Palmitic acid coating of allogeneic cancellous bone for local antibiotic treatment: A porcine impaction bone grafting model.

Introduction: The worldwide rising number of joint replacements results in increasing revision surgery including a relevant portion of septic loosening accompanied by bone deficiencies. Loading of allogeneic bone with antibiotics provides high local antibiotic concentrations and might eradicate bacteria which appear resistant to systemic antibiotic application. Hydrophobic palmitic acid was shown to be a suitable carrier for antibiotics and prevents biofilm. Methods: Cancellous bone derived from 6 to 7 months old piglets was used for a standardized in vitro impaction bone grafting model according to previous studies. The specimens were either thermodisinfected or remained native and palmitic acid with one third and two third partial weight were added and compared with control. Shear force at the interface prosthesis to cement and between cement and bone was measured. The relative micromovements were measured with 6 inductive sensors with a resolution of 0.1 µm at three different measuring heights up to a maximum movement of 150 µm between cement and bone. Taking into account the corresponding applied torque the measured values were normalized in µm/Nm. Statistical analysis was done with SPSS Statistics® Version 26.0 IBM. Results: Smallest movement was measured for thermodisinfected cancellous bone and a not significant decrease of shear force resistance with addition of palmitic acid was found since supplementing native cancellous bone reduced shear force resistance significantly depending on the weight percentage of palmitic acid. Conclusion: Supplementation of porcine cancellous bone with palmitic acid did not significantly reduce shear force resistance of thermodisinfected bone since adding palmitic acid to native bone decreased it significantly depending on the volume added. Palmitic acid seems to be a suitable coating for allogeneic cancellous bone to deliver high local antibiotic concentrations and thermodisinfected cancellous bone might be able to store larger volumes of palmitic acid than native bone without relevant influence on shear force resistance.

Material modifications enhancing the antibacterial properties of two biodegradable poly(3-hydroxybutyrate) implants.

The aim of this study was to evaluate the antimicrobial efficacy of adding a gentamicin palmitate (GP) coating and zirconium dioxide (ZrO2) to biodegradable poly(3-hydroxybutyrate) (PHB) to reduce biofilm formation. Cylindrical pins with and without a coating were incubated in Müller-Hinton broth inoculated with 2 × 105 colony-forming units (CFU) ml-1 of Staphylococcus aureus for 2 d or 7 d, then sonicated to disrupt biofilms. Pure PHB (PHB + GP) and PHB pins with ZrO2 added (PHBzr + GP) were coated with GP and compared with PHB pins lacking a coating (PHB). Cells (CFU) were counted to quantify the number of bacteria in the biofilm and a cell proliferation assay was employed to evaluate metabolic activity, and scanning electron microscopy (SEM) was performed to visualize the structure of the biofilm. After 2 d of incubation there were significantly more cells in biofilms on PHB pins than PHB + GP and PHBzr + GP pins (p < 0.0001), and cells in the sonication fluid obtained from GP-coated pins exhibited significantly lower metabolic activity than cells from uncoated PHB pins (p < 0.0001). After 7 d of incubation metabolic activity was lowest for PHBzr + GP, with significant differences between PHB and PHBzr + GP (p = 0.001). SEM revealed more cells attached to the surface, and more structured biofilms, on pins without a coating. Coating pins with GP significantly reduced early biofilm formation on PHB implants. This could lower the potential risk of surgical site infections when using PHB implants. Addition of ZrO2 might further enhance the antibacterial properties. Such modification of the implant material should therefore be considered when developing new biodegradable PHB implants.

Molecular dissection of TNFR-TNFα bidirectional signaling reveals both cooperative and antagonistic interactions with p75 neurotrophic factor receptor in axon patterning.

During neural development, complex organisms rely on progressive and regressive events whereby axons, synapses, and neurons are overproduced followed by selective elimination of a portion of these components. Tumor necrosis factor α (TNFα) together with its cognate receptor (Tumor necrosis factor receptor 1; TNFR1) have been shown to play both regressive (i.e. forward signaling from the receptor) and progressive (i.e. reverse signaling from the ligand) roles in sympathetic neuron development. In contrast, a paralog of TNFR1, p75 neurotrophic factor receptor (p75NTR) promotes mainly regressive developmental events in sympathetic neurons. Here we examine the interplay between these paralogous receptors in the regulation of axon branch elimination and arborization. We confirm previous reports that these TNFR1 family members are individually capable of promoting ligand-dependent suppression of axon growth and branching. Remarkably, p75NTR and TNFR1 physically interact and p75NTR requires TNFR1 for ligand-dependent axon suppression of axon branching but not vice versa. We also find that p75NTR forward signaling and TNFα reverse signaling are functionally antagonistic. Finally, we find that TNFα reverse signaling is necessary for nerve growth factor (NGF) dependent axon growth. Taken together these findings demonstrate several levels of synergistic and antagonistic interactions using very few signaling pathways and that the balance of these synergizing and opposing signals act to ensure proper axon growth and patterning.

[Potential of allogeneic bone grafts as antibiotic carriers : Effect of different preparation processes on efficacy]. / Allogene spongiöse Knochenpräparate als Antibiotikaträger : Einfluss verschiedener Aufbereitungsverfahren auf die Wirksamkeit.

BACKGROUND: The rising number of primary joint replacements worldwide is causing an increase of endoprosthetic revision surgery due bacterial infection. Revision surgery using non-cemented implants seems beneficial for the long-term outcome, and the use of antibiotic-impregnated bone grafts might control the infection and provide a good support for the implant. In this study, we evaluated the release of antibiotics from fresh-frozen and lyophilized allogeneic bone grafts. METHODS: Heat-treated, lyophilized and fresh frozen cryopreserved bone chips were impregnated with gentamicin sulphate, gentamicin palmitate and vancomycin, and calcium carbonate/calcium sulphate treated with antibiotics. The efficacy of each preparation was measured by drug release tests and bacterial susceptibility using B. subtilis, S. aureus and methicillin-resistant Staphylococcus aureus. RESULTS: The release of gentamicin from lyophilized bone was similar to the release rate from fresh frozen bone during the entire experiment. This might be related to the similar porosity and microstructure of the bone chips. The release of gentamicin from lyophilized and fresh frozen bone was high on the first and second days, then decreased and stayed at a low rate until the end of the second week. CONCLUSION: Depending on the surgical strategy, either polymethylmethacrylate or allogeneic bone are able to deliver sufficient concentrations of gentamicin to achieve bacterial inhibition within 2 weeks after surgery. In the case of uncemented revision of joint replacements, allogeneic bone can deliver therapeutic doses of gentamicin and peak levels immediately and a fortnight after implantation.

[Bone substitute materials as local drug carriers : Current status of substitutes of various origins]. / Knochenersatzwerkstoffe als lokale Wirkstoffträger : Aktueller Stand bei Ersatzstoffen verschiedenen Ursprungs.

BACKGROUND: Autologous bone grafts (autografts) are used in surgery for defect filling and impaction grafting during hip socket and femur reconstruction. Because of their superior osteoinductive capacity, autografts are considered the "gold standard" for these treatments. However, because of a better cost-benefit ratio, allografts are also often used. In the case of limited donor availability for autologous or allogenic bone grafts, bone substitute materials (BSMs) are a reasonable alternative or supplement. BSM are based on or combine different substances. Growth factors of the bone morphogenetic protein family BMP are recombinant proteins that specifically induce the growth of bone and cartilage tissue. CHARACTERISTICS: One advantage of BSM is the option to combine them with several anti-infective agents. The choice of the anti-infective substance should not only be based on the antimicrobial efficacy, but should also take into account possible dose-dependent cellular and pharmacological side effects at the implantation site. Thus, microbiologists, pharmacists and surgeons should decide together which combination is the most appropriate. COMBINATION PRODUCTS: BSM with active agent additives are considered combination products that are characterized by a main effect (bone replacement function) and a secondary effect (prophylaxis of bacterial recolonization of BSM). Both functions must be thoroughly (clinically) evidenced in the course of the registration process as a class III medical device. Drug authorities evaluate the active agents, their function and corresponding indication. Currently, only a few combination products are available on the market. As a consequence of the only limited availability of such commercial combination products, surgeons in clinical practice often manually add the active agent to BSM in the theatre prior to implantation. However, such a customized addition of antibiotics places the surgeon in a situation of a manufacturer where he assumes liability for the product.

In vitro evaluation of novel antimicrobial coatings for surgical sutures using octenidine.

BACKGROUND: Sutures colonized by bacteria represent a challenge in surgery due to their potential to cause surgical site infections. In order to reduce these type of infections antimicrobially coated surgical sutures are currently under development. In this study, we investigated the antimicrobial drug octenidine as a coating agent for surgical sutures. To achieve high antimicrobial efficacy and required biocompatibility for medical devices, we focused on optimizing octenidine coatings based on fatty acids. For this purpose, antimicrobial sutures were prepared with either octenidine-laurate or octenidine-palmitate at 11, 22, and 33 µg/cm drug concentration normalized per length of sutures. Octenidine containing sutures were compared to the commercial triclosan-coated suture Vicryl® Plus. The release of octenidine into aqueous solution was analyzed and long-term antimicrobial efficacy was assessed via agar diffusion tests using Staphylococcus aureus. For determining biocompatibility, cytotoxicity assays (WST-1) were performed using L-929 mouse fibroblasts. RESULTS: In a 7 days elution experiment, octenidine-palmitate coated sutures demonstrated much slower drug release (11 µg/cm: 7%; 22 µg/cm: 5%; 33 µg/cm: 33%) than octenidine-laurate sutures (11 µg/cm: 82%; 22 µg/cm: 88%; 33 µg/cm: 87%). Furthermore sutures at 11 µg/cm drug content were associated with acceptable cytotoxicity according to ISO 10993-5 standard and showed, similar to Vicryl® Plus, relevant efficacy to inhibit surrounding bacterial growth for up to 9 days. CONCLUSIONS: Octenidine coated sutures with a concentration of 11 µg/cm revealed high antimicrobial efficacy and biocompatibility. Due to their delayed release, palmitate carriers should be preferred. Such coatings are candidates for clinical testing in regard to their safety and efficacy.

[Augmentation with PMMA cement]. / Augmentation mit PMMA-Zement.

Cements based on polymethyl methacrylate (PMMA) can be used without any problem in a variety of clinical augmentations. Cement-related complications in surgical procedures involving PMMA cements, such as embolism, thermal necrosis, toxicity and hypersensitivity, are often due to other causes. Knowledge about the properties of the cement helps the user to safely employ PMMA cements in augmentations. High radio-opacity is required in vertebral body augmentations and this is provided in particular by zirconium dioxide. In vertebral body augmentations, a low benzoyl peroxide (BPO) content can considerably prolong the liquid dough phase. In augmentations with cement fillings in the region of a tumor, a high BPO content can specifically increase the peak temperature of the PMMA cement. In osteosynthetic augmentations with PMMA, necrosis is rare because heat development in the presence of metallic implants is low due to heat conduction via the implant. Larger cement fillings where there is no heat conduction via metal implants can exhibit substantially higher peak temperatures. The flow properties of PMMA cements are of particular importance for the user to allow optimum handling of PMMA cements. In patients with hypersensitivity to antibiotics, there is no need to avoid the use of PMMA as there are sufficient PMMA-based alternatives. The PMMA cements are local drug delivery systems and antibiotics, antiseptics, antimycotics and also cytostatics can be mixed with the cement. Attention must be paid to antagonistic and synergistic effects.

Novel fatty acid gentamicin salts as slow-release drug carrier systems for anti-infective protection of vascular biomaterials.

Infections of vascular prostheses are still a major risk in surgery. The current work presents an in vitro evaluation of novel slow release antibiotic coatings based on new gentamicin fatty acid salts for polytetrafluoroethylene grafts. These grafts were coated with gentamicin sodium dodecyl sulfate, gentamicin laurate and gentamicin palmitate. Drug release kinetics, anti-infective characteristics, biocompatibility and haemocompatibility of developed coatings were compared to commercially available gelatin sealed PTFE grafts (SEALPTFE™) and knitted silver coated Dacron(®) grafts (InterGard(®)). Each gentamicin fatty acid coating showed a continuous drug release in the first eight hours followed by a low continuous release. Grafts coated with gentamicin fatty acids reduced bacterial growth even beyond pathologically relevant high concentrations. Cytotoxicity levels depending on drug formulation bringing up gentamicin palmitate as the most promising biocompatible coating. Thrombelastography studies, ELISA assays and an amidolytic substrate assay confirmed haemocompatibility of developed gentamicin fatty acid coatings comparable to commercially available grafts.

New anti-infective coatings of surgical sutures based on a combination of antiseptics and fatty acids.

Wound infection is a complication feared in surgery. The aim of this study was to develop new anti-infective coatings of surgical sutures and to compare the anti-microbial effectiveness and biocompatibility to the well-established Vicryl Plus. Synthetic absorbable PGA surgical sutures were coated with three different chlorhexidine concentrations and two different octenidine concentrations in combination with palmitic acid and lauric acid. Drug-release kinetics lasting 96 h were studied in phosphate-buffered saline at 37 degrees C. Anti-infective characteristics were determined by measuring the change in optical density of Staphylococcus aureus suspensions charged with coated sutures over time. Microorganisms adsorbed at the surface of coated sutures were assessed on blood agar plates and coated sutures eluted for 24 h were placed on bacterial lawns cultured on Mueller-Hinton plates to prove retained anti-microbial potency. A cell proliferation assay was performed to assess the degree of cytotoxicity. Anti-infective characteristics and biocompatibility were compared to Vicryl Plus. A coating technology for slow-release drug-delivery systems on surgical sutures could be developed. All coatings showed a continuous drug release within 96 h. Individual chlorhexidine and octenidine coated sutures showed superior anti-infective characteristics but inferior biocompatibility in comparison to Vicryl Plus. We conclude that the developed anti-infective suture coatings consisting of lipid-based drug-delivery systems in combination with antiseptics are highly effective against bacterial colonization in vitro; however, drug doses have to be adjusted to improve biocompatibility.

Evaluation of the stability of gentamicin in different antibiotic carriers using a validated MEKC method.

The quality control of gentamicin in different antibiotic carriers, using MEKC as stability-indicating method is described. Baseline separations of gentamicin C1, C1a, C2, C2a and C2b and, furthermore the impurities and degradation products garamin (GARA), 2-deoxy-streptamine (DSA) and sisomicin (SISO) were achieved with a background electrolyte containing 20mM deoxycholic acid, 15 mM beta-cyclodextrin and 100mM tetraborate (pH 10.0). After derivatization with o-phthaldialdehyde reagent (OPA), UV detection at 340 nm was possible. The method was validated with respect to selectivity, limit of detection (LOD) and quantification (LOQ) of the impurities, linearity, accuracy, precision and robustness. Evaluation of four different antibiotic carriers stored under stability conditions according to the International Conference on Harmonization (ICH) guidelines and older pharmaceutical formulations disclosed good stability.

Release of gentamicin from bone regenerative materials: an in vitro study.

Antibiotic loading of bone regenerative materials is a promising way to protect augmentation procedures from infection during the resorption phase of bone substitutes. Especially in the early stage of implantation, it should protect the grafted site against microbiological pathogens. The present study reports the release kinetics of gentamicin after loading from two synthetic bone filling materials. The first, BONITmatrix, is a biphasic calcium phosphate silica composite obtained by the sol-gel route consisting of 13% silicon dioxide (w/w) and calcium phosphates (hydroxyapatite/beta-tricalcium phosphate 60/40 w/w). The second, Synthacer, is a sintered hydroxyapatite ceramic. Gentamicin was loaded by dipping and by vacuum coating. Release kinetics of the loaded Gentamicin was investigated by fluorescence polarization immunoassay and by staphylococcus aureus assay. By dipping, loading failed for Synthacer, and it was 12.7 mg gentamicin per gram bone substitute for BONITmatrix. By vacuum coating, loading was 11.3 mg gentamicin per gram bone substitute for Synthacer and 7.4 mg gentamicin per gram bone substitute for BONITmatrix. Distinct release kinetics were measured. For Synthacer, a high initial release was followed by a lower protracted release level up to 28 days. For BONITmatrix release was continuous over the investigated 70-day period. The present data suggest that the porosity properties at the nano- and microscopic levels, or the composition are responsible for antibiotic loading and subsequent release.

[Bone substitutes]. / Knochenersatzwerkstoffe.

A large variety of different bone substitutes are available for the treatment of congenital or acquired bone defects as an alternative to bone transplantation. Complications associated with graft harvesting, limited donor resources, and the potential risk of transmission of infectious diseases have led to the development of multiple concepts of new bone substitutes to minimize the wellknown problems. This article intends to give an overview of the products currently available on the market. Inorganic materials such as ceramics from hydroxyapatite and/or tricalcium phosphate, calcium phosphate cements, calcium sulfates and bioglass,organic materials (polymers) and composites, xenografts,and glass ionomer cements are discussed.

[Bone cements based on polymethylmethacrylate]. / Knochenzemente auf Basis von Polymethylmethacrylat.

Bone cements based on polymethylmethacrylate (PMMA) remain an important material for anchorage of artificial joints. Polymers based on PMMA originally developed for dental surgery have been successfully used in bone surgery for more than 40 years. At first sight the cold-curing PMMA bone cement seems to be a rather simple material consisting of a powder and a liquid. But in fact it is a complex material fulfilling various functions at its application site after the implantation. Its properties vary according to the composition of its basic elements. They already play a decisive role for the working behavior during mixing of both components. The differences in the working behavior considerably affect the cementing technique and the accurate application in vivo. These influence the mechanical performance of the cured cement mantle and the long-term results of the implantation. Standardized test methods are used to characterize bone cements,whereas the clinical relevance of the test methods has to be evaluated critically.Additionally,PMMA bone cements act as a drug delivery system as a local carrier of antibiotics. This paper gives a review of the composition and properties of PMMA bone cements and their influence on practical application.