Marcia W. Patchan

Liquid-Filled Metal Microcapsules

A moisture-sensitive diisocyanate liquid is microencapsulated within a metal shell measuring less than 2 μm thick and 50 μm in diameter. This mild synthesis takes place through a series aqueous processing steps that occur at or near room temperature. Through a combination of emulsification, interfacial polymerization, and electroless plating, one can microencapsulate moisture- or air-sensitive chemicals within a metal seal. The liquid-filled metal microcapsules promise a number of advantages compared to conventional polymeric microencapsulation, including improved mechanical properties and improved barrier properties to gases and organic molecules.

Robust Composite-Shell Microcapsules via Pickering Emulsification

Microencapsulation technology has been increasingly applied toward the development of self-healing paints. Added to paint as a dry powder prior to spraying, the microcapsules store a liquid that can repair the protective barrier layer if released into a scratch. However, self-healing will not occur unless the microcapsules can withstand spray-painting, aggressive solvents in the paint, and long-term exposure to the elements. We have therefore developed a one-pot synthesis for the production of Pickering microcapsules with outstanding strength, solvent resistance, and barrier properties. Octadecyltrimethoxysilane-filled (OTS) microcapsules form via standard interfacial polycondensation, except that silica nanopowder (10-20 nm diameter) replaces the conventional surfactant or hydrocolloid emulsifier. Isophorone diisocyanate (IPDI) in the OTS core reacts with diethylenetriamine, polyethylenimine, and water to form a hard polymer shell along the interface. Compared to pure polyurea, the silica-polyurea composite improves the shelf life of the OTS by 10 times. The addition of SiO2 prevents leaching of OTS into xylenes and hexanes for up to 80 days, and the resulting microcapsules survive nebulization through a spray gun at 620 kPa in a 500 cSt fluid.

Synthesis and properties of regenerated cellulose-based hydrogels with high strength and transparency for potential use as an ocular bandage

Cellulose is a biologically derived material with excellent wound-healing properties. The high strength of cellulose fibers and the ability to synthesize gels with high optical transparency make these materials suitable for ocular applications. In this study, cellulose materials derived from wood pulp, cotton, and bacterial sources were dissolved in lithium chloride/N,N-dimethylacetamide to form regenerated cellulose hydrogels. Material properties of the resulting hydrogels, including water content, optical transparency, and tensile and tear strengths, were evaluated. Synthesis parameters, including activation time, dissolution time, relative humidity, and cellulose concentration, were found to impact the material properties of the resulting hydrogels. Overnight activation time improves the optical transparency of the hydrogels from 77% to 97% at 550 nm, whereas controlling cellulose concentration improves their tear strength by as much as 200%. On the basis of the measured transmittance and strength values of the regenerated hydrogels prepared via the optimized synthesis parameters, Avicel PH 101, Sigma-Aldrich microcrystalline cellulose 435236, and bacterial cellulose types were prioritized for future biocompatibility testing and potential clinical investigation.

Evaluation of the biocompatibility of regenerated cellulose hydrogels with high strength and transparency for ocular applications

Prompt emergency treatment for ocular injury, particularly in a battlefield setting, is essential to preserve vision, reduce pain, and prevent secondary infection. A bandage contact lens that could be applied in the field, at the time of injury, would protect the injured ocular surface until hospital treatment is available. Cellulose, a natural polymer, is widely used in biomedical applications including bandage materials. Hydrogels synthesized from different cellulose sources, such as plants, cotton, and bacteria, can have the optical transparency and mechanical strength of contact lenses, by tailoring synthesis parameters. Thus, we optimized the fabrication of cellulose-based hydrogels and evaluated their in vivo biocompatibility and related physical properties. Our data demonstrate that along with tailorable physical properties, our novel cellulose-based hydrogels could be made with contact lens geometry, exhibit no significant signs of material toxicity after 22 days of in vivo testing, and show significant promise for use as a corneal bandage immediately following ocular trauma.

Synergy between Galvanic Protection and Self-Healing Paints.

Painting is a cost-effective technique to delay the onset of corrosion in metals. However, the protection is only temporary, as corrosion begins once the coating becomes scratched. Thus, an increasingly common practice is to add microencapsulated chemical agents to paint in order to confer self-healing capabilities. The additives ability to protect the exposed surface from corrosion depends upon (i) how long the chemical agent takes to spread across the exposed metal; (ii) how long the agent takes to form an effective barrier layer; and (iii) what happens to the metal surface before the first two steps are complete. To understand this process, we first synthesized 23 ± 10 μm polyurea microcapsules filled with octadecyltrimethoxysilane (OTS), a liquid self-healing agent, and added them to a primer rich in zinc, a cathodic protection agent. In response to coating damage, the microcapsules release OTS into the scratch and initiate the self-healing process. By combining electrochemical impedance spectroscopy, chronoamperometry, and linear polarization techniques, we monitored the progress of self-healing. The results demonstrate how on-demand chemical passivation works synergistically with the cathodic protection: zinc preserves the surface long enough for self-healing by OTS to reach completion, and OTS prolongs the lifetime of cathodic protection.