Optimizing Soluble Cues for Salivary Gland Tissue Mimetics Using a Design of Experiments (DoE) Approach

Bridging systems biology and tissue engineering: Unleashing the full potential of complex 3D in vitro tissue models of disease

Rapid advances in tissue engineering have resulted in more complex and physiologically relevant 3D in vitro tissue models with applications in fundamental biology and therapeutic development. However, the complexity provided by these models is often not leveraged fully due to the reductionist methods used to analyze them. Computational and mathematical models developed in the field of systems biology can address this issue. Yet, traditional systems biology has been mostly applied to simpler in vitro models with little physiological relevance and limited cellular complexity. Therefore, integrating these two inherently interdisciplinary fields can result in new insights and move both disciplines forward. In this review, we provide a systematic overview of how systems biology has been integrated with 3D in vitro tissue models and discuss key application areas where the synergies between both fields have led to important advances with potential translational impact. We then outline key directions for future research and discuss a framework for further integration between fields.

Slow hydrogel matrix degradation enhances salivary gland mimetic phenotype

We recently developed a salivary gland tissue mimetic (SGm), comprised of salivary gland cells encapsulated in matrix metalloproteinase (MMP)-degradable poly(ethylene glycol) hydrogels within arrays of ∼320 µm diameter spherical cavities molded in PDMS. The SGm provides a functional and physiologically relevant platform well-suited to high-throughput drug screening for radioprotective compounds. However, the utility of the SGm would benefit from improved retention of acinar cell phenotype and function. We hypothesized that tuning biochemical cues presented within the PEG hydrogel matrix would improve maintenance of acinar cell phenotype and function by mimicking the natural extracellular matrix microenvironment of the intact gland. Hydrogels formed using slower-degrading MMP-sensitive peptide crosslinkers showed >2-fold increase in sphere number formed at 48 h, increased expression of acinar cell markers, and more robust response to calcium stimulation by the secretory agonist, carbachol, with reduced SGm tissue cluster disruption and outgrowth during prolonged culture. The incorporation of adhesive peptides containing RGD or IKVAV improved calcium flux response to secretory agonists at 14 days of culture. Tuning the hydrogel matrix improved cell aggregation, and promoted acinar cell phenotype, and stability of the SGm over 14 days of culture. Furthermore, combining this matrix with optimized media conditions synergistically prolonged the retention of the acinar cell phenotype in SGm. STATEMENT OF SIGNIFICANCE: Salivary gland (SG) dysfunction occurs due to off-target radiation due to head and neck cancer treatments. Progress in understanding gland dysfunction and developing therapeutic strategies for the SG are hampered by the lack of in vitro models, as salivary gland cells rapidly lose critical secretory function within 24 hours in vitro. Herein, we identify properties of poly(ethylene glycol) hydrogel matrices that enhance the secretory phenotype of SG tissue mimetics within the previously-described SG-microbubble tissue chip environment. Combining slow-degrading hydrogels with media conditions optimized for secretory marker expression further enhanced functional secretory response and secretory marker expression.

Leveraging the Exploratory and Predictive Capabilities of Design of Experiments in Development of Intraarticular Injection of Imatinib Mesylate Containing Lipospheres

An intraarticular, liposphere-based, formulation of Imatinib mesylate for weekly administration was developed. Lipospheres were prepared using double emulsion technique using dierucoyl phosphatidylcholine, 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt), cholesterol, and tricaprylin as lipid phase in dichloromethane in a four-step process. Primary emulsion, formed using a high-pressure homogenizer, was diluted using a secondary aqueous phase in an Inline mixer to form the liposomal dispersion. Nitrogen flushing was done to remove dichloromethane, and the dispersion was finally centrifuged and adjusted for potency. The amount of cholesterol and triglyceride was taken as formulation variables, and speed of homogenization was used as a process variable in the Box-Behnken design while particle size, % drug entrapment, and drug release at the end of 4 h and 5 days were taken as response variables. Multivariate data analysis grouped the variables in two latent variable sets, one based on the speed and the other on the composition of lipospheres. Multiple linear regression analysis was used to generate mathematical model for each response. Constraints were put on the values of responses, as per the requirements of the final product, and the "freedom to operate" design space was located using an overlay plot. The center point batch sufficed all the set criteria, and Monte Carlo simulations on the factor variables indicated a defect rate of 5%. The center point batch was characterized for viscosity, osmolality, pH, drug release, and lipocrit value. The dispersion was charged in a prefilled syringe and studied for stability. The product was found to be stable at 2-8°C over a period of 6 months.