Christopher Tsui

Infection at the surgical site for dental implants results in failed procedures, patient pain, burdensome economic impact, and the over-prescription of prophylactic antibiotics. Mesoporous silica films as coatings for implants may provide an ideal antimicrobial drug storage and local release vector to the site of infection, however traditional drug loading techniques result in insufficient drug load and short-term release kinetics. In this work, we have applied a method to use a surfactant-antimicrobial drug octenidine dihydrochloride (OCT) as a template for mesostructured silica, to demonstrate silica–OCT composite films. The films are synthesized by evaporation induced self-assembly (EISA) and we explore the effects of synthesis parameters on porous film structure, OCT incorporation, and OCT drug release rates. Drug micelle incorporation into the silica mesostructure was highly dependent on silica precursor pre-reaction to form silica oligomers before film spin-casting. The OCT drug concentration of the synthesis solution dictated the time required for effective incorporation (without phase separation), with total loading in the film of up to 90% by mass. The OCT content in the films was found to directly determine the timescale of drug release, from 2 to 8 h for a single layer film. The total release timescale was increased by the addition of multiple layers of OCT–silica films to nearly 2 weeks. Drug release from films completely inhibited Streptococcus mutans (UA159) growth, while drug-free porous silica films showed no increase in bacterial growth over non-porous control. These OCT–silica films have a significant potential to store and release antimicrobial drugs from dental implant surfaces.

Microglia are the resident immune cells of the central nervous system that mediate the life and death of nervous tissue. During normal function, they exhibit a surveying phenotype and maintain vital functions in nervous tissue. In the event of injury or disease, chronic inflammation can result, wherein microglia develop a hyper-activated phenotype, shed their regenerative function, actively kill contiguous cells, and can partition injured tissue by initiating scar formation. With recoverable injury, microglia can develop a primed phenotype, where they appear to recover from an inflammatory event, but are limited in their support functions and show inappropriate responses to future injury often associated with neurodegenerative disorders. These microglial phenotypes were acutely recreated in vitro with potent pro- and anti-inflammatory treatments. Primary cultured microglia or mixed glia (microglia, astrocytes, and oligodendrocytes) were treated for 6 h with lipopolysaccharide (LPS). Recovery from an inflammatory state was modeled with 18-h treatment of the anti-inflammatory steroid dexamethasone. The cells were then treated for 24 h with interferon gamma (IFNγ) to detect inflammatory memory after recovery. Surveying was best represented in the untreated vehicle (Veh) cases and was characterized by negligible secretion of pro-inflammatory factors, limited expression of immune proteins such as induced nitric oxide synthase (iNOS), major histocompatibility complex class II (MHCII), relatively high expression of brain-derived and glial-derived neurotrophic factors (BDNF and GDNF), and thinly branched smaller microglia. Activation was noted in the LPS- and IFNγ-treated microglia with increased cytokines, NO, NGF, iNOS, proliferation, phagocytosis, reduced BDNF, and flattened round amoeboid-shaped microglia. Priming was observed to be an incomplete surveying restoration using dexamethasone from an activation comparison of LPS, IFNγ, and LPS/IFNγ. Dexamethasone treatments resulted in the most profound dysregulation of expression of NO, TNF, IL-1β, NGF, CD68, and MHCII as well as ramified morphology and uptake of myelin. These findings suggest microglial priming and hyper-activation may be effectively modeled in vitro to allow mechanistic investigations into these key cellular phenotypes.

The tissue environment is exceptionally complex, with well-controlled biochemical communication occurring between similar and dissimilar cells, as well as, between these cells and local extracellular matrices (ECM). In order to build an artificial ECM that can directly affect regional cell populations, a designer system should allow for controlled degradation, molecular release, and reorganization as related to local cellular function. (RADA)4 self-assembling peptide (SAP) hydrogels are excellent candidates for precisely tuned ECMs, or nanoscaffolds, with several beneficial qualities. They are a class of materials with uncomplicated fabrication and potentially allow for a diverse set of release strategies for many types of bioactive ligands. Enzyme-induced degradation and release of peptide sequences, synthesized within the SAP for on-demand cell signalling, could prove impactful to a plethora of human health applications. However, the degradation products and their release kinetics from these nanoscaffolds may greatly affect the overall system. To address this, enzyme kinetics in self-assembled hydrogels were studied by tethering matrix metalloproteinase 2 (MMP-2) cleavable peptide substrates of differing activities to the C-terminus of (RADA)4. High and low activity sequences, GPQG+IASQ (CP1) and GPQG+PAGQ (CP2), were respectively chosen for tunable release. When incubated with 5 nM MMP-2, over 3 days, both CP1 and CP2 sequences showed product formation values of ~32 and ~9% of the original substrate, respectively. On-demand product formation was found to be dependent upon both SAP composition and enzyme concentrations, and could be tuned over the course of several days and weeks. Despite the fact that the self-assembling peptides are not directly cleavable by MMP-2, the CP1 and CP2 nanoscaffold morphology was visibly degraded by the protease. This degradation yielded a lower fractal dimensions for the matrix and suggested clearance of these materials may be possible over time.