in vitro/in vivoevaluation of the efficiency of teicoplanin-loaded biodegradable microparticles formulated for implantation to infected bone defects

Nanomedicine for safe healing of bone trauma: Opportunities and challenges

Historically, high-energy extremity injuries resulting in significant soft-tissue trauma and bone loss were often deemed unsalvageable and treated with primary amputation. With improved soft-tissue coverage and nerve repair techniques, these injuries now present new challenges in limb-salvage surgery. High-energy extremity trauma is pre-disposed to delayed or unpredictable bony healing and high rates of infection, depending on the integrity of the soft-tissue envelope. Furthermore, orthopedic trauma surgeons are often faced with the challenge of stabilizing and repairing large bony defects while promoting an optimal environment to prevent infection and aid bony healing. During the last decade, nanomedicine has demonstrated substantial potential in addressing the two major issues intrinsic to orthopedic traumas (i.e., high infection risk and low bony reconstruction) through combatting bacterial infection and accelerating/increasing the effectiveness of the bone-healing process. This review presents an overview and discusses recent challenges and opportunities to address major orthopedic trauma through nanomedical approaches.

Vancomycin microspheres reduce postoperative spine infection in an in vivo rabbit model

Background

Surgical site infections are common and devastating complications after implants related surgeries. Staphylococcus aureus contamination is a leading cause of surgical site infections. This study aims at assessing the effect of vancomycin microspheres on reducing Staphylococcus aureus infection in an in vivo rabbit model.

Methods

Sixty surgical sites of 20 New Zealand White rabbits underwent spinal implant were randomly divided to three groups: the control group, the vancomycin group and vancomycin microspheres group. The surgical sites were incubated with 100 μl 1 × 10⁷ CFU S. aureus ATCC 25923. Prior to closure, vancomycin and vancomycin microspheres were placed into the wounds of the rabbits in the vancomycin group and the vancomycin microspheres group, respectively. The rabbits were killed on postoperative day 7. Standard quantification techniques were used to analyze biomaterial centered and soft tissue bacterial growth. The bacteria were further confirmed by PCR with primers from the thermostable nuclease gene of S. aureus.

Results

All the rabbits survived the surgery and no postoperative wound complications or systemic illness occurred. Results showed that the bacterial cultures were 76.9, 30.8, and 15.4% in the control group, vancomycin group, and vancomycin microspheres group. Vancomycin microspheres treatments significantly decreased the infection rate compared to the control group (p < 0.05).

Conclusion

Vancomycin microspheres combined with preoperative ceftriaxone is effective to reduce postoperative S. aureus infection compared with the control group.

Two-Stage Cementless Revision Total Hip Arthroplasty for Infected Primary Hip Arthroplasties

The main purpose of the present study was to analyze the clinical features, the most common infective agents, and the results of two-stage total hip revision using a teicoplanin-impregnated spacer. Between January 2005 and July 2011, 41 patients were included. At the clinical status analysis, physical examination was performed, Harris hip score was noted, isolated microorganisms were recorded, and the radiographic evaluation was performed. The mean Harris hip score was improved from 38.9 ± 9.6 points to 81.8 ± 5.8 points (P<0.05). Infection was eradicated in 39 hips. Radiographic evidence of stability was noted in 37 acetabular revision components, and all femoral stems. Two-stage revision of the infected primary hip arthroplasty is a time-consuming but a reliable procedure with high rates of success.

Gatifloxacine-loaded PLGA and β-tricalcium phosphate composite for treating osteomyelitis

Gatifloxacine (GFLX)-containing poly(lactide-co-glycolide) (PLGA) was introduced to the pores and surfaces of porous β-tricalcium phosphate (βTCP) granules by melt compounding whereby no toxic solvent was used. The granular composite of GFLX-loaded PLGA and βTCP released GFLX for 42 days in Hanks' balanced solution and exhibited sufficient in vitro bactericidal activity against Streptococcus milleri and Bacteroides fragilis for at least 21 days. For in vivo evaluation, the granular composite was implanted in the dead space created by the debridement of osteomyelitis lesion induced by S. milleri and B. fragilis in rabbit mandible. After a 4-week implantation, the inflammation area within the debrided area was markedly reduced accompanied with osteoconduction and vascularization in half of the rabbits, and even disappeared in one of the six rabbits without any systemic administration of antibiotics. Outside the debrided area, inflammation and sequestrum were observed but the largest of such affected areas amounted to only 0.125 times of the originally infected and debrided area. These findings showed that the granular composite was effective for the local treatment of osteomyelitis as well as an osteoconductive scaffold which supported and encouraged vascularization.

Biodegradable microspherical implants containing teicoplanin for the treatment of methicillin-resistant Staphylococcus aureus osteomyelitis

BACKGROUND

The aim of this study was to prepare poly(d,l-lactide-co-glycolide) (PLGA) microspherical implants containing teicoplanin (TCP) using a double emulsion solvent evaporation method and to evaluate its efficacy for the local treatment of chronic osteomyelitis.

METHODS

The particle size and distribution, morphological characteristics, thermal behaviour, drug content, encapsulation efficiency and in vitro release assessments of the formulations were carried out. Sterile TCP–PLGA microspheres were implanted in the proximal tibia of rats with methicillin resistant Staphylococcus aureus (MRSA) osteomyelitis. After 3 weeks of treatment, bone samples were analysed with a microbiological assay and evaluated histopathologically.

RESULTS

Microspheres between the size ranges of 2.01 and 3.91 μm were obtained. Production yield of all formulations was found to be higher than 82% and encapsulation efficiencies of 33.6–69.8% were obtained. DSC thermogram showed that the TCP was in an amorphous state in microspheres. In vitro drug release studies had indicated that the drug release rate of microspheres was decreased upon increasing the polymer:drug ratio. Based on the in vivo data, rats treated with implants and intramuscular injection showed 1.7 × 10(3) ± 1.3 × 10(3) and 5.8 × 10(4) ± 5.3 × 10(4) colony forming unit of MRSA in 1 g bone samples (CFU/g), respectively (P < 0.01).

CONCLUSIONS

The in vitro and in vivo studies had shown that the TCP–PLGA microspheres were effective for the treatment of chronic osteomyelitis in an animal experimental model. Hence, these microspheres may be potentially useful in the clinical setting with the need for further investigation for optimal dosing of TCP–PLGA microspheres.

Implantation of vancomycin microspheres in blend with human/rabbit bone grafts to infected bone defects

In orthopaedic applications, allografts are used for restoration of bone defects. In order to combine the effects of bone repair and to prevent the infection, antibiotic-impregnated bone grafts are under current investigation with promising early results. In this study, to preserve the stability of antibiotics and to provide appropriate release profiles for 4-6 weeks, antibiotic-loaded microspheres were administered in combination with allografts and vancomycin was the antibiotic loaded to microspheres. Particle size, surface characteristics, loading capacity and in vitro release characteristics of the microspheres with and without allografts were determined. In vivo studies were performed on rabbits and antibiotic amount was determined by a fluorescence polarization immunoassay (FPIA) method from synovial fluid sample aspirated. According to the results, although the in vitro study demonstrated effective antibiotic release of vancomycin from antibiotic-impregnated allografts for 5 weeks, in vivo conditions led to an early instability of the antibiotic (in powder form) and contrary to the high initial loading dose an effective release could not be obtained from the allografts after the first week. Following these studies, it was determined that antibiotic release over a minimum inhibitory concentration (MIC) for 6 weeks was realized from vancomycin-loaded microspheres which were implanted in a blend with allografts in bone defects. In conclusion, preservation of the antibiotic in microspheres maintained the bioactivity and provided the controlled antibiotic release, thus implantation of microspheres in a blend with allografts seemed to be a promising carrier system for the orthopaedic applications.

Characterization andin vitrodegradation of salicylate-derived poly(anhydride-ester microspheres)

The aim of this study was to investigate how glass transition temperature (Tg) influenced polymer microsphere formation and degradation of three chemically, similar novel salicylatebased poly(anhydride-esters): poly[1,6-bis(o-carboxyphenoxy)hexanoate] (CPH), Tg = 59 degrees C; poly[1,8-bis(o-carboxyphenoxy)octanoate] (CPO), Tg = 30 degrees C; and poly[1,10-bis(ocarboxyphenoxy) decanoate] (CPD), Tg = 27 degrees C. Microspheres of these polymers were prepared using a modified oil-in-water solvent evaporation method and processed by either resuspension or washed by centrifugation. The morphology of the microspheres determined by scanning electron microscopy (SEM) revealed that an extra washing step appears to increase aggregation as the Tg decreases; whereas only limited aggregation occurred in the polymer with the lowest Tg, CPD, in those not washed by centrifugation. Residual polyvinyl alcohol apparently affected the drug release rates from the microspheres by a stabilization process that produced an 8 h lag time and a 5% decrease in the amount of drug released over a 7 day period compared to microspheres washed free of PVA. These results demonstrate that salicylate-based poly(anhydride-esters) with sufficiently high Tgs, can be processed into microspheres that release salicylate over a time period amenable for drug delivery applications.

Formulation and In Vitro Evaluation of Bisphosphonate Loaded Microspheres for Implantation in Osteolysis

Chitosan and poly(lactide-co-glycolide) acid (PLGA) microspheres loaded with alendronate sodium (AS) were prepared for orthopedic as well as dental applications. In orthopedics the aim was to make the total joint prostheses stay in the body for a long time without causing bone tissue loss, while in dentistry it was aimed to treat the alveolar bone resorption caused by periodontitis and also to make the dental treatment using implants easier by reducing the bone loss in patients with osteoporosis. Solvent evaporation method was used to prepare AS loaded PLGA microspheres and emulsion polimerization method was used to prepare AS loaded chitosan microspheres. Particle size, loading efficacy, surface characteristics, and in vitro release characteristics were examined on prepared formulations. After the examination of the scanning electron microscopy photographs of microspheres, chitosan microspheres were observed to have spherical structure and smooth surface characteristics while PLGA microspheres were observed to have spherical porous surface structure. Loading efficacy was found to be 3.30% for chitosan microspheres and 7.70% for PLGA microspheres. It was observed that 85% of AS had been released at the end of the third day from chitosan microspheres whereas 58% was released at the end of the fifth day from PLGA microspheres. It was found that chitosan microspheres gave first order release while PLGA microspheres gave zero order release.

Polylactide-polyglycolide antibiotic implants

Surgeons continually struggle to reduce orthopaedic infections, but no current treatment offers minimum side effects with maximum effectiveness. Antibiotics mixed in plaster of paris have been successful in treating large bony defects in patients with chronic osteomyelitis, and have the advantage of being well tolerated and absorbed by the body. Antibiotics impregnated in polymethylmethacrylate (PMMA) have offered local antibiotic delivery with some success. However, the effect of the antibiotic on the bone cement, the inconsistent elution of the antibiotic, and the need to remove the PMMA implant drives the need for a better system of antibiotic delivery. Polymers or copolymers of antibiotic-impregnated polylactic acid, polyglycolic acid or polyparadioxanone may provide an absorbable system for localized antibiotic delivery. Similar biodegradable systems used to treat small bone fractures have been successful with minimal side effects. In vitro studies have shown promising results of antibiotic elution from bioabsorbable microspheres and beads. Animal in vivo tests have shown that antibiotic impregnated polymers can successfully treat induced osteomyelitis in rabbits and dogs. These studies have provided consistent reproducible results, and now it is time to plan human trials to assess the efficacy of antibiotic microspheres implanted in infected bone and to plan in vivo and in vitro animal testing to investigate the feasibility of antibiotic-polymer-coated components.