for various biomedical research and applications (Zhong et al., 2023; Samuel et al., 2020; Makvandi et al., 2020). When CPC is employed as a drug delivery device for bone infections, a small quantity of ions within the calcium phosphate lattice can be substituted by other ions. Several studies have corroborated that the doping of metal ions, such as silver, copper, and zinc, into the bone cement matrix enables calcium phosphate to exhibit antibacterial properties (Kamphof et al., 2023).

Silver (Ag) is among the most extensively studied metal ions incorporated into calcium phosphate due to its remarkable antibacterial properties (Kamphof et al., 2023). Notably, silver nanoparticles (AgNPs) exhibit potent antibacterial activity by releasing silver ions that attach to the bacterial cell membrane, altering the lipid bilayer or surface charge state. This process generates reactive oxygen species (ROS) and free radicals, which damage organelles and biomolecules and regulate associated signal transduction pathways, ultimately leading to antibacterial efficacy (Zheng et al., 2018; Lee and Jun, 2019).

Choi et al. (2023) conducted a study evaluating the antibacterial effect of TTCP-dicalcium phosphate dihydrate (DCPD) cement impregnated with AgNPs. In a rat tibial infection model, local treatment with TTCP-DCPD cement containing varying concentrations of AgNPs was administered for either 3 or 12 weeks. The findings revealed a decrease in bacterial colony counts in the 12-week treatment group compared to the 3-week group. Furthermore, a trend towards a lower bacterial colony count was observed in groups treated with higher doses of AgNPs compared to those without AgNP impregnation. Separately, Köse et al. (2021) established a model of methicillin-induced osteomyelitis in the proximal tibia of New Zealand white rabbits. The animals were divided into three groups: the control group received vancomycin-impregnated PMMA bone cement beads, the experimental group received silver ion-doped calcium phosphate beads, and the negative control group received pure calcium phosphate beads. After 10 weeks, radiographic assessments demonstrated significant improvement in osteomyelitis in the experimental group compared to the control group. These results suggest that silver ion-doped calcium phosphate beads have the potential to stimulate bone tissue growth, resist infection, and ultimately treat experimental chronic osteomyelitis in animal models. However, it is crucial to acknowledge that the cytotoxicity of silver towards normal tissues and cells cannot be overlooked, posing a limitation to its widespread application in the treatment of bone infections (Mijnendonckx et al., 2013; Rizzello, 2014).

Copper (Cu), an essential trace element in the human body, possesses diverse biological functions, including broad-spectrum antibacterial effects, bone regeneration capabilities, and angiogenesis properties (Shen et al., 2021; Marziya et al., 2023; Holloway, 2019).

Foroutan et al. (2019) conducted a study to investigate the influence of Cu²⁺ release on the properties and underlying mechanisms of CPCs. They synthesized CPC containing varying concentrations of Cu²⁺ (0, 2, 4, and 6 mol%) through a room temperature precipitation reaction. In vitro experiments demonstrated that as the Cu content increased, the release of phosphorus and calcium decreased, while the release of Cu²⁺ escalated. Furthermore, an analysis of the antibacterial activity against S. aureus revealed that the antimicrobial potential of the bone cement enhanced with increasing Cu²⁺ concentration. Additionally, when human osteoblast-like osteosarcoma cells (Saos-2, HTB85) were inoculated onto the bone cement particles for a defined period, a significant increase in cell count was observed, thereby confirming its biocompatibility. This study underscores the dual benefits of copper-doped CPCs, which not only exhibit antimicrobial activity but also possess bone regeneration properties. Näf et al. (2024) developed bilayer nanocomposites consisting of PLGA and amorphous calcium phosphate, incorporating various copper nanoparticles, specifically copper oxide (CuONPs) and copper-doped tricalcium phosphate (CuTCPNPs). To assess the antimicrobial properties of these copper-containing materials, clinically isolated S. aureus and S. epidermidis were employed. Furthermore, the angiogenic potential of these nanocomposites was evaluated using the chick embryo chorioallantoic membrane (CAM) model. The findings revealed that both CuONPs and CuTCPNPs possess antimicrobial activities and serve as effective components for stimulating angiogenesis.

Moreover, numerous in vitro and in vivo experiments have demonstrated the antimicrobial properties of metals and their alloys, including magnesium, strontium, and zinc, when incorporated into CPCs against bone infections. Additionally, these metals have been shown to enhance the antimicrobial effectiveness of existing therapeutic agents (Daskalova et al., 2023; Sikder et al., 2020; Wang Y. et al., 2023; Dapporto et al., 2022; Shu et al., 2024; Wolf-Brandstetter et al., 2020). However, it is crucial to emphasize that the precise correlation between the antimicrobial activity and cytotoxicity of metal-doped CPCs remains to be elucidated in future investigations (Kamphof et al., 2023).

Graphene, an allotropic isomer of carbon, has been shown to enhance the mechanical properties of CPC matrices and improve their biocompatibility for bone repair and regeneration (Seonwoo et al., 2022; Ozder et al., 2023). Furthermore, studies have confirmed the antimicrobial efficacy of graphene against a broad range of bacteria, including both Gram-positive and Gram-negative strains (Akhavan et al., 2011; Gurunathan et al., 2012; He et al., 2015; Veerapandian et al., 2013).

Wu et al. (2020b) pioneered the preparation of an injectable CPC-CS-GO slurry through the doping of graphene oxide (GO) into CPC. This novel slurry exhibited a robust inhibitory effect against S. aureus, demonstrating an inhibition zone of 55.2 ± 2.5 mm, significantly surpassing that of the control CPC-CS (30.1 ± 2.0 mm) (p < 0.05). Furthermore, CPC-CS-GO displayed superior antibacterial activity against S. aureus biofilm in vitro (p > 0.05). Khosalim et al. (2022) synthesized biomaterials composed of HA, agarose, and GO. Incorporating 1.0wt% GO into these biomaterials resulted in a notable reduction of S. aureus in vitro colony-forming unit tests. Additionally, the excellent biocompatibility of these materials was confirmed through tests using mouse embryo osteoblast precursor cells (MC3T3-E1).

Iodine possesses a broad antimicrobial spectrum, demonstrating effectiveness against viruses, Mycobacterium tuberculosis, fungi, and bacteria (Tsuchiya et al., 2012). In a groundbreaking study, Morinaga et al. (2023) impregnated CPC with various concentrations of iodine to assess its in vitro antibacterial activity and in vivo biocompatibility. Their findings revealed that CPC containing 5% iodine retained a higher iodine content compared to other CPCs after 1 week of release. Furthermore, this CPC formulation exhibited antimicrobial efficacy against S. aureus and E. coli for up to 8 weeks, while maintaining a similar number of fibroblast colony formations as the control sample.

However, there are limited reports on the application of doping graphene or iodine into CPCs for the treatment of bone infections, and further exploration of these possibilities is warranted.