Biology and engineering have distinct vocabularies for describing the same physical reality. A biologist studying how endothelial cells respond to their environment will focus on receptor signaling, cytoskeletal reorganization, and gene expression. A materials engineer examining the same environment will focus on stiffness, viscoelasticity, pore geometry, and degradation rate. Both are describing factors that determine how a cell behaves — but they are measuring different things, using different instruments, and asking different questions.
Justin Jadali’s research at Yale University sits precisely at the interface between these two modes of description. His work on alginate-based microparticle systems for vascularized tissue engineering is, at its core, a study in how the physical properties of a crosslinked polymer network — properties defined by materials science — determine whether cells in a biological environment receive the signals they need to form functional microvascular structures.
What Makes a Hydrogel a Useful Research and Clinical Material
Hydrogels are three-dimensional polymer networks that absorb and retain large volumes of water — in some cases, more than 90 percent of their total mass. That water content makes them structurally and mechanically similar to soft biological tissue, which is why hydrogels have been widely investigated as scaffold materials for tissue engineering applications.
Alginate hydrogels, specifically, offer a combination of properties that makes them useful in both research and clinical contexts. They are biocompatible, meaning they do not trigger significant immune responses in mammalian cell cultures or animal models under standard conditions. They gel under mild ionic conditions that do not denature sensitive biological molecules. Their mechanical properties — stiffness, elasticity, degradation behavior — can be adjusted by varying polymer concentration, molecular weight distribution, and crosslinking chemistry. And in microparticle form, they can encapsulate and release bioactive factors over a defined time course, acting as controlled-delivery vehicles embedded within a larger construct.
Each of these properties is relevant to the vascularization problem Jadali’s research addresses. But each is also directly dependent on how the gel is formed — and specifically, on the crosslinking chemistry used to set the network.
Ionic Crosslinking: How the Chemistry Determines the Structure
Alginate is a block copolymer composed of two uronic acid monomers — mannuronic acid and guluronic acid — arranged in sequences along the chain. When exposed to divalent cations, these sequences form coordination bonds with the metal ions, and adjacent polymer chains are bridged into a three-dimensional network. This is ionic crosslinking: no covalent bonds are formed, no thermal or photochemical initiators are required, and the process occurs rapidly under aqueous conditions compatible with sensitive biological cargo.
The identity of the crosslinking cation matters. Calcium is the most frequently used crosslinker in alginate research. It produces gels with well-characterized mechanical properties and crosslinks through preferential binding to guluronic acid-rich sequences in the polymer chain. The resulting gel has a defined stiffness range and a degradation profile that depends on calcium ion concentration in the surrounding medium — in physiological environments, calcium exchange with competing ions gradually erodes the crosslink density and softens the gel over time.
Zinc crosslinks alginate through the same ionic mechanism but with different binding geometry and coordination chemistry. Zinc-alginate gels can exhibit different stiffness profiles, different swelling behavior, and different degradation kinetics compared to calcium-crosslinked counterparts prepared from the same alginate stock. They also introduce zinc ions — which are biologically active at physiological concentrations — into the surrounding cell culture environment as the gel degrades, a factor with potential downstream effects on cell behavior that must be characterized rather than assumed.
Justin Jadali’s research at Yale directly investigates these distinctions. By fabricating microparticle batches using each crosslinker under equivalent processing conditions and characterizing the resulting gels — measuring mechanical properties and assessing how each formulation affects cell behavior in co-culture — his work builds a quantitative map of how crosslinker choice propagates from the fabrication stage into biological outcomes.
Why Stiffness Is a Biological Signal
One of the more counterintuitive findings from the last two decades of biophysics research is that cells are not passive inhabitants of their mechanical environment. They actively sense the stiffness of the matrix they are embedded in or adhering to — through integrin-mediated focal adhesions and cytoskeletal tension — and they adjust their behavior in response. This phenomenon, called mechanosensing, has been demonstrated across multiple cell types and has direct relevance to vascular biology.
Endothelial cells — the cell type primarily responsible for forming the inner lining of blood vessels — respond to substrate stiffness in ways that affect their organization, migration, and tube-forming behavior. On very stiff substrates, endothelial cells tend toward a spread, nonmigratory morphology. On softer substrates closer to the mechanical properties of native soft tissue, they can organize into tubular structures that resemble capillary networks. The stiffness of a hydrogel matrix is not, therefore, simply a structural variable — it is a parameter that shapes the biological process the researcher is trying to study or promote.
This means that crosslinker-dependent differences in alginate gel stiffness are not only a materials science concern. They are a biological one. A gel crosslinked with calcium to a given stiffness and a gel crosslinked with zinc to a different stiffness will not produce equivalent biological environments, even if all other variables are held constant. Characterizing that difference — quantifying how each crosslinking condition affects gel stiffness and then connecting that mechanical data to cell behavior in culture — is the kind of systematic experimental work that makes a materials platform designable rather than empirical.
The Fabrication Side: Microparticle Production and Protocol Discipline
Fabricating alginate microparticles with reproducible properties requires control over several processing variables: polymer concentration, crosslinker concentration, mixing conditions, droplet generation method, and gelation time, among others. Each variable affects particle size distribution, crosslink density, and the uniformity of the resulting gel network — and batch-to-batch variability in any of them can introduce noise that obscures the biological signal the researcher is trying to measure.
Jadali’s experimental work involves not only running cell culture assays but maintaining the fabrication-side protocol discipline that makes those assays interpretable. Every particle batch must be produced under documented conditions that can be reproduced in subsequent experiments. Characterization data — particle size, mechanical properties, factor loading and release — must be tracked and linked to the biological outcomes observed in downstream culture experiments. Without that chain of documentation, a positive result in one experiment cannot be confirmed in the next, and the platform cannot be rationally optimized.
This kind of protocol rigor is a technical skill in its own right. It is also one where Jadali’s background in entrepreneurship — operating a business that required consistent, documented processes to function reliably across 10 employees — provides habits that transfer directly to the lab.
Materials Science as the Enabling Layer
The vascularization problem in tissue engineering is fundamentally a biological problem — cells need to receive the right signals to form vessels. But the solution, increasingly, is a materials one. The ability to deliver those signals with spatial precision, at a controlled rate, from a substrate with defined mechanical properties, is what makes biological self-organization tractable in an engineered environment.
Justin Jadali’s research at Yale addresses that materials layer with the systematic rigor it requires. By characterizing how crosslinking chemistry determines gel properties, and by quantifying how those gel properties determine what cells do in culture, his work builds the kind of parameter map that allows future researchers — and future clinical developers — to make informed design decisions about the material systems they choose.
The junction between materials science and cell biology is where some of the most productive tissue engineering research is currently being done. Jadali’s position at that junction — trained as a mechanical engineer, fluent in cell biology, and working in a materials science program at Yale — puts him in a place to contribute to it in ways that researchers trained within a single disciplinary tradition cannot.
About Justin Jadali
Justin Jadali is a mechanical engineer and biomedical engineering researcher currently completing his M.S. in Mechanical Engineering and Materials Science at Yale University. He earned his B.S. in Mechanical Engineering from UCLA as part of the Class of 2025, following three Associate of Science degrees in Physics, Mathematics, and Natural Sciences from Irvine Valley College. At Yale, his research focuses on alginate microparticle fabrication, crosslinking systems, and the quantification of microvessel self-assembly in three-dimensional tissue constructs. He has hands-on experience in polymer processing, cell culture, and microscopy workflows, and has served as a teaching assistant for the Yale mechanical engineering capstone. He is also the founder of an e-commerce company that he grew to approximately 10 employees before selling at a six-figure valuation.