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Daniel Cohn

Institute of Chemistry
Faculty of Science
The Hebrew University of Jerusalem, Jerusalem 91904, Israel
Tel: +972-2-6584520; Fax: + 972-2-6516312
E-mail:danielc@vms.huji.ac.il

Generating thermo-responsive surfaces

Surfaces can be rendered responsive to minor changes triggered by environmental stimuli, such as pH, light, and most importantly, temperature. Due to their temperature-dependent water solubility, the reverse thermo-responsive surface grafted chains adopt an extended conformation at a lower temperature, while at a higher temperature, they collapse generating nano-sized globular structures Thermo-responsive surfaces, were generated by covalently binding chains of various molecular weights comprising PEO-PPO-PEO triblocks, to the various polymeric substrates The thermo-responsiveness of the chains grafted was demonstrated, as shown in the figure below.

Also, the biocompatibility of the surfaces generated is shown below, which show the behavior of PET-NH-HDI-F127-HDI-GRGDSG surface, stained with PECAM-1 (left) and E-selectin (right)

Generating thermo-responsive surfaces

Here, work was conducted along two pathways: {i} Nano-fibrous polymeric biomedical structures and {ii} Thermo-responsive biomedical nano-shells. {i} Nano-fibrous polymeric biomedical structures Mono- and multi-component nano-fibrous structures were developed for a variety of applications, from membranes to scaffold for tissue regeneration, following two basic strategies. The first capitalized primarily on the electrispinning technique, to generate structures as the one showed below (left). Additionally, for the in situ generation of scaffolds for Tissue Engineering, nano-fibrous scaffolds were produced harnessing the unique properties of crosslinkable, thermo-responsive polymers, as shown below (right).

{ii} Thermo-responsive biomedical nano-shells "Thermo-responsiveness", the ability of a polymeric system present in an aqueous medium, to undergo large chemical, mechanical or physical transformations due to small temperature differentials, can be harnessed to engineering nano-metric architectures. Totally thermo-responsive nano-structures, comprising poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblocks were generated and investigated. The uniqueness of these novel nano-sized constructs stems from their ability to display a remarkable and reversible change in size (hundreds of times by volume), within a very narrow temperature interval. These supramolecular architectures were produced by cross-linking intra-micellarly end-capped PEO-PPO-PEO dimethacrylates, while these amphiphilic triblocks are constrained to the specific spatial configuration dictated by their micellar organization. Thermo-responsive nano-tubes were created by "sculpturing" them from rod-like micelles at higher temperatures. By varying the compo sition of the triblock, the transition temperature was fine tuned, and the nano-shells were rendered biodegradable by incorporating aliphatic oligoesters into their structure, as shown below, as they degrade over 6 (a), 13 (b), 22 (c) and 27 (d) days

In addition to individual nanoshells, covalently bound nano-shell arrays were formed, by capitalized on the presence of reactive double bonds on their surface (see figure below).

Aiming at illustrating the flexibility of the dimensional response of these thermo-responsive nano-shells, the temperature was rapidly and repeatedly changed during their synthesis, whereby surprising nano-sized structures were generated, as shown below

Numerous applications for these nano-structures are foreseen in various biomedical areas, such as in drug and gene delivery and in the Tissue Engineering field.

Specific research topics related to nanosciences and nanotechnology:

  • Thermo-responsive biomedical nano-shells
  • Nano-fibrous polymeric biomedical structures
  • Polymeric reactive nano-materials
  • Surface grafted thermo-responsive nanometric constructs

List of publications in nanoscience and nanotechnology (2010- 2011)

  • "Crosslinkable PEO-PPO-PEO triblocks as building blocks of thermo-responsive nanoshells" Guoguang Nui, Alexandra Benyamin Djaoui and Daniel Cohn Polymer 52, 2524-2530 (2011)
  • "Surface grafting thermo-responsive PEO-PPO-PEO chains" Ram Malal, Maya Malal and Daniel Cohn Tissue Engineering and Regenerative Medicine, 5(5), 394-401 (2011).
  • "Smart polymers in the design of micro- and nano-sized biomedical systems" Daniel Cohn, Matthew Zarek and Alejandro Sosnik Advanced Materials. Invited Review. Under preparation

Cooperation with industries and defense projects (2010-2011):

Expertissues European Network of Excellence, developing thermo-responsive nano-architectures, nanofibrous scaffolds for tissue regeneration and "tunable" biomedical surfaces

Cooperation with other researchers/universities in Israel:

Within Hebrew University:

Prof. Shlomo Magdassi: Formation of macroscopic structures from polymeric nanoparticles

Students, postdocs and researchers

Post docs:  Dr. Guoguang Nui
Ph.D. students:  (present and graduated) – Dr. Ram Malal, Alexandra Benyamin Djaoui, Revital Zarka
M.Sc. students: Yael Ben Basat, Eran Cohen, Yuval Cohen, Hadas Kaminski

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