Gentamicin release from two-solution and powder-liquid poly(methyl methacrylate)-based bone cements by using novel pH method

Hybrid system with stable structure of hard/soft tissue substitutes induces re-osseointegration in a rat model of biofilm-mediated peri-implantitis

Re-osseointegration of an infected/contaminated dental implant poses major clinical challenges. We tested the hypothesis that the application of an antibiotic-releasing construct, combined with hard/soft tissue replacement, increases the efficacy of reconstructive therapy. We initially fabricated semi-flexible hybrid constructs of β-TCP/PHBHHx, with tetracycline (TC) (TC amounts: 5%, 10%, and 15%). Thereafter, using in vitro assays, TC release profile, attachment to rat bone marrow-derived stem cells (rBMSCs) and their viability as well as anti-bacterial activity were determined. Thereafter, regenerative efficacies of the three hybrid constructs were assessed in a rat model of peri-implantitis induced by Aggregatibacter actinomycetemcomitans biofilm; control animals received β-TCP/Bio-Gide and TC injection. Eight weeks later, maxillae were obtained for radiological, histological, and histomorphometric analyses of peri-implant tissues. Sulcus bleeding index was chronologically recorded. Serum cytokines levels of IL-6 and IL-1β were also evaluated by enzyme-linked immunosorbent assay. Substantial amounts of tetracycline, from hybrid constructs, were released for 2 weeks. The medium containing the released tetracycline did not affect the adhesion or viability of rBMSCs; however, it inhibited the proliferation of A. actinomycetemcomitans. Osteogenesis and osseointegration were more marked for the 15% hybrid construct group than the other two groups. The height of attachment and infiltration of inflammatory cells within fibrous tissue was significantly reduced in the experimental groups than the control group. Our protocol resulted in re-osseointegration on a biofilm-contaminated implant. Thus, an antibiotic releasing inorganic/organic construct may offer a therapeutic option to suppress infection and promote guided tissue regeneration thereby serving as an integrated multi-layer substitute for both hard/soft tissues.

A novel chlorhexidine-releasing composite bone cement: Characterization of antimicrobial effectiveness and cement strength

The addition of calcium phosphate fillers or antimicrobials to bone cements seems to produce inferior materials. In this study, a two-solution bone cement composite was designed for high viscosity and high pseudoplasticity to improve injection and mitigate the risk of extravasation. By pre-mixing these cements, the fillers are incorporated into the matrix and should not detrimentally affect the performance properties. To expand the functionality of this cement system, the addition of bioactive and antimicrobial phases were explored. Brushite and chlorhexidine were used as calcium phosphate filler and the antimicrobial phase, respectively. By controlling the free radical quenching mechanism provided by the chlorhexidine molecule, it was possible to achieve high polymer conversion rates. This phenomenon led to cement strength retention while successfully preventing microbial proliferation in an environment exposed to the cement surface. Based on these results, two-solution cement composite prepared with high concentrations of brushite and chlorhexidine diacetate salt hydrate may provide an attractive bioactive and antimicrobial cement for load-bearing applications.

An Approach for determining antibiotic loading for a physician-directed antibiotic-loaded PMMA bone cement formulation

BACKGROUND

When a physician-directed antibiotic-loaded polymethylmethacrylate (PMMA) bone cement (ALBC) formulation is used in total hip arthroplasties (THAs) and total knee arthroplasties (TKAs), current practice in the United States involves arbitrary choice of the antibiotic loading (herein defined as the ratio of the mass of the antibiotic added to the mass of the cement powder). We suggest there is a need to develop a rational method for determining this loading.

QUESTIONS/PURPOSES

We propose a new method for determining the antibiotic loading to use when preparing a physician-directed ALBC formulation and illustrate this method using three in vitro properties of an ALBC in which the antibiotic was daptomycin.

MATERIALS AND METHODS

Daptomycin was blended with the powder of the cement using a mechanical mixer. We performed fatigue, elution, and activity tests on three sets of specimens having daptomycin loadings of 2.25, 4.50, and 11.00 wt/wt%. Correlational analyses of the results of these tests were used in conjunction with stated constraints and a nonlinear optimization method to determine the daptomycin loading to use.

RESULTS

With an increase in daptomycin loading, the estimated mean fatigue limit of the cement decreased, the estimated elution rate of the antibiotic increased, and the percentage inhibition of staphylococcal growth by the eluate remained unchanged at 100%. For a daptomycin-loaded PMMA bone cement we computed the optimum amount of daptomycin to mechanically blend with 40 g of cement powder is 1.36 g.

CONCLUSIONS

We suggest an approach that may be used to determine the amount of antibiotic to blend with the powder of a PMMA bone cement when preparing a physician-directed ALBC formulation, and highlighted the attractions and limitations of this approach.

CLINICAL RELEVANCE

When a physician-directed ALBC formulation is selected for use in a TKA or THA, the approach we detail may be employed to determine the antibiotic loading to use rather than the empirical approach that is taken in current clinical practice.

1H and13C NMR Chemical Shifts of Methacrylate Molecules Associated with DMPC and/or DPPC Liposomes

In the light of recent developments, changes in (1)H and (13)C NMR chemical shifts of methacrylate molecule associated with DMPC (L-alpha dimyristoylphosphatidylcholine) or DPPC (L-alpha-dipalmitoylphosphatidylcholine) liposomes as a model for mimic native lipid bilayers were studied at 30, 37, and 52 degrees C. The chemical shifts of 3Ha, 3C, and 4C resonances in methacrylates (see Fig. 2) were greatly shifted higher field, suggesting the methacrylate molecule-lipid bilayer interaction. Comparison of the findings with methyl methacrylate (MMA), ethylene dimethacrylate (EDMA), and triethyleneglycol dimethacrylate (TEGDMA) revealed that the interaction of dimethacrylates (EDMA, TEGDMA) was greater than monomethacrylate, MMA. Their interaction with DMPC liposomes was also judged by a differential scanning calorimetry (DSC), indicating that the interaction was characterized by decreasing the enthalpy, entropy, and transition co-operativity. The evidence of the upfield NMR-shifts for methacrylate molecules was also judged by the descriptors such as the reactivity (HOMO-LUMO energy) and the electrostatic function (partial charges) between methacrylate molecules and DPPC, calculated by a PM 3 semiempirical MO method. The upfield NMR shifts were considerably well interpreted from the descriptors. NMR screening technique in methacrylates to phospholipid targets would be highly valuable in biomaterial developments. Figure 2 Changes in (1)H and (13)C NMR chemical shifts of methacrylate molecule associated with DMPC or DPPC liposomes. DMPC liposomes/MMA (1:1, molar ratio) and DMPC/TEGDMA (1:1) liposomes were measured at 30 degrees C. In DPPC liposome system, the rippled gel phase was measured at 30 degrees C, whereas the liquid crystalline phase for MMA and for both EDMA and TEGDMA were measured at 52 degrees C and 37 degrees C, respectively.

Foot and ankle reconstruction after blast injuries

Foot and ankle reconstruction following blast trauma is particularly challenging based on the devastating soft tissue injuries associated with open comminuted fractures. Considering the difficulties encountered in reconstruction, the functional limitations associated with many salvaged limbs, and the superior performance of contemporary prosthetics, many injured service members may benefit more from below knee amputation than from limb salvage. Limb salvage of blast-injured extremities is a multidisciplinary effort directed toward eradication of infection, treatment of soft tissue and bone defects, and management of late reconstructive procedures. External ring fixators have an important and expanding role in the treatment algorithm.