The initial rate of the polymerization of methyl acrylate photoinitiated by Cdimethylamino-4'-isopropylbenzophenone (2) varies linearly with monomer concentration and the square-root of light intensity. For small absorbances, the initial polymerization rate, %, varies linearly with the square-root of the photoinitiator concentration. For high absorbance values, I$ is independent of the photoinitiator concentration in a well-stirred system and decreases as the photoinitiator concentration increases in an unstirred system. This marked difference between the polymerization kinetics in well-stirred and unstirred systems is discussed. The ratio of the propagation rate constant and the square-root of the termination rate constant, $,/&I/*, and the quantum yield of photoinitiation were determined and related to the results previously obtained in a study on the photoreactivity of 2.Materials: Methyl acrylate (MA) from Fluka A 0 was washed 3 times with portions of 10 v01.-% aqueous sodium hydroxide to remove the inhibitor and then 3 times with distilled water. The monomer was dried over anhydrous MgSO, and then distilled under reduce pressure before using. 4-Dirnethylamino-4'-isopropylbenzophenone (2) was prepared according to the method described in ref.'). Benzene (fluorescence grade from Carlo Erba) was used without further purification.Polymerizution procedure: The required amounts of monomer, solvents and photoinitiator were charged into a dilatometer which was degassed under vacuum by the conventional freezeand-thaw technique and sealed off under vacuum (lo-, mmHg). The dilatometer, being constructed by attaching two capillary branches (internal diameter: 0,s mm) to a cylindrical reaction vessel (internal diameter: 2 cm; volume: 13 cm'), was placed into a constant temperature bath in which the cylindrical reaction vessel fitted perfectly into the space of the metallic base of the bath, provided with two parallel quartz windows. The bath was placed on an optical bench, including a Hg-He lamp (200 W Hanovia 901B1), quartz lens, and interference 365 nm filter (International Light NB-365). A radiometer was placed immediately behind the second quartz window which allowed changes in the light intensity to be measured. Aberchrome 540 (Edward Davis Chemical Laboratories) actinometry was used to relate the digital display of the radiometer to an absolute value for the number of incident quanta per unit time'). The polymerizations were carried out to low conversion (2-4%) and invariably at 30 f 0,Ol 'C; the reaction mixture in each run was removed from the dilatometer and the polymer precipitated into cold methanol. The polymer, isolated by filtration, was washed several times with methanol and then dried at 40 "C under vacuum. The rates of all photoinitiated polymerizations were corrected to allow for the changes from run to run of the incident light intensity, assuming in all cases a square-root dependence on the intensity.Viscosity measurements: Viscosity measurements were performed in a Ubbelohde viscometer at 30°C with b...
Fibrosis remains a significant cause of failure in implanted biomedical devices and early absorption of proteins on implant surfaces has been shown to be a key instigating factor. However, lipids can also regulate immune activity and their presence may also contribute to biomaterial‐induced foreign body responses (FBR) and fibrosis. Here it is demonstrated that the surface presentation of lipids on implant affects FBR by influencing reactions of immune cells to materials as well as their resultant inflammatory/suppressive polarization. Time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS) is employed to characterize lipid deposition on implants that are surface‐modified chemically with immunomodulatory small molecules. Multiple immunosuppressive phospholipids (phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, and sphingomyelin) are all found to deposit preferentially on implants with anti‐FBR surface modifications in mice. Significantly, a set of 11 fatty acids is enriched on unmodified implanted devices that failed in both mice and humans, highlighting relevance across species. Phospholipid deposition is also found to upregulate the transcription of anti‐inflammatory genes in murine macrophages, while fatty acid deposition stimulated the expression of pro‐inflammatory genes. These results provide further insights into how to improve the design of biomaterials and medical devices to mitigate biomaterial material‐induced FBR and fibrosis.
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