Design and fabrication of auxetic PCL nanofiber scaffold for tissue regeneration

Auxetic materials also known as negative Poisson?s ratio materials play significant role and are of great interest for biomedical applications, particularly in field of tissue engineering as scaffolds with their distinctive mechanical and cell responsive behavior. Scaffold-based tissue engine

Project Title

Design and fabrication of auxetic PCL nanofiber scaffold for tissue regeneration

Project Area of Specialization

Biomedical Engineering

Project Summary

Auxetic materials also known as negative Poisson’s ratio materials play significant role and are of great interest for biomedical applications, particularly in field of tissue engineering as scaffolds with their distinctive mechanical and cell responsive behavior.

Scaffold-based tissue engineering involves culturing of isolated cells from a patient or donor into a scaffolding system that supports growth of isolated cells into specific tissue, which will be transplant or graft back to the patient's defective site where tissue regeneration is needed. There are components or constituent parts which determine the success or accomplishment of tissue engineering which include:

• Cells
• Engineered matrices (also called Scaffolds)
• Cell-matrix interactions

According to a research article, the conventional Nano-fiber membrane are limited by inadequate and insufficient mechanical properties such as flexibility, elongation, and poor cellular infiltration in 3D, which are essential characteristics for tissue engineering applications where mechanical cues play major role in controlling cell fate and function.

As a result, in order to counter such problem our goal is to fabricate and design the polymeric auxetic Nano fiber membrane, which has adequate cell responsiveness and excellent mechanical properties such as flexibility, indentation resistance, fracture toughness, resilience, vibration control, shear resistance, and deformation mechanism when compared to conventional materials (non-auxetic) due to their unique structural designed pattern.

Yan et al, investigated role of auxetic scaffolds with tunable Poisson's ratio in providing biophysical 3D microenvironment, which is favorable for tissue regeneration. The POISSON’S RATIO can be define as the ratio of transverse to longitudinal strain in material under tension.

The auxetic patterned membranes get wider when stretched, narrower when squeezed. We initiate this procedure by using electrospinning apparatus to create membrane (non-auxetic). 10% PCL solution was formed and poured into 5 ml syringe. Syringe was loaded in electrospinning apparatus and set system parameters. Different thicknesses of Nano fiber membranes were fabricated by altering the electrospinning time, resulting in thin and thick Nano fiber membranes with diameters ranging from  40 ?m<thickness<180 ?m. The fabricated membrane is a non-auxetic conventional membrane, which must be converted to auxetic membrane by introducing auxetic structure into membrane. Using a laser cut micromachining approach; auxetic patterns were tailored on different thicknesses of PCL membrane samples. Finally, we completed characterization and acquired the results. The following are the characterization techniques:

• SEM analysis
• Mechanical analysis
• ATR analysis
• Thermal and Optical analysis

Project Objectives

The project objectives to be achieved, they are mentioned as below:

1. To fabricate (PCL) poly (?-caprolactone) based nano-fibrous membranes
2. To carve auxetic patterns on poly-caprolactone (PCL) based nano-fiber membranes using a precision laser cut technique
3. To characterize each synthesized nano-fiber membranes for their mechanical and physicochemical properties

Project Implementation Method

The project implementation method is to achieve all the objectives as mentioned in the Fig 1 and it is all about fabricating auxetic Nano-fiber membranes based on poly (-caprolactone) and characterizing the membrane for mechanical and physicochemical properties. The objectives are accomplish as discussed below

For the first objective, we formed a 10% PCL solution and then employed an electrospinning process to create a nonwoven web of micro- or nan fibers, as illustrated in Figure 1. This method involves delivering high-voltage electricity to a liquid solution and a collector, causing the solution to extrude from a nozzle and generate a jet. The jet generated fibers during the drying process, which were subsequently deposited on the collector.

For the second objective, we used Solidworks software to develop auxetic patterns, and then used laser cut micromachining to build the auxetic patterns on Nano fibrous membrane to create auxetic Nano fibrous membrane.

This can be accomplished by producing a standard (non-auxetic) nanofibrous membrane and then incorporating auxetic structure to turn it into an auxetic Nano fibrous membrane. We'll observe, which reveal that there were no substantial changes in chemical functionality or thermal behavior among auxetic membranes. However mechanical qualities, on the other hand, were noticeably different. The magnitude of elongation in the thin auxetic Nano fiber membrane was nearly ten times larger than in the control, demonstrating the exceptional flexibility of auxetic Nano fiber membranes.

For third objective, we will use characterization techniques such as SEM, ATR analysis, mechanical analysis, thermal and optical analysis to characterize Nano-fiber membranes (auxetic and conventional) for their mechanical and physicochemical properties.

Fig 1. Flow Chart for the Project Impementation Method

Benefits of the Project

There are some of the benefits which can be achieved by the implementation of this project, they are mentioned as under:

• It is the most effective solution to the problem of nano-fiber membrane for their limited, inadequate, and in-sufficient mechanical properties, which play crucial part in scaffolding system
• In long term path there are future prospects for this project to test via in vivo or in vitro, in order to come-up with such results which can accommodate it to be used as a 3D auxetic scaffold rather than using a conventional (non-auxetic) membrane, for tissue regeneration.
• Due to the auxetic structures in membrane, it brings about the advantage of expansion and elongation in all directions when it is under load than the non-auxetic ones.
• The auxeticity introduced in membrane help it to reduce the deformation ability of that membrane and resist its rupture/fracture.

Conventional nanofiber membranes are more likely that they lack physicochemical and mechanical properties which are major cues for any tissue engineering scaffold in the field of Biomedical engineering. Hence our project will help to fabricate and characterized such membranes like auxetic membrane or scaffold which are of great importance for biomedical field, in particular, tissue engineering as a scaffolds owing to their unique mechanical and cell responsive behavior due to new structural design patterns.

It can be very helpful to come-up customizing such auxetic membranes which have that ability to undergo wider when stretched, thinner when compressed and behave synclastically on bending. There are some of the naturally occurring biological auxetic systems such as are cat skin, cow teat skin, salamander skin, load-bearing cancellous bone from human shins and arterial endothelium tissue. Since we are fabricating our own auxetic membrane that can act as a substitute for the naturally occurring scaffolding system and the auxetic materials are used for tissue engineering applications in the form of scaffolding systems, stents, dilators, artificial blood vessels.

Technical Details of Final Deliverable

At the end of our project, we expect to have the poly-caprolactone based auxetic nanofibrous membrane that can be used as auxetic scaffold to support tissue regeneration. The examples for auxetic scaffolds include vascular graft, heart valves and skin graft.

Our scaffold that will be used for tissue regeneration, will have some major required properties for it to qualify to be used as Nano fiber auxetic scaffolds. Those required properties are as under

• good cell attachment
• high flexibility and elongation
• proliferation
• high ultimate strength
•  biocompatibility and appropriate degradation rate
• High porosity (90%)
• Average fiber diameter 517nm

The 3D auxetic structures are shown below in Fib 2, It clearly shows rotating unit cell structures were designed to generate an auxetic effect in nanostructure-networked polymers and foams by the connection of triangles, rectangles, a squares that can be hinged at selected vertices. The auxetic effects
were generated by the rotation of the triangles, squares, and rectangles in response to the loading.

Fig 2. 3D Auxetic patterns and rotating units

A single square unit of auxetic structure, in the form of a 3D cube with dimensions as (20 ?m x20 ?m x20 ?m) is shown in Figure 3.

Fig 3. Single square 3D unit of auxetic structure

All this is aimed at developing a biocompatible, biodegradable auxetic nanofibrous membrane which have numerous mechanical properties, for it to be used as a substitute skin scaffolding system.

Final Deliverable of the Project

HW/SW integrated system

Core Industry

Health

Other Industries

Medical

Core Technology

Wearables and Implantables

Other Technologies

Others

Sustainable Development Goals

Good Health and Well-Being for People

Required Resources

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