Biomedical subjects

R F Falk

Publications and source records attributed to R F Falk.

3 recordsLinked to original sources

PubMed1998

Preparation and in vitro characterization of gentamycin-impregnated biodegradable beads suitable for treatment of osteomyelitis.

A new method for preparing poly(L-lactide) (PLA) biodegradable beads impregnated with an ionic aminoglycoside, gentamycin, is described. The process employs hydrophobic ion pairing to solubilize gentamycin in a solvent compatible with PLA, followed by precipitation with a compressed antisolvent (supercritical carbon dioxide). The resulting precipitate is a homogeneous dispersion of the ion-paired drug in PLA microspheres. The microspheres are approximately 1 microm in diameter and can be compressed into beads (3-6 mm in diameter) strung on surgical sutures for implantation. The bead strings exhibit no significant change in release kinetics upon sterilization with a hydrogen peroxide plasma (Ster-Rad). The kinetics of gentamycin release from the PLA beads are consistent with a matrix-controlled diffusion mechanism. While nonbiodegradable poly(methyl methacrylate) (PMMA) beads initially release gentamycin in a similar manner, the drug release from PMMA ceases after 8 or 9 weeks, while the PLA beads continue to release drug for over 4 months. Moreover, only 10% of the gentamycin is released from the PMMA beads, while PLA beads release more than 60% of their load, if serum is present in the release medium. The PLA system displays improved release kinetics relative to PMMA, is biodegradable, is unaltered by gas sterilization, can be used for a range of antibiotics, and can be manipulated without disintegration. These are all desirable properties for an implantable drug delivery system for the prevention or treatment of osteomyelitis.

Absorption↗

PubMed1998

Process variable implications for residual solvent removal and polymer morphology in the formation of gentamycin-loaded poly (L-lactide) microparticles.

PURPOSE: The purpose was to determine the influence of process parameters in the precipitation with a compressed antisolvent (PCA) process on the morphology and residual dichloromethane (DCM) levels in gentamycin-loaded PLA microparticles. METHODS: The three variables studied were the rate of CO2 co-flowed during the polymer and drug post-precipitation, the post-precipitation pure CO2 flush rate, and the post-precipitation CO2 flush volume. Residual DCM levels were determined from headspace gas chromatography-mass spectroscopy (GC-MS) with single ion monitoring. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to estimate the crystallinity within microparticles. DCM was extracted from drug-loaded microparticles by both supercritical CO2 extraction and vacuum drying for up to two days to determine a lower limit for solvent removal. RESULTS: Increasing either the post-precipitations CO2 flow rate or flush volume resulted in lower residual DCM levels in the microparticle. The CO2 co-flow rate showed an opposite trend. Increasing in value resulted in a higher DCM value after precipitation. XRD and DSC analysis on these samples suggest that those produced at lower CO2 co-flow rates have a higher degree of crystallinity, which increases the diffusivity of DCM through the polymer matrix. Finally, samples subjected to extended (48 hr) CO2 extraction resulted in DCM levels on the order of one to three ppm. CONCLUSIONS: Specific PCA process conditions during microparticle formation have a strong influence on the residual solvent levels within the microparticles. Polymer morphology affects the diffusivity of solvent through the polymer matrix, which in turn determines the solvent removal rates.

Gas Chromatography-Mass Spectrometry↗

PubMed1993

The influence of health on family contacts and family feelings in advanced old age: a longitudinal study.

This study provides a longitudinal analysis of the influences of health, age, gender, and socioeconomic status on family contacts and family feelings in a sample of 62 members of the Berkeley Older Generation Study. Stability in family contacts and in family feelings was observed over 14 years of advanced old age. Of the four predictor variables, health and socioeconomic status accounted for the largest proportion of observed variance. Contrary to our hypotheses, study participants in better health had greater amounts of contact with family than did those in poorer health. The former also had more feelings of closeness to family members, a finding that may reflect greater possibilities for reciprocity between elders in good health and their family members.

Activities of Daily Living↗