Hi Qiaobing, thank you for your insightful questions. I’m currently interested in the fundamental understanding of the sequestration of PEGylated enzymes in a lamellar block copolymer model system. One area of interest is the effect of the PEGylated enzymes’ hydrodynamic radius on their sequestration (as shown in the poster for inorganic functionalized nanoparticles). I’ve selected model enzyme systems that are well represented in literature: Trypsin (~2.3 nm), Bovine Serum Albumin (~3.4 nm), and Glucose Oxidase (~5 nm) in order to determine the effect of size on dispersion without concern for enzyme functionality at this point.
The properties of the PEG attached to the enzyme surface are very important in this study. The degree of polymerization (length of the polymer) and the grafting density (number of PEG chains per surface area) can affect the miscibility of the functionalized enzymes in the block copolymer and the resulting microstructure. With increased degree of polymerization and increased grafting density, the miscibility of the functionalized enzymes in the block copolymer increases. We are trying to attain the maximum achievable enzyme loading while maintaining the lamellar microstructure and preventing macrophase separation. Thanks again for your interest in our project!

Hi Aparna, thank you for your questions about the applications of the block copolymer/enzyme blend systems. Yes, you are correct in saying that the PEGylated enzyme would sit in the cylindrical phase of the block copolymer in the self-regulatory membrane application. While I am not yet at this stage of the research project, the governing parameters determined for PEGylated enzyme sequestration in the lamellar block copolymer model system can be applied to the cylindrical block copolymer system used for the self-regulatory membrane application.
The main idea of that application is to use the biological response of the enzyme in order to trigger a phase change (swelling and de-swelling) in the cylindrical domain. There are two main challenges associated with the achievement of this:
1. In order to gain membrane functionality, we would replace PS-PMMA with a block copolymer with LCST (lower critical solution temperature) type behavior such as PS-b-PHEMA, formally known as poly(styrene-b-hydroxyethylmethacrylate). The BCP can phase separate due to a change in temperature, pressure, or pH. We will focus on a change in pH prompted by the creation of H ions when a biologically active agent comes in contact with the enzyme in the BCP. The result is a membrane with an open state and a closed state.
2. The second challenge is to prevent leakage in the closed state of the membrane. In order to do this, we will explore routes of chemical linkage of the PEGylated enzyme to the block copolymer after sequestration has occurred.
The long term goal, a self-regulatory membrane or coating, could be used to actively regulate the permeation of biologically active agents.
Thank you again for your time and interest!

Hi Natalia, thanks for the kind words! Rachel and I had a great time making the video. Very insightful question! I am glad you asked this and you are absolutely correct!

The scattering cross section of embedded particles (that is the scattering of the composite) depends on two major components: the volume of the inclusion squared (or radius to the sixth power) and the difference in dielectric constants of the filler and matrix squared.

Because of this, we see that when nanoparticles aggregate, the volume of the inclusion increases and thus results in a significant increase in light scattering.

The purpose of the surface modification of our nanoparticles is not only to index match, but to also facilitate dispersion of particles in the polymer matrix.

Given the thermodynamics of mixing in this specific system, miscibility in the non-index matched system cannot be achieved in solid state form and thus the contribution of these two components (scattering due to inclusion volume vs dielectric contrast) cannot be separated. I am basing my conclusion on parallel studies performed in the solution state where dispersion can be achieved and where we saw significant reduction of the particle scattering facilitated by effective index matching. (Adv. Mater. 19, (2007), 4486-4490)

Due to the limited scope of the poster presentation I chose not to elaborate on solution experiments, though I would love to talk about it more if you were interested! I am sorry if this caused any confusion, and once again thanks for taking the time to ask such an insightful question!

Thank you for the kind words and great question, Qi-Huo! It is too bad we could only go three minutes as we had so much more to say!

Our main aim is to minimize scattering through both creating a homogenous dispersion as well as minimizing the dielectric differences between the filler and the matrix.
We achieve index matching through coating our core particle (SiO2) with a polymer shell (SAN) that not only compatiblizes the particle to the polymer matrix (PMMA), but can also modulate the effective dielectric constant.

When core shell particles are small enough, light will not interact with the core and shell components separately, but rather interact with the core shell particle as if it were one entity with an averaged dielectric constant.

In our system, we know that our core (SiO2) dielectric constant is less than the matrix (PMMA) dielectric constant and that our shell (SAN) has a dielectric constant greater than both of these.

Because of this, we can coat our SiO2 with SAN and modulate the effective dielectric constant of our core shell particle, or particle brush, to equal that of PMMA. We have used the Maxwell Garnett effective medium approximation to predict what core shell volume fractions will render a dielectric constant identical to PMMA.

It is important to note, however, that despite its fantastic predictions, this approximation is limited to non-interacting fillers with sizes smaller than the wavelength of light. One thing I hope to achieve in my time here will be to see just exactly where those limits lie!

Hi Hyunjoon, thank you for your interest in our project! To provide some background, block copolymers can form lamellar, gyroid, cylindrical, or spherical morphologies depending on the volume fraction, f, of one block (the volume fraction of the other block is 1-f) as well as the XN value (Flory Huggins ‘chi’ parameter and the degree of polymerization). Since our XN is well above 10.5 (corresponding to the order-disorder transition), I’ll focus on the effect of volume fraction.
Typically lamellar morphologies occur when the volume fraction is between 0.34 and 0.62. The PS-b-PMMA we are using is considered symmetric in that the volume fraction for both blocks is f=0.5. The amount of PEGylated enzyme that would be necessary to shift the volume fraction of the PMMA (PEG is miscible with PMMA) from 0.5 (without any PEG-enzyme) to 0.62 (with PEG-enzyme) is calculated to be 31.6 weight percent with respect to the total block copolymer. The addition of 31.6 weight percent or more of PEGylated enzymes would result in a shift from a lamellar morphology to a cylindrical one.
Part of this research project is to determine the solubility limits of the PEGylated enzymes in the block copolymer by systematically studying the addition of PEGylated enzymes to the block copolymer at specific weight percent values. Thank you again for your question.

Thank you very much, Myisha! It was lots of fun making it!

Hahaha, thank you Janaki! I think the particle brushes accentuate Rachel and my good features. <3

Thanks, Zenille!

Thank you for your kind words, Terri! We are very excited about the future applications too!

Thanks, John!

Hi Sarah, thank you for your interest in our work!
In short, the range of potential targets would be equal to the range of biochemical molecules that can trigger enzymatic responses. In our project we’ll be focusing on organic simulants of chemical/biological toxins due to the preference of our industrial collaborator. It would be possible to also blend different types of enzymes to generate sensitivity of our membranes to multiple targets.
We expect the governing parameters controlling dispersion of these specific PEGylated enzymes in BCPs to be generalizable to all PEGylated enzyme systems, since the outer chemistry (PEG) is constant for all systems. Therefore, once we understand structure formation for BCP/enzyme blend systems and the effect of processing on the enzymatic stability, we should be able to extend this approach to various other enzyme systems.
To answer the second part of your question, we consider the Flory-Huggins X (Chi) Parameter for PS-PEG and for PMMA-PEG as a first approximation. Since X PMMA-PEG is negative and X PS-PEG is strongly positive, we expect the PEGylated enzymes to sequester to the PMMA domain.
Thanks again for your questions!