Biomedical subjects

Michael J Cima

Publications and source records attributed to Michael J Cima.

22 records · Page 2Linked to original sources

PubMed2002

Iterative high-throughput polymorphism studies on acetaminophen and an experimentally derived structure for form III.

Three crystal forms of acetaminophen were prepared and characterized using a newly developed high-throughput crystallization platform, CrystalMax. The platform consists of design software, robotic sample dispensing and handling, and high-throughput microanalytics and is capable of running thousands of crystallizations in parallel using several different methods to drive supersaturation and subsequent crystallization. Additionally, structural models of the elusive third form of acetaminophen will be discussed on the basis of powder X-ray diffraction data. One structure suggested has a bilayer motif, held together by O-H...O(H) hydrogen bonds, and helps explain the difficulty associated with preparing this form from solution.

Acetaminophen↗

PubMed2002

Spreading and infiltration of inkjet-printed polymer solution droplets on a porous substrate.

Simultaneous spreading and infiltration of inkjet-printed droplets has been studied. Small (54- and 63-microm diameter) droplets of an aqueous polymer solution (2.4 vol% polyacrylic acid, PAA, MW 60,000) were deposited on high green density porous ceramic beds, and the wetting-induced spreading and infiltration of the droplets were characterized. The time scales for spreading and infiltration were comparable (approximately milliseconds), resulting in interruption of the spreading prior to completion by infiltration of the liquid into the powder bed, a situation that has received little treatment in the literature. The infiltration time was varied by changing the pore size (via particle size) in the powder bed, and it was confirmed that slower infiltration resulted in greater spreading of the liquid. The spreading and infiltration of the droplet were modeled to examine the coupling between the two processes and allow prediction of the maximum extension of the droplet as a function of the powder bed particle size. The liquid spreading was found to follow r(t)=a(b+t)(n) behavior, and the effect of particle size on infiltration time was used to predict the point at which spreading ceases due to infiltration for various particle sizes.

Journal Article↗

PubMed2002

Surface adsorption effects in the inkjet printing of an aqueous polymer solution on a porous oxide ceramic substrate.

The inkjet printing of a polymeric solution into a porous substrate was studied, with the focus on phenomena occurring within the pore space during infiltration. Lines of aqueous polyacrylic acid (PAA) solution were printed onto the surface of porous, high-green-density ceramic powder beds. The PAA is a binder for the ceramic particles, allowing removal of the printed line structure ("primitive") and characterization of the extent of polymer penetration. Large differences in cross section of the retrieved printed structure were observed between ceramic systems and for different specific surface area powders. A mechanism for "filtration" of the polymer by adsorption onto the ceramic particle surfaces during infiltration was proposed. The adsorption of PAA onto Al2O3, SiO2, and TiO2 was characterized via adsorption isotherms, and the trend of primitive cross section with PAA adsorption was consistent with the filtration hypothesis, as was the variation with powder-specific surface area. These results can be generalized to other systems where a solution is inkjet printed onto a porous substrate (e.g., inks on plain paper, porous coated papers, etc.) Utilization of the adsorption effects may allow confinement of the solute molecules (e.g., colorant) to a small region near the substrate surface.

Journal Article↗

PubMed2002

Carbon dioxide extraction of residual chloroform from biodegradable polymers.

Biodegradable polymeric devices for drug delivery and tissue engineering are often fabricated with the use of organic solvents and may still contain significant amounts of solvent (> 1 wt%) even after aggressive vacuum drying. This excess solvent can interfere with tissue response and the mechanical properties of the devices. The aim of this article is to demonstrate that liquid CO(2) extraction can be used to reduce residual solvent in dense poly(L-lactide-co-glycolide) devices to 50 ppm relatively quickly and with minimal changes in architecture under some conditions. Two liquid CO(2) extraction systems were developed to examine the removal of residual solvents from bar-shaped PLGA devices: (1) a low-pressure (1400 psi) batch system, and (2) a high-pressure (5000 psi) continuous-flow system. Eight hours of extraction in the high-pressure system reduced residual chloroform in 3 mm thick bars below the 50-ppm target. A simple Fickian diffusion model was fit to the extraction results. Diffusion coefficients ranged from 1.10 x 10(-6) cm(2)/s to 2.64 x 10(-6) cm(2)/s. The model predicts that approximately 1 h is needed to dry 1-mm bars to chloroform levels below 50 ppm, and 7 h are needed for 3 mm thick bars. The micro- and macroarchitectures of porous PLGA scaffolds created by particulate leaching were not significantly altered by CO(2) drying if the salt used to make the pores was not removed before drying.

Absorbable Implants↗