13 biomaterials

BiomaterialsTissue Engineering Nanotechnology

Liu Nanobionics Lab

Biomaterials

Biomaterials encompasses aspects of medicine, biology, chemistry, engineering and materials science.

Biomaterials are : “Non-viable materials used in a medical devices intended to interact with biological systems” [D.F. Williams, 1987]

Disease (e.g cancer, infection, degenerative diseases).

Trauma (e.g accidental, surgery). Congenital abnormalities (e.g birth

defects).

Current clinical treatment based on:

Human Tissue Damage

Grafts and Transplants

Artificial Biomaterials

Tissue loss as a result of injury or disease, provides reduced quality

of life for many at significant socioeconomic cost.

Thus a shift is needed from tissue replacement to tissue regeneration by stimulation the body’s natural regenerative mechanisms.

Biomaterials: Examples Joint replacements Bone plates Bone cement Hip Joint Artificial ligaments

and tendons Dental implants for

tooth fixation Blood vessel

prostheses Heart valves Skin repair devices Cochlear

replacements Contact lenses

Hip jointHeart valve

Knee joint Skin

Biomaterials

Prostheses have significantly improved the quality of life ( Joint replacement, Cartilage meniscal repair, Large diameter blood vessels, dental)

However, incompatibility due to elastic mismatch leads to biomaterials failure.

National Science Foundation first defined tissue engineering in 1987 as “ an interdisciplinary field that applies the principles of engineering and the life sciences towards the development of biological substitutes that restore, maintain or improve tissue function”

Tissue Engineering

Tissue engineering

Potential advantages: unlimited supply no rejection issuescost-effective

Tissue Engineering

Remove cells from the body.

Expand number in culture

Seed onto an appropriate scaffold with suitable growth factors and cytokines

Place into culture

Re-implant engineered tissue repair damaged site

SCAFFOLDS

PLGA Scaffold

Synthetic polymers

More controllable from a compositional and materials processing viewpoint.

Scaffold architecture are widely recognized as important parameters when designing a scaffold

They may not be recognized by cells due to the absence of biological signals.

Natural polymers

Natural materials are readily recognized by cells.

Interactions between cells and biological materials are catalysts to many critical functions in tissues

These materials have poor mechanical properties.

Tissue engineering scaffold: controlled architecture

Featured with: Pre-defined channels;

with highly porous structured matrix;

With suitable chemistry for tissue growth – Collagen or HA

No toxic solvent involved, it offers a strong potential to integrate cells/growth factors with the scaffold fabrication process.

Architecture of Hard Tissue

Staggered mineral platelets (hydroxyapataite) embedded in a collagen matrix

Arrangement of platelets in preferred orientations makes biocomposites intrinsically anisotropic

Under an applied tensile stress, the mineral platelets carry most of the tensile load

Protein matrix transfers the load between mineral crystals via shear

Tissue engineering scaffold: Electrospinning

This process involves the ejection of a charged polymer fluid onto an oppositely charged surface.

Multiple polymers can be combined Control over fiber diameter and scaffold architecture

Printing Techniques for Tissue Engineering

Techniques to study scaffolds:Scanning Probe Microscopy

Atomic Force Microscopy :Surface irregularities

Scanning Tunneling Microscopy: Conducting Surfaces

Adhesion Force Microscopy: Functionalised tips

Surface Modification of Biomaterials

Enhanced intrinsic biomechanical properties of osteoblasticmineralized tissue on roughened titanium surface

Nano-indentation

Acid-etched vs. Machined surfaces

culturing osteoblasts on rougher titanium surfaces enhances hardness and elastic modulus of the mineralized tissue

Protecting Bionic Implants

Immunoisolation for Cell-encapsulation therapy

Liver Dysfunction: Encapsulation of Hepatic Cells

Pancreas Dysfunction: Encapsulation of Islets of Langerham

Disorders of the CNS: Parkinson’s, Alzheimer’s

Pre-requisites for cell encapsulation

continued and optimal tissue/cell supply

maintenance of cell viability and function

successful prevention of immune rejection

Nanoporous Silicone-based biocapsules serves as Artificial Pancreas(Desai et al. 2001)

What are the drawbacks of such an artificial pancreas?

Nanoengineering Bio-analogous Structures

Bone-cartilage composite ?

Muscle ?

Brain-machine Interface ?

An Ink-Jet Printer for Tissue Engineering?