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08.10.2019Jack Kendall

10/8/2019Jack Kendall 1

Paper 1 – Particle Hydrogels on Hyaluronic acid building blocksMaterials and Mechanics in Medicine HS 2019

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15.15-15.30: Paper Overview

15.30-16.00: Solve the Quiz (optional)

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Today

Jack Kendall

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Paper 1

Jack Kendall

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Linear, non sulfated GAGs Natural ECM component biodegradable, non-immunogeneic Multiple sites for modification:

Carboxyl and hydroxyl groups

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Hyaluronic Acid (HA) = Hyaluronan

Jack Kendall

PresenterPresentation NotesBackground informations1)An unbranched polysaccharid2)One of the most important components of the ECM Can be naturally metabolized and cleared in the body without producing toxic degradation products3)It can form a hydrogel under mild conditions e.g. chemical modification, crosslinking or photo-crosslinking

GAGs= GlycosaminoglycanGlucoronic acid=uronic acid

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Hydrophilic crosslinked polymers Natural/synthetic polymeric building blocks For example: Hyaluronic acid, Chitasan, Alginate, PEG,…

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Hydrogels

Jack Kendall

PresenterPresentation NotesBackground informationIn the paper: Hyaluronic acid used as building blocks

hydrogels can be chemical OR physical:Chemical: Crosslinking occurs by covalent bondingPhysical: Crosslinking is given by weaker forces e.g. hydrogen bonds, hydrophobic interactions or electrostatic forces.

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Mimic ECM 3D structural framework Moldable Tunable mechanical properties Water-based Swollen mesh (mesh size: 10-100nm)

Degradation is required for cellular infiltration.

Why?

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Why polymeric hydrogels?

Jack Kendall

PresenterPresentation NotesFor example: By incorporation of chemical and physical bioactive cuesIn which cells grow and secrete ECM.Can take the form of any mold before complete gelation (sol-gel transition)4) For example: elastic, viscoelastic, stress relaxing. It depends on the chosen chemistry5) Keep wounds hydrated and protected from bacterial infectionsBecause: Cells are in micrometers in size (Cells are bigger than the mesh sizes Cells can’t go through)

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How to modulate it?a) Integration of degradation sitesb) Noncovalent bonds Stress relaxing

Challenge: Too slow degradation no cell infiltration, fibrotic

encapsulation Too fast degradation no mechanical support

Need for balance between degradability and long-term mechanical support

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Degradation rate

Jack Kendall

PresenterPresentation NotesHOW to modulate (The 2 methods presented in the paper)a) For example: hydrolysable bonds, protease degradable peptides allow cellular infiltrationb) Noncovalent bondsallow material to stress relaxingallow cellular infiltrationAllow cellular infiltration

Ideally, a scaffold should be biodegradable at a rate that matches with the anabolic activity of the cells to create space for new tissue.

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Why is cellular infiltration essential?

Jack Kendall

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Why is cellular infiltration essential?

To allow endogeneous tissue integration

Jack Kendall

PresenterPresentation NotesCells will produce ECM to take over the structural role of the scaffold, which will degrade over time.

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Hydrogel (Paper)

Jack Kendall

PresenterPresentation Notesporous scaffold from voids between the packed beads.Advantage of standard bulk hydrogel: No harsh chemical methods which limit bioactive signal incorportation and injectability

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Methods to produce microporous scaffolds

Salt leaching Gas foaming Lyophilization Sphere templating

Jack Kendall

PresenterPresentation Notes4 commonly emploiyed methods for producting microporous scaffolds

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Salt leaching

Jack Kendall

PresenterPresentation Notes 1)Salt crystals such as NaCl (common table salt) are put into a mold and polymer is poured over the salt, penetrating into all the small spaces left between the salt crystals.2)  The polymer is hardened and then the salt is removed by dissolving it in a solvent e.g. water or alcoholOpen holes/pores where the salt once wasThe pore size can be altered by simply changing the porogen size

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Gas foaming

Jack Kendall

PresenterPresentation Notes(b): Gas foaming: Used the nucleation and growth of gas bubbles dispersed throughout a polymer to generate a porous structure. 

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Lyophilization (=Freeze drying)

Jack Kendall

PresenterPresentation NotesWorks by freezing the material, then reducing the pressure and adding heat to allow the frozen water in the material to sublimate

(a low temperature dehydration process that involves freezing the product, lowering pressure, then removing the ice by sublimation)

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Sphere templating

Jack Kendall

PresenterPresentation NotesAll pores with the same sizeAll pores interconnected in 3 dimensions

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Deeper characterization of HA MAP gels Generation of particle hydrogels using 3 different

annealing approaches Demonstrate the versality of those 3 approaches by

exploration of physical differences: Pores connectivity Pore area/void fraction Mechanical properties of the scaffold Cell spreading

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Aim (Paper)

Jack Kendall

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Enzymatic reaction FXIIIa

Light-based radical polymerization Eosin Y

Amine/carboxylic acid-based cross-linking PEG-NHSAll three leads to the formation of a stable 3D scaffold

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3 Orthogonal annealing chemistries

Jack Kendall

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FXIIIa A coagulation factor

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Enzymatic reaction

Jack Kendall

PresenterPresentation NotesA new approach in hydrogel formationEnzymes can be used to cleave or establish a chemical bond with greater efficiency than other methodsShort reaction times and specificityEnzyme-substrate specificityAvoids undesired or toxic side reactions.

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Light-based radical polymerization(Eosin Y)

Eosin

Jack Kendall

PresenterPresentation NotesEosin. Most common staining method in histology; H&E= Hematoxylin and Eosin

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PEG-NHS

PEG NHS

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Amine/carboxylic acid-based cross-linking

Jack Kendall

PresenterPresentation NotesCross-linking via amide bond

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In HA based MAP Hydrogel:

Pore sizes are smaller than in other scaffolds Annealing of the beads is required Pore diameter depends on the packing density Cells loading during scaffold formation is possible Pores are interconnected HDFs cells spread in HA within 2 days

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Key Findings (Paper)

Jack Kendall

PresenterPresentation Notesa)

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References and further reading

https://parjournal.net/article/view/2342

https://pubs.rsc.org/en/content/articlehtml/2013/cs/c3cs60040h

https://www.sciencedirect.com/science/article/pii/S1742706119304003

https://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.5b00671

https://www.intechopen.com/books/emerging-concepts-in-analysis-and-applications-of-

hydrogels/in-situ-forming-cross-linking-hydrogel-systems-chemistry-and-biomedical-

applications

Jack Kendall

https://parjournal.net/article/view/2342https://pubs.rsc.org/en/content/articlehtml/2013/cs/c3cs60040hhttps://www.sciencedirect.com/science/article/pii/S1742706119304003https://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.5b00671https://www.intechopen.com/books/emerging-concepts-in-analysis-and-applications-of-hydrogels/in-situ-forming-cross-linking-hydrogel-systems-chemistry-and-biomedical-applications

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Quiz

Jack Kendall

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