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Textile scaffolds: a new development in tissue engineering
Medical textiles

Textile scaffolds: a new development in tissue engineering

Written by: Madan Badariya

Introduction

The basis of tissue engineering is to develop or regenerate new tissues from the organ (or tissue) of interest on porous, biodegradable scaffolds by culturing isolated cells. A 3D structure that aids in the process of tissue engineering by providing a location for cells to attach to, proliferate in three dimensions, distinguish and secrete an extra-cellular matrix, ultimately leading to tissue formation, are known as scaffolds. The scaffold acts as an extracellular matrix for cell adhesion and regeneration or growth.

 

Usually, scaffolds serve at least one of the following purposes:

                   1.   Enabling cells to attach and migrate

                   2.   Allow diffusion of vital cell nutrients

                   3.   Deliver and retain cells and biochemical factors

                   4.   Exert biological and mechanical influences to alter cell behaviour

 

 

 

 

A tissue scaffold is a highly porous, artificial cellular matrix. Because of their inherent properties, textiles have a major role to play in making this scaffold. A scaffold can be broadly categorised into three groups based on the processing methods: foams, 3D printed substrates and textile structures. Textile structures form an important class of porous scaffolds used in tissue engineering.

 

Tissue engineered biological substitute

Scaffold structures

Bladder

Nonwovens

Blood vessel

Woven, knitted, braided, nonwoven

Bone

Nonwovens, foam

Cartilage

Nonwovens

Dental

Foam (porous membrane), nonwoven

Heart valve

Woven, nonwoven

Tendon

Woven, nonwoven

Ligament

Yarn, braided, nonwoven

Liver

Foam, nonwoven, 3D printed

Nerve

Foam, nonwoven

Skin

Foam, woven

 

Using tissue engineering approach to make biological substitutes fundamentally includes the following phases:

1.                  Scaffold material selection

2.                  Fabrication of scaffold

3.                  Preparation of scaffold

4.                  Cell harvest from human or animal

5.                  Cell seeding onto the scaffold

6.                  Cell proliferation and differentiation

7.                  Growth of mature tissue

8.                  Surgical transplantation

9.                  Implant adaptation and assimilation

 

Scaffold Design Parameters

 

An ideal scaffold system possesses the following features.

 

 •   Material should be biocompatible, ultra-pure, and easily reproducible into a variety of sizes and structures.

 •   In a majority of applications, the support of a scaffold is required only for a limited period of time. However, these temporary scaffolds cannot be removed easily because of tissue grown into its porous structure. Hence, scaffolds require to be manufactured from a biodegradable material in which the degradation rate has to be accustomed to match the rate of tissue formation. Also, the scaffold has to sustain its volume, mechanical stability and structure long enough to allow ample formation of tissue inside the scaffold, keeping in mind that the degraded products should not provoke toxicity or inflammation.

 •   Structure of scaffolds must be reproducible at macroscopic and microscopic levels with a high surface area to volume ratio in order to permit a significant amount of cell surface interaction.

 •   The pore size of scaffolds should be optimal to allow cells to grow in multiple layers in order to form a three-dimensional structure.

 •   Porosity of pore size reflects the interconnectivity of the scaffold, i.e. high porosity maximises the volume of tissue in growth and minimises the amount of material being used.

 •   Scaffold surface should be appropriate for cell proliferation and cell attachment.

 •   The suppleness of a scaffold ought to be near to that of its neighbouring tissue, so that once the vascularisation starts, no intense change in the mechanical properties between the scaffold and the host tissue can be experienced by the new growing tissues.

 

Hence, for a scaffold to perform efficiently, it must possess the optimum structural parameters, favourable to cellular activities leading to new tissue formation, cell penetration, migration and cell attachment onto the scaffold surface. The following table describes the scaffold design parameters with reference to the cellular activities.

 

Scaffold functional requirement

Scaffold design parameters

Not to incite toxicity or inflammatory

response

Non-carcinogenic, non-toxic and

biocompatible

Aid in the growth of three-dimensional

tissue

Three dimensional scaffold of required

shape

Support a evenly high cell seeding density

High porosity and good interconnectivity between them

 

Encourage cell proliferation and migration

resulting into tissue growth throughout

the scaffold

Optimum pore size for allowing cell

penetration, with high porosity and interconnectivity

To guide the cellular orientation of the

new tissues

Right fibre orientation within the scaffold

Allow the movement of waste and nutrients

in and out of the scaffold

High porosity and good interconnectivity between the pores

Scaffold should degrade leaving only the

natural tissue

Match rate of degradation and tissue

formation also degraded products must

not be toxic

Acquire sufficient structural integrity and

good mechanical strength to retain shape

and support developing tissues

Scaffold should match with the mechanical

properties of the new developing tissue

 

Textile scaffolds

As cells cannot survive on their own and are substrate-dependent, the need for scaffolds in tissue engineering is undisputed. However, no single universal scaffold can meet all the requirements of various tissues and hence the choice of scaffold for a tissue depends on its characteristics. The following are some aspects which need to critically examine for the selection of textile scaffolds.

1.                  Microstructural aspects

 

Porosity, pore size, pore size distribution, reproducibility of pores and pore connectivity are included in the microstructural aspects of scaffolds. These are fundamental as they determine the successful integration of the natural tissue and the scaffold and provide optimal spatial and nutritional conditions for the cells. The reproducibility of scaffolds decides their dimensional stability as well as the uniformity of the tissue formation. The following table compares the different microstructural aspects of textile structures with foams.

 

 

 

Textile structures

Fabrication

Foam

Non-woven

Woven

Braid

Knit

Pore size(m)

0.5-500

10-1000

0.5-1000

0.5-1000

50-1000

Porosity (%)

0-90

40-95

30-90

30-90

40-95

 

Reproducibility of

porosity

Poor to good

Poor

Excellent

Excellent

Good to

excellent

Pore connectivity

Good

Good

Excellent

Excellent

Excellent

Processability

Good

Good

Excellent

Excellent

Good

Other comments

Current techniques

are associated with

processing

undesirable residues

such as solvents, salt

particles

Equipment

cost is high.

 

Shapes are

limited

Limited to

tubular or

uniform cross-

sectional

shapes

Limited by the

low bending

properties of

current

biodegradable

fibres

 

In a textile scaffold, three levels of porosity can be achieved. The inter-fibre space or the arrangement of fibres within the yarn is considered the first level of porosity, which can be controlled by changing the yarn packing density or the number of fibres in the yarn. Also, further variations in porosity can be attained by altering the amount of twist or texture of continuous or spun yarn.

 

The second level of porosity are the inter-yarn spaces or the gap between the yarns. Porosity can be diverse by varying the stitch pattern and stitch density in case of knitted fabric and altering the bias angle of the interlacing yarn for braided scaffolds. It is possible to alter the porosity by controlling the inter yarn space through a beating action in the case of woven scaffold.

 

The third level of porosity can be introduced by subjecting secondary operations like rolling, folding, stacking, crimping etc to the textile structures.

 

2.                  Mechanical aspects

 

Mechanical aspects of scaffolds include structural stability, strength, stiffness and drapeability. They have a significant influence on cellular activity. Woven scaffolds are generally inflexible and rigid due to the tight interlacement of the yarns which makes them applicable for tissue engineering of bones and ace tabular cups. In scaffolds, the next stiff layer is the braided scaffold. Of all the scaffolds, knit scaffolds shows significant deformability due to their looped yarn arrangements, making them apt for blood vessel and bladder tissue engineering applications. The following table displays the various mechanical aspects of scaffolds.

 

 

Textile structures

Fabrication

Foam

Non-woven

Woven

Braid

Knit

Stiffness

Low

Low

High

High

Medium

Strength

Low

Low

High

High

Low

Structural stability

Good

Poor to

good

Excellent

Excellent

Poor to good

Drapeability

Poor

Good

Poor

Poor

Excellent

Other comments

Isotropic

behaviour

Isotropic

behaviour

Anisotropic, with

good properties

parallel to fibres

and poor properties

normal to fibres

Anisotropic, with

good properties in

axial direction and

poor properties in

transverse direction

Behaviour

can be

tailored from

isotropic to

anisotropic

 

Conclusion

There is no universal scaffold that can meet all the requirements of the various tissues of the human body. That is why scaffolds play a vital role in tissue engineering. Textiles are chiefly preferred in the field of tissue engineering since they have the ability to modify a wide spectrum of scaffolds with an ample range of properties.

 

References:

 

1. Ntcresearch.org

2. Web.iitd.ac.in

3. Eng.nus.edu.sg

4. Autexrj.com

5. Smart fibres, fabrics and clothing by Xiaoming Tao

6. Synthetic polymer scaffolds for tissue engineering by Elsie S. Place

 

Image courtesy:

 

1. Reorbit.com

 

 

About the Author:

Madan Badariya is a Phd scholar from National Institute of Technology, Jalandhar.

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