03 Fakultät Chemie

Now showing 1 - 5 of 5

Open Access
Novel X-ray lenses for direct and coherent imaging
(2019) Sanli, Umut Tunca; Schütz, Gisela (Prof. Dr.)
Open Access
Chiral metamaterials
(2016) Eslami, Sahand; Fischer, Peer (Prof. Dr.)
Open Access
Advanced analysis of battery materials via correlative charged particle characterisation techniques
(2023) Cressa, Luca; Schmitz, Guido (Prof. Dr. Dr. h.c.)
Open Access
Soft materials for acoustic applications
(2022) Choi, Eunjin; Fischer, Peer (Prof. Dr.)
Ultrasound finds wide application in imaging and testing because ultrasound can penetrate tissue and is benign. Gaseous microbubbles strongly scatter ultrasound and are therefore used as contrast agents. Ultrasound responsive materials can be used for many industrial and biomedical applications. Ultrasound can also be used to exert forces and manipulate particles solution and biological cells. In this thesis, material systems are developed for three application areas: 1) models of human organs for the quantitative evaluation of surgical procedures with ultrasound; 2) the fabrication of soft objects by assembling polymeric particles with ultrasound and the acoustic hologram; and 3) the characterization of antibubbles as novel contrast agents that can carry a fluid load. Organ phantoms serve as tools in medical fields to train and plan medical procedures. However, current organ phantoms miss important features or are not realistic. Current models tend to possess a Young’s modulus that is much higher than that of tissue. Furthermore, many of the current models do not show the correct contrast in a medical imaging setting. This thesis presents high fidelity organ phantoms that possess the correct elasticity, compliance, optical appearance, and correct ultrasound contrast. One model is developed for cystoscopy (CY) of the bladder. Another phantom for the transurethral resection of the prostate (TURP). The quality of the phantoms is validated by medical practitioners. For CY, the execution time of the medical practitioners is recorded to completely map the inside of the bladder phantom while localizing tumor models that have been embedded in the bladder wall. For TURP, the quality of the resection is compared with ultrasound imaging before and after the surgical simulation. Parameters are defined to quantify the success of the procedure. The phantoms developed as part of this thesis have received high satisfaction scores from medical practitioners. The parameters reflect the experience of the surgeons. In assembling soft matter, one challenge is that existing 3D printing methods are slow. In contrast, the use of ultrasound patterns shaped with a recently invented acoustic hologram allows objects to be built at once. In this thesis, polydimethylsiloxane (PDMS) particles have been assembled into two-dimensional shapes with ultrasound. To fix the assembly, the PDMS has been physically functionalized with an initiator using swelling. Suitable swelling solutions have been determined based on their solubility. The stability of the physisorbed initiators is evaluated, and the functionalized PDMS particles are fixed via photopolymerization after assembly in aqueous polyethylene glycol dimethacrylate (PEG-DMA) solutions. The fabrication steps can be repeated to increase the thickness of structures that are mechanically stable. The antibubble is an emerging ultrasound contrast agent. It has an inverse form to a conventional bubble in that a substance in the core is surrounded by a gaseous layer. The antibubble is acoustically responsive and, compared to conventional microbubbles, can carry a much greater load. In this thesis, the structure of antibubbles is examined. In particular, the volume of the load is quantified, and the amount of gas per bubble is estimated. The stability of the core substance against diffusion is investigated and shown to be stable for over 11 h.
Open Access
Development of super-specific epigenome editing by targeted allele-specific DNA methylation
(2023) Rajaram, Nivethika; Kouroukli, Alexandra G.; Bens, Susanne; Bashtrykov, Pavel; Jeltsch, Albert
Background. Epigenome editing refers to the targeted reprogramming of genomic loci using an EpiEditor which may consist of an sgRNA/dCas9 complex that recruits DNMT3A/3L to the target locus. Methylation of the locus can lead to a modulation of gene expression. Allele-specific DNA methylation (ASM) refers to the targeted methylation delivery only to one allele of a locus. In the context of diseases caused by a dominant mutation, the selective DNA methylation of the mutant allele could be used to repress its expression but retain the functionality of the normal gene. Results. To set up allele-specific targeted DNA methylation, target regions were selected from hypomethylated CGIs bearing a heterozygous SNP in their promoters in the HEK293 cell line. We aimed at delivering maximum DNA methylation with highest allelic specificity in the targeted regions. Placing SNPs in the PAM or seed regions of the sgRNA, we designed 24 different sgRNAs targeting single alleles in 14 different gene loci. We achieved efficient ASM in multiple cases, such as ISG15, MSH6, GPD1L, MRPL52, PDE8A, NARF, DAP3, and GSPT1, which in best cases led to five to tenfold stronger average DNA methylation at the on-target allele and absolute differences in the DNA methylation gain at on- and off-target alleles of > 50%. In general, loci with the allele discriminatory SNP positioned in the PAM region showed higher success rate of ASM and better specificity. Highest DNA methylation was observed on day 3 after transfection followed by a gradual decline. In selected cases, ASM was stable up to 11 days in HEK293 cells and it led up to a 3.6-fold change in allelic expression ratios. Conclusions. We successfully delivered ASM at multiple genomic loci with high specificity, efficiency and stability. This form of super-specific epigenome editing could find applications in the treatment of diseases caused by dominant mutations, because it allows silencing of the mutant allele without repression of the expression of the normal allele thereby minimizing potential side-effects of the treatment.

03 Fakultät Chemie

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