Antibiotic-eluting resorbable bone-void filler evaluated in a large animal infection prevention model.

Periprosthetic infection in total knee arthroplasty is a difficult-to-treat complication. Current implant revision procedures use non-degradable, antibiotic-loaded bone cement for local antimicrobial delivery. As a permanent foreign body, antibiotic-loaded bone cement is susceptible to bacterial colonisation after antibiotic release. In this first step, of a multi-study approach, an infection prevention model assessed a resorbable, antibiotic-eluting bone-void filler for preventing infection in a large animal model. Four groups of sheep were utilised to monitor antibiotic-eluting bone-void filler-induced osteoconductivity, infection prevention, and implant resorption. Explanted bone and surrounding tissues were evaluated using quantitative microbiology, backscattered electron microscopy, bone mineral apposition, and Sanderson's staining at the 12-week endpoint. Control groups received commercially available bone-void filler, implanted into a surgically created defect on the right medial femoral condyle. Experimental groups received six antibiotic-eluting bone-void filler devices placed into identically sized defects. One control and one experimental group tested osteoconductivity. An additional control and experimental group were each inoculated with 5 × 105 colony forming units/mL Staphylococcus aureus during implant placement for bactericidal effects. Osteoconductivity was confirmed for both antibiotic-eluting bone-void filler and commercially available bone-void filler. The experimental group inoculated with S. aureus showed no detectable bacteria at the study's 12-week endpoint, while infection controls required euthanasia 6-11 d post-inoculation due to infection. This large animal study validated this antibiotic-eluting bone-void filler as osteoconductive, in situ degradable, and bactericidal. All groups, except the infection control, exhibited bone formation comparable to commercial filler ProOsteon®500R.

Antibiotic elution and compressive strength of gentamicin/vancomycin loaded bone cements are considerably influenced by immersion fluid volume.

The effect of doubling the immersion fluid (eluate) volume on antibiotic concentrations and on mechanical stability from vancomycin and gentamicin loaded bone cements was investigated in vitro. Antibiotic loaded bone cements containing premixed 1.34% gentamicin antibiotic concentration in the cement powder (wt), premixed 1.19% gentamicin wt and 4.76% vancomycin wt and premixed 1.17% wt gentamicin additionally manually blended with 4.68% wt vancomycin were tested. Six specimens per group were immersed in 4 ml and 8 ml for 6 weeks while the eluate was exchanged every 24 h. The antibiotic concentrations were repeatedly measured. Then the specimens were tested for compressive strength. Doubling the eluate volume significantly decreased gentamicin and vancomycin concentrations from 6 h and 24 h on, except for the gentamicin concentration of the additionally manually blended formulation after 3 weeks. The additionally manually blended vancomycin formulation produced significantly higher gentamicin concentrations in 8 ml compared to the other formulations. The reduction ratios of the vancomycin concentrations were significantly smaller than the reduction ratios of the gentamicin concentrations for the manually blended vancomycin formulation. Vancomycin containing formulations showed significantly lower compressive strengths than the vancomycin free formulation after immersion. Doubling the eluate volume lead to significant compressive strength reduction of the vancomycin containing formulations. Eluate volume change influences antibiotic elution dependent on the antibiotic combination and loading technique. The reducing effect is higher on vancomycin than on gentamicin elution. Compressive strength of gentamicin/vancomycin loaded bone cements after immersion is eluate volume dependent.

Cement Distribution Patterns in Osteoporotic Vertebral Compression Fractures with Intravertebral Cleft: Effect on Therapeutic Efficacy.

OBJECTIVE: To determine cement distribution patterns on therapeutic efficacy after percutaneous vertebroplasty treatment of osteoporotic vertebral compression fractures (OVCFs) with intravertebral cleft (IVC). METHODS: Patients who were treated with percutaneous vertebroplasty for single OVCFs with IVC and met this study's inclusion criteria were retrospectively reviewed. The follow-up period was at least 2 years. Distribution patterns of cement in the IVC area were respectively specified into 2 groups: group 1: solid lump distribution pattern (n = 22); group 2: the comparatively diffused pattern (n = 90). Radiologic and clinical parameters were analyzed and compared. Then, associations of recollapse with covariates and a risk score were further analyzed and developed to predict recollapse of the augmented vertebrae. RESULTS: At the immediate postoperative period, all patients benefited from significant improvement in vertebrae height and kyphotic angle correction. However, significant recollapse was observed at the 2 years postoperative follow-up for the patients in group 1. Furthermore, we found that preoperative severe kyphotic deformity (a cutoff value of 12.5°), solid lump cement distribution pattern, and larger reduction angle (a cutoff value of 8.3°) was significantly associated with increased risk for recollapse. A risk score was developed based on the number of risk factors present in each patient and the receiver operating characteristic curve of the risk score generated an area under the curve of 0.788 (95% confidence interval 0.702-0.873, P = 0.000). CONCLUSIONS: The comparatively diffused pattern shows better long-term radiologic and clinical outcomes for the treatment for OVCFs with IVC. A risk score can be used to predict the incidence of recollapse.

Polymethylmethacrylate distribution is associated with recompression after vertebroplasty or kyphoplasty for osteoporotic vertebral compression fractures: A retrospective study.

BACKGROUND: Osteoporotic vertebral compression fracture, always accompanied with pain and height loss of vertebral body, has a significant negative impact on life quality of patients. Vertebroplasty or kyphoplasty is minimal invasive techniques to reconstruct the vertebral height and prevent further collapse of the fractured vertebrae by injecting polymethylmethacrylate into vertebral body. However, recompression of polymethylmethacrylate augmented vertebrae with significant vertebral height loss and aggressive local kyphotic was observed frequently after VP or KP. The purpose of this study was to investigate the effect of polymethylmethacrylate distribution on recompression of the vertebral body after vertebroplasty or kyphoplasty surgery for osteoporotic vertebral compression fracture. METHODS: A total of 281 patients who were diagnosed with vertebral compression fracture (T5-L5) from June 2014 to June 2016 and underwent vertebroplasty or kyphoplasty by polymethylmethacrylate were retrospectively analyzed. The X-ray films at 1 day and 12 months after surgery were compared to evaluate the recompression of operated vertebral body. Patients were divided into those without recompression (non-recompression group) and those with recompression (recompression group). Polymethylmethacrylate distribution pattern, including location and relationship to endplates, was compared between the two groups by lateral X-ray film. Multivariate logistic regression analysis was performed to assess the potential risk factors associated with polymethylmethacrylate distribution for recompression. RESULTS: One hundred and six (37.7%) patients experienced recompression after surgery during the follow-up period. The polymethylmethacrylate distributed in the middle of vertebral body showed significant differences between two groups. In non-recompression group, the polymethylmethacrylate in the middle portion of vertebral body were closer to endplates than that in the recompression group (upper: t = 31.41, p<0.001; lower: t = 12.19, p<0.001). The higher percentage of the height of polymethylmethacrylate in the middle portion of vertebral body indicates the lower risk of recompression (odds ratio [OR]<0.01, p<0.001). The recompression group and non-recompression group showed significant difference in "contacted" polymethylmethacrylate distribution pattern (polymethylmethacrylate contacted to the both upper/lower endplates) (χ2 = 66.23, p<0.001). The vertebra with a "contacted" polymethylmethacrylate distribution pattern has lower risk of recompression (OR = 0.09, p<0.001). CONCLUSIONS: Either more polymethylmethacrylate in the middle portion of vertebral body or "contacted" polymethylmethacrylate distribution pattern had a significantly less incidence of recompression. The findings indicated that the control of polymethylmethacrylate distribution during surgery may reduce the risks of recompression after vertebroplasty or kyphoplasty.

In Vivo Release of Vancomycin from Calcium Phosphate Cement.

Calcium phosphate cement (CPC) has good release efficiency and has therefore been used as a drug delivery system for postoperative infection. The release profile of CPC has mainly been evaluated by in vitro studies, which are carried out by immersing test specimens in a relatively large amount of solvent. However, it remains unclear whether antibiotic-impregnated CPC has sufficient clinical effects and release in vivo. We examined the in vivo release profile of CPC impregnated with vancomycin (VCM) and compared this with that of polymethylmethacrylate (PMMA) cement. To evaluate the release profile in vitro, the test specimens were immersed in 10 mL sterile phosphate-buffered saline per gram of test specimen and incubated at 37°C for 56 days in triplicate. For in vivo experiments, the test specimens were implanted between the fascia and muscle of the femur of rats. Residual VCM was extracted from the removed test specimens to determine the amount of VCM released into rat tissues. CPC released more VCM over a longer duration than PMMA in vitro. Released levels of VCM from CPC/VCM in vivo were 3.4-fold, 5.0-fold, and 8.6-fold greater on days 1, 7, and 28, respectively, than those released on the corresponding days from PMMA/VCM and were drastically greater on day 56 due to inefficient release from PMMA/VCM. The amount of VCM released from CPC and PMMA was much higher than the minimum inhibitory concentration (1.56 µg) and lower than the detection limit, respectively. Our findings suggest that CPC is a suitable material for releasing antibiotics for local action against established postoperative infection.

Cement mantle thickness does not influence serum or local gentamicin concentrations in hybrid total hip arthroplasty: a randomised controlled trial.

INTRODUCTION: We investigated the in vivo gentamicin elution kinetics of Hi-Fatigue Gentamicin Bone Cement (AAP Biomaterials GmbH) in serum and drain fluid after hybrid hip arthroplasty and the relationship with cement mantle thickness. METHODS: We compared in a randomised, non-blinded prospective study, the local and systemic gentamicin concentrations in 2 groups. The thin cement mantle group ( n = 16) received a stem implanted line-to-line with the broach, whereas the thick group ( n = 14) had an undersized stem. Gentamicin concentrations were measured in drain fluid and serum at set intervals for 3 days postoperatively. RESULTS: In both groups, local gentamicin concentrations were similar. After a high initial burst above the minimal inhibitory concentration (thin: 57.2 mg/L (SD 34.4), thick: 54.9 mg/L (SD 19.9), p = 0.823) local gentamicin concentrations declined rapidly. In both groups, serum concentrations never exceeded toxic levels (maximum 1.08 mg/L). CONCLUSION: In hybrid total hip arthroplasty, Hi-Fatigue Gentamicin Bone Cement resulted in effective and safe gentamicin concentrations. Clinical trial protocol number: PMCI 12/02.

Antibiotic-loaded cement spacers - lessons learned from the past 20 years.

INTRODUCTION: The use of antibiotic-impregnated cement spacers is an established method in the treatment of periprosthetic hip and knee joint infections. Over the past 20 years, the indications for spacer implantation have expanded, and various modified surgical techniques have been proposed to manage difficult anatomical situations. To ensure clinical success, knowledge about the cement impregnation and the pharmacokinetic properties of antibiotic-loaded bone cement is an indispensable premise. AREAS COVERED: In this review, techniques for the fabrication of cement spacers, the incorporation of antibiotics into bone cement, elution kinetics, the clinical performance of spacers, individualized surgical techniques as well as possible postoperative complications are presented. Moreover, the possibility of bacterial colonization of cement spacers during the interim phase which might lead to persistence of infection is also discussed. EXPERT COMMENTARY: The use of articulating spacers is established in hip surgery. However, in knee surgery it is still debated whether articulating or static spacers provide more advantages. The concern about the possible colonization of antibiotic-loaded spacers during the interim phase does not seem to be actually substantiated by hard scientific data due to the lack of important information in the published studies.

Bone regeneration capacity of magnesium phosphate cements in a large animal model.

Magnesium phosphate minerals have captured increasing attention during the past years as suitable alternatives for calcium phosphate bone replacement materials. Here, we investigated the degradation and bone regeneration capacity of experimental struvite (MgNH4PO4·6H2O) forming magnesium phosphate cements in two different orthotopic ovine implantation models. Cements formed at powder to liquid ratios (PLR) of 2.0 and 3.0 g ml-1 were implanted into trabecular bone using a non-load-bearing femoral drill-hole model and a load-bearing tibial defect model. After 4, 7 and 10 months the implants were retrieved and cement degradation and new bone formation was analyzed by micro-computed tomography (µCT) and histomorphometry. The results showed cement degradation in concert with new bone formation at both defect locations. Both cements were almost completely degraded after 10 months. The struvite cement formed with a PLR of 2.0 g ml-1 exhibited a slightly accelerated degradation kinetics compared to the cement with a PLR of 3.0 g ml-1. Tartrat-resistant acid phosphatase (TRAP) staining indicated osteoclastic resorption at the cement surface. Energy dispersive X-ray analysis (EDX) revealed that small residual cement particles were mostly accumulated in the bone marrow in between newly formed bone trabeculae. Mechanical loading did not significantly increase bone formation associated with cement degradation. Concluding, struvite-forming cements might be promising bone replacement materials due to their good degradation which is coupled with new bone formation. STATEMENT OF SIGNIFICANCE: Recently, the interest in magnesium phosphate cements (MPC) for bone substitution increased, as they exhibit high initial strength, comparably elevated degradation potential and the release of valuable magnesium ions. However, only few in vivo studies, mostly including non-load-bearing defects in small animals, have been performed to analyze the degradation and regeneration capability of MPC derived compounds. The present study examined the in vivo behavior of magnesiumammoniumphosphate hexahydrate (struvite) implants with different porosity in both mechanically loaded and non-loaded defects of merino sheep. For the first time, the effect of mechanical stimuli on the biological outcome of this clinically relevant replacement material is shown and directly compared to the conventional unloaded defect situation in a large animal model.

Trivalent chromium incorporated in a crystalline calcium phosphate matrix accelerates materials degradation and bone formation in vivo.

Remodeling of calcium phosphate bone cements is a crucial prerequisite for their application in the treatment of large bone defects. In the present study trivalent chromium ions were incorporated into a brushite forming calcium phosphate cement in two concentrations (10 and 50 mmol/mol ß-tricalcium phosphate) and implanted into a femoral defect in rats for 3 and 6 month, non-modified brushite was used as reference. Based on our previous in vitro findings indicating both an enhanced osteoclastic activity and cytocompatibility towards osteoprogenitor cells we hypothesized a higher in vivo remodeling rate of the Cr3+ doped cements compared to the reference. A significantly enhanced degradation of the modified cements was evidenced by micro computed tomography, X-ray and histological examinations. Furthermore the formation of new bone tissue after 6 month of implantation was significantly increased from 29% to 46% during remodeling of cements, doped with the higher Cr3+ amount. Time of flight secondary ion mass spectrometry (ToF-SIMS) of histological sections was applied to investigate the release of Cr3+ ions from the cement after implantation and to image their distribution in the implant region and the surrounding bone tissue. The relatively weak incorporation of chromium into the newly formed bone tissue is in agreement to the low chromium concentrations which were released from the cements in vitro. The faster degradation of the Cr3+ doped cements was also verified by ToF-SIMS. The positive effect of Cr3+ doping on both degradation and new bone formation is discussed as a synergistic effect of Cr3+ bioactivity on osteoclastic resorption on one hand and improvement of cytocompatibility and solubility by structural changes in the calcium phosphate matrix on the other hand. STATEMENT OF SIGNIFICANCE: While biologically active metal ions like strontium, magnesium and zinc are increasingly applied for the modification of ceramic bone graft materials, the present study is the first report on the incorporation of low doses of trivalent chromium ions into a calcium phosphate based biomaterial and testing of its performance in bone defect regeneration in vivo. Chromium(III)-doped calcium phosphate bone cements show improved cytocompatibility and both degradation rate and new bone formation in vivo are significantly increased compared to the reference cement. This important discovery might be the starting point for the application of trivalent chromium salts for the modification of bone graft materials to increase their remodelling rate.

Elution kinetics of vancomycin and gentamicin from carriers and their effects on mesenchymal stem cell proliferation: an in vitro study.

BACKGROUND: Musculoskeletal infections remain a major complication in orthopedic surgery. The local delivery of antibiotics provides the high levels required to treat an infection without systemic toxicity. However, the local toxicity of antibiotic carriers to the mesenchymal stem cells, as a result of both the peak concentrations and the type of carrier, may be significant. METHODS: To address this concern, the elution kinetics of vancomycin and gentamicin from several commercially available antibiotic carriers and several carriers impregnated by a surgeon (10 ml of each sterile carrier were manually mixed with a 500 mg vancomycin and an 80 mg gentamicin solution, and the duration of impregnation was 30 min) were assessed. Moreover, the effects of these antibiotic carriers on stem cell proliferation were investigated. The following two types of stem cells were used: bone marrow and dental pulp stem cells. RESULTS: The high eluted initial concentrations from antibiotic impregnated cancellous allogeneic bone grafts (which may be increased with the addition of fibrin glue) did not adversely affect stem cell proliferation. Moreover, an increased dental pulp stem cell proliferation rate in the presence of antibiotics was identified. In contrast to allogeneic bone grafts, a significant amount of antibiotics remained in the cement. Despite the favorable elution kinetics, the calcium carriers, bovine collagen carrier and freeze-dried bone exhibited decreased stem cell proliferation activity even in lower antibiotic concentrations compared with an allogeneic graft. CONCLUSIONS: This study demonstrated the benefits of antibiotic impregnated cancellous allogeneic bone grafts versus other carriers.

Influences of doping mesoporous magnesium silicate on water absorption, drug release, degradability, apatite-mineralization and primary cells responses to calcium sulfate based bone cements.

In this study, composite cements containing mesoporous magnesium silicate (m-MS) and calcium sulfate (CS) were fabricated. The results revealed that the setting time of the m-MS/CS composite cements (m-MSC) slightly prolonged with the increase of m-MS content while the compressive strength suffered a little loss. The doping of m-MS improved the water absorption, drug release (vancomycin) and degradability of the m-MSC in Tris-HCl solution (pH=7.4). In addition, addition of m-MS facilitated the apatite-mineralization of m-MSC in simulated body fluid (SBF), indicating good bioactivity. For cell cultural experiments, the results revealed that the m-MSC promoted the cells adhesion and proliferation, and improved the alkaline phosphatase (ALP) activity of MC3T3-E1 cells, revealing good cytocompatibility. It could be suggested that the m-MSC might be promising cements biomaterials for bone tissue regeneration.

Local and systemic diffusion of antineoplastic drugs following vertebroplasty using acrylic cement mixed with cisplatin or methotrexate: experimental study in pigs.

PURPOSE: To determine the efficacy of cisplatin- or methotrexate-containing acrylic cement for local and systemic antineoplastic drug diffusion. Among the uses of acrylic cement or Polymethylmethacrylate (PMMA), there is the possibility to employ it as vehicle for drug diffusion. This capability is of interest in the treatment of pathological fractures: The curative effects of the cement (cytotoxicity of the monomer and increased temperature) are added to the antineoplastic effect of the drugs. METHODS: In the experimental study, two groups of ten pigs underwent vertebroplasty using cement mixed with 500 mg of powder cisplatin or 1000 mg of powder methotrexate. Vertebroplasty was performed in two non-consecutive lumbar vertebrae with bipedicular cement injection. Transpedicular bone biopsy was performed weekly to measure levels of antineoplastic agent in bone tissue and blood plasma. Cisplatin was studied by atomic absorption spectrometry and methotrexate by fluorescence polarization immunoassay. Renal and hepatic function and blood analysis were performed weekly. RESULTS: Cisplatin and methotrexate levels were found in bone tissue at more than 5 weeks following surgery. The cisplatin peak occurred at week 3 (mean 1269 µg/g bone) and the methotrexate peak at week 1 (mean 862.76 µg/g bone). Plasma drug levels were found 72 h after surgery, with a peak at 24 h for cisplatin (mean 0.23 µmol/L) and at 30 min for methotrexate (mean 0.92 µmol/L). None of the animals died during the study. Animals with intracanal cement leaks showed no neurological involvement. Renal, hepatic and hemogram studies remained within normal limits. CONCLUSIONS: There is local diffusion of antineoplastic agents from the cement to bone and plasma. We found methotrexate and cisplatin levels in bone at up to 5 weeks, comparable to previous in vitro reports. At the doses administered, there were no cases of myelosuppression, hepatotoxicity, or nephrotoxicity.

Design and Fabrication of Complex Scaffolds for Bone Defect Healing: Combined 3D Plotting of a Calcium Phosphate Cement and a Growth Factor-Loaded Hydrogel.

Additive manufacturing enables the fabrication of scaffolds with defined architecture. Versatile printing technologies such as extrusion-based 3D plotting allow in addition the incorporation of biological components increasing the capability to restore functional tissues. We have recently described the fabrication of calcium phosphate cement (CPC) scaffolds by 3D plotting of an oil-based CPC paste under mild conditions. In the present study, we have developed a strategy for growth factor loading based on multichannel plotting: a biphasic scaffold design was realised combining CPC with VEGF-laden, highly concentrated hydrogel strands. As hydrogel component, alginate and an alginate-gellan gum blend were evaluated; the blend exhibited a more favourable VEGF release profile and was chosen for biphasic scaffold fabrication. After plotting, two-step post-processing was performed for both, hydrogel crosslinking and CPC setting, which was shown to be compatible with both materials. Finally, a scaffold was designed and fabricated which can be applied for testing in a rat critical size femur defect. Optimization of CPC plotting enabled the fabrication of highly resolved structures with strand diameters of only 200 µm. Micro-computed tomography revealed a precise strand arrangement and an interconnected pore space within the biphasic scaffold even in swollen state of the hydrogel strands.

[An experimental study on a slow-release complex with rifampicin-polylactic-co-glycolic acid-calcium phosphate cement].

OBJECTIVE: To prepare the slow-release complex with rifampicin (RFP)-polylactic-co-glycolic acid (PLGA)-calcium phosphate cement (CPC) (RFP-PLGA-CPC complex), and to study its physical and chemical properties and drug release properties in vitro.
 METHODS: The emulsification-solvent evaporation method was adopted to prepare rifampicin polylactic acid-glycolic acid (RFP-PLGA) slow-release microspheres, which were divided into 3 groups: a calcium phosphate bone cement group (CPC group), a CPC embedded with RFP group (RFP-CPC group), and a PLGA slow-release microspheres carrying RFP and the self-curing CPC group (RFP- PLGA-CPC complex group). The solidification time and porosity of materials were determined. The drug release experiments in vitro were carried out to observe the compressive strength, the change of section morphology before and after drug release. 
 RESULTS: The CPC group showed the shortest solidification time, while the RFP-PLGA-CPC complex group had the longest one. There was statistical difference in the porosity between the CPC group and the RFP-CPC group (P<0.05); Compared to the RFP-PLGA-CPC complex group, the porosity in the CPC group and the RFP-CPC group were significantly changed (both P<0.01). There was significant difference in the compressive strength between the RFP- PLGA-CPC complex group and the CPC group (P<0.01), while there was significant difference in the compressive strength between the RFP-CPC group and the CPC group (3 days: P<0.05; 30 and 60 days: P<0.01). The change of the compressive strength in the CPC was not significant in the whole process of degradation. The sizes of PLGA microspheres were uniform, with the particle size between 100-150 µm. The microspheres were spheres or spheroids, and their surface was smooth without the attached impurities. There was no significant change in the section gap in the CPC group after soaking for 3 to 60 days. The microstructure change in the RFP-CPC group was small, and the cross section was formed by small particles. The pores of section in the RFP-PLGA-CPC complex group increased obviously, and PLGA microspheres gradually disappeared until the 60th day when there were only empty cavities left. The RFP-PLGA-CPC complex group had no obvious drugs sudden release, and the cumulative drug release rate was nearly 95% in the 60 days. The linear fitting was conducted for the drug release behavior of the complex, which was in accordance with zero order kinetics equation F=0.168×t.
 CONCLUSION: The porosity of RFP-PLGA-CPC complex is significantly higher than that of CPC, and it can keep slow release of the effective anti-tuberculosis drugs and maintain a certain mechanical strength for a long time.

Decreased extrusion of calcium phosphate cement versus high viscosity PMMA cement into spongious bone marrow-an ex vivo and in vivo study in sheep vertebrae.

BACKGROUND CONTEXT: Vertebroplasty or kyphoplasty of osteoporotic vertebral fractures bears the risk of pulmonary cement embolism (3.5%-23%) caused by leakage of commonly applied acrylic polymethylmethacrylate (PMMA) cement to spongious bone marrow or outside of the vertebrae. Ultraviscous cement and specific augmentation systems have been developed to reduce such adverse effects. Rapidly setting, resorbable, physiological calcium phosphate cement (CPC) may also represent a suitable alternative. PURPOSE: This study aimed to compare the intravertebral extrusion of CPC and PMMA cement in an ex vivo and in vivo study in sheep. STUDY DESIGN/SETTING: A prospective experimental animal study was carried out. METHODS: Defects (diameter 5 mm; 15 mm depth) were created by a ventrolateral percutaneous approach in lumbar vertebrae of female Merino sheep (2-4 years) either ex vivo (n=17) or in vivo (n=6), and injected with: (1) CPC (L3); (2) CPC reinforced with 10% poly(l-lactide-co-glycolide) (PLGA) fibers (L4); or (3) PMMA cement (L5; Kyphon HV-R). Controls were untouched (L1) or empty defects (L2). The effects of the cement injections were assessed in vivo by blood gas analysis and ex vivo by computed tomography (CT), micro-CT (voxel size: 67 µm), histology, and biomechanical testing. RESULTS: Following ex vivo injection, micro-CT documented significantly increased extrusion of PMMA cement in comparison to CPC (+/- fibers) starting at a distance of 1 mm from the edge of the defect (confirmed by histology); this was also demonstrated by micro-CT following in vivo cement injection. In addition, blood gas analysis showed consistently significantly lower values for the fraction of oxygenized hemoglobin/total hemoglobin (FO2Hb) in the arterial blood until 25 minutes following injection of the PMMA cement (p ≤ .05 vs. CPC; 7, 15 minutes). Biomechanical testing following ex vivo injection showed significantly lower compressive strength and Young modulus than untouched controls for the empty defect (40% and 34% reduction, respectively) and all three cement-injected defects (21%-27% and 29%-32% reduction, respectively), without significant differences among the cements. CONCLUSIONS: Because of comparable compressive strength, but significantly lower cement extrusion into spongious bone marrow than PMMA cement, physiological CPC (+/- PLGA fibers) may represent an attractive alternative to PMMA for vertebroplasty or kyphoplasty of osteoporotic vertebral fractures to reduce the frequency or severity of adverse effects.

Controlled Release of Chemotherapeutic Platinum-Bisphosphonate Complexes from Injectable Calcium Phosphate Cements.

Herein, we present a method to release chemotherapeutic platinum-bisphosphonate (Pt-BP) complexes from apatitic calcium phosphate cements (CPCs). Pt-BP-loaded hydroxyapatite nanoparticles (HA NPs) were added at different ratios to the powder phase of the cements, which contained poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres as porogens to accelerate their degradation. In vitro release kinetics of Pt-BP complexes revealed that the release rate of Pt species can be tuned by varying the amount of drug-loaded HA NPs as well as modifying the chemical structure of the Pt-BP complex to tailor its affinity with HA NPs. In addition, the incorporation of PLGA microspheres into the CPCs increased the degradation rate of the materials without affecting the release rate of Pt species. Finally, the antiproliferative activity of the free Pt-BP complexes and Pt-BP-loaded CPCs was evaluated using both human osteosarcoma cancer cells (MG-63) and human bone marrow-derived mesenchymal stromal cells (h-BMMSCs). This study demonstrated that both free Pt-BP complexes and the releasates from the CPCs were antiproliferative in a dose-dependent manner. Moreover, their antiproliferative activity was higher on MG-63 cells compared to h-BMMSC primary cells. In summary, it was shown that injectable CPCs can be rendered chemotherapeutically active by incorporation of HA NPs loaded with HA-binding Pt-BP complexes.

Self-Setting Calcium Phosphate Cements with Tunable Antibiotic Release Rates for Advanced Antimicrobial Applications.

Osteomyelitis, an infectious disease predominantly tied to poor sanitary conditions in underdeveloped regions of the world, is in need of inexpensive, easily in situ synthesizable and administrable materials for its treatment. The results of this study stem from the attempt to create one such affordable and minimally invasive therapeutic platform in the form of a self-setting, injectable cement with a tunable drug release profile, composed of only nanoparticulate hydroxyapatite, the synthetic version of the bone mineral. Cements comprised two separately synthesized hydroxyapatite powders, one of which, HAP2, was precipitated abruptly, retaining the amorphous nature longer, and the other one of which, HAP1, was precipitated at a slower rate, more rapidly transitioning to the crystalline structure. Cements were made with four different weight ratios of the two hydroxyapatite components: 100/0, 85/15, 50/50, and 0/100 with respect to HAP1 and HAP2. Both the setting and the release rates measured on two different antibiotics, vancomycin and ciprofloxacin, were controlled using the weight ratio of the two hydroxyapatite components. Various inorganic powder properties were formerly used to control drug release, but here we demonstrate for the first time that the kinetics of the mechanism of formation of a solid compound can be controlled to produce tunable drug release profiles. Specifically, it was found that the longer the precursor calcium phosphate component of the cement retains the amorphous nature of the primary precipitate, the more active it was in terms of speeding up the diffusional release of the adsorbed drug. The setting rate was, in contrast, inversely proportional to the release rate and to the content of this active hydroxyapatite component, HAP2. The empirical release profiles were fitted to a set of equations that could be used to tune the release rate to the therapeutic occasion. All of the cements loaded with vancomycin or ciprofloxacin inhibited the growth of Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Pseudomonas aeruginosa in both agar diffusion assays and broth dilution tests with intensities either comparable to the antibiotic per se, as in the case of ciprofloxacin, or even larger than the antibiotic alone, as in the case of vancomycin. Interestingly, even the pure cements exhibited an antibacterial effect ranging from moderate to strong, while demonstrating high levels of biocompatibility with osteoclastic RAW264.7 cells and only slightly affecting the viability of the osteoblastic MC3T3-E1 cells, in direct proportion with the amount of the more active hydroxyapatite component in the cements. This antibacterial effect was especially noticeable against Gram-negative bacteria, where the growth inhibition by the cements was comparable to or even stronger than that of the pure antibiotics. The antibiofilm assay against P. aeruginosa biofilms reiterated the antibiotic effectiveness of pure, antibiotic-free cements. That the carrier per se, composed of a nontoxic, easily prepared, bone mineral composite, can exhibit a strong antibacterial effect even in the absence of an antibiotic drug is an insight highly relevant in view of the rising resistance of an array of pathogens to traditional antibiotic therapies and the demands for the timely development of suitable alternatives.

Influence of implant properties and local delivery systems on the outcome in operative fracture care.

Fracture fixation devices are implanted into a growing number of patients each year. This may be attributed to an increase in the popularity of operative fracture care and the development of ever more sophisticated implants, which may be used in even the most difficult clinical cases. Furthermore, as the general population ages, fragility fractures become more frequent. With the increase in number of surgical interventions, the absolute number of complications of these surgical treatments will inevitably rise. Implant-related infection and compromised fracture healing remain the most challenging and prevalent complications in operative fracture care. Any strategy that can help to reduce these complications will not only lead to a faster and more complete resumption of activities, but will also help to reduce the socio-economic impact. In this review we describe the influence of implant design and material choice on complication rates in trauma patients. Furthermore, we discuss the importance of local delivery systems, such as implant coatings and bone cement, and how these systems may have an impact on the prevalence, prevention and treatment outcome of these complications.

A novel liposomal drug delivery system for PMMA bone cements.

The population in developed countries is ageing and the number of people experiencing joint-related conditions, such as osteoarthritis, is expected to increase. Joint replacements are currently the most effective treatment for severe joint conditions and although many of these procedures are successful, infection developing after the procedure is still an issue, requiring complex and expensive revisions. Whilst incorporating a powdered antibiotic within the bone cement can reduce infection rates, the powder frequently agglomerates, resulting in poor antibiotic release characteristics and compromised mechanical performance of the cement. To overcome these issues, a novel delivery system consisting of antibiotic-loaded nano-sized liposomes was developed for inclusion into polymethyl methacrylate (PMMA) bone cement. This system was tested in a commercial cement (Palacos R) and consistently delivered a higher percentage (22%) of the incorporated antibiotic when compared to the powdered antibiotic cement (9%), meaning less antibiotic needs to be incorporated than with conventional cement. The novel system resulted in a controlled and gradual release of antibiotic over a longer, 30-day period and enhanced the toughness, bending strength and Vickers hardness of the cement, without altering its polymerization or molecular structure. This new material has the potential to significantly reduce infections in cemented joint replacements leading to enhanced patient quality of life and reduced healthcare costs. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1510-1524, 2016.

Porous calcium phosphate-poly (lactic-co-glycolic) acid composite bone cement: A viable tunable drug delivery system.

Calcium phosphate based cements (CPCs) are frequently used as bone void fillers for non-load bearing segmental bone defects due to their clinically relevant handling characteristics and ability to promote natural bone growth. Macroporous CPC scaffolds with interconnected pores are preferred for their ability to degrade faster and enable accelerated bone regeneration. Herein, a composite CPC scaffold is developed using newly developed resorbable calcium phosphate cement (ReCaPP) formulation containing degradable microspheres of bio-compatible poly (lactic-co-glycolic acid) (PLGA) serving as porogen. The present study is aimed at characterizing the effect of in-vitro degradation of PLGA microspheres on the physical, chemical and structural characteristics of the composite cements. The porosity measurements results reveal the formation of highly interconnected macroporous scaffolds after degradation of PLGA microspheres. The in-vitro characterizations also suggest that the degradation by products of PLGA reduces the pH of the local environment thereby increasing the dissolution rate of the cement. In addition, the in-vitro vancomycin release from the composite CPC scaffold suggests that the drug association with the composite scaffolds can be tuned to achieve control release kinetics. Further, the study demonstrates control release lasting for longer than 10weeks from the composite cements in which vancomycin is encapsulated in PLGA microspheres.