PubMed · 9785730
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L G Meshel, W Jessen. 1998. Ocular prostheses.. https://pubmed.ncbi.nlm.nih.gov/9785730/
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A new positively charged, submicronized fat emulsion with appropriate stability during the autoclaving process was developed. Only the emulsions prepared with a combination of ABA block co-polymer (F68) and chitosan were stable enough to resist the thermic shock induced by autoclaving sterilization. The results indicate that a mixed film consisting of the ABA block co-polymer and chitosan molecules was formed at the o/w interface with an overall positive surface charge. Conversely, a combination between chitosan with phospholipids and/or with a mixture of phospholipids with ABA block co-polymer showed a phase separation during autoclaving. A chitosan type with a low viscosity was used which was intended for a possible use in the ocular and parenteral application. An experimental factorial design 32 was used to investigate the effect of chitosan and F68 concentrations on the physicochemical properties of the system and consequently their influence on the stability of emulsions during autoclaving. Both size and surface charge of emulsions were significantly affected as a function of the chitosan concentration. Formulation with a mean particle size ranging from 125 to 130 nm and with a positive surface charge of 20-23 mV was achieved. Moreover, the chitosan emulsions were autoclaved without a significant change in their particle size. However, increasing the concentration of chitosan needs a higher amount of F68 in order to achieve stable emulsions during autoclaving. This may be due to the interaction between the positively-charged chitosan and the negatively-charged free fatty acids, which are contained in the oil phase (castor oil).
STUDY DESIGN: A prospective study of tissue surrounding spinal instrumentation was performed using histologic and chemical analysis. OBJECTIVES: To identify and quantify the amount of metal debris generated by titanium pedicle screw instrumentation and to evaluate the histologic response in the spinal tissues. SUMMARY OF BACKGROUND DATA: Microscopic metal particles from the soft tissue surrounding joint arthroplasties have been shown to activate a macrophage response that leads to bone resorption and increased inflammation. The use of titanium spinal implants for spine surgery projects the possibility of generating wear debris in the spine. METHODS: Nine patients with titanium instrumentation from a prior lumbar decompression and fusion procedure who were undergoing reoperation were entered into this study. Tissue samples were collected from areas near the pedicle screw-rod junction, the scar tissue overlying the dura, and the pedicle screw holes. Metal levels for titanium were determined by electrothermal atomic absorption spectroscopy, and histologic analysis was performed by light and electron microscopy. RESULTS: Tissue concentrations of titanium were highest in patients with a pseudarthrosis (30.36 micrograms/g of dry tissue). Patients with a solid fusion had low concentrations of titanium (0.586 microgram/g of dry tissue). Standard light microscopy identified metal particles in the soft tissues. Transmission electron microscopy demonstrated macrophages with numerous secondary lysosomes containing electron-dense bodies and collagenous stroma with electron-dense rod-like profiles consistent with metal debris. CONCLUSIONS: Wear debris is generated by the use of titanium spinal instrumentation in patients with a pseudarthrosis. These particles activate a macrophage cellular response in the spinal tissues similar to that seen in surrounding joint prostheses. Patients with a solid spinal fusion have negligible levels of particulate matter.
Poly(d,l-lactic-co-glycolic acid) (PLGA) was chemically conjugated to a model drug, N-(9-fluorenylmethoxycarbonyl-N-tert-butoxycarbonyl-l-tryptophan (Fmoc-Trp(Boc)) via an ester linkage. Various coupling reaction conditions were tested to optimize the conjugation process between a hydroxyl terminal group of PLGA and a carboxylic acid group of Fmoc-Trp(Boc). Two different lactic/glycolic acid compositions of PLGA (50/50 and 75/25) were used for the conjugation. The Fmoc-Trp(Boc)-PLGA conjugates were formulated into microspheres by a solvent evaporation technique for controlled release of Fmoc-Trp(Boc) over an one month period. A linear constant release of Fmoc-Trp(Boc) and its water-soluble PLGA oligomer conjugates was observed over an extended period without any initial burst effect, while unconjugated Fmoc-Trp(Boc) encapsulated within microspheres exhibited a rapid release profile. In addition, Fmoc-Trp(Boc) release rate solely depended on the PLGA composition that affected polymer degradation rate. The release rate of Fmoc-Trp(Boc) conjugated with fast degrading 50/50 PLGA was more rapid than that conjugated with relatively slow degrading 75/25 PLGA. This study demonstrates that PLGA-drug conjugation approach is a new and novel strategy to control the drug release rate from PLGA microspheres by utilizing the chemical degradation rate of PLGA backbone.