Does the Addition of Poly(glycolide-co-lactide) to Teicoplanin-Containing Poly(methyl methacrylate) Beads Change the Elution Characteristics?

Abstract

Background

The objective of our study was to measure and compare the elution characteristics of teicoplanin from poly(methyl methacrylate) PMMA beads with those of poly(glycolide-co-lactide) PGLA-added beads.

Methods

The study included two groups of PMMA + teicoplanin beads. PMMA was added to teicoplanin in Group 1 and PMMA + PGLA was added to teicoplanin in Group 2. A total of 16 beads of 1 cm³ were created for each group. Samples were added individually to tubes containing 3 ml of phosphate-buffered saline (PBS). Antibiotic elution was measured by measuring absorbance values of 1-ml samples taken at regular intervals using a UV–Vis spectrophotometer and cumulative percentages of drug release were calculated. In addition, the spectra of teicoplanin were identified using a FTIR spectrophotometer in a wavelength range of 400–4000 cm⁻¹.

Results

Drug elution in the PBS medium was measured and compared for Groups 1 and 2. The cumulative percentage of drug release from the PGLA-added beads (Group 2) was significantly higher (p = 0.01). The molecular structure of teicoplanin was also confirmed using FTIR.

Conclusion

The in vitro results showed that the addition of biodegradable PGLA into bone cement functions as a water-soluble porogen which allows for significant increases in the elution of teicoplanin from cement. This increase in elution suggests that the PGLA would allow for further fluid contact and exchange with the previously entrapped drug. These results may have important clinical applications.

Introduction

Thanks to modern surgical techniques and antibiotic prophylaxes, orthopedic infections are less common, yet remain a challenge for orthopedists [1]. Debridement and systemic antibiotics chosen based on culture results are used in the treatment of orthopedic infections. However, because of the bacterial biofilms formed during the infection stage, antibiotic efficacy cannot be achieved in the infected tissues, which may interfere with effective treatment [2]. High concentrations of antibiotics in the infected area cannot be achieved through intravenous administration but instead through the placement of antibiotic-added bone cement in the infection site [3, 4]. Although this method has been in use for a long time, however, it remains a matter of debate. Questions include the preparation method of the antibiotic cement, antibiotics selection, antibiotics elution and biomechanical effects [3]. The amount of antibiotic release may vary based on the surface shape, cement type, selected antibiotic and tissue conditions. Several studies have shown that most of the antibiotic from bone cement is released within hours or days [5–8].

New drug delivery systems have been developed for the improvement of local drug elution [7]. The literature suggests that porosity or inhomogeneity should be increased to improve the elution of antibiotics from poly(methyl methacrylate) (PMMA) beads [9]. Through the process of hydrolysis, when introduced into the body, poly(glycolide-co-lactide) PGLA produces the biodegradable and biocompatible metabolite monomers of glycolic and lactic acid which are eventually concerted by the citric acid cycle. For this reason, PGLA is among the most successfully utilized biodegradable polymers [10].

The prevalence of methicillin-resistant Staphylococcus aureus-related infections has resulted in an increase in the use of teicoplanin, a glycopeptide antibacterial. Although it cannot be absorbed orally, teicoplanin is tolerated intravenously and intramuscularly. Therapeutic concentrations can be obtained with less delay with high loading doses [11, 12].

A review of the literature found a lack of studies on the elution characteristics of antibiotic-impregnated PMMA containing PGLA and teicoplanin. This study aims to measure and compare the elution characteristics of teicoplanin from antibiotic-impregnated cement beads before and after the addition of PGLA.

Materials and Methods

Experimental Design and Preparation of Beads

Two groups of 16 antibiotic-loaded beads were prepared for the evaluation of the drug release. Group 1 consisted of 40-g bone cement beads (BioFix1; Synimed SARL, Chamberet, France) that included 2 g of teicoplanin. Group 2 consisted of the same cement beads to which 2 g of teicoplanin and a total of 8 packs of PGLA were added (Pegelak^® No. 0, 75 cm; Dogsan, Trabzon, Turkey), a pack for each 5 g of cement. Each surgical suture was cut to 3–5 mm in size and manually mixed into the cement. Both cements were then poured into silicone molds to form standard-sized cubic beads of 1 cm³ (Fig. 1).

Fig. 1.

a, b Preparation of the PMMA beads (10 × 10 mm) using a flexible mold

Characterization

FTIR spectra of teicoplanin were characterized using a FTIR spectrophotometer (TENSOR II; Bruker Corp., Billerica, MA, USA) in the 400–4000 cm⁻¹ wavelength range.

Preparation of the Calibration Curve

1-ml sterile injection water was added to 400 mg of teicoplanin. The final concentration was calculated as 133 mg/ml. The 133 mg/ml stock was then diluted in the concentration range of 0.02–133 mg/ml. Absorbance values of the diluted solutions were measured using a UV–Vis spectrophotometer (UV-2600, Shimadzu, Japan). Three measurements were taken for each sample and averaged. Consequently, the absorbance versus concentration calibration curve was obtained (Fig. 2).

Fig. 2.

Calibration curve of teicoplanin

Drug Elution Experiments in PBS Medium

The release of antibiotic from two groups of 16 antibiotic-loaded beads was investigated by elution in 100 ml of PBS at pH 7.4 and 37 °C for 35 days. Samples were taken at 3, 6, 12, 24, 36, 48 h and on days 7, 14, 21 and 35 of elution. The amount of drug release at each sampling time was measured based on the concentrations. It is also valuable to mention that for each sampling, 1 ml of release medium was taken and replaced with fresh medium. A sample of 1 ml was taken from the tubes and 2 ml of PBS was added again. Absorbance values of these samples were determined using a UV–Vis spectrophotometer. Although the processes of diffusion are theoretically infinite, the final sampling was taken after 35 days.

Statistical Analysis

Statistical analysis was performed with IBM SPSS v.23.0 (IBM Corp., Armonk, NY, USA) software. Results were reported as mean ± standard deviation (SD). Normal distribution of data was assessed using the Shapiro–Wilk test. The independent samples t test was used for comparison of the groups which showed normal distribution. Tukey’s test was employed for multiple comparisons. The significance level was set at p < 0.05.

Results

The molecular structure of teicoplanin was verified by FTIR, as shown in Fig. 2. The first of the characteristic peaks of teicoplanin is the wide and strong peak seen at approximately 3400 cm⁻¹, which is attributed to –NH₂ primary amine bending vibration. The second wide peak is that of carboxylic acid seen at approximately 3000 cm⁻¹. The C–C bending vibrations in the aromatic rings at 1506 cm⁻¹ and 1590 cm⁻¹ and the C–H bending vibration at 1400 cm⁻¹ indicated the molecular structure of teicoplanin (Fig. 3).

Fig. 3.

FTIR spectra of teicoplanin

In this study, the calibration curve of teicoplanin was obtained first (Fig. 2). The difference between the teicoplanin concentrations of the two groups was statistically significant. Since the significance values of the Shapiro–Wilk normality test were greater than 0.05 (p = 0.351 for Group 1 and p = 0.954 for Group 2), the data were considered to be normally distributed. Independent samples t-test exhibited a significant difference between Group 1 and Group 2, with a higher rate of drug release in Group 2 (p < 0.001) (Table 1). According to the data obtained at the end of the 35th day, the cumulative percentages of drug releases in Group 1 and Group 2 were determined. However, as shown in Fig. 4, the amount of elution was fixed after 24 h.

Table 1.

Cumulative release of different bead with three replicates

Time (h)	Cumulative release (%)
	Teicoplanin	Teicoplanin + PGLA
0	0	0
3	48	40
6	60	55
12	64	71
24	65	72
36	69	73
48	68	72

Fig. 4.

Cumulative percentage of drug amounts released in Group 1 and Group 2

Discussion

This experimental study was designed to determine if PGLA would modify the elution characteristics of teicoplanin-added PMMA beads. Antibiotic release in the PGLA-added group was better than the group with teicoplanin added alone.

Despite the development of surgical techniques and the introduction of new antibiotics, infection still stands as a major problem for orthopedists [13]. In the treatment of infection, surgical debridement and antibiotherapy are applied [14]. Although intravenous administration of antibiotics can reach an adequate blood concentration, it cannot sufficiently penetrate the infected area. For this reason, antibiotic-impregnated PMMA beads and spacers are usually placed in the infected area [5]. Numerous studies regarding the use of spacers in the treatment of infection can be found in the literature, although studies regarding antibiotic release are limited. The present study is important in that it presents a practical new method that modifies the elution characteristics of antibiotic-impregnated PMMA beads, which are frequently used in challenging cases.

Decades have passed since Buchholz and Engelbrecht first recommended the use of gentamicin-added PMMA in total hip arthroplasty and Klemm advocated the use of gentamycin-added PMMA chains in local antibiotherapy [15, 16]. Today, antibiotic-added PMMA beads are widely used in the treatment of orthopedic infections, however, the topic is still a matter of debate. Authors have sought answers to questions such as, “Is PMMA an ideal drug delivery system?”, “Which antibiotics can be added to PMMA at what dose?”, “Should handmade or commercial spacers be used?” and “Can the antibiotic elution characteristics be changed?” [6, 7, 17, 18]. In the current study, we examined whether the elution characteristics of teicoplanin were enhanced by adding PGLA to PMMA. PGLA, used here as a surgical suture, is extremely easy to access in every operating room. In this respect, our study offers orthopedic surgeons with an effective and easily applicable method. PGLA is used as a drug delivery system because of its excellent biocompatibility and biodegradability [19]. In addition, the compatibility of PGLA with bone tissue has also been reported in the literature [20].

One pack of PGLA surgical suture was added to every 5 g of cement. Various recommendations have been made in the literature to change the elution characteristics of PMMA beads, which may be examined under three main headings: the use of another biodegradable drug delivery system instead of PMMA [9], the use of combined or different doses of antibiotics [21] and the addition of another biodegradable substance to PMMA along with antibiotics [22]. Previous studies have reported how elution is increased by the addition of biodegradable substances to PMMA beads. Accordingly, increasing cement porosity, increasing inhomogeneity, increasing fluid contact and adding a bioabsorbable material creating a channel for drug escape positively affect elution [9, 23, 24]. These studies are in line with our results and indicate how PGLA in teicoplanin-loaded PMMA beads increases elution.

For the current study, teicoplanin, which is widely used in orthopedic infections, was added to PMMA beads, as it is compatible with PMMA [25]. Furthermore, previous studies have shown that teicoplanin added to PMMA shows a good elution kinetic [8].

Several studies have examined the elution of antibiotic-impregnated PMMA beads that were implanted during surgery [26, 27]. The highest release levels are generally recorded following implementation before decreasing 3–4 days following implementation and remaining at a stable level. Our results are in agreement with the literature (Fig. 4).

Some researchers have recommended commercial products for the use of antibiotic-loaded PMMA beads; while, others have recommended manual mixing during surgery. The main disadvantage of manual mixing is the lack of homogeneity in the diffusion of antibiotics, while the intraoperative addition of antibiotic to PMMA at the desired dose and variety are its advantages [3]. Commercial beads are not widely used since accessing them is difficult and costly. In this context, the novelty of our study is the enhancement of elution kinetics via an inexpensive, easily applicable and accessible method.

We acknowledge several limitations to our study. First, although the study was designed to mimic an in vivo environment, it was an in vitro study. In vivo conditions may exhibit different diffusion properties and may alter antibiotic elution results. Second, we used a single dose of antibiotics and PGLA in our study. Different antibiotics and PGLA combinations at different doses were not included in this study. However, meeting these standard conditions was important for comparing both methods.

Conclusion

The in vitro results showed that the addition of biodegradable PGLA into bone cement functions as a water-soluble porogen that allows for significant increases in teicoplanin elution from cement. The significant increase in elution indicates that the addition of PGLA allows for further fluid contact and exchange with the previously entrapped drug. These results may have important clinical applications. Further in vivo studies are needed to better evaluate the effects of adding PGLA sutures in PMMA beads on the elution characteristics of antibiotics.

Funding

The authors received no financial support for the research and/or authorship of this article.

Compliance with Ethical Standards

Conflict of interest

The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

Ethical standard statement

This article does not contain any studies with human or animal subjects performed by the any of the authors.

Informed consent

For this type of study informed consent is not required.