Investigation of Dopamine Analogues: Synthesis, Mechanistic Understanding, and Structure-Property Relationship.

Dopamine, perhaps the simplest molecule that covalently links catechol and amine, together with its derivatives, has shown impressive adhesive and coating properties with its polymers. However, the scope of the molecules is rather limited, and the polymerization mechanisms are still elusive. We designed a general synthetic scheme and successfully synthesized a series of dopamine analogues with different alkyl chain lengths between the catechol and amine. Taking these new dopamine analogues, together with the molecular systems that have separate catechol and alkyl amine, we show that having both catechol and amine in the molecular system, whether covalently linked via an alkyl chain or not, is sufficient to polymerize under a similar reaction condition to that of dopamine polymerization. However, the time-dependent UV-vis characterization of the individual polymerization indicates that the polymerization for individual molecular systems likely proceeds via different reaction intermediates, depending on the length of the alkyl chain and whether there is a covalent linkage. Interestingly, whereas the covalent linkage via an alkyl chain is not necessary for showing the adhesive property, it is required to achieve the impressive coating property. Our results offer new insights into the design and synthesis of dopamine analogues for future applications, as well as a further mechanistic understanding of the polymerization of these dopamine analogues.

The role of temperature in forming sol-gel biocomposites containing polydopamine.

To further improve the physical strength and biomedical applicability of bioceramicsbuilt on hydroxyapatite-gelatin (HAp-Gel) and siloxane sol-gel reactions, we incorporated mussel adhesive inspired polydopamine (PD) into our original composite based on HAp-Gel cross-linked with siloxane. Surprisingly, with the addition of PD, we observed that the processing conditions and temperatures play an important role in the structure and performance of these materials. A systematic study to investigate this temperature dependence behavior discloses that the rate of crosslinking of silane during the sol-gel process is significantly influenced by the temperature, whereas the polymerization of the dopamine only shows minor temperature dependence. With this discovery, we report an innovative thermal process for the design and application of these biocomposites.

An Investigation of Siloxane Cross-linked Hydroxyapatite-Gelatin/Copolymer Composites for Potential Orthopedic Applications().

Causes of bone deficiency are numerous, but biomimetic alloplastic grafts provide an alternative to repair tissue naturally. Previously, a hydroxyapatite-gelatin modified siloxane (HAp-Gemosil) composite was prepared by cross-linking (N, N'-bis[(3-trimethoxysilyl)propyl]ethylene diamine (enTMOS) around the HAp-Gel nanocomposite particles, to mimic the natural composition and properties of bone. However, the tensile strength remained too low for many orthopedic applications. It was hypothesized that incorporating a polymer chain into the composite could help improve long range interaction. Furthermore, designing this polymer to interact with the enTMOS siloxane cross-linked matrix would provide improved adhesion between the polymer and the ceramic composite, and improve mechanical properties. To this end, copolymers of L-Lactide (LLA), and a novel alkyne derivatized trimethylene carbonate, propargyl carbonate (PC), were synthesized. Incorporation of PC during copolymerization affects properties of copolymers such as molecular weight, T(g), and % PC incorporation. More importantly, PC monomers bear a synthetic handle, allowing copolymers to undergo post-polymerization functionalization with graft monomers to specifically tailor the properties of the final composite. For our investigation, P(LLA-co-PC) copolymers were functionalized by an azido-silane (AS) via copper catalyzed azide-alkyne cycloaddition (CuAAC) through terminal alkyne on PC monomers. The new functionalized polymer, P(LLA-co-PC)(AS) was blended with HAp-Gemosil, with the azido-silane linking the copolymer to the silsesquioxane matrix within the final composite.These HAp-Gemosil/P(LLA-co-PC)(AS) composites were subjected to mechanical and biological testing, and the results were compared with those from the HAp-Gemosil composites. This study revealed that incorporating a cross-linkable polymer served to increase the flexural strength of the composite by 50%, while maintaining the biocompatibility of HAp-Gemosil ceramics.