Three-dimensional matrix stiffness and adhesive ligands affect cancer cell response to toxins.

There is an immediate need to develop highly predictive in vitro cell-based assays that provide reliable information on cancer drug efficacy and toxicity. Development of biomaterial-based three-dimensional (3D) cell culture models as drug screening platforms has recently gained much scientific interest as 3D cultures of cancer cells have been shown to more adequately mimic the in vivo tumor conditions. Moreover, it has been recognized that the biophysical and biochemical properties of the 3D microenvironment can play key roles in regulating various cancer cell fates, including their response to chemicals. In this study, we employed alginate-based scaffolds of varying mechanical stiffness and adhesive ligand presentation to further explore the role of 3D microenvironmental cues on glioblastoma cell response to cytotoxic compounds. Our experiments suggested the ability of both matrix stiffness and cell-matrix adhesions to strongly influence cell responses to toxins. Cells were found to be more susceptible to the toxins when cultured in softer matrices that emulated the stiffness of brain tissue. Furthermore, the effect of matrix stiffness on differential cell responses to toxins was negated by the presence of the adhesive ligand RGD, but regained when integrin-based cell-matrix interactions were inhibited. This study therefore indicates that both 3D matrix stiffness and cell-matrix adhesions are important parameters in the design of more predictive in vitro platforms for drug development and toxicity screening.

Impacts of compacting methods on the delivery of erythromycin and vancomycin from calcium polyphosphate hydrogel matrices.

Designing hydrogels for controlled drug delivery remains a big challenge. We developed a calcium polyphosphate hydrogel (CPP) as matrix for delivery of vancomycin (VCM) and erythromycin (EM) by unique ionic binding and physical wrapping. In this continuing study, we investigated if gel discs prepared by mechanical compaction (at 3000 psi pressure, C-discs) is superior to that of discs prepared by regular manual compaction (M-discs) for the release of VCM and EM (10 wt.%). Data demonstrated a significant reduction of burst release of VCM and EM in C-discs (1.8% and 5%, respectively) as compared to that from M-discs within 72 hr (55% and 60%, respectively, p < 0.05). In addition, C-discs significantly extended the VCM release (1500 hr) and EM (800 hr) as compared to M-discs (160 and 96 hr, respectively, p < 0.05). The VCM released from C-discs retained its bactericidal activity much longer (1500 hr) than that from M-discs (700 hr, p < 0.05). Raman Spectroscopy indicated an ionic bond of both VCM and EM with fully hydrated polyphosphate chains of CPP hydrogel matrix for both M-discs and C-discs. Micro CT showed that C-discs had much denser microstructures and less number/depth of microcracks as a result of high pressure. We propose that CPP hydrogel represents an excellent tool for the controllable and sustained delivery of VCM and EM. Extensive experiments are currently underway to evaluate the potential impacts of the modification of compaction techniques, other antibiotics, gel concentrations on the drug release, degradation behavior and infection control both in vitro and in vivo.

Comparing the release of erythromycin and vancomycin from calcium polyphosphate hydrogel using different drug loading methods.

Calcium polyphosphate (CPP) hydrogel is used to load erythromycin (EM) and vancomycin (VCM) by means of two loading methods: they are either added directly to the formed CPP hydrogel (Gel Mixture method) or mixed with CPP powders, followed by the formation of CPP-antibiotic hydrogel (Powder Mixture method). The release of loaded antibiotics from CPP hydrogel is measured up to 48 hr. Compared to Powder Mixture method, Gel Mixture method significantly reduced the burst release of embedded antibiotics. A significant change in CPP hydrogel Raman characteristic peaks is observed only in Gel Mixture method, indicating a close interaction between embedded antibiotics with CPP hydrogel matrix. In contrast, a similarity between characteristic peaks of CPP hydrogel and Powder Mixture method shows that antibiotic incorporation does not interfere with CPP gel formation, resulting in no ionic interaction between antibiotic and polyphosphate chains. Rheometer analysis further confirms that the hydrophobic nature of EM impacts the viscoelastic properties of CPP hydrogel, whereas the hydrophilic VCM exhibits a higher loading efficiency. The potential application of CPP hydrogel as a ceramic matrix for sustained drug release warrants further investigation.

Homogenization Theory for the Prediction of Obstructed Solute Diffusivity in Macromolecular Solutions.

The study of diffusion in macromolecular solutions is important in many biomedical applications such as separations, drug delivery, and cell encapsulation, and key for many biological processes such as protein assembly and interstitial transport. Not surprisingly, multiple models for the a-priori prediction of diffusion in macromolecular environments have been proposed. However, most models include parameters that are not readily measurable, are specific to the polymer-solute-solvent system, or are fitted and do not have a physical meaning. Here, for the first time, we develop a homogenization theory framework for the prediction of effective solute diffusivity in macromolecular environments based on physical parameters that are easily measurable and not specific to the macromolecule-solute-solvent system. Homogenization theory is useful for situations where knowledge of fine-scale parameters is used to predict bulk system behavior. As a first approximation, we focus on a model where the solute is subjected to obstructed diffusion via stationary spherical obstacles. We find that the homogenization theory results agree well with computationally more expensive Monte Carlo simulations. Moreover, the homogenization theory agrees with effective diffusivities of a solute in dilute and semi-dilute polymer solutions measured using fluorescence correlation spectroscopy. Lastly, we provide a mathematical formula for the effective diffusivity in terms of a non-dimensional and easily measurable geometric system parameter.