**2. Antiadhesive and antibiofilm properties of HA**

**1. Introduction**

180 Hydrogels

tical applications [21, 22].

Up to 80% of human bacterial infections are biofilm-related, according to the U.S. National Institutes of Health [1]. Among these, implant-related infections in orthopedics and trauma still have a tremendous impact [2]. In fact, periprosthetic joint infection (PJI) (**Figure 1**) is among the first reasons for implant failure [3], posing challenging diagnostic and therapeutic

Similarly, surgical site infections after osteosynthesis, with a reported incidence ranging from 3.9 to 10% for closed fractures [8–11] and even more after open fractures [12], are associated

Whenever a biomaterial is implanted, a competition between host and bacterial cells occurs for surface colonization. In the event of bacterial adhesion to an implant, immediate biofilm formation starts, making the bacteria extremely resistant to host's defense mechanisms and to antimicrobials [14–16]. According to recent evidence, fully formed biofilm can be found few hours after the first bacterial adhesion [17]; thus, the destiny of an implant is decided at the very time of surgery. To reduce or prevent bacterial adhesion and biofilm formation, a number of different antimicrobial finishing or coatings of implants are under study [18]. However, their clinical application appears particularly challenging, due to the many requirements they need to fulfill [19]. Hyaluronic acid (HA) is mucopolysaccharide, occurring naturally in mammals. It is abundant in skin and in connective tissues, being one of the main components of extracellular matrices. HA has several clinical applications in dermatology, esthetic surgery, dentistry, urology, orthopedics and ophthalmology [20]. In fact, due to its high biocompatibility, and nonimmunogenicity, hyaluronic acid is considered as an ideal biomaterial for medical and pharmaceu-

**Figure 1.** Infected, exposed, knee prosthesis in a 60-year-old woman. Approximately one million joint replacements are performed annually in Europe, and infection is currently among the first three most common reasons for failure of implants. Septic complications are associated with prolonged and complex medical and surgical treatments, often leading to implant removal. Poor functional results, possible infection recurrence, risk of amputation and increased mortality rate are all well known and feared consequences of periprosthetic and implant-related infections. Direct costs

of treatment of periprosthetic infection exceeds 100,000 euros, per case, according to a recent analysis [7].

dilemmas [4] and with high economic and social costs [5–7].

with high morbidity and possible mortality raise [9] and elevated costs [13].

Pavesio et al. [26] were probably the first to describe HA nonfouling properties and its ability to resist bacterial adhesion, with particular reference to *Staphylococcus epidermidis* [27], proposing coated polymeric medical devices to reduce implant-related infections. In particular, a hydrophilic HA overlayer, linked to the surface of polymethylmethacrylate intraocular lenses (IOLs), was shown to be able to significantly reduce the adhesion of *Staphylococcus epidermidis* to the implant surface [28].

In line with this observation, Kadry and coworkers, reported the ability of hyaluronan to reduce bacterial adhesion to IOLs of a *S. epidermidis* wild strain [29]; based on these findings, the authors proposed the use of HA as an antiadhesive, adjuvant therapy, in combination with antibiotics in irrigating solutions for bacterial ocular infections.

More recently, Drago et al. reported on the *in vitro* antiadhesive and antibiofilm activity of HA toward bacterial species commonly isolated from respiratory infections [30]. In this experimental study, HA was shown to be able to reduce bacterial adhesion to a cellular substrate in a concentration-dependent manner. The antibiofilm action, exerted by HA in ear, nose and throat districts, has been recently reviewed [31]. The authors conclude that "its efficacy in treating rhinosinusitis, whether or not associated with polyposis, is well documented, as well as results from its effects on mucociliary clearance, free radical production and mucosal repair."

vs. 52.7 ± 33.4 days, P < 0.001) after HA treatment, compared with placebo [43]. No adverse events were reported. A recent multicenter European study confirmed the efficacy of intravescical administration of combined HA and chondroitin sulfate (CS) for the treatment of

Hyaluronic-Based Antibacterial Hydrogel Coating for Implantable Biomaterials in Orthopedics…

http://dx.doi.org/10.5772/intechopen.73203

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In dentistry, the effect of the application of HA-containing gels in early wound healing after scaling and root planing (SRP) on clinical variables, subgingival bacteria and local immune response was investigated [45, 46]. Eick et al. [47] reported on 34 individuals affected by chronic periodontitis and treated with full-mouth SRP; in the test group (n = 17), a 0.8% hyaluronan-containing gel was introduced into all periodontal pockets during SRP and a 0.2% HA gel was applied by the patients onto the gingival margin twice daily during the following 2 weeks, while the control group (n = 17) was treated with SRP only; no placebo was used. Probing depth (PD) and clinical attachment level (CAL) were recorded at baseline and after 3 and 6 months, and subgingival plaque and sulcus fluid samples were taken for microbiologic and biochemical analysis. The changes in PD and the reduction of the number of pockets with PD ≥ 5 mm were significantly higher in the test group after 3 (P = 0.014 and 0.021) and 6 (P = 0.046 and 0.045) months. Six months after SRP, the counts of *Treponema denticola* were significantly reduced in both groups (both P = 0.043), as were those of Campylobacter rectus in the test group only (P = 0.028). *Prevotella intermedia* and *Porphyromonas gingivalis* increased

in the control group. No adverse effects of HA were observed during the study.

Composed of covalently linked hyaluronan and poly-d,l-lactide, the "Defensive Antibacterial Coating" (DAC®, Novagenit Srl, Mezzolombardo, Italy) was specifically developed in order to protect implanted biomaterials used in orthopedics, traumatology, dentistry and maxillo-

**Figure 2.** DAC® HA-g-PLA, fast-resorbable, hydrogel coating. Composed of covalently linked hyaluronan and poly-d, l-lactide, the "Defensive Antibacterial Coating" (DAC®, Novagenit Srl, Mezzolombardo, Italy) is the first antibacterial-

coating cleared for clinical use in orthopedics, trauma, dentistry and maxillofacial surgery in Europe.

**4. Synthesis of DAC® HA-g-PLA hydrogel coating**

facial surgery from bacterial colonization [24, 48] (**Figure 2**).

female recurrent urinary tract infections [44].

HA has also been reported to exert bacteriostatic, dose-dependent effect on different planktonic microorganisms [32, 33]. Radaeva et al. showed the inhibiting activity of HA with respect to some *Pseudomonas* species [34], while Ardizzoni and coworkers [23] investigated the effects of HA on 15 ATCC bacterial strains, representative of clinically relevant bacterial and fungal species. According to their results, different microbial species and strains are differently affected by HA. In particular, staphylococci, enterococci, *Streptococcus mutans*, two *Escherichia coli* strains, *Pseudomonas aeruginosa*, *Candida glabrata* and *C. parapsilosis* showed a dose-dependent growth inhibition, while no HA effects were detected in *E. coli* ATCC 13768 and *C. albicans*, and *S. sanguinis* was favored by the highest HA dose.

Carlson and coworkers [33] compared the potential bacteriostatic effect of collagen type I, hyaluronic acid, hydroxyapatite, polylactic acid and polyglycolic acid on some of the most common orthopedic bacterial pathogens (*S. aureus*, *S. epidermidis*, *β-hemolytic Streptococcus* and *Pseudomonas aeruginosa*): HA had the most significant bacteriostatic properties on the studied organisms. Similarly, Pirnazar et al. [32] did demonstrate the bacteriostatic effect of HA in different concentrations and molecular weight on oral and nonoral microorganisms (*Staphylococcus aureus*, *Propionibacterium acnes*, *Actinobacillus actinomycetemcomitans*, *Prevotella oris* and *Porphyromonas gingivalis*). The authors concluded that the clinical application of hyaluronan in the form of membranes, gels or sponges may reduce bacterial contamination of the surgical wound, thereby lessening the risk of postsurgical infection and promoting more predictable regeneration.

Concerning orthopedic applications, Harris and Richards [35] showed how coating titanium with sodium hyaluronate significantly decreased the density of *S. aureus* adhering to the surfaces and proposed its potential use to protect osteosynthesis, orthopedic or dental implants.

In a recent review, focused on the use of polysaccharide-based coatings to prevent biofilm formation, hyaluronic acid was discussed as one of the most promising [36]; displaying hydrophilic characteristics, this coating was in fact reported to reduce adhesion of *S. aureus*, *S. epidermidis* and *E. coli* by several orders of magnitude compared to unmodified surfaces.
