CHITOSAN FILM AS A POTENTIAL SURGICALLY ADAPTABLE IMPLANT FOR INFECTION PREVENTION

J. Keaton Smith, B.S.1; Warren O. Haggard, Ph.D.1; Joel D. Bumgardner, Ph.D.1; Harry S. Courtney, Ph.D.2; Mark S. Smeltzer, Ph.D.3 1The University of Memphis Department of Biomedical Engineering, 2The Memphis Veteran Affairs Medical Center,

3The University of Arkansas for Medical Sciences Department of Microbiology and Immunology

IntroductionMusculoskeletal injuries due to surgery or trauma involve bone and surrounding soft tissue; e.g. open fractures. These wounds are highly susceptible to infection. Staphylococcus aureus is the most common bacteria found in musculoskeletal wound sites. In the past 20 years resistant bacteria, such as Methicillin-resistant Staphylococcus aureus, have become more prevalent in contaminating musculoskeletal wounds.

This research investigated chitosan film’s potential for use as an adaptable implant for adjunctive musculoskeletal wound treatments. Dehydrated chitosan film is known to absorb and elute drugs over time and biodegrade in the body. The novelty of chitosan as a drug delivery device would be its ability to be customized by a surgeon through (1) in situ antibiotic loading and (2) maintaining rehydrated mechanical integrity.

1 – In situ loading is how a manufactured chitosan film absorbs antibiotics during rehydration. In situ loading will allow the surgeon to tailor the chitosan film to the patient’s need through (a) antibiotic choice and (b) antibiotic concentration.

2 – The mechanical integrity, specifically adhesive strength, after film rehydration will enable it to adhere to and increase the stability of orthopaedic prosthetics.

These two properties, if adequately achieved with chitosan film, would allow for its novel use in musculoskeletal treatment. The device’s main goals in musculoskeletal treatment are to (1) prevent infection through localized drug delivery, (2) stabilize prosthetic devices by using chitosan’s adhesive strength, and (3) eliminate revision surgery for device recovery due to chitosan’s natural biodegradation.

MaterialsChitosan Film – a linear polysaccharide, dehydrated matrix derived from the exoskeletons of crustaceans; combinations of 61, 71 and 80% degrees of deacetylation (DDA) and lactic (LA) and acetic (HAc) acid solvents were investigated.

Vancomycin – a glycopeptide antibiotic with concentration dependant activity against Gram-positive and resistant bacteria.

Daptomycin – a semi-synthetic lipopeptide antibiotic with activity against Gram-positive and resistant bacteria

Figure 3: Degradation of chitosan film as affected by daptomycin and vancomycin in situ loading, n = 3.

ConclusionFilms using 80%DDA showed the ability to absorb large quantities of antibiotics and degrade to the great extent. Films using LA showed the benefit of increased adherence to implant alloys. After comparing the presented studies and others involved with this research, an undefined relationship between the chitosan matrix, antibiotic, and acid solvent became evident. Further investigation into using different antibiotics and in situ loading times could provide insight into the drug–film relationship. Defining the drug–film relationship and altering the film accordingly could provide a film optimized to absorb multiple antibiotics and have extended antibiotic release. Finally, ensuring film biocompatibility and establishing a procedure for its use in prosthetic device stabilization must occur prior to in vivo testing. However, this research has determined that, when used with novel in situ loading, chitosan film shows potential for use as an adjunctive treatment in musculoskeletal wounds where bacterial contamination is likely and orthopaedic fixation devices are used.

ReferencesPanlilo A. Methicillin-Resistant Staphylococcus Aureus in U.S. Hospitals,

1975–1991. ICHE 1992;13:582–586.Moucha C, et al. Orhtopaedic Infection Prevention and Control: An Emerging

New Paradigm. 2009; Las Vegas, Nevada. AAOS.Zalavras C, et al. Management of Open Fractures. Infect Dis Clin North Am

2005;19:915–929.Esterhai J, et al. Musculoskeletal Infection. Park Ridge, IL: AAOS;1992.Hanssen A. Local Antibiotic Delivery Vehicles in the Treatment of

Musculoskeletal Infection. Clin Orthop Relat Res 2005;437:91–96.

MethodsAntibiotic Uptake. In order to determine the ability of chitosan to absorb the antibiotics, an antibiotic uptake study was performed. This study determined the amount of both vancomycin and daptomycin that each chitosan film variation could absorb during 1 minute of rehydration from an antibiotic solution of known concentration.

Adhesive Strength. To investigate the adhesive strength of chitosan films to implant devices, an adhesive strength protocol was developed by modifying an ASTM standard (D5179–02) for adhesive strength measurement. After 1 minute of rehydration, chitosan films were placed between the flat, superfinished surfaces of two implant grade alloy fixtures, either 316L stainless steel (ASTM F138) or 6–4 titanium (ASTM F136). These fixtures were gripped by a universal testing machine which measured the strength required to pull the implant alloys apart.

Chitosan Film Degradation. To determine the effect that antibiotic loading had on film degradation, the chitosan film variations that showed promising antibiotic uptake results were subjected to in vitro degradation supplemented with lysozyme. The amount of film degradation was determined by drying and weighing the film after every time point and comparing the recorded weight to the initial film weight.

Statistical Analysis. The data is reported as the mean ± standard deviation. One-way ANOVA was used to analyze if there were statistically significant differences in the data sets. Differences between chitosan film variations were determined using the Student t-test. All analysis was performed using JMP v7.0.1 and statistical significance occurred when p < 0.05.

Figure 1: Antibiotic uptake by chitosan film for both daptomycin Figure 2: Film variation adhesive strength to implant grade alloysand vancomycin after 1 minute in antibiotic solution, n = 6. after 1 minute of rehydration, n = 6.

ResultsUptake results indicated the antibiotic concentration that a dehydrated film could absorb normalized to chitosan film weight(figure 1). Antibiotic uptake between variations V80HAc, D71LA, D61LA, and D80LA was similar and significantly higher than all other variations. LA acid films absorbed significantly more daptomycin than HAc films, whereas HAc films absorbed significantly more vancomycin than LA films.

Adhesion testing indicated the adhesive strength, i.e. the maximum tensile load per area, in kPa (figure 2). 71LA films on titanium alloy fixtures had significantly higher adhesive strength than all other variations except for SS61LA and Ti71LA.

Degradation experiments indicated the percentage of the original film weight that remained after every 20 hours of degradation over 100 hours. Chitosan film variations with 61% DDA degraded less and there was no significance between antibiotic loaded and non-loaded variations. Both 71 and 80% DDA variations degraded to a greater extent and indicated that antibiotic loading decreased the degradation rate. After approximately 60 hours, the degradation rate slowed considerably in all variations.