Raheel Akram

Post-infiltration and subsequent photo-crosslinking strategy for layer-by-layer fabrication of stable dendrimers enabling repeated loading and release of hydrophobic molecules

The layer-by-layer (LbL) technique has been intensively investigated as a straightforward method for the incorporation of drug molecules or other bioactive species, enabling retarded release in drug delivery devices, in bioactive interfaces, in tissue engineering, and in regenerative medicine. The preparation of crosslinked LbL multilayers with embedded drug reservoirs for delayed release remains a challenging task, however. In the present study we have developed a method for the simultaneous utilisation of covalent interlayer linkages and drug reservoirs that can hold model drug molecules. A strategy of post-infiltration of photoactive bifunctional small molecules followed by UV irradiation has been employed for crosslinking the LbL multilayers, incorporating poly(amido amine) (PAMAM) molecules, which serve as a drug reservoir. The covalent linkage significantly alters the release profile of the model drug from the multilayers, with retarded release of hydrophobic molecules from a solvent, and enabling the loaded multilayers to withstand rinsing with 75% ethanol, the most commonly used sterilization procedure.

Toward Understanding Whether Interactive Surface Area Could Direct Ordered Macroscopic Supramolecular Self-Assembly

The mismatching phenomena are ubiquitous in complex and advanced self-assembly, such as hierarchical assembly, macroscopic supramolecular assembly, and so on. Recently, for macroscopic supramolecular assembly, the strategy of maximizing the interactive surface area was used and supposed to handle this problem; however, now there is little understanding of whether interactive surface area is the dominant factor to guide the assembly patterns. Herein by taking millimeter cylinder building blocks with different diameter/height (d/h) ratios as model systems, we have investigated the interactive-surface-area-dependent assembling behaviors in macroscopic supramolecular assembly. The results showed that the increasing d/h ratio of cylinders contributed to selectivity of face-to-face assembled pattern over face-to-side or side-to-side geometries, thus having improved the ordering degree of the assembled structures; however, the mismatching phenomena could not be totally avoided due to high colliding chances in kinetics and the thermally favorable stability of these structures. We further confirmed the above hypothesis by in situ measurements of interactive forces of building blocks with different assembled patterns. This work of macroscopic supramolecular assembly provides an in situ visible platform, which is significant to clarify the influences of interactive surface area on the assembly behaviors.