Silk fibroin - characterization and chemical modification of a unique biomaterial for controlled release

Around 100 years ago, Paul Ehrlich postulated the “magic bullet”, a personalized and tailored drug that can hit the affected tissue like a bullet from a gun. Since then on a lot of research has been conducted to develop such “magic bullets”. To deliver a drug to the target location, usually a carrier/vehicle is needed (drug delivery system). Conventional ways to administer drugs are by tablets or parenterals, whereas the latter often suffers from high plasma concentration for a short time period, followed by a more or less fast decrease of the plasma concentration. Depending on the elimination constant, repeated drug administration can lead either to a diminished effect if the active ingredient is fast eliminated, or to side effects if the active ingredient cumulates. To control the release, local drug release might be considered with the advantage that systematic side effects can be reduced. As a result, local drug delivery systems gain more and more interest with the challenge to achieve a sustained release without impacting the surrounding healthy tissue. In order to achieve this controlled drug delivery and an optimal therapeutic effect, a lot of research has been carried out for targeted delivery with a controlled release rate. However, a drug delivery system has to meet several requirements, e.g. mechanical stability, controllable structure and degradation. Due to its extraordinary properties (e.g. mechanical strength, biocompatibility, biodegradability into non-toxic products, FDA-approved), silk fibroin (SF) has been in the focus of research since a long time, especially in terms of sustained release drug delivery systems. One of the major advantages of SF compared to other biomaterials is that it can be assembled into a variety of matrices (e.g. particles, foams, gels, electrospun mats) [1, 2]. The objective of the first study was to characterize silk fibroin in more detail. The focus was set on different purification processes of SF in order to efficiently remove sericin and a method to detect residual sericin was established. This is important to ensure biocompatibility since the combination of sericin and silk fibroin can cause allergic reactions. The degumming process significantly affected SF integrity, particularly mechanical strength and molecular weight distribution. These factors are crucial for the preparation of drug delivery systems, since they can influence the degradation rate of the drug delivery system and as a result, the release rate of the drug. The second study aimed to investigate the release behaviour of differently charged macromolecular drugs from SF films. Since biologicals and nucleic acids (respectively nucleic acid/polymer complexes) are becoming an emerging field, the importance to understand the release behaviour of these macromolecular, charged compounds is growing. Therefore, differently charged, high molecular weight dextran derivatives, used as model drugs, were encapsulated into SF films and their release behaviour was studied. Additionally, the effect of SF purification process, with focus on degumming time, on drug release was elucidated. The release rate was found to be highly dependent on matrix properties, controllable via the purification process. In the third part, silk fibroin films were chemically modified via copper (I)-catalyzed alkyne-azide cycloaddition (CuAAC) to further control drug release. The already existing, extraordinary features of silk fibroin can be enlarged by chemical modification, extending their range of applications. By varying the modification degree, the release was controlled, aiming a more pronounced sustained release, and additionally, the surface properties with regard to hydrophilicity were tuned

Effects of silk degumming process on physicochemical, tensile, and optical properties of regenerated silk fibroin

Sericin removal from silk (degumming) affects material characteristics of silk fibroin (SF). Sodium carbonate is most commonly used for degumming, but numerous alternative methods are available. Herein, a systematic comparison of degumming methods is provided. Sodium carbonate, sodium oleate, trypsin, and ionic liquid are used, and materials are characterized regarding mass loss, SF content, molecular integrity of SF, refractive index, and tensile properties. Complete degumming is achieved within 30 min of using sodium carbonate, but results in significant reduction of molecular weight, shift toward less acidic charge variants, and reduction of yield- and rupture force. Sodium oleate and trypsin are inefficient and negatively affect tensile properties, while ionic liquid shows good efficiency and marginal degradation of SF but also reduced yield- and rupture force. Refractive index is not affected by degumming. These results allow rational selection of the degumming method and tuning of SF properties for biomedical applications

Chemical Clearing and Dehydration of GFP Expressing Mouse Brains

Generally, chemical tissue clearing is performed by a solution consisting of two parts benzyl benzoate and one part benzyl alcohol. However, prolonged exposure to this mixture markedly reduces the fluorescence of GFP expressing specimens, so that one has to compromise between clearing quality and fluorescence preservation. This can be a severe drawback when working with specimens exhibiting low GFP expression rates. Thus, we screened for a substitute and found that dibenzyl ether (phenylmethoxymethylbenzene, CAS 103-50-4) can be applied as a more GFP-friendly clearing medium. Clearing with dibenzyl ether provides improved tissue transparency and strikingly improved fluorescence intensity in GFP expressing mouse brains and other samples as mouse spinal cords, or embryos. Chemical clearing, staining, and embedding of biological samples mostly requires careful foregoing tissue dehydration. The commonly applied tissue dehydration medium is ethanol, which also can markedly impair GFP fluorescence. Screening for a substitute also for ethanol we found that tetrahydrofuran (CAS 109-99-9) is a more GFP-friendly dehydration medium than ethanol, providing better tissue transparency obtained by successive clearing. Combined, tetrahydrofuran and dibenzyl ether allow dehydration and chemical clearing of even delicate samples for UM, confocal microscopy, and other microscopy techniques

Cyanobacteria in motion

This work was supported by a grant from the DFG (WI 2014/7-1) to A.W

Rural waste generation: a geographical survey at local scale

"The paper examines the per capita waste generation rates from from rural areas of Neamț County (Romania) using thematic cartography. Geographical approach of this issue is difficult because the lack of a geostatistic database at commune scale. Spatial analysis of waste indicators reveals several disparities between localities. Comparability of data between communes located in various geographical conditions must be carrefully made according to local waste management systems. Several dysfunctionalities are outlined in order to compare these results, on the one hand, between localities and on the one hand, between recent years. Geographical analysis of waste generation rates is imperative for a proper monitoring of this sector. Data from 2009, 2010 and 2012 shows that rural waste management is in a full process of change towards a more organized, stable and efficient system." (author's abstract