1. Tissue Engineering and Regenerative Medicine
2012

2. Thoughts?
What products in biomedical engineering have you encountered?
What products in biomedical engineering will be produced in the future?

3. Tissue Engineering
Tissue Engineering is the in vitro development (growth) of tissues or organs to replace or support the function of defective or injured body parts, or the directed management of the repair of tissues within the body (in vivo).
Research is presently being conducted on several different types of tissues and organs, including:
Skin
Cartilage
Blood Vessels
Bone
Muscle
Nerves
Liver
Kidney
etc. etc. etc.

4. Tissue Engineering is comprised of…
Bioengineers Material Scientists Cell and molecular biologists Immunologists Policy Makers Chemical Engineers Electrical Engineers Surgeons

5. “all tissues are comprised of several levels of structural hierarchy”
Tissue Organization
Before a tissue can be developed in vitro (outside of the body), first we must understand how tissues are organized in our body.
“all tissues are comprised of
several levels of structural hierarchy”
These structural levels exist from the macroscopic level (centimeter range) all the way down the molecular level (nanometer range)
there can be as many as 7-10 distinct levels of structural organization in some tissues or organs

6. Organization of the Tendon

7. Organization of the Kidney

8. How can we build the functional subunit outside of the body
Functional Subunits
The smallest level at which the basic function of the tissue/organ is provided is called a “functional subunit”:
functional subunits are in the order of ~100 mm (whereas cells are of the order of ~10 mm)
each organ is comprised between x 106 functional subunits
each functional subunit is comprised of a mixture of different cell types and extracellular matrix (ECM) molecules
Separation of the functional subunit into individual cohorts (i.e. cells and ECM) leads to a loss of tissue function. For this reason, this is the scale that tissue-engineering tries to reconstruct.
How can we build the functional subunit outside of the body
(in vitro)?

9. Cellular Microenvironment
Since cells are entirely responsible for synthesizing tissue constituents and assembly of the functional subunit, much attention is paid to the microenvironment surrounding the cell(s) of interest.
The microenvironment, which can be very different depending on the type of cell, is typically characterized by the following:
Different cell types
Cell- Cell Communications
Local Chemical Environment
Local Geometry

10. Cellularity Packing Density: Cellular Communication:
cell densities in tissues typically vary between 10 – 500 x 106 cells/cm3
relates to about cells per microenvironment (100 mm)3
extreme cases, such as cartilage which has ~ 1 cell per (100 mm)3
thus its microenvironment is essentially 1 cell plus associated ECM
Cellular Communication:
Cells communicate in three principal ways:
secretion of soluble signals
cell-to-cell contact (geometry)
cell- extracellular (ECM) interactions
Cellular communication can affect all “cellular fate” processes (migration, replication, differentiation, cell proliferation and cell death) and the method(s) of communication used depends, in part, on how the cells are packed within the tissue.

11. Cellular Communications
Soluble Signals:
includes small proteins such as growth factors and cytokines (15-20 kDa), steroids, hormones
bind to membrane receptors usually with high affinity (low binding constants: pM)
S. Waldman/B. Amsden

12. Cellular Communications
Cell-to-Cell Contact:
serve to create junctions between adjacent cells allowing for direct cytoplasmic communication
gap junctions
1.5-2 nm diameter and only allow transport of small molecules ~1 kDa
A gap junction or nexus is a specialized intercellular connection between a multitude of animal cell-types.[1][2][3] It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells.[4][5]
S. Waldman/B. Amsden

13. Cellular Communications
Cell-ECM Interactions:
ECM is multifunctional and also provides a substrate that cells can communicate through
since cells synthesize the ECM, they can modify the ECM to elicit specific cellular responses
cells possess several specialized receptors that allow for cell-ECM interactions
integrins, CD44, etc.
also a mechanism by with cells respond to external stimuli (“mechanical transducers”)
extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.
S. Waldman/B. Amsden

14. Local Geometry
Geometry of the microenvironment depends on the individual tissue:
needs to be re-created for proper tissue growth
two-dimensional layers or sheets
three-dimensional arrangements
transport issues
local geometry also affects how cells interact with the ECM
the ECM serves as a substrate for cellular communications
For these reasons, considerable effort has been geared at creating artificial ECM’s (aka scaffolds) to provide the appropriate substrate to guide in vitro tissue growth and development.

15. 3D cultures Proliferation Gene expression Cell morphology
Uniform, controllable size
Metabolism
Standardized
Proliferation
Low proliferation rate
Gene expression
Mimics native tissue

16. Tissue Engineering
SJ Shieh and JP Vacanti Surgery 137 (2005) 1-7

17. Sources of Cells 2. Allograft 1. Autograft 4. Xenograft 3. Synograft
Same-Species
Autologous (donor back to donor)
Allogenic (donor to recipient, same species)
Syngeneic (genetically identical donor)
Xenogenic (cross-species)
4. Xenograft
3. Synograft
Patient
Identical Twin
Cross-Species

18. Culturing of Cells Types of Cell Culture monolayer (adherent cells)
suspension (non-adherent cells)
three-dimensional (scaffolds or templates)
S. Waldman/B. Amsden

19. Culturing of Cells Sterilization Methods Growth Conditions
ultraviolet light, 70% ethanol, steam autoclave, gamma irradiation, ethylene oxide gas
Growth Conditions
simulate physiological environment
pH 7.4, 37°C, 5% CO2, 95% relative humidity
culture (growth) media replenished periodically
(depends on the cell type, cell concentrations that
you are using)
Culture (Growth) Media
appropriate chemical environment
pH, osmolality, ionic strength, buffering agents
appropriate nutritional environment
nutrients, amino acids, vitamins, minerals, growth factors, etc.

20. HOW?

21. Cells as Therapeutic Agents
Blood transfusion
RBCS into anemic patients to restore adequate O2
Platelet transfusion
Platelets into patients with blood-clotting defects
Bone-marrow transplantation
Cancer patients undergoing high-dose of chemo or radiotherapies

22. More recent developments
Encapsulated b-islet cells for diabetes
Sheets of dermal fibroblasts for uclers and burns
Chondrocytes for cartilage repair
Liver and kidney cells grown in extracorporeal support devices

23. Cartilage – Carticel® C. A. B. D.

24. More recent developments
Encapsulated b-islet cells for diabetes
Sheets of dermal fibroblasts for uclers and burns
Chondrocytes for cartilage repair
Liver and kidney cells grown in extracorporeal support devices

25. Bioartificial Liver (BAL)

26. Tissue Engineering - Building Body Parts (video)
Thinking question:
What are the four steps that are used to engineer new tissue?

27. What are the four main steps used to engineer new tissue?
Extract the cells from either the donor or the recipient
Build a scaffold for the cells to grow on
Supply nutrients and oxygen to the cells
Grow cells on the scaffold until the scaffold dissolved and the tissue structure is robust enough for cells to continue to grow and attach

28. Cell-Scaffold Tissue Engineering
Ohba, S. et al, IBMS BoneKEy, 2009,

29. Cells are the functional units that make up tissues
Cells are the functional units that make up tissues. Tissues then become the functional units that make up---
A. enzymes B. organs C. other cells D. DNA

30. Cells are the functional units that make up tissues
Cells are the functional units that make up tissues. Tissues then become the functional units that make up---
A. enzymes B. organs C. other cells D. DNA

31. What is the tissue that researchers believe is the easiest to grow and why?
Cartilage cells do not need a great deal of oxygen
Cartilage cells receive nutrients by diffusion
Cartilage do not require a large network of blood to survive

32. Tissue Engineering Scaffolds
Scaffold Materials:
synthetic polymers
poly(lactide) ,poly(lactide-co-glycolide), poly(caprolactone)….
foams, hydrogels, fibres, thin films
natural polymers
collagen, elastin, fibrin, chitosan, alginate….
fibres, hydrogels
ceramic
calcium phosphate based for bone tissue engineering
porous structures
permanent versus resorbable
degradation typically by hydrolysis (except for natural materials)
must match degradation rate with tissue growth
Chemical and Physical Modifications (synthetic materials):
attachment of growth factors, binding sites for integrins, etc.
nanoscale physical features

33. Tissue Engineering Scaffolds
smooth muscle cells on unmodified poly(CL-LA) elastomer (L) and modified surface having bound peptide sequence (R)
S. Waldman/B. Amsden

34. Emerging Medical Technologies
Drug-Loaded Stents
Guided Tissue Regeneration
Resorbable Stents
Transgenic Organ Generation
Robotic Surgery
Genomics/Proteomics
Implantable Mini Blood Pump
Glycomics
Ventricle-Coronary Artery Shunt
Protein Engineering
Functional Electrical Stimulation
Gene Therapy
Nanotechnology
Gene Expression Analysis (u-arrays)
Tissue Augmentation
Immunotherapy
High-throughput Biomaterial Discovery
Cell Multiplication & Transplantation
Sustained, Local Drug Delivery
Cell Function Regulation
Scar Prevention/Reduction
Stem cell Expression and Therapy
Slide Courtesy of Art Coury

35. Medical “Holy Grails” Small diameter vascular prostheses
Artificial trachea, esophagus, larynx
Devices to prevent surgical adhesions
Cartilage (articular, meniscal, disc) regeneration techniques
Permanent cardiac assist implants
Ligament replacement devices
Fully functional artificial skin
Bone healing devices
Tissue adhesives, sealants
Artificial blood
Artificial vision, hearing devices
Artificial cells
Nerve regeneration devices
Devices to reconstruct sections of the digestive tract
Synthetic leaflet heart valves
Devices to treat cancer
Bioartificial internal organs (liver, pancreas, kidney, intestine)
Cellular heart pacemaker
Closed loop drug delivery devices
Slide Courtesy of Art Coury