Antibiotic microspheres: preliminary testing for potential treatment of osteomyelitis

Local Antibiotic Delivery Ceramic Bone Substitutes for the Treatment of Infected Bone Cavities and Bone Regeneration: A Systematic Review on What We Have Learned from Animal Models

AIMS

the focus of this study is to evaluate if the combination of an antibiotic with a ceramic biomaterial is effective in treating osteomyelitis in an infected animal model and to define which model and protocol are best suited for in vivo experiments of local bone infection treatment.

METHODS

a systematic review was carried out based on PRISMA statement guidelines. A PubMed search was conducted to find original papers on animal models of bone infections using local antibiotic delivery systems with the characteristics of bone substitutes. Articles without a control group, differing from the experimental group only by the addition of antibiotics to the bone substitute, were excluded.

RESULTS

a total of 1185 records were retrieved, and after a three-step selection, 34 papers were included. Six manuscripts studied the effect of antibiotic-loaded biomaterials on bone infection prevention. Five articles studied infection in the presence of foreign bodies. In all but one, the combination of an antibiotic with bioceramic bone substitutes tended to prevent or cure bone infection while promoting biomaterial osteointegration.

CONCLUSIONS

this systematic review shows that the combination of antibiotics with bioceramic bone substitutes may be appropriate to treat bone infection when applied locally. The variability of the animal models, time to develop an infection, antibiotic used, way of carrying and releasing antibiotics, type of ceramic material, and endpoints limits the conclusions on the ideal therapy, enhancing the need for consistent models and guidelines to develop an adequate combination of material and antimicrobial agent leading to an effective human application.

In Situ Gelling Hydrogel with Anti-Bacterial Activity and Bone Healing Property for Treatment of Osteomyelitis

Background

Despite the development of progressive surgical techniques and antibiotics, osteomyelitis is a big challenge for orthopedic surgeons. The main aim of this study is to fabricate an in situ gelling hydrogel that permits sustained release of antibiotic (for control of infection) and growth factor (for induction of new bone formation) for effective treatment of osteomyelitis.

Methods

An in situ gelling alginate (ALG)/hyaluronic acid (HA) hydrogel containing vancomycin (antibiotic) and bone morphogenetic protein-2 (BMP-2; growth factor) was prepared by simple mixing of ALG/HA/Na₂HPO₄ solution and CaSO₄/vancomycin/BMP-2 solution. The release behaviors of vancomycin and BMP-2, anti-bacterial effect (in vitro); and therapeutic efficiency for osteomyelitis and bone regeneration (in vivo, osteomyelitis rat model) of the vancomycin and BMP-2-incorporated ALG/HA hydrogel were investigated.

Results

The gelation time of the ALG/HA hydrogel was controlled into approximately 4 min, which is sufficient time for handling and injection into osteomyelitis lesion. Both vancomycin and BMP-2 were continuously released from the hydrogel for 6 weeks. From the in vitro studies, the ALG/HA hydrogel showed an effective anti-bacterial activity without significant cytotoxicity for 6 weeks. From an in vivo animal study using Sprague-Dawley rats with osteomyelitis in femur as a model animal, it was demonstrated that the ALG/HA hydrogel was effective for suppressing bacteria (Staphylococcus aureus) proliferation at the osteomyelitis lesion and enhancing bone regeneration without additional bone grafts.

Conclusions

From the results, we suggest that the in situ gelling ALG/HA hydrogel containing vancomycin and BMP-2 can be a feasible therapeutic tool to treat osteomyelitis.

In vivo efficacy of tobramycin-loaded synthetic calcium phosphate beads in a rabbit model of staphylococcal osteomyelitis

Background

Osteomyelitis is an acute or chronic inflammatory process of the bone following infection with pyogenic organisms like Staphylococcus aureus. Tobramycin (TOB) is a promising aminoglycoside antibiotic used to treat various bacterial infections, including S. aureus. The aim of this study was to investigate the efficacy of tobramycin-loaded calcium phosphate beads (CPB) in a rabbit osteomyelitis model.

Methods

Tobramycin (30 mg/mL) was incorporated into CPB by dipping method and the efficacy of TOB-loaded CPB was studied in a rabbit osteomyelitis model. For juxtaposition, CPB with and without TOB were prepared. Twenty-five New Zealand white rabbits were grouped (n = 5) as sham (group 1), TOB-loaded CPB without S. aureus (group 2), S. aureus only (group 3), S. aureus + CPB (group 4), and S. aureus + TOB-loaded CPB (group 5). Groups infected with S. aureus followed by CPB implantation were immediately subjected to surgery at the mid-shaft of the tibia. After 28 days post-surgery, all rabbits were euthanized and the presence or absence of chronic osteomyelitis and the extent of architectural destruction of the bone were assessed by radiology, bacteriology and histological studies.

Results

Tobramycin-loaded CPB group potentially inhibited the growth of S. aureus causing 3.2 to 3.4 log₁₀ reductions in CFU/g of bone tissue compared to the controls. Untreated groups infected with S. aureus showed signs of chronic osteomyelitis with abundant bacterial growth and alterations in bone architecture. The sham group and TOB-loaded CPB group showed no evidence of bacterial growth.

Conclusions

TOB-incorporated into CPB for local bone administration was proven to be more successful in increasing the efficacy of TOB in this rabbit osteomyelitis model and hence could represent a good alternative to other formulations used in the treatment of osteomyelitis.

Electronic supplementary material

The online version of this article (10.1186/s12941-018-0296-3) contains supplementary material, which is available to authorized users.

Polyester-based particles to overcome the obstacles of mucus and biofilms in the lung for tobramycin application under static and dynamic fluidic conditions

Pulmonary infections with Pseudomonas aeruginosa and Burkholderia cepacia complex (Bcc) are difficult to treat and related with high mortality in some diseases like cystic fibrosis due to the recurrent formation of biofilms. The biofilm formation hinders efficient treatment with inhaled antibiotics due to a low penetration of the antibiotics through the polyanionic biofilm matrix and increased antimicrobial resistance of the biofilm-embedded bacteria. In this study, tobramycin (Tb) was encapsulated in particles based on poly(d,l,-lactide-co-glycolide) (PLGA) and poly(ethylene glycol)-co-poly(d,l,-lactide-co-glycolide) diblock (PEG-PLGA) to overcome the biofilm barrier with particle sizes of 225-231 nm (nanoparticles) and 896-902 nm (microparticles), spherical shape and negative zeta potentials. The effectiveness against biofilms of P. aeruginosa and B. cepacia was strongly enhanced by the encapsulation under fluidic experimental condition as well as under static conditions in artificial mucus. The biofilm-embedded bacteria were killed by less than 0.77 mg/l encapsulated Tb, whereas 1,000 mg/l of free Tb or the bulk mixtures of Tb and the particles were ineffective against the biofilms. Moreover, encapsulated Tb was even effective against biofilms of the intrinsically aminoglycoside-resistant B. cepacia, indicating a supportive effect of PEG and PLGA on Tb. No cytotoxicity was detected in vitro in human lung epithelial cells with any formulation.

Formulation and Characterization of Ciprofloxacin loaded PLGA Microspheres for Applications in Orthopedic Infections

ABSTRACT: Purpose-Osteomyelitis is a bone infection that appears as a complication after a fracture or orthopedic surgery. Ciprofloxacin is a broad spectrum antibiotic that can be used in local drug delivery systems for the treatment of bone related infections due to its bactericidal activity against both Gram-negative and Gram-positive bacteria. The purpose of the present study was to include ciprofloxacin in poly (lactic-co-glycolic acid) (PLGA) microspheres. Material and methods-Microspheres were prepared by both water/oil/water (w/o/w) solvent evaporation method and solid/oil/water (s/o/w) dispersion solvent evaporation method. The obtained microspheres were characterized by Fourier Transform Infrared Spectroscopy. High performance liquid chromatography method was deployed to determine the encapsulation ratio. Results-The solvent evaporation method chosen for this experiment resulted in microspheres with good entrapment efficiency. Furthermore the microspheres obtained by the s/o/w method displayed better entrapment efficiency. Conclusion-The particles obtained through the s/o/w technique should be further investigated in order to develop a local drug delivery system.

Antimicrobial technology in orthopedic and spinal implants

Infections can hinder orthopedic implant function and retention. Current implant-based antimicrobial strategies largely utilize coating-based approaches in order to reduce biofilm formation and bacterial adhesion. Several emerging antimicrobial technologies that integrate a multidisciplinary combination of drug delivery systems, material science, immunology, and polymer chemistry are in development and early clinical use. This review outlines orthopedic implant antimicrobial technology, its current applications and supporting evidence, and clinically promising future directions.

Antibiotic-eluting hydrophilized PMMA bone cement with prolonged bactericidal effect for the treatment of osteomyelitis

Osteomyelitis is still considered to be one of the major challenges for orthopedic surgeons despite advanced antiseptic surgical procedures and pharmaceutical therapeutics. In this study, hydrophilized poly(methyl methacrylate) (PMMA) bone cements containing Pluronic F68 (EG79PG28EG79) as a hydrophilic additive and vancomycin ( F68-VA cements) were prepared to allow the sustained release of the antibiotic for adequate periods of time without any significant loss of mechanical properties. The compressive strengths of the bone cements with Pluronic F68 compositions less than 7 wt% were not significantly different compared with the control vancomycin-loaded bone cement ( VA cement). The F68 (7 wt%)-VA cement showed sustained release of the antibiotic for up to 11 weeks and almost 100% release from the bone cement. It also prohibited the growth of S. aureus (zone of inhibition) over six weeks (the required period to treat osteomyelitis), and it did not show any notable cytotoxicity. From an animal study using a femoral osteomyelitis rat model, it was observed that the F68 (7 wt%)-VA cement was effective for the treatment of osteomyelitis, probably as a result of the prolonged release of antibiotic from the PMMA bone cement. On the basis of these findings, it can be suggested that the use of Pluronic F68 as a hydrophilic additive for antibiotic-eluting PMMA bone cement can be a promising strategy for the treatment of osteomyelitis.

Are the leading drugs against Staphylococcus aureus really toxic to cartilage?

Many studies have shown that the toxic effects of local antibiotics on bone and cartilage limit orthopedic surgeons. In this study, we evaluated three antibacterial agents used locally to treat highly mortal and morbid diseases in the field of orthopedics, such as septic arthritis. Are vancomycin, teicoplanin, and linezolid, which are archenemies of Staphylococcus aureus, really toxic to chondrocytes? The purpose of the study was to investigate the effects of antibiotics, which are used against S. aureus, on human chondrocytes in vitro. Primary cell cultures obtained from gonarthrosis patients were divided into two main groups. One of these groups was designated as the control chondrocyte culture. The other group was divided into three subgroups, and each group was exposed to vancomycin, teicoplanin, or linezolid. Cell culture samples were characterized by immunophenotyping following incubation with the three different antibiotics. Before and after the agents were administered, the cultures were subjected to inverted and environmental scanning electron microscopy. The number of live cells and the proliferation rate were monitored with the MTT-assay. We found that vancomycin, teicoplanin, and linezolid do not have chondrotoxic effects. Vancomycin, teicoplanin, and linezolid had no chondrotoxic activity during in vitro culture, which supports the argument that these agents can safely be used in orthopedic surgery, especially against methicillin-resistant S. aureus agents.

Nanostructured Architectures by Assembling Polysaccharide-Coated BSA Nanoparticles for Biomedical Application

Nanostructured architectures are produced on Ti surfaces by layer-by layer (LbL) self-assembling of polysaccharide-coated BSA nanoparticles (BNPs), which created cellular microenvironments mimicking natural extracellular matrix. The BMP-2 encapsulated BNPs are prepared by a desolvation method, and are further coated by chitosan (CHI) coatings to obtain positively charged NPs (CBNPs). Vancomycin (Van) encapsulated CBNPs are obtained by the same method and subsequently coated by oxidized alginate (OALG) to obtain negatively charged NPs (OCBNPs). The CBNPs and OCBNPs are assembled on Ti surfaces to construct nanostructured coatings via electrostatic and covalent interactions. The nanostructured architectures realize the sustained release of BMP-2 and Van for a long term. Bone marrow stromal cells (BMSCs) culture tests confirm that the bare nanostructured architectures intrinsically facilitate attachment, proliferation, and differentiation of cells, which is attributed to the nanoscale porous structures that are similar to the size of cellular filopodia. Incorporating BMP-2 into the nanostructured architectures significantly enhances osteogenetic differentiation of BMSCs, which reveals the synergistic effects of nanostructures and growth factors on cell activity. The antibacterial tests indicate that controlled release of Van has good antibacterial ability against Staphylococcus epidermidis, while not affecting the normal biological activity of BMSCs.

Local gentamicin delivery from resorbable viscous hydrogels is therapeutically effective

BACKGROUND

Local delivery can achieve the high antimicrobial concentrations necessary to kill biofilm-related microbes. Degradation times for resorbable carriers are too long. Hydrogels (gels of hydrophilic polymer in water) can degrade faster but release antimicrobials too quickly. We previously developed hydrogels based on the copolymer poly(N-isopropylacrylamide-co-dimethyl-γ-butyrolactone acrylate-co-Jeffamine® M-1000 acrylamide) (PNDJ) with delivery times of several days with complete degradation in less than 6 weeks.

QUESTIONS/PURPOSES

We asked: (1) What is the elution profile of gentamicin from PNDJ hydrogels? (2) Is gentamicin released from gentamicin-loaded PNDJ (G-PNDJ) hydrogel effective for treatment of orthopaedic infection? (3) Does local gentamicin delivery from G-PNDJ hydrogel cause renal dysfunction?

METHODS

(1) Two formulations of G-PNDJ, lower dose (1.61 wt%) and higher dose (3.14 wt%), five samples each, were eluted in buffered saline under infinite sink conditions. (2) Infections were induced in 16 New Zealand White rabbits by inserting a Kirschner wire in a devascularized radius segment and inoculating with 7.5×10(6) colony-forming units Staphylococcus aureus. At 3 weeks, débridement was performed and a new Kirschner wire was placed in the dead space. Treatment was randomized to higher-dose G-PNDJ or no hydrogel. No systemic antimicrobials were used. Positive culture and acute inflammation on histology were used to determine the presence of infection 4 weeks postdébridement. (3) 3.14 wt% G-PNDJ, 0.75, 1.5, or 3.0 mL, was injected subcutaneously in nine Sprague-Dawley rats, three of each dose. Serum gentamicin, blood urea nitrogen, and creatinine were measured on Days 1, 3, 7, 14, and 28.

RESULTS

(1) Gentamicin release was sustained over 7 days with the higher-dose formulation release profile similar to release from high-dose antimicrobial-loaded bone cement. (2) Four weeks postdébridement, infection was present in eight of eight no-hydrogel rabbits but zero of eight rabbits treated with G-PNDJ hydrogel (p<0.001). (3) Blood urea nitrogen and creatinine were transiently elevated (p<0.05) only for the two of three rats receiving the 3.0-mL dose on Days 3 and 7.

CONCLUSIONS

Gentamicin is delivered from PNDJ hydrogel with low systemic exposure and decreased treatment failure for orthopaedic infection. Transient renal dysfunction occurs at high doses. Biodistribution and toxicity testing are needed for G-PNDJ to be clinically usable.

CLINICAL RELEVANCE

Resorbable viscous hydrogels for local antimicrobial delivery may improve outcomes for one-stage management of implant infections when uncemented reconstructions are performed.

Review: emerging developments in the use of bioactive glasses for treating infected prosthetic joints

Bacterial contamination of implanted orthopedic prostheses is a serious complication that requires prolonged systemic antibiotic therapy, major surgery to remove infected implants, bone reconstruction, and considerable morbidity. Local delivery of high doses of antibiotics using poly(methyl methacrylate) (PMMA) cement as the carrier, along with systemic antibiotics, is the standard treatment. However, PMMA is not biodegradable, and it can present a surface on which secondary bacterial infection can occur. PMMA spacers used to treat deep implant infections must be removed after resolution of the infection. Alternative carrier materials for antibiotics that could also restore deficient bone are therefore of interest. In this article, the development of bioactive glass-based materials as a delivery system for antibiotics is reviewed. Bioactive glass is osteoconductive, converts to hydroxyapatite, and heals to hard and soft tissues in vivo. Consequently, bioactive glass-based carriers can provide the combined functions of controlled local antibiotic delivery and bone restoration. Recently-developed borate bioactive glasses are of particular interest since they have controllable degradation rates coupled with desirable properties related to osteogenesis and angiogenesis. Such glasses have the potential for providing a new class of biomaterials, as substitutes for PMMA, in the treatment of deep bone infections.

Evaluation of antibiotic-impregnated microspheres for the prevention of implant-associated orthopaedic infections

BACKGROUND

Prevention of infection associated with uncemented orthopaedic implants could lead to improved implant stability and better patient outcomes. We hypothesized that coating porous metal implants with antibiotic-containing microspheres would prevent infections in grossly contaminated wounds.

METHODS

Bioresorbable polymer microspheres containing tobramycin were manufactured and pressed into porous metal cylinders that were then implanted into radial defects in rabbits. Control implants that did not contain antibiotic microspheres were also implanted into the contralateral limbs. Each implant was then contaminated with Staphylococcus aureus prior to closure of the wound. The animal was euthanized after clinical signs of infection appeared, or at two weeks after surgery. Periprosthetic tissue was cultured for the presence of S. aureus, and integration of the implant with the surrounding bone was measured.

RESULTS

The antibiotic microspheres successfully prevented infection in 100% of the eleven limbs with treated implants, which represented a significant improvement (p = 0.004) compared with the infection rate of 64% (seven of eleven) for the limbs with control implants. Implant integration averaged 38.87% ± 12.69% in the fifteen uninfected limbs, which was significantly better (p = 0.012) than the average of 19.46% ± 14.49% in the seven infected limbs.

CONCLUSIONS

The antibiotic delivery system successfully prevented infection in 100% of the cases studied, resulting in an increase in implant integration.

CLINICAL RELEVANCE

Antibiotic delivery utilizing the system described here may be effective in preventing implant-associated infections after orthopaedic surgery and increasing the longevity of orthopaedic implants.

Osteomyelitis: an overview of antimicrobial therapy

Osteomyelitis is an inflammatory bone disorder caused by infection, leading to necrosis and destruction of bone. It can affect all ages, involve any bone, become a chronic disease and cause persistent morbidity. Treatment of osteomyelitis is challenging particularly when complex multiresistant bacterial biofilm has already been established. Bacteria in biofilm persist in a low metabolic phase, causing persistent infection due to increased resistance to antibiotics. Staphylococcus aureus and Staphylococcus epidermidis are the most common causative organism responsible for more than 50% of osteomyelitis cases. Osteomyelitis treatment implies the administration of high doses of antibiotics (AB) by means of endovenous and oral routes and should take a period of at least 6 weeks. Local drug delivery systems, using non-biodegradable (polymethylmethacrylate) or biodegradable and osteoactive materials such as calcium orthophosphates bone cements, have been shown to be promising alternatives for the treatment of osteomyelitis. These systems allow the local delivery of AB in situ with bactericidal concentrations for long periods of time and without the toxicity associated with other means of administration. This review examines the most recent literature evidence on the causes, pathogeneses and pharmacological treatment of osteomyelitis. The study methodology consisted of a literature review in Google Scholar, Science Direct, Pubmed, Springer link, B-on. Papers from 1979 till present were reviewed and evaluated.

Intra-discal vancomycin-loaded PLGA microsphere injection for MRSA discitis: an experimental study

OBJECTIVE

To prepare the vancomycin hydrochloride (VA)-loaded poly lactic acid-glycolic acid (PLGA) copolymer microsphere by the multiple emulsion method and evaluate its therapeutic effects on infective discitis.

METHODS

Firstly, the particle diameter distribution, shape, encapsulation efficiency, drug-loaded dosage and release curve of VA-PLGA microspheres were evaluated in vitro. Rabbits with methicillin-resistant Staphylococcus aureus infective discitis were treated with VA-PLGA intra-discal injection. Meanwhile, VA intravenous injection, blank PLGA microspheres intra-discal injection served as controls. Thirty days later, therapeutic effects were evaluated through X-ray radiophotography, histopathological and bacteriological examination.

RESULTS

Mean particle diameter was between 61.57 ± 4.37 and 67.45 ± 8.13 μm, and mean encapsulation efficiency was between 60.20 ± 1.61 and 75.27 ± 1.60 %m/m. In vitro release experiment showed that the release time was over 30 days. The result of in vivo experiment showed that inflammatory reaction in the VA-PLGA intra-discal injection group was milder than the intravenous injection group (P < 0.05), also with less inflammation. The bacterial count was also significantly lower (1.02 × 10(3) ± 1.22 × 10(3) CFU/g) than the intravenous injection group (7.51 × 10(4) ± 7.16 × 10(4) CFU/g) (P < 0.05). Besides these data, the amount used in VA-PLGA intra-discal injection group is about 20 mg, and that used in the intravenous injection group is about 2.4 g. So, we just use 1/120 of VA i.v. to obtain the better results with our microparticles.

CONCLUSION

Intra-discal injection with VA-PLGA sustained-release microspheres can use much less dosage, and effectively control and reduce infective discitis, and the therapeutic effect is superior to that of intravenous injection. A need for the clinical trials will be carried out in the near future.

Poly(D,L-lactide-co-glycolide)/hydroxyapatite core-shell nanospheres. Part 1: A multifunctional system for controlled drug delivery

Biodegradable poly(d,l-lactide-co-glycolide) (PLGA) and bioactive hydroxyapatite (HAp) are selected for the formation of a multifunctional system with the specific core-shell structure to be applied as a carrier of a drug. As a result, both components of PLGA/HAp core-shells are able to capture one part of the drug. Polymeric shells consisting of small nanospheres up to 20nm in size act as a matrix in which one part of the drug is dispersed. In the same time, ceramic cores are formed of rod-like hydroxyapatite particles at the surface of which another part of the drug is adsorbed onto the interface between the polymer and the ceramics. The content of the loaded drug, as well as the selected solvent/non-solvent system, have a crucial influence on the resulting PLGA/HAp morphology and, finally, unimodal distribution of core-shells is obtained. The redistribution of the drug between the organic and inorganic parts of the material is expected to provide an interesting contribution to the kinetics of the drug release resulting in non-typical two-step drug release.

Sustained release of vancomycin from polyurethane scaffolds inhibits infection of bone wounds in a rat femoral segmental defect model

Infection is a common complication in open fractures that compromises the healing of bone and can result in loss of limb or life. Currently, the clinical standard of care for treating contaminated open fractures comprises a staged approach, wherein the wound is first treated with non-biodegradable antibiotic-laden poly(methyl methacrylate) (PMMA) beads to control the infection followed by bone grafting. Considering that tissue regeneration is associated with new blood vessel formation, which takes up to 6 weeks in segmental defects, a biodegradable bone graft with sustained release of an antibiotic is desired to prevent the implant from becoming infected, thus allowing the processes of both vascularization and new bone formation to occur unimpeded. In the present study, we utilized biodegradable porous polyurethane (PUR) scaffolds as the delivery vehicle for vancomycin. Hydrophobic vancomycin free base (V-FB) was obtained by precipitating the hydrophilic vancomycin hydrochloride (V-HCl) at pH 8. The decreased solubility of V-FB resulted in an extended vancomycin release profile in vitro, as evidenced by the fact that active vancomycin was released for up to 8 weeks at concentrations well above both the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). Using PUR prepared from lysine triisocyanate (LTI) (PUR(LTI)), the extended in vitro release profile observed for V-FB translated to improved infection control in vivo compared to V-HCl in a contaminated critical-sized fat femoral segmental defect. The performance of PUR(LTI)/V-FB was comparable to PMMA/V-HCl beads in vivo. However, compared with PMMA, PUR is a biodegradable system which does not require the extra surgical removal step in clinical use. These results suggest that PUR scaffolds incorporating V-FB could be a potential clinical therapy for treatment of infected bone defects.

A programmed release multi-drug implant fabricated by three-dimensional printing technology for bone tuberculosis therapy

In the world, bone tuberculosis is still very difficult to treat and presents a challenge to clinicians. In this study, we utilized 3D printing technology to fabricate a programmed release multi-drug implant for bone tuberculosis therapy. The construction of the drug implant was a multi-layered concentric cylinder divided into four layers from the center to the periphery. Isoniazid and rifampicin were distributed individually into the different layers in a specific sequence of isoniazid-rifampicin-isoniazid-rifampicin. The drug release assays in vitro and in vivo showed that isoniazid and rifampicin were released orderly from the outside to the center to form the multi-drug therapeutic alliance, and the peak concentrations of drugs were detected in sequence at 8 to 12 day intervals. In addition, no negative effect on the proliferation of rabbit bone marrow mesenchymal stem cells was detected during the cytocompatibility assay. Due to its ideal pharmacologic action and cytocompatibility, the programmed release multi-drug implant with a complex construction fabricated by 3D printing technology could be of interest in prevention and treatment of bone tuberculosis.

Bone tissue engineering therapeutics: controlled drug delivery in three-dimensional scaffolds

This paper provides an extensive overview of published studies on the development and applications of three-dimensional bone tissue engineering (TE) scaffolds with potential capability for the controlled delivery of therapeutic drugs. Typical drugs considered include gentamicin and other antibiotics generally used to combat osteomyelitis, as well as anti-inflammatory drugs and bisphosphonates, but delivery of growth factors is not covered in this review. In each case reviewed, special attention has been given to the technology used for controlling the release of the loaded drugs. The possibility of designing multifunctional three-dimensional bone TE scaffolds for the emerging field of bone TE therapeutics is discussed. A detailed summary of drugs included in three-dimensional scaffolds and the several approaches developed to combine bioceramics with various polymeric biomaterials in composites for drug-delivery systems is included. The main results presented in the literature are discussed and the remaining challenges in the field are summarized with suggestions for future research directions.

Injectable biomaterials for regenerating complex craniofacial tissues

Engineering complex tissues requires a precisely formulated combination of cells, spatiotemporally released bioactive factors, and a specialized scaffold support system. Injectable materials, particularly those delivered in aqueous solution, are considered ideal delivery vehicles for cells and bioactive factors and can also be delivered through minimally invasive methods and fill complex 3D shapes. In this review, we examine injectable materials that form scaffolds or networks capable of both replacing tissue function early after delivery and supporting tissue regeneration over a time period of weeks to months. The use of these materials for tissue engineering within the craniofacial complex is challenging but ideal as many highly specialized and functional tissues reside within a small volume in the craniofacial structures and the need for minimally invasive interventions is desirable due to aesthetic considerations. Current biomaterials and strategies used to treat craniofacial defects are examined, followed by a review of craniofacial tissue engineering, and finally an examination of current technologies used for injectable scaffold development and drug and cell delivery using these materials.

2007 AIChE Alpha Chi Sigma Award: From Material to Tissue: Biomaterial Development, Scaffold Fabrication, and Tissue Engineering

The need for techniques to facilitate the regeneration of failing or destroyed tissues remains great with the aging of the worldwide population and the continued incidence of trauma and diseases such as cancer. A 16-year history in biomaterial scaffold development and tissue engineering is examined, beginning with the synthesis of novel materials and fabrication of 3D porous scaffolds. Exploring cell-scaffold interactions and subsequently cellular delivery using biomaterial carriers, we have developed a variety of techniques for bone and cartilage engineering. In addition to delivering cells, we have utilized growth factors, DNA, and peptides to improve the in vitro and in vivo regeneration of tissues. This review covers important developments and discoveries within our laboratory, and the increasing breadth in the scope of our work within the expanding field of tissue engineering is presented.

Sustained release of ciprofloxacin from an osteoconductive poly(DL)-lactide implant

BACKGROUND AND PURPOSE

Antibiotic-releasing bioresorbable implants are used for local treatment of bone infections, but most drug delivery systems release antibiotic for too short a time.

METHODS

We used pellets (0.9 x 1.0 mm) made of bioabsorbable poly(DL) lactic acid matrix, ciprofloxacin (7.3 +/- 0.4 wt%), and bioactive glass microspheres of 90-125 microm (29.3 +/- 0.2 wt%). The ciprofloxacin release and antibacterial activity was measured in elution tests in vitro and local tissue concentrations were measured in rabbits.

RESULTS

In elution tests in vitro, the therapeutic level (> 2 microg/mL) of ciprofloxacin was achieved within 6 h of the start of the test, and it was maintained for up to 300 days. The antibacterial activity of the antibiotic released from sterilized composites was similar to that of the unprocessed ciprofloxacin. In vivo measurements showed high local tissue concentrations (16-86 micrg/g of bone tissue) for 3 months. Compared to previous experiments on two-component polymeric matrices (PLGA or PDLLA) with ciprofloxacin alone, adding bioactive glass microspheres into the composite resulted in morphological changes that facilitated fluid intrusion into the microstructure and quickened ciprofloxacin release.

INTERPRETATION

This type of composition of implant may fulfill the requirements of bone infection therapy, for sustained local release of the selected antibiotic over several months.

In vitro and in vivo testing of bioabsorbable antibiotic containing bone filler for osteomyelitis treatment

The use of local antibiotics from a biodegradable implant is appealing concept for treatment of chronic osteomyelitis. Our aim was to develop a new drug delivery system based on controlled ciprofloxacin release from poly(D/L-lactide). Cylindrical composite pellets (1.0 x 0.9 mm) were manufactured from bioabsorbable poly(D/L-lactide) matrix and ciprofloxacin (7.4 wt %). In vitro studies were carried out to delineate the release profile of the antibiotic and to verify its antimicrobial activity by means of MIC testing. A long-term study in rabbits was performed to validate the release of ciprofloxacin from the composite in vivo. Therapeutic level of ciprofloxacin (>2 microg/mL) was maintained between 60 and 300 days and the concentration remained below the potentially detrimental level of 20 microg/mL in vitro. The released ciprofloxacin had retained its antimicrobial properties against common pathogens. In an exploratory long-term in vivo study with three rabbits, ciprofloxacin could not be detected from the serum after moderate filling (160 mg) of the tibia (follow-up 168 days), whereas after high dosing (a total dose of 1,000 mg in both tibias) ciprofloxacin was found temporarily at low serum concentrations (14-34 ng/mL) during the follow-up of 300 days. The bone concentrations of ciprofloxacin could be measured in all samples at 168 and 300 days. The tested copolylactide matrix seems to be a promising option in selection of resorbable carriers for sustained release of antibiotics, but the composite needs modifications to promote ciprofloxacin release during the first 60 days of implantation.

Cyanoacrylate adhesive provides efficient local drug delivery

Biodegradable drug delivery systems have advanced treatment of a wide spectrum of musculoskeletal problems. However, their lack of availability and cost can restrict use. To find an easily available and inexpensive biodegradable implant, we tested a widely used tissue adhesive, n-butyl-2-cyanoacrylate, as a drug-trapping material. We tested vancomycin with commercially available absorbable gelatin-sponge pieces as the scaffold. We evaluated the in vitro and in vivo drug release profiles and in vivo inflammatory response. A mouse muscle pouch model was used for in vivo evaluations. The released vancomycin level was measured by fluorescence polarization immunoassay technique, and a leukocyte count-based grading system was used to evaluate inflammatory response. Our findings suggest the proposed implant provides effective drug release for as much as 42 days in vitro and 14 days in vivo. The presence of n-butyl-2-cyanoacrylate led to a local inflammatory response which decreased after 3 weeks in the group with less adhesive. These results showed that n-butyl-2-cyanoacrylate could efficiently trap and slowly release a drug when used in the structure of a biodegradable local drug delivery device.

Diagnosis and Treatment of Septic Arthritis

Septic arthritis (SA) is a common orthopedic condition encountered in horses that are presented to equine veterinarians. Successful out-come is dependent on prompt and thorough evaluation and treatment. This article briefly reviews the pathophysiology, outlines diagnostics, describes treatment options and prognostics, and discusses current research in diagnosis and treatment of SA.

Local antibiotic delivery vehicles in the treatment of musculoskeletal infection

The primary benefit achieved with local antibiotic delivery vehicles is the ability to obtain extremely high levels of local antibiotics without increasing systemic toxicity. Antibiotic-loaded bone cement represents the current standard as an antibiotic delivery vehicle in orthopaedic surgery. Biodegradable alternatives to antibiotic-loaded bone cement also are being used clinically and there are many new products in the active stages of development. These alternatives can be categorized as bone graft, bone graft substitutes or extenders, natural polymers (protein-based products), and synthetic polymers. Composite biomaterials that simultaneously provide the functions of variable antibiotic delivery patterns and also contribute to the process of bone regeneration represent the most ideal class of local antibiotic delivery vehicles. High concentrations of certain antibiotics have been shown to affect the process of normal bone regeneration adversely in a dose dependent response. Considerable investigation still is required to determine the proper use of locally administered antibiotics to negotiate the balance between eradicating infection without excessively inhibiting the processes of bone regeneration.

Efficacy of ciprofloxacin-releasing bioabsorbable osteoconductive bone defect filler for treatment of experimental osteomyelitis due to Staphylococcus aureus

The concept of local antibiotic delivery via biodegradable bone defect fillers with multifunctional properties for the treatment of bone infections is highly appealing. Fillers can be used to obliterate surgical dead space and to provide targeted local bactericidal concentrations in tissue for extended periods. Eventually, the osteoconductive component of the filler could guide the healing of the bone defect. The present experimental study was carried out to test this concept in a localized Staphylococcus aureus osteomyelitis model in the rabbit (n = 31). A metaphyseal defect of the tibia was filled with a block of bone cement, followed by insertion of a bacterial inoculum. After removal of the bone cement and surgical debridement at 2 weeks, the defect was filled with a ciprofloxacin-containing (7.6% +/- 0.1%, by weight) composite (treated-infection group) or with a composite without antibiotic (sham-treated group). Both a positive control group (untreated-infection group) and a negative control group were also produced. The treatment response, monitored by positron emission tomography (PET) with fluorine-18-labeled fluorodeoxyglucose ([18F]FDG) at 3 and 6 weeks, showed rapidly decreasing amounts of [18F]FDG uptake in the treated-infection group (P = 0.001 compared with the results for the untreated-infection group at 6 weeks). The bacteriological analysis confirmed the eradication of the bone pathogen in the treated-infection group. However, three animals had culture-positive soft tissue infections. All animals in the sham-treated and untreated-infection groups had culture-positive bone infections with typical radiographic changes of osteomyelitis. Histomorphometry, peripheral quantitative computed tomography, and backscattered electron imaging of scanning electron microscopy images verified the osteoconductive properties of the bioactive glass microspheres within the composite. The median bone ciprofloxacin concentrations were 1.2 and 2.1 microg/g at two anatomic locations of the tibia. This is the first report to show the value of [18F]FDG PET for quantitative monitoring of the treatment response in bone infections. The collaborative results of bacteriologic and [18F-FDG] PET studies showed that use of the multifunctional composite was successful for eradication of the S. aureus pathogen from bone.

Efficacy of bioabsorbable antibiotic containing bone screw in the prevention of biomaterial-related infection due to Staphylococcus aureus

Impregnation of antimicrobial agents within biodegradable orthopedic implants provides a possibility for local antimicrobial prophylaxis of biomaterial-related infections. The objective of this study was to evaluate the efficacy of a bioabsorbable ciprofloxacin containing bone screw (Ab-PLGA) in the prevention of biomaterial-related infection due to Staphylococcus aureus in a rabbit model. Animals in Group I (n=8) received a Ab-PLGA screw contaminated with S. aureus, while animals in Group II (n=8) received a stainless steel (SS) screw contaminated with S. aureus. In two negative control groups, the animals received a Ab-PLGA screw (Group III, n=4) or a SS screw (Group IV, n=4) without bacterial contamination. 18F-FDG-PET imaging, performed at 6 weeks, was applied as a novel quantitative in vivo imaging modality of implant-related infection. Infection was verified by swab cultures, direct cultures of the retrieved implant, and quantitative cultures of pulverized bone. The concentrations of ciprofloxacin in serum and local bone tissue were determined by a high performance liquid chromatographic (HPLC) method with fluorescence (FLD) detection. In the group of contaminated Ab-PLGA screws, all cultures were negative. In the group of contaminated SS screws, all cultures of retrieved implants and six cultures out of eight of pulverized bone were positive for inoculated S. aureus. In negative control groups, all cultures were negative except one contaminant (S. cohnii) found in a SS screw culture. Verified infection of contaminated SS screws was collaborated by the increased 18F-FDG-PET uptake (P=0.004 compared with the group of contaminated Ab-PLGA screws). The mean bone tissue concentration of ciprofloxacin varied from 2.54 to 0.83 microg/g bone as a function of distance from the implantation site. The serum concentration of ciprofloxacin remained undetectable and below the resolution of the analytic method (<5.0 ng/ml). This study confirmed the in vivo efficacy of bioabsorbable antibiotic containing bone screw in the prevention of biomaterial-related infection due to S. aureus.

Evolving concepts in bone tissue engineering

The field of tissue engineering integrates the latest advances in molecular biology, biochemistry, engineering, material science, and medical transplantation. Researchers in the developing field of regenerative medicine have identified bone tissue engineering as an attractive translational target. Clinical problems requiring bone regeneration are diverse, and no single regeneration approach will likely resolve all defects. Recent advances in the field of tissue engineering have included the use of sophisticated biocompatible scaffolds, new postnatal multipotent cell populations, and the appropriate cellular stimulation. In particular, synthetic polymer scaffolds allow for fast and reproducible construction, while still retaining biocompatible characteristics. These criteria relate to the immediate goal of determining the ideal implant. The search is becoming a reality with widespread availability of biocompatible scaffolds; however, the desired parameters have not been clearly defined. Currently, most research focuses on the use of bone morphogenetic proteins (BMPs), specifically BMP-2 and BMP-7. These proteins induce osteogenic differentiation in vitro, as well as bone defect healing in vivo. Protein-scaffold interactions that enhance BMP binding are of the utmost importance, since prolonged BMP release creates the most osteogenic microenvironment. Transition into clinical studies has had only mild success and relies on large doses of BMPs for bone formation. Advances within the field of bone tissue engineering will likely overcome these challenges and lead to more clinically relevant therapies.

Alternative materials to acrylic bone cement for delivery of depot antibiotics in orthopaedic infections

Acrylic bone cement has considerable laboratory and clinical data validating it as a delivery material for depot administration of antibiotics. However, an alternate material that does not require a secondary procedure for removal is desired. Many biodegradable materials have been evaluated as alternatives including protein-based materials (collagen, fibrin, thrombin, clotted blood), bone-graft, bone-graft substitutes and extenders (hydroxyapatite, beta-tricalcium phosphate, calcium sulfate, bioglass), and synthetic polymers (polyhanhydride, polylactide, polyglycolide, polyhydroxybutyrate-co-hydroxyvalerate, polyhydroxyalkanoate). Various forms and combinations of these materials have been investigated worldwide, characterizing their elution properties and performance in treating osteomyelitis in animal models. Many of these have had limited clinical evaluation. Outside the United States, some of these materials are used clinically. In the United States, none have been approved. None are commercially available for clinical use. Morselized cancellous bone and calcium sulfate are the two materials that have been used clinically in the United States on a physician-prescribed, hand-mixed, basis. Considering the limited clinical data that currently are available, the use of these materials still is experimental. Clinical application should be cautious, limiting the total antibiotic load. Until definitive data are available, a prudent dose would be no higher than one that would have acceptable toxicity risk if administered intravenously over 24 hours.

Effective treatment of osteomyelitis with biodegradable microspheres in a rabbit model

Biodegradable microspheres were manufactured from a high molecular weight copolymer of 50% lactic and 50% glycolic acid and the antibiotic tobramycin. It was hypothesized that the microspheres would be more effective than polymethylmethacrylate beads in the local delivery of tobramycin and that the microspheres would not inhibit bone healing. Osteomyelitis was established in 40 New Zealand White rabbits using Staphylococcus aureus. All animals had irrigation and debridement of the infected radii four weeks after inoculation and were divided into five treatment groups: debridement alone, microspheres alone, microspheres containing tobramycin plus parenteral treatment with cefazolin, polymethylmethacrylate beads containing tobramycin plus parenteral cefazolin, and parenteral cefazolin. All animals were sacrificed after 4 weeks of treatment. The group treated with microspheres plus parenteral antibiotics was the only group to have a significantly higher percentage of animals without bacteria after 4 weeks of treatment when compared with the control group. Additionally, the animals treated with microspheres had a higher degree of bone healing in the defect than the animals treated with bone cement. The most effective treatment was biodegradable microspheres combined with parenteral antibiotic in this rabbit osteomyelitis model.