Polymers in Biology, Bioengineering and Medicine

Kristi AnsethDept. of Chemical and Biological Engineering and

the Howard Hughes Medical Institute

Traditional 2D Cultures:-polystyrene w/ &w/out surfacemodifications

Emerging 3D Cultures:-Collagen-Matrigel

Polymers in Biology

Many Cells Behave Differentlyin 2D vs 3D Culture

Tumorigenic cells (middle panel) can be reverted to a near-normalmorphology by down-modulation of EGFR signaling. The effect is notobserved in 2D.

Bissell et al., Current Opinion in Cell Biology, 15,753-62 (2003)

Designing Polymer Niches for Cell Culture:

ECM-like Molecules,Growth Factors,Differentiation Factors

Size scale,Kinetic of degradation,Transport

Permissive Promoting

Encapsulation

Cells

Seeding

Synthetic Natural

Polymers as ECM mimetics

Lutolf & Hubbell, Nature Biotechnology 23, 47 - 55 (2005) D. TirrellJ. Hubbell

Cells also Sense and Respond toMechanical Environment

Discher et al., Science 18 November 2005:Vol. 310. no. 5751, pp. 1139 - 1143

PLA

Matrigel

Artery-derivedECM

What biologists could use….

• Tools to temporally control presentation ofmolecules

• Spatial control of ligands to guide cell attachmentand protein interactions on multiple scalesranging from nms to 10s of µms scale

• Better mimics of the extracellular matrix and the invivo environment

• Presentation of complex (heterogeneous) andmultiple functionalities

What polymer scientists andengineers are trying to develop….• Materials that allow temporal control of cell

interactions• Spatial control of chemistry and mechanics at

multiple scales• Spatiotemporal control of functionalities in three-

dimensional settings• Presentation of complex and multiple

functionalities• Mimicking properties of natural materials and

integrating multiple functionalities• Using materials to direct cell-cell and cell-tissue

interactions

Polymer Science in Bioengineering

• Delivery of new molecular targets• High through-put assays• Directing cellular interactions and

tissue regeneration

Advanced ProcessingControl on multipletime and size scales

New Chemistries

Polymer Assisted Delivery ofTherapeutics

• Human genome project --> Accelerated discovery ofbiomolecular products (proteins, plasmid DNAs,various forms of RNA)

• Broad challenges:– Stability of molecules– Non-specific interactions with cells– Limited intracellular entry of nucleic acids– Delivering new classes of molecules (e.g., miRNA)

• Significant efforts in targeting and functional cues toenhance delivery (e.g., loading into biomaterials,complexation and chemical fusion)

Polymer Chemistry-Structure-PropertyRelationships for Intracellular Delivery

Hubbell, Science, 300, 595 (2003).

Role of the Microenvironment inRegulating Therapeutic Effects

Kong & Mooney, Nature Reviews,6, 455 (2007)

Polymers for stimulatory and/or inhibitory effects

• Through directed celladhesion• Chemical structure ofadhesion cue• Physical properties andarchitecture of the ECN• Presence of supplementalmolecules to up or down-regulate adhesion-receptors

Polymer-Directed Cell-InteractionsPolymer-Directed Cell-Interactions

Density/Spacing of Cell-Adhesive Ligand

Controlling Cell Adhesion

Spatial Control of Cell Attachment

• Grafting to andgrafting fromapproaches

• Diverse chemicaland biologicalfunctionalities

• Chemistry vstopography

• Clustering of ligands

• Decouple mechanicsfrom chemistry

• Highly regulatedstructures

• Tunable surfaces

C).

Milan Mrksich,UChicago mrksich-group.uchicago.edu

Responsive substratesallow temporal and externalcontrol of materialproperties andfunctionalities

High Throughput Screening Methods

6 x 6 array of100 nl gels withvarying chemicalfunctionality.

On-chip, IHC or FISH

lmrt.mit.edu/personnel/sangeeta.aspSangeeta Bhatia, MIT

Directing expansion and differentiation of stem cellsImproving cell-based therapies

Polymer-Directed Cell AssemblyPolymer-Directed Cell Assembly

Fetal rat forebrain cells (E16-17)

Directing Cell-assemblyLocal Delivery of therapeutics

Mark Saltzman, Yale

Directing expansion and differentiation of stem cellsImproving cell-based therapies

How do cells receive informationfrom their environment?

PolymerArchitecture

RGDSurface Modification

Polymer Chemistry& Mechanics

Cell

Drug Delivery

Gene Delivery

MoleculeRelease

Matrix molecules

Enzymes

Collectively, these extrinsic factors trigger signaling pathways thataffect diverse aspects of cell behavior, modifying differentiation,proliferation, expression of ECM, activation of growth factors, andeven preventing apoptosis. Using this information to engineer andmanipulate cell behavior relevant to medical problems.

Polymer Science in Medicine

Fundamental Studies Clinical Application

Minimalist approachHistory of human applicationProcessing and manufacturingSafety and practicalityNearer-term impact

Sophisticated approachedBroad diversity of chemistryLong-term potentialWhat if?

Cell Therapies in Clinical Medicine

• Bone marrow transplants• Blood transfusions• Islet transplantations• Autologous chondrocyte

implantation• Over 2000 clinical trials related

to cell therapies:– Stem cells delivered to

ischemic heart regions– Neural precursor cells for

treating Parkinson’s disease– ……

Existing Therapies

Cell Delivery in Clinical Medicine

• Cell-based therapies will continueto grow as a clinical method totreat diseased or injured tissues.

• To date, treatments are often sub-optimal because carriers areneeded for the cells.

• Minimally, carriers are needed thatcan immobilize cells while allowingthem to grow.

• How to exploit polymers for theseapplications.

• Bone marrow transplants• Blood transfusions• Islet transplantations• Autologous chondrocyte

implantation• Over 2000 clinical trials related

to cell therapies:– Stem cells delivered to

ischemic heart regions– Neural precursor cells for

treating Parkinson’s disease– ……

Existing TherapiesMotivation for Polymer Development

Polymers in Medicine• How to learn from and mimic wound

healing? Or Development?• How much micromanaging of cellular

behavior is necessary? What level ofinformation is required?

• Controlling polymer structure and chemistryon multiple size and time scales

• Expand the repertoire of polymers used inhuman medicine and/or exploitingprocessing of existing materials to impartnew properties

Polymers in Biology, Bioengineering, andMedicine: Needs and Opportunities

• Expand the repertoire of polymers that areconsidered ‘biomaterials’ and exploit advancedprocessing methods

• Marriage of knowledge from genomics, proteomics,tissue morphogenesis, evolution of disease, stemcells and their differentiation, …with the design ofpolymers

• Better integrate multiscale modeling as a tool toguide experimental design and test hypotheses.

• Exploiting advanced tools in imaging, molecularanalysis, etc. to better characterize and quantify cell-bimolecule polymer constructs on multiple scales

• Seamless collaborations between basic sciences,engineering, and clinical sciences

HHMI’s Janelia Farm

Janelia Farm• HHMI’s first research campus• 281 acres, 760,000 gross sq ft, 380,000 sq ft of laboratories• Opened: Fall 2006• Cost: $500M USD• Focus: collaborative and innovative research that calls forthe development of cutting-edge technological tools.• Targets of recruitment: Early-career-stage investigator whoenjoy engaging in research themselves and working closelywith others•People: Group Leaders, Fellows, Students, Core Support,Visitors (individuals and project teams)• Steady state: 24 Group Leaders and collective populationof ~120 scientists