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Biomedical subjects

K Kratz

Publications and source records attributed to K Kratz.

17 recordsLinked to original sources
PubMed2006

Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers.

In shape-memory polymers, changes in shape are mostly induced by heating, and exceeding a specific switching temperature, T(switch). If polymers cannot be warmed up by heat transfer using a hot liquid or gaseous medium, noncontact triggering will be required. In this article, the magnetically induced shape-memory effect of composites from magnetic nanoparticles and thermoplastic shape-memory polymers is introduced. A polyetherurethane (TFX) and a biodegradable multiblock copolymer (PDC) with poly(p-dioxanone) as hard segment and poly(epsilon-caprolactone) as soft segment were investigated as matrix component. Nanoparticles consisting of an iron(III)oxide core in a silica matrix could be processed into both polymers. A homogeneous particle distribution in TFX could be shown. Compounds have suitable elastic and thermal properties for the shape-memory functionalization. Temporary shapes of TFX compounds were obtained by elongating at increased temperature and subsequent cooling under constant stress. Cold-drawing of PDC compounds at 25 degrees C resulted in temporary fixation of the mechanical deformation by 50-60%. The shape-memory effect of both composite systems could be induced by inductive heating in an alternating magnetic field (f = 258 kHz; H = 30 kA x m(-1)). The maximum temperatures achievable by inductive heating in a specific magnetic field depend on sample geometry and nanoparticle content. Shape recovery rates of composites resulting from magnetic triggering are comparable to those obtained by increasing the environmental temperature.

Journal Article↗
PubMed2005

Smart implant materials.

The combination of stimuli-sensitive implant materials and minimally invasive surgery techniques is expected to give rise to numerous applications. Biodegradable thermoplastic elastomers are presented here as an example of a group of biodegradable implant materials with shape-memory properties. Their capabilities and use in a smart suture are described.

Absorbable Implants↗
PubMed2000

Nitric oxide synthase distribution in the cat superior colliculus and co-localization with choline acetyltransferase.

Nitric oxide and acetylcholine are important neuromodulators implicated in brain plasticity and disease. We have examined the cellular and fiber localization of nitric oxide in the cat superior colliculus (SC) and its degree of co-localization with ACh using nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry and an antibody to neuronal nitric oxide synthase. ACh was localized using an antibody against choline acetyltransferase. We also made injections of biocytin into the region of the parabrachial brainstem to confirm that this region is a source of nitric oxide containing fibers in SC. NADPHd labeled neurons within the superficial layers of the superior colliculus included pyriform, vertical fusiform, and horizontal morphologies. Labeled neurons in the intermediate gray layer were small to medium in size, and mostly of stellate morphology. Neurons in the deepest layers had mostly vertical or stellate morphologies. NADPHd labeled fibers formed dense patches of terminal boutons within the intermediate gray layer and streams of fibers within the deepest layers of SC. Choline acetyltransferase antibody labeling in adjacent sections indicated that many fibers must contain both labels. Over 94% of neurons in the pedunculopontine tegmental and lateral dorsal tegmental nuclei were also labeled by both NADPHd and choline acetyltransferase. In addition, biocytin labeled fibers from this region were localized in the NADPHd labeled patches. We conclude that nitric oxide is contained in a variety of cell types in SC and that both nitric oxide and ACh likely serve as co-modulators in this midbrain structure.

Animals↗
PubMed1992

A comparison of the accuracy of unit dose cart fill with the Baxter ATC-212 computerized system and manual filling.

Pharmacy Service of the Department of Veteran Affairs Medical Center in Lincoln, Nebraska recently implemented a computerized Baxter ATC-212 Unit Dose System. During implementation of this system, pharmacy technicians completed an accuracy comparison with manual filling. The Baxter ATC-212 System was 99.98% accurate and manual filling was 92.62% accurate. The accuracy of the combination of manually and ATC-212 filled drawers was 98.77%. The technicians had a median error rate of three errors per day with an average 352 doses filled per day.

Child↗
PubMed1991

Substrate and inhibitor specificity of 3-hydroxy-3-methylglutaryl-CoA reductase determined with substrate-analogue CoA-thioesters and CoA-thioethers.

1) Analogues of 3-hydroxy-3-methylglutaryl-CoA were prepared in which the substituents at C-3 of the acyl residue were altered. The same analogues were additionally modified by replacement of the thioester oxygen by hydrogen to yield reduction-resistant CoA-thioethers. The interaction of both types of CoA derivatives with a 58-kDa catalytic fragment of human 3-hydroxy-3-methylglutaryl-CoA reductase was studied. 2) This enzyme reduces glutaryl-CoA at a very low rate whereas 3-hydroxyglutaryl-CoA is well reduced, the maximal rate of reduction being 7% that of the physiological substrate. Only half of total 3-hydroxyglutaryl-CoA was attacked, thus reflecting the stereo-specificity of the enzyme for (3S)-3-hydroxy-3-methylglutaryl-CoA. The results invalidate the hitherto assumed absolute substrate specificity of the enzyme. 3) The affinity of both 3-hydroxyglutaryl-CoA and its thioether variant S-(4-carboxy-3-hydroxybutyl)CoA to the reductase, Ki = 0.3 microM and Ki = 0.4 microM, respectively, is higher than that of the physiological substrate, Km = 1.5 microM (data related to (S)-diastereomer). The results show for the first time that the methyl-group effect observed with the inhibitor lovastatin is an intrinsic property of the enzyme. 4) All of the prepared CoA derivatives are purely competitive inhibitors of the reductase, the affinities varying within a range of two powers of ten (Ki = 0.3-32 microM). On variation of the substituents at C-3 of the acyl residue of the physiological substrate the affinity of both CoA-thioesters and CoA-thioethers increases in the sequence CH2, C(CH3)2, CH(CH3), C(OH)CH3, CH(OH).

Acyl Coenzyme A↗