External light guidance for percutaneous dilatational tracheotomy.

BACKGROUND: Percutaneous dilatational tracheotomy (PDT) is considered a safe technique; however, there is still room for improvement. We present our initial experience with an external white light guide to position the endotracheal tube and guide needle placement during PDT. METHODS: This is a retrospective series of 15 consecutive patients undergoing external light-guided PDT. A white light source was placed on the anterior trachea wall externally and the transmitted light was identified in the tracheal lumen with a bronchoscopic to predict the needle entrance point. RESULTS: The transmitted light was rapidly identified in all 15 patients, facilitated endotracheal tube tip placement in the subglottis in approximately 10 seconds in 13 of 15 patients, and predicted needle penetration into the trachea within 1 to 2 mm of the external light in all patients. CONCLUSIONS: External light guidance facilitates rapid, accurate placement of the needle through the tracheal wall and can reduce surgeon anxiety, especially in teaching situations.

Immobilized sonic hedgehog N-terminal signaling domain enhances differentiation of bone marrow-derived mesenchymal stem cells.

The signaling domain of Sonic hedgehog (Shh), a potent upstream regulator of cell fate that has been implicated in osteoblast differentiation from undifferentiated mesenchymal cells in its endogenous form, was investigated in an immobilized form as a means for accelerating differentiation of uncommitted cells to the osteoblast phenotype. A recombinant cysteine-modified N-terminal Shh (mShh) was synthesized, purified, and immobilized onto interpenetrating polymer network (IPN) surfaces also grafted with a bone sialoprotein-derived peptide containing the Arg-Gly-Asp (RGD) sequence (bsp-RGD (15)), at calculated densities of 2.42 and 10 pmol/cm2, respectively. The mitogenic effect of mShh was dependent on the mode of presentation, as surfaces with immobilized mShh and bsp-RGD (15) had no effect on the growth rate of rat bone marrow-derived mesenchymal stem cells (BMSCs), while soluble mShh enhanced cell growth compared to similar surface without mShh supplementation. In conjunction with media supplemented with bone morphogenetic protein-2 and -4, mShh and bsp-RGD (15)-grafted IPN surfaces enhanced the alkaline phosphatase activity of BMSCs compared with tissue culture polystyrene and bsp-RGD (15)-grafted IPN surfaces supplemented with soluble mShh, indicating enhanced osteoblast differentiation. The adhesive peptide bsp-RGD (15) was necessary for cell attachment and proliferation, as well as differentiation in response to immobilized mShh. The addition of immobilized Shh substantially improved the differentiation of uncommitted BMSCs to the osteoblast lineage, and therefore warrants further testing in vivo to examine the effect of the stated biomimetic system on peri-implant bone formation and implant fixation.

The effect of enzymatically degradable IPN coatings on peri-implant bone formation and implant fixation.

Short-term osseointegration of orthopedic implants is critical for the long-term stability of the implant-bone interface. To improve initial implant stability, one strategy under consideration involves the presentation of adhesion ligands on the implant surface to stimulate bone regeneration in the peri-implant region. To assess the relative effects of implant surface chemistry and topography on osseointegration within the rat femoral ablation implant model, a nonfouling, enzymatically degradable interpenetrating polymer network (edIPN) of poly(AAm-co-EG/AAc) amenable to presenting the cell signaling domain Arg-Gly-Asp (RGD), was developed. Moderate enhancement of peri-implant bone formation was found after 28 days using the edIPN without peptide modification (p = 0.032). However, no data supported a benefit of peptide modification, as bone-implant contact, normalized bone volume and normalized fixation strength was equivalent or poorer than dual acid-etched (DAE) treated implants after 28 days. Surface topography was determined to be the dominant factor in modulating osseointegration, as DAE implants produced equivalent roughness-normalized fixation strength versus previously reported data on plasma-sprayed hydroxyapatite/tricalcium phosphate-coated implants (Barber et al., J Biomed Mater Res A, forthcoming). An ideal osseointegrated implant will require optimization of all three aforementioned parameters, and may take the form of biomolecule delivery from thin degradable polymer networks.

Peri-implant bone formation and implant integration strength of peptide-modified p(AAM-co-EG/AAC) interpenetrating polymer network-coated titanium implants.

Interpenetrating polymer networks (IPNs) of poly (acrylamide-co-ethylene glycol/acrylic acid) functionalized with an -Arg-Gly-Asp- (RGD) containing 15 amino acid peptides, derived from rat bone sialoprotein (bsp-RGD(15), were grafted to titanium implants in an effort to modulate bone formation in the peri-implant region in the rat femoral ablation model. Bone-implant contact (BIC) and bone formation within the medullary canal were determined using microcomputed tomography at 2 and 4 weeks postimplantation. BIC for bsp-RGD(15)-IPN implants was enhanced relative to hydroxyapatite tricalcium phosphate (HA-TCP) coated implants, but was similar to all other groups. Aggregate bone formation neither indicated a dose-dependent effect of bsp-RGD(15) nor a meaningful trend. Mechanical testing of implant fixation revealed that only the HA-TCP coated implants supported significant (>1 MPa) interfacial shear strength, despite exhibiting lower overall BIC, an indication that bone ingrowth into the rougher coating was the primary mode of implant fixation. While no evidence was found to support the hypothesis that bsp-RGD(15)-modified IPN coated implants significantly impacted bone-implant bonding, these results point to the lack of correlation between in vitro studies employing primary osteoblasts and in vivo wound healing in the peri-implant region.