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Joachim Kohn

Publications and source records attributed to Joachim Kohn.

21 records · Page 2Linked to original sources

Hydrophobic drug delivery by self-assembling triblock copolymer-derived nanospheres.

We describe the synthesis and characterization of a family of biocompatible ABA-triblock copolymers that comprised of hydrophilic A-blocks of poly(ethylene glycol) and hydrophobic B-blocks of oligomers of suberic acid and desaminotyrosyl-tyrosine esters. The triblock copolymers spontaneously self-assemble in aqueous solution into nanospheres, with hydrodynamic diameters between 40 and 70 nm, that do not dissociate under chromatographic and ultracentrifugation conditions. These nanospheres form strong complexes with hydrophobic molecules, including the fluorescent dye 5-dodecanoylaminofluorescein (DAF) and the antitumor drug, paclitaxel, but not with hydrophilic molecules such as fluorescein and Oregon Green. The nanosphere-paclitaxel complexes retain in vitro the high antiproliferative activity of paclitaxel, demonstrating that these nanospheres may be useful for delivery of the hydrophobic drugs.

Antineoplastic Agents↗

Using surrogate modeling in the prediction of fibrinogen adsorption onto polymer surfaces.

We present a Surrogate (semiempirical) Model for prediction of protein adsorption onto the surfaces of biodegradable polymers that have been designed for tissue engineering applications. The protein used in these studies, fibrinogen, is known to play a key role in blood clotting. Therefore, fibrinogen adsorption dictates the performance of implants exposed to blood. The Surrogate Model combines molecular modeling, machine learning and an Artificial Neural Network. This novel approach includes an accounting for experimental error using a Monte Carlo analysis. Briefly, measurements of human fibrinogen adsorption were obtained for 45 polymers. A total of 106 molecular descriptors were generated for each polymer. Of these, 102 descriptors were computed using the Molecular Operating Environment (MOE) software based upon the polymer chemical structures, two represented different monomer types, and two were measured experimentally. The Surrogate Model was developed in two stages. In the first stage, the three descriptors with the highest correlation to adsorption were determined by calculating the information gain of each descriptor. Here a Monte Carlo approach enabled a direct assessment of the effect of the experimental uncertainty on the results. The three highest-ranking descriptors, defined as those with the highest information gain for the sample set, were then selected as the input variables for the second stage, an Artificial Neural Network (ANN) to predict fibrinogen adsorption. The ANN was trained using one-half of the experimental data set (the training set) selected at random. The effect of experimental error on predictive capability was again explored using a Monte Carlo analysis. The accuracy of the ANN was assessed by comparison of the predicted values for fibrinogen adsorption with the experimental data for the remaining polymers (the validation set). The mean value of the Pearson correlation coefficient for the validation data sets was 0.54 +/- 0.12. The average root-mean-square (relative) error in prediction for the validation data sets is 38%. This is an order of magnitude less than the range of experimental values (i.e., 366%) and compares favorably with the average percent relative standard deviation of the experimental measurements (i.e., 17.9%). The effects of each of the user-defined parameters in the ANN were explored. None were observed to have a significant effect on the results. Thus, the Surrogate Model can be used to accurately and unambiguously identify polymers whose fibrinogen absorption is at the limits of the range (i.e., low or high) which is an essential requirement for assessing polymers for regenerative tissue applications.

Adsorption↗

Preliminary development of a novel resorbable synthetic polymer fiber scaffold for anterior cruciate ligament reconstruction.

We are developing novel resorbable fiber-based scaffolds for reconstruction of the anterior cruciate ligament (ACL). For the first time, we report fabrication of fibers from poly(DTE carbonate) polymer. Poly(L-lactic acid) fibers were also fabricated for comparison purposes. The study was performed in three phases. In phase I, first-generation fibers were found to promote tissue ingrowth in a subcutaneous model. In phase II, second-generation fibers were fabricated from poly(DTE carbonate) and poly(L-lactic acid), with diameters of 79 and 72 microm, ultimate tensile strengths of 230 and 299 MPa, moduli of 3.1 and 4.9 GPa, and molecular weights of 65000 and 170000, respectively. These fibers were evaluated on the basis of molecular weight retention, strength retention, and cytocompatibility. After 30 weeks of incubation in phosphate-buffered saline, poly(DTE carbonate) and poly(L-lactic acid) fibers had 87 and 7% strength retention, respectively. Similar trends were observed for molecular weight loss. Fibroblasts attached and proliferated equally well on both scaffold types in vitro. Finally, in phase III, a prototype ACL reconstruction device was fabricated from poly(DTE carbonate) fibers with strength values comparable to those of the normal ACL (57 MPa). Collectively, these data suggest that poly(DTE carbonate) fibers are potentially useful for development of resorbable scaffolds for ACL reconstruction.

Animals↗