Using self-consistent field theory (SCFT), we study the conformational properties of polyelectrolyte dendrimers. We compare results for three different models of charge distributions on the polyelectrolytes: (1) a smeared, quenched charge distribution characteristic of strong polyelectrolytes; (2) a smeared, annealed charge distribution characteristic of weak polyelectrolytes; and (3) an implicit counterion model with Debye-Huckel interactions between the charged groups. Our results indicate that an explicit treatment of counterions is crucial for the accurate characterization of the conformations of polyelectrolyte dendrimers. In comparing the quenched and annealed models of charge distributions, annealed dendrimers were observed to modulate their charges in response to the density of polymer monomers, counterions, and salt ions. Such phenomena is not accommodated within the quenched model of dendrimers and is shown to lead to significant differences between the predictions of quenched and annealed model of dendrimers. In this regard, our results indicate that the average dissociated charge α inside the dendrimer serves as a useful parameter to map the effects of different parametric conditions and models onto each other. We also present comparisons to the scaling results proposed to explain the behavior of polyelectrolyte dendrimers. Inspired by the trends indicated by our results, we develop a strong segregation theory model whose predictions are shown to be in very good agreement with the numerical SCFT calculations.

The unique architecture of dendrimers has attracted interest in a wide variety of biomedical applications such as drug delivery. In order to gain insight into the solubilization of drugs inside dendrimer architectures, we have developed and numerically implemented a self-consistent field theory model for the equilibrium characteristics of charged dendrimer molecules in the presence of weakly acidic drug molecules. Using such a model, we examine the relative influence of excluded volume, electrostatic, and local enthalpic interactions upon the solubilization of drugs in dendrimers. When only excluded volume interactions are accounted, there is no driving force for drug solubilization inside the dendrimer, and hence depletion of the drug from the dendrimer molecule (relative to the bulk drug concentration) is observed. The inclusion of electrostatic interactions within the model results in solubilization of drugs within the dendrimer. The solubilization of the drugs is shown to increase with increasing drug charge density and increasing dendrimer generation number. We probe the effect of enthalpic interactions and demonstrate that the number of drug molecules encapsulated through enthalpic interaction is dependent upon the number of dendrimer monomers, the enthalpic interaction parameters between the dendrimer and drug (χPD), and the drug and solvent (χDS). We also analyze the combined effects of the preceding interactions to identify the synergism in their influence and delineate the relative importance of different parameters such as pOH, size of the drugs, and the Bjerrum length of the solution in influencing the encapsulation of drugs by dendrimer molecules.

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We examine the role of neutral dendrimer grafts upon the conformations and the drug complexation efficacy of weakly basic polyelectrolyte dendrimers by using a self-consistent field theory approach. Our results indicate that grafted chains modify the conformations of the dendrimers and lead to a swelling of the dendrimer, the degree of which increases with increasing chain length of the grafts. In turn, such conformational changes leads to a higher charge being carried by the dendrimer molecule. We compare the encapsulation efficacy of grafted and non-grafted dendrimers and find that for strong enough enthalpic and/or electrostatic interactions, the grafted dendrimers are capable of higher amounts of encapsulation than the non-grafted counterparts. By isolating the influences of electrostatic and enthalpic interactions, we clarify the physics behind the observed enhanced encapsulation.

We use polymer self-consistent field theory to study the physics involved in the permeation of charged dendrimer molecules across anionic lipid bilayer membranes. We specifically examine the influence of dendrimer shape deformations, neutral grafts, and pH conditions on the interactions between dendrimers and membranes. Our results indicate that the ability of the dendrimer to undergo conformational rearrangements plays a crucial role in influencing the interactions between the dendrimer and the membrane. At neutral pH, we observe that dendrimers with grafted chains are repelled by the anionic bilayers. However, decreasing the solution pH to endosomal conditions results in attractive dendrimer-membrane interactions under some parametric conditions. We observe that dendrimer insertion into the membrane results in a decreased value in membrane tension at which rupture occurs and, furthermore, that the rupture tension decreases with the addition of grafts to the dendrimer. Our results suggest that dendrimers grafted with neutral polymers can serve as effective pH sensitive delivery vectors.