Thermal decomposition of generation-4 polyamidoamine dendrimer films: decomposition catalyzed by dendrimer-encapsulated Pt particles.

The thermal decomposition of hydroxyl-terminated generation-4 polyamidoamine dendrimer (G4OH) films deposited on Au surfaces has been compared with decomposition of the same dendrimer encapsulating an approximately 40-atom Pt particle (Pt-G4OH). Infrared absorption reflection spectroscopy studies showed that, when the films were heated in air to various temperatures up to 275 degrees C, the disappearance of the amide vibrational modes occurred at lower temperature for the Pt-G4OH film. Dendrimer decomposition was also investigated by thermogravimetric analysis (TGA) in both air and argon atmospheres. For the G4OH dendrimer, complete decomposition was achieved in air at 500 degrees C, while decomposition of the Pt-G4OH dendrimer was completed at 400 degrees C, leaving only platinum metal behind. In a nonoxidizing argon atmosphere, a greater fraction of the G4OH decomposed below 300 degrees C, but all of the dendrimer fragments were not removed until heating above 550 degrees C. In contrast, Pt-G4OH decomposition in argon was similar to that in air, except that decomposition occurred at temperatures approximately 15 degrees C higher. Thermal decomposition of the dendrimer films on Au surfaces was also studied by temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) under ultrahigh vacuum conditions. Heating the G4OH films to 250 degrees C during the TPD experiment induced the desorption of large dendrimer fragments at 55, 72, 84, 97, 127, 146, and 261 amu. For the Pt-G4OH films, mass fragments above 98 amu were not observed at any temperature, but much greater intensities for H(2) desorption were detected compared to that of the G4OH film. XPS studies of the G4OH films demonstrated that significant bond breaking in the dendrimer did not occur until temperatures above 250 degrees C and heating to 450 degrees C caused dissociation of C=O, C-O, and C-N bonds. For the Pt-G4OH dendrimer films, carbon-oxygen and carbon-nitrogen bond scission was observed at room temperature, and further decomposition to atomic species occurred after heating to 450 degrees C. All of these results are consistent with the fact that the Pt particles inside the G4OH dendrimer catalyze thermal decomposition, allowing dendrimer decomposition to occur at lower temperatures. However, the Pt particles also catalyze bond scission within the dendrimer fragments so that decomposition of the dendrimer to gaseous hydrogen is the dominant reaction pathway compared to desorption of the larger dendrimer fragments observed in the absence of Pt particles.

Dimethyl methylphosphonate decomposition on Cu surfaces: supported Cu nanoclusters and films on TiO2(110).

The thermal decomposition of dimethyl methylphosphonate (DMMP), which is a simulant molecule for organophosphorus nerve agents, has been investigated on Cu clusters as well as on Cu films deposited on a TiO(2)(110) surface. Scanning tunneling microscopy studies were conducted to characterize the cluster sizes and surface morphologies of the deposited Cu clusters and films. Temperature-programmed desorption experiments demonstrated that the surface chemistry of DMMP is not sensitive to the size of the Cu clusters over the range studied in this work. DMMP reaction on an annealed 40 monolayer Cu film resulted in the desorption of H(2), methane, methyl, formaldehyde, methanol, and molecular DMMP, and reaction on the small (4.4 +/- 0.9 nm diameter, 1.8 +/- 0.6 nm height) and large (10.7 +/- 1.9 nm diameter, 4.8 +/- 1.0 nm height) Cu clusters generated similar products. Formaldehyde and methane production is believed to occur via a methoxy intermediate on the Cu surface. These products are favored on the higher coverage Cu films that completely cover the TiO(2) surface since competing reaction pathways on TiO(2) are suppressed. X-ray photoelectron spectroscopy studies showed that DMMP begins to decompose on the Cu clusters upon adsorption at room temperature and that atomic carbon, atomic phosphorus, and PO(x) remain on the surface after DMMP decomposition.

Facial function in hearing preservation acoustic neuroma surgery.

OBJECTIVE: To determine if facial function is worse after hearing preservation acoustic neuroma surgery (retrosigmoid and middle fossa) than in translabyrinthine surgery. DESIGN: Retrospective medical record review. SETTING: Private neuro-otology subspecialty practice of patients operated on in a tertiary care hospital. PATIENTS: This study evaluated 315 consecutive acoustic neuroma surgical procedures between April 1989 and July 1998. A total of 209 translabyrinthine procedures and 106 hearing preservation surgical procedures were performed. The hearing preservation procedures were equally divided between retrosigmoid (n = 48) and middle fossa (n = 58) procedures. METHODS: Medical records were reviewed and tabulated for tumor size, surgical approach, and House-Brackmann facial function grade at short-, intermediate-, and long-term intervals. RESULTS: Postoperative facial function in hearing preservation surgical procedures at short- and long-term follow-up was not worse than facial function after translabyrinthine surgical procedures in comparably sized tumors. CONCLUSION: Concern about postoperative facial function should not be the deciding factor in selecting hearing preservation vs nonhearing preservation acoustic neuroma surgery.

Stability of somatropin stored in plastic syringes for 28 days.

The stability of somatropin stored in two types of plastic syringes was studied. Reconstituted somatropin at high (3.33-mg/mL) and low (1.0-mg/mL) concentrations was stored in polypropylene and propylene-ethylene copolymer syringes at 2-8 degrees C for 28 days. The contents of all syringes were analyzed immediately and at 7, 14, 21, and 28 days by high-performance liquid chromatography for purity, potency, and preservative (m-cresol) content; pH, physical appearance, clarity, and preservative effectiveness were analyzed at the same times. Glass vials of somatropin reconstituted with diluent served as controls. Somatropin did not show significant losses in purity or potency during the 28-day study. m-Cresol concentrations decreased in both types of plastic syrings, more so in the polypropylene syringes, but remained in excess of the minimum required to pass the USP test of preservative effectiveness. On average, the contents of the propylene-ethylene copolymer syringes had greater turbidity than the contents of the polypropylene syringes and, after 21 days, had an unacceptable level of turbidity. No visible particulates were present except at 28 days in high-concentration samples stored in propylene-ethylene copolymer syringes. Somatropin 3.33 and 1.0 mg/mL was stable in polypropylene syringes for up to 28 days and in propylene-ethylene copolymer syringes for up to 14 days when stored at 2-8 degrees C.

Rapid verification of disulfide linkages in recombinant human growth hormone by tandem column tryptic mapping.

An automated tryptic mapping method was developed for characterization of disulfide linkages in recombinant human growth hormone (rhGH). The hormone was trypsin digested and the peptide fragments concentrated by eluting rhGH through an immobilized trypsin column and transferring the peptides directly to a reversed-phase liquid chromatography (RP-LC) column where they were collected. Reaction time was controlled by the flow-rate. Following tryptic digestion of a sample, the immobilized enzyme column was uncoupled from the flow train by a switching valve and the RP-LC column eluted with a solvent gradient ranging from 0.1% trifluoroacetic acid (TFA) with 1% acetonitrile (ACN) to ACN with 0.1% TFA and 5% water. This two-step mapping process was achieved within 2 h on both native and reduced rhGH samples. The chromatographic elution position and mass spectra matrix-assisted laser desorption ionization time-of-flight mass spectrometry of native rhGH and sulfur-containing peptides were determined with standards. Standards of the individual sulfhydryl (-SH) containing peptides and all possible disulfide linked peptides that could result from coupling the -SH peptides in disulfide linkages were obtained by synthesis and chromatographic purification. This approach allowed the chromatographic elution position of all possible mismatched disulfide containing peptides to be established and samples of rhGH to be examined for improper folding.

Bone cement reconstruction of the ossicular chain: a preliminary report.

OBJECTIVE: To determine the feasibility and efficacy of using a bone cement, Oto-Cem, to reconstruct the ossicular chain. STUDY DESIGN: Prospective clinical trial on nine consecutively chosen adult patients with ossicular chain defects. PATIENTS AND SETTING: Nine patients with ossicular chain defects involving the long process of the incus were treated at the Carolina Ear and Hearing Clinic. The ossicular chain was reconstructed using bone cement by itself or in conjunction with a stapes prosthesis. MAIN OUTCOME MEASURES: Preoperative audiograms were compared with audiograms 3, 6, and 12 months after reconstruction. RESULTS: There was a mean pure-tone average (PTA) improvement of 15 dB in patients undergoing incus to stapes suprastructure reconstruction with the bone cement. The incus to mobile footplate reconstruction (using a stapes prosthesis attached to the newly reconstructed incus) resulted in a 34-dB PTA postoperative improvement. Two of the three patients with incus to oval window repairs experienced a 10-dB improvement in PTA. One of the three patients experienced a loss in speech discrimination and a 2-dB loss in PTA. CONCLUSIONS: Despite the limited number of patients, this preliminary study demonstrates the effectiveness of Oto-Cem in reconstructing a foreshortened incus. There was a substantial hearing improvement in all but one patient in the incus to stapes or the incus to footplate categories.

Technical refinements in retraction for middle fossa surgery.

OBJECTIVE: This report describes an alternative technique for exposure of the floor of the middle fossa. STUDY DESIGN: Descriptive review of alternative middle fossa retraction techniques on a retrospective case series. SETTING: Tertiary referral center. PATIENTS: Patients undergoing middle fossa or combined petrosal craniotomy were studied. INTERVENTIONS: Dural elevation was carried anteriorly past the middle meningeal artery to permit separation of the dura from connective tissue over the Gasserian ganglion. With the dural release, flexible spatula retractors (Fukushima) can be used. RESULTS: The advantages of this technique are 1) this system is "low profile," with the back of the retractor posing no obstruction to vision or angle of instrument manipulation; 2) the anterior dural release permits extensive exposure with less force than is necessary when dural attachments to the trigeminal nerve remain intact; and 3) anterior exposure of the clivus and petrous apex is achieved without the need for transection of V3 (3rd division fifth cranial nerve). CONCLUSIONS: The authors find these refinements of practical benefit for breadth of exposure, visibility, and room for instrumentation during middle fossa surgery.

Fatal meningitis and brain abscess resulting from foreign body-induced otomastoiditis.

Herein we report what we believe to be the only published case of an intracranial complication of otomastoiditis resulting from foreign-body material. The presence of a foreign body must be ruled out in any chronically draining ear, and all foreign material must be removed. The key to minimizing the morbidity of complications of infectious ear disease is early recognition and treatment. Early symptoms of complication include vertigo, new onset of headache or otalgia, or worsening headache or otalgia. Fever, malodorous ear drainage, and the presence of granulation tissue are warming findings. A high index of suspicion of infectious complications must be maintained in evaluating all patients with ear disease.

Cerebellopontine angle tumor outcomes in patients with hazardous occupations.

Cerebellopontine angle (CPA) tumor surgery can produce a spectrum of sensory and motor deficits that can alter a patient's lifestyle and occupation. An important consideration is whether patients can return to full occupational status especially when hazardous duties are involved. Outcome data in CPA tumor surgery usually report that most patients are able to return to preoperative function; however, whether these patients can return to hazardous duties is not specified. A retrospective study of 380 consecutive, operated CPA tumor patients was performed and 37 were identified who engaged in hazardous occupations including active military service, working at dangerous heights, piloting jet aircraft, aircraft navigating, and factory work with high-impact machinery. Overall, patients were able to resume full-time work in their previous occupations and 86% of patients reported that they were able to resume hazardous duties. CPA tumor surgery is compatible with continued full occupational duties after surgery, even for patients employed in hazardous situations.

Surgical treatment of uncompensated vestibular disease.

Uncompensated vestibular disease is a serious, disabling disorder that substantially alters quality of life. Fortunately, most dizziness and vestibular disorders are managed conservatively or with medications and are self-limited. When medical management is unsuccessful, however, there is a wide array of surgical interventions that can significantly improve the symptoms. This article reviews the broad array of surgical techniques available for managing dizziness.

Individualizing hearing preservation in acoustic neuroma surgery.

Surgical series of hearing preservation in acoustic neuroma usually emphasize a team's results with one particular technique. This report reviews acoustic neuroma outcomes of individualizing the surgical approach to patient and tumor characteristics. This study reviews 60 consecutive hearing preservation acoustic neuroma surgeries in a total series of 330 acoustic neuromas. Tumor sizes ranged from 0.3 to 4 cm in patients ranging from 23 to 74 years of age. Middle fossa surgery was performed in 57%, retrosigmoid in 43%. Overall, measurable hearing was preserved in 77%, and useful hearing in 67%. Among middle fossa cases, 85% had measurable and 74% had useful hearing. Among retrosigmoid surgeries, 65% had measurable hearing and 58% had useful hearing. Overall, long-term facial nerve function was excellent (grade I or II) in 90% and poor (grade V or VI) in 2%. There was one case of bacterial meningitis (2%), and cerebrospinal fluid leaks requiring surgery occurred in four patients (7%). The hearing preservation and other outcome parameters in this series compare favorably with other reports. We believe that individualizing the surgical approach to the patient's tumor characteristics and clinical features contributed to the high rate of hearing preservation.

The learning curve for acoustic tumor surgery.

Although operative experience is considered to be critically important in the surgical management of acoustic tumors, little objective evidence substantiates this claim. The present study was undertaken to determine whether a learning curve exists for acoustic tumor surgery. The first 96 acoustic tumor patients managed surgically by a new neurotologic team were retrospectively reviewed. A significant improvement (P<.0003; F=6.32) in the ability to achieve good (grade II or better) postoperative facial nerve function was identified. Improving trends for complete resection rate and hearing preservation were documented, and the incidence of cerebrospinal fluid (CSF) leaks declined; however, statistical significance was not achieved. For postoperative facial nerve function, approximately 60 cases were necessary before the new team achieved results similar to those of highly experienced surgeons. The frequencies of complete resection, CSF leaks, hearing preservation, stroke, and mortality were comparable to those of experienced neurotologic teams. The findings of this study may have implications for both patient care and physician training.

An implant of a composite of bovine bone morphogenetic protein and plaster of paris for treatment of femoral shaft nonunions.

Sixteen patients with nonunion of femoral shaft fractures were treated by implantation of a composite of bovine bone morphogenetic protein and plaster of Paris (bBMP/PLP). There was an average of 1.5 surgical procedures per patient attempting union prior to bBMP/PLP implantation The implant was prepared in an aggregate of 50 mg bBMP in 1 gram of plaster of Paris. It was implanted directly to fill the fracture gaps and packed around the fracture lines. Seventeen operations were done on the 16 patients. Union was obtained in 16 of the 17 operations. The average time of union for the 16 successful operations was 5.7 months. There were no significant clinically manifested postoperative complications.

Ossiculoplasty with polymaleinate ionomeric prosthesis.

With the continued concern over the possible transmission of viral infections through homologous middle ear implants, there is increasing pressure to develop a truly biocompatible alloplastic middle ear prosthesis. The polymaleinate ionomer, which has been used in dentistry as a filling and luting material for more than 15 years, has recently been used to construct total and partial ossicular replacement prostheses. In an attempt to evaluate these new implants, a multicenter prospective clinical trial was initiated. To date, 92 patients have undergone implantation. The follow-up interval ranged from 3 months to 22 months. Although it is premature to discuss the long-term results, the preliminary surgical experience and audiometric data with these implants are reviewed. From a surgical perspective, the ionomeric prostheses were easily contoured with a diamond burr and were not prone to shattering. Preliminary follow-up audiometric data were available on 80 patients (59 partial ossicular replacement prostheses and 21 total ossicular replacement prostheses). Of the 59 partial ossicular replacement prostheses the air-bone gaps (average of 500 Hz, 1 kHz, 2 kHz and 3 kHz) were as follows: 0 dB to 10 dB, 15 (25%) of 59; 11 dB to 20 dB, 20 (34%) of 59; 21 dB to 30 dB, 11 (19%) of 59; and greater than 30 dB, 13 (22%) of 59. Of the 21 total ossicular replacement prostheses the air-bone gaps were as follows: 0 dB to 10 dB, 6 (29%) of 21; 11 dB to 20 dB, 6 (29%) of 21; 21 dB to 30 dB, 5 (24%) of 21; and greater than 30 dB, 4 (19%) of 21.

A nonprescription cerumenolytic.

Cerumen impaction and removal is a very common otologic problem. The perfect cerumenolytic agent has yet to be developed. After years of trying multiple different cerumenolytics without satisfaction, a stool softener, docusate sodium, has become our agent of choice. A commonly used stool softener, it is widely available without prescription. It is a highly effective cerumenolytic, but remains relatively unknown in this capacity.

Management of head injury. The skull and meninges.

Injuries to the skull and meninges frequently occur concomitantly with head trauma. Controversies over the operative versus nonoperative management of depressed skull fractures, frontal sinus fractures, cerebrospinal fluid leaks, and cranial nerve injuries are discussed in this article.