Dr Shwan Hamad

Shwan Hamad

Shwan graduated as a PhD in 2012 in Prof Paunov research group at the University of Hull and is currently working as a Lecturer at the University of Sulaimani, Iraq.

PhD supervisor: Prof Vesselin Paunov (PI) 

Research project 1 (PhD thesis):

Triggered Release of Cells from Composite Microcapsules

 We report the fabrication of novel shellac-cells composite microcapsules with programmed release of cells upon change of pH in a narrow range [1]. The microcapsules were prepared from yeast cells as a model for probiotics combined with aqueous solution of ammonium shellac doped with a pH sensitive polyelectrolyte, like carboxymethyl cellulose or polyacrylic acid. The cells dispersions in aqueous ammonium shellac were spray-dried or spray co-precipitated to yield composite shellac-cell microcapsules in which the cells retained their viability even when treated with aqueous solutions of very low pH and subjected to mechanical stress (Fig. 1). We demonstrated two types of triggered release of cells from these microcapsules with pH trigger and cell growth trigger and evaluated the microcapsules disintegration rates. Depending on the type of the polyelectrolyte integrated in the shellac microcapsules they can be programmed to give very versatile responses ranging from slow cell release to instant swelling and disintegration at higher pH or exposure to growth media. We showed that the cells retain their viability following their release from the microcapsules into the aqueous media. We developed a kinetic model of the kinetics of living cell release from the composite shellac microcapsules triggered by: (i) pH change, which dissolves the shell and (ii) the growth of the encapsulated cells, when placed in a culture media. For pH triggered release of cells from the composite microcapsules, the rate constant of cell release depends on the swelling/dissolution rate of the shellac matrix and varies with the pH of the aqueous media [2]. The model links the microcapsules disintegration time with the cell release rate constant. For growth triggered release of cells from the composite microcapsules, the rate constant of cell release depends on concentration of nutrients in the culture media and the cells volume fraction in the microcapsules. In a complementary experimental study we compared the release rate constants of cells from shellac-cell microcapsules at different value of the pH in the aqueous media. We also demonstrated both theoretically and experimentally how the growth rate constants of individual cells compares with the release rates of cells released from microcapsules in culture media. Such composite microcapsules could find applications in formulations for protection and delivery of probiotic and other cell cultures with programmed and triggered release of the encapsulated cells in cell implants, including stem cells and live vaccines.

Shellac-cell capsules

Fig. 1. SEM, optical and fluorescence images of composite yeast-shellac microcapsules for triggered release of cells.


  1. Hamad, S.A., Stoyanov, S.D., Paunov, V.N., “Triggered cell release from shellac-cell composite microcapsules”, Soft Matter, 8 (2012) 5069-5077.
  2. Hamad, S.A., Stoyanov, S.D., Paunov, V.N., “Triggered release kinetics of living cells from composite microcapsules”, Phys. Chem. Chem. Phys., 15 (2012) 2337-2344.
  3. Hamad, S.A., Stoyanov, S.D., Paunov, V.N., “Triggered Cell Release from Shellac-Cells Composite Microcapsules”, MRS Proceedings 1499, mrsf12-1499-n05-181 doi:10.1557/opl.2013.399.

Research project 2:

 Microencapsulation of Viable Cells into Sporopollenin Microcapsules

 We demonstrated for the first time how living cells can be encapsulated inside sporopollenin microcapsules derived from Lycopodium clavatum[1]. Sporopollenin is a major part of the exine of spores and pollens. It can be found in soils and rock sediments and has been recognised as one of the most extraordinary resistant materials of bioorganic origin[1]. Sporopollenin can be isolated from the pollens by consecutive acidic and basic solvent treatment, which removes the inner cellulose wall but morphologically preserves the exine. Recently, we reported a simple and robust method for loading sporopollenin exine of Lycopodium clavatum with functional inorganic and organic nanoparticles synthesized in situ [2]. This technique uses sporopollenin microcapsules as micro-reactors where a chemical reaction generates a low soluble product inside, which precipitates in the form of nanoparticles usually much larger than the pores of the sporopollenin membrane [2]. To encapsulate large objects like cells, the sporopollenin particles are compressed into a pellet which forces their trilite scars to open up. The method involves exposing a sporopollenin pellet to an aqueous suspension of cells in the presence of a surface active agent which facilitates the capillary suction of the cells suspension inside the compressed sporopollenin and its ‘‘re-inflating’’ and closure of trilite scars (see Fig.2). We demonstrate that the viability of the cells is preserved after the encapsulation in the sporopollenin capsules which contain a significant amount of entrapped cells and show biological activity when placed into a culture medium. Since the sporopollenin nanopores allow nutrient transport across the capsule wall, it could be used for controlling the rate of in situ fermentation reactions or as bio-reactors. We also show that sporopollenin can be loaded with magnetic nanoparticles and live cultures simultaneously which would allow remote manipulation, fixation, removal or potentially targeted delivery of such bio-microreactors. The encapsulation of living cells inside sporopollenin can be used for many different purposes in the food and pharmaceutical industries, including protection of probiotics in foods and delivery of live vaccines for pharmaceutical applications.


yeast in sporopollenin

Fig.2. TOP: Schematic representation of the process of encapsulating of cells into sporopollenin microcapsules. Bottom image: SEM of cracked open sporopollenin microcapsule after being loaded with yeast cells [2,3].


  1. Paunov, V.N., Mackenzie, G., Stoyanov, S.D., “Sporopollenin micro-reactors for in-situ preparation, encapsulation and targeted delivery of active components“, J. Mater. Chem., 17 (2007) 609-612. [Highlighted in Chemical Science]
  2. Hamad, S. A., Dyab, A.F.K., Stoyanov, S.D., Paunov, V.N., “Encapsulation of living cells into sporopollenin microcapsules”, J. Mater. Chem., 21 (2011) 18018-18023.
  3. Hamad, S.A., Dyab, A.K.F., Stoyanov, S.D., Paunov, V.N., “Sporopollenin microcapsules for encapsulation of living cells”, MRS proceedings N – Fall 2012, N.181.1-6.