We demonstrate the formation of polyethylene glycol (PEG) based hydrogels via oxime ligation and the photo-initiated thiol-ene 3D patterning of peptides within the hydrogel matrix post-gelation. The gelation process and final mechanical strength of hydrogels can be tuned using pH and the catalyst concentration. The time scale to reach the gel point and complete gelation can be shortened from hours to seconds using both pH and aniline catalyst, which facilitates the tuning of the storage modulus from 0.3 kPa to over 15 kPa. Azide and alkene functionalized hydrogels were also synthesized and we have shown the post gelation “click” type Husigen 1,3 cycloaddition and thiolene-based radical reactions for spatially defined peptide incorporation. These materials are the initial demonstration for translationally relevant hydrogel materials that possess tunable mechanical regimes attractive to soft tissue engineering and possess atom neutral chemistries attractive for post gelation patterning in the presence or absence of cells.
A new class of L-phenylalanine-based poly(ester urea)s (PEU) was developed that possess tunable mechanical properties and degradation rates. Our preliminary data have shown that 1,6-hexanediol-L-phenylalanine-based poly(ester urea)s possess an elastic modulus nearly double that of poly(lactic acid). The data in this article detail the synthesis of a series of L-phenylalanine-based poly(ester urea)s possessing a variation in diol chain length and how these subtle structural differences influence the mechanical properties and in vitro biodegradation rates. The mechanical data span a range of values that overlaps with several currently clinically available degradable polymers. Increasing the diol chain lengths increases the amount of flexible segment in the chemical structure, which results in reduced elastic modulus values and increased values of elongation at break. The L-phenylalanine-based poly(ester urea)s also exhibited a diol length dependent degradation process that varied between 1 and 5% over 16 weeks. Compared with PLLA, PEUs degrade more quickly, and the rate can be tuned by changing the diol chain length.
In most synthetic elastomers,c hanging the physical properties by monomer choice also results in ac hange to the crystallinity of the material, which manifests through alteration of its mechanicalperformance.Using organocatalyzed stereospecific additions of thiols to activated alkynes,h igh-molarmass elastomers were isolated via step-growth polymerization. The resulting controllable double-bond stereochemistry defines the crystallinity and the concomitant mechanical properties as well as enabling the synthesis of materials that retain their excellent mechanical properties through changing monomer composition. Using this approacht oe lastomer synthesis,f urther end group modification and toughening through vulcanization strategies are also possible.The organocatalytic control of stereochemistry opens the realm to an ew and easily scalable class of elastomers that will have unique chemical handles for functionalization and post synthetic processing.Nature has evolved the ability to create large and complex molecules in which the precise control over the spatial arrangement of the atoms is critical to their performance.The three-dimensional control over the arrangement of bonds is as important to the function and behavior of molecules as any other factor and is critical to the structure-function relationships that govern the role of arange of molecules.While the effect of stereochemistry on functionality is probably best known in the examples of small molecule drugs such as thalidomide (one enantiomer is effective against morning sickness,t he other is teratogenic) or naproxen (one enantiomer is used to treat arthritis pain, the other causes liver poisoning with no analgesic effect), it is less well-studied with respect to materials design.Elastomeric materials are applied widely to demanding applications on account of their inherent reversible deformation behavior. Many synthetic elastomer materials are tri-or multi-block copolymers that are based on the concept of an amorphous-crystalline or hard-soft phase-separated system in which organization of the hard and soft domains endows the strong but elastic properties upon the materials.[1] While these materials have found widespread application, changes to the monomers or stoichiometry designed to elicit ac hange in physical properties also alter the chain packing and hence the mechanical properties of the materials.I nterestingly,n atural rubber and gutta percha are homopolymers of poly(cisisoprene) and poly(trans-isoprene) respectively.W hile these materials differ by only the double bonds of the backbone,the superior elastomeric properties of natural rubber [2] are attributed to the enhanced chain packing afforded by its stereochemical orientation.[3] While the design principles to control crystallinity and the associated mechanical properties in these materials are clear,the inability to incorporate awide range of functional groups in ac ontrolled manner or rationally define the chain end functionality limits the applications of both these materials a...
Amino acid-based poly(ester urea) (PEU) copolymers functionalized with pendant catechol groups that address the need for strongly adhesive yet degradable biomaterials have been developed. Lap-shear tests with aluminum adherends demonstrated that these polymers have lap-shear adhesion strengths near 1 MPa. An increase in lap-shear adhesive strength to 2.4 MPa was achieved upon the addition of an oxidative cross-linker. The adhesive strength on porcine skin adherends was comparable with commercial fibrin glue. Interfacial energies of the polymeric materials were investigated via contact angle measurements and Johnson-Kendall-Roberts (JKR) technique. The JKR work of adhesion was consistent with contact angle measurements. The chemical and physical properties of PEUs can be controlled using different diols and amino acids, making the polymers candidates for the development of biological glues for use in clinical applications.
Amino acid-based poly(ester urea)s (PEU) are emerging as a new class of degradable polymers that have shown promise in regenerative medicine applications. Herein, we report the synthesis of PEUs carrying pendent "clickable" groups on modified tyrosine amino acids. The pendent species include alkyne, azide, alkene, tyrosine−phenol, and ketone groups. PEUs with M w exceeding to 100K Da were obtained via interfacial polycondensation methods, and the concentration of pendent groups was varied using a copolymerization strategy. The incorporation of derivatizable functionalities is demonstrated using 1 H NMR and UV−vis spectroscopy methods. Electrospinning was used to fabricate PEU nanofibers with a diameters ranging from 350 to 500 nm. The nanofiber matricies possess mechanical strengths suitable for tissue engineering (Young's modulus: 300 ± 45 MPa; tensile stress: 8.5 ± 1.2 MPa). A series of bioactive peptides and fluorescent molecules were conjugated to the surface of the nanofibers following electrospinning using bio-orthogonal reactions in aqueous media. The ability to derivatize PEUs with biological molecules using translationally relevant chemical methods will significantly expand their use in vitro and in vivo.
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