Correlation of the Adhesive Properties of Cells to N-Isopropylacrylamide/N-tert-Butylacrylamide Copolymer Surfaces with Changes in Surface Structure Using Contact Angle Measurements, Molecular Simulations, and Raman Spectroscopy

Abstract

A series of copolymers of N-isopropylacrylamide (NIPAM) and the more hydrophobic comonomer N-tert-butylacrylamide (NTBAM), with increasing NTBAM content (i.e., increasing hydrophobicity) were prepared. The adhesion of human epithelial cells on polymer films prepared from copolymers of NIPAM: NTBAM was observed to increase with increasing polymer hydrophobicity. However, in the absence of serum, cell adhesion to the different surfaces was statistically indistinguishable. Thus, it appears that the copolymer films differentially support cell adhesion due to selective adsorption of proteins from the physiological environment (the serum). Using contact angle measurements, molecular simulations, and Raman spectroscopy to characterize the different surfaces, we show evidence that the different behavior of cells on the films of increasing hydrophobicity is actually due to the different chemical properties of the surfaces with increasing content of NTBAM in the copolymers. As the NTBAM content is increased, the number of NH residues at the surface decreases, due to the additional steric hindrance of the bulkier NTBAM group, which results in decreased hydrogen bonding and thus decreased adsorption of proteins such as albumin. However, in some cases, the adsorption is driven by hydrophobic interactions, and proteins such as fibronectin were found to adsorb more to the films with a higher content of NTBAM. There appears, thus, to be a direct correlation between surface composition, i.e., the functional groups exposed at the surface, and protein binding and subsequent cell adhesion.

Preparation, characterization of NIPAM and NIPAM/BAM copolymer nanoparticles and their acute toxicity testing using an aquatic test battery

“…For all media types, increasing the ratio of BAM in the copolymer nanoparticles was shown to cause a decrease in their zeta potential. This increasingly negative value of the zeta potential of the co-polymer particle surface is consistent with the reduced hydrophillicity (as determined by contact angle measurements) as a result of the increased BAM content (Lynch et al, 2005;Allen et al, 2003). A similar trend was observed with all the media tested but was most significant when the nanoparticles were tested in MQ water.…”

“…Copolymerisation of NIPAM with the more hydrophobic monomer N-tert-butylacrylamide (BAM) reduces the PNIPAM LCST with increasing percentage of the BAM monomer. As the ratio of BAM increases, the amount of N-H groups exposed at the surface decreases, and the amount of -C-(CH 3 ) 3 (Lynch et al, 2005). Because of this reversible phase transition, PNIPAM has been widely used in the preparation of stimuli responsive systems for biomedical applications, such as in the controlled release of drugs and in tissue engineering (Xu et al, 2004;Zhang et al, 2005;Kavanagh, 2005;.…”

Polarity Assessment of Thermoresponsive Poly(NIPAM-co-NtBA) Copolymer Films Using Fluorescence Methods

“…The polymer case however, is more complex because of structural, energetic, and dynamic microscopic inhomogeneity. In the case of poly(NIPAM-co-NtBA) thermoresponsive polymers, which are random linear copolymers, there is the added possibility of local microscale hydrophilic/hydrophobic microenvironments [18,19]. The fluorescence emission spectra from all 3-HF fluorophores are strongly dependent on copolymer composition, with increasing hydrophobicity (greater NtBA fraction) leading to a decrease in the ratio between the emission intensity from the N* and T* bands (I N* /I T* ) as shown in Figure 5A, 5C, and 5E.…”

“…The LCST of these poly-N-isopropylacrylamide -N-tert-butylacrylamide (pNIPAM-co-NtBA) thermoresponsive copolymers can be decreased by increasing the NtBA fraction. The importance of this study lies in the fact that these pNIPAM-co-NtBA copolymers are currently being investigated as potential drug elution matrices and for cell culture applications [16][17][18][19][20]. Because these copolymers are relatively hydrophilic and will uptake water, it can be difficult to characterise the materials using conventional techniques like Contact Angle Measurements.…”

Measuring the Micro-Polarity and Hydrogen-Bond Donor/Acceptor Ability of Thermoresponsive N-Isopropylacrylamide/N-tert-Butylacrylamide Copolymer Films Using Solvatochromic Indicators

“…These NIPAM/NtBA copolymers are currently being investigated as potential drug elution matrices and for cell culture applications. [14][15][16] To better understand the physicochemical performance of these hydrophilic polymers it is necessary to accurately measure the polarity of these materials. Polarity in its broadest sense will impact on aspects of polymer behavior such as water uptake, processability, surface energy, drug elution profiles, and mechanical properties.…”