advances in medical textiles

ADVANCES IN MEDICAL TEXTILESGopalakrishnan D & Karthik T – Assistant professor (SG)

Department of Textile Technology, PSG College of Technology,Coimbatore - 641004

Manufacture and in vitro bioactivity of sol-gel-

derived silica fibre :Silica fibers made of sodium silicate (water glass) are used

in heat protection (including asbestos substitution) and in

packings and compensators. They can be made such that they are

substantially free from non-alkali metal compounds. Sodium

silicate fibers may be used for subsequent production of

silica fibers, which is better than producing the latter from

a melt containing SiO2 or by acid-leaching of glass fibers. The

silica fibers are useful for producing wet webs, filter

linings and reinforcing material. They can also be used to

produce silicic acid fibers by a dry spinning method. These

fibers have properties which make them useful in friction-

lining materials.

Fiber Composition:

Most optical fibers consist of two different types of

optically transmittive materials. The core, about 75-90 % of

the fiber depending on the fiber diameter, has a higher

refractive index than the cladding. This creates a reflecting

interface between core and cladding which keeps the light

within the core due to total reflection. Most optical fibers

are made from glass, plastic or synthetic fused silica (often

GOPALAKRISHNAN D & Dr.T.KARTHIK

http://en.wikipedia.org/wiki/Silicic_acid

http://en.wikipedia.org/wiki/Silica

http://en.wikipedia.org/wiki/Alkali_metal

http://en.wikipedia.org/wiki/Asbestos

http://en.wikipedia.org/wiki/Water_glass

http://en.wikipedia.org/wiki/Sodium_silicate

referred to as “quartz”). Each fiber has different properties

producing various advantages and disadvantages. Due to their

low attenuation silica fibers are commonly used in data

communication. Glass is still the best choice for illumination

and sensing applications, due to a reasonale cost- benefit

ratio. Plastic fibers can be used for assemblies not requiring

heat above 175°F. Single plastic fibers are usually larger in

diameter than glass fibers, which results in restricted

bending radii.

High temperature silica materials

Silica materials are a superb high temperature insulation and

can be used for a long time without changing of properties at

the temperature higher than 10000С (material Puresil up to

12000С) and for a short period of time at higher temperatures.

Articles made of silica glass are extremely inert to the

majority of chemical reagents, resistant to organic and

mineral acids of any concentration even at high temperatures

(except of hydrofluoric, phosphoric and hydrochloric acid) and

weak alkalis, molten metals (except of Mg, Na, Si) and alloys.

They have high chemical resistance to water and high pressure

steam, are capable to absorb moisture, but are not split in

the presence of water, are stable in vacuum. The given

materials are used as replacement of asbestos in different

branches of industry: oil-refining, aerospace industry, in

metallurgy and shipbuilding, atomic power engineering.

Silica fabrics


The enterprise manufactures a wide range of silica fabrics

with the weight from 120 to 1400 g/sq.m. with the width up to

2 m with different types of finish improving their properties.

One of the considerable sectors of silica fabric application —

production of welding blankets, fire protective blankets,

screens and curtains, casing as a thermal barrier for

protection of the equipment, high temperature insulation of

furnaces, turbines, screens for protection from molten metal

splashes, sparks, thermal insulation.

Silica meshes

They are used as an effective filtering material for cleaning

of ferrous and non-ferrous metal melts while their pouring

into moulds. Usage of filters from silica mesh allows to

reduce moulding defects 1,5-2 times, improve metal structure,

increase its physical-mechanical and technological properties.

Silica yarns

Silica yarns are a superb raw material for weaving of tapes,

fabrics, making of insulation braiding, sleeves, tubings,

paddings, cords.

Silica fiber

The main field of application — production of needle felt,

having a wide application in car building, metallurgy, atomic

and thermal power stations, insulation in electric and

combustion furnaces.

Ready-made articles made of silica materials

The most widely used are fire protective blankets designated

for isolation of combustion at the initial stage of fire, as


well as for extinguishing of clothes of an injured person by

oxygen supply shut-off. Blankets are made from silica fabrics.

Also JSC “Polotsk-Steklovolokno” manufactures other articles

from silica fabrics, for example, thermal insulation sleeves

for insulation of mufflers and other ready-made articles at

the orders of the customers.

Silicon is the second most common element on the Earth's crust

and its oxide (SiO2) the most abundant mineral. Silica and

silicates are widely used in medicine and industry as well as

in micro- and nano-optics and electronics. However, the

fabrication of glass fibres and components requires high

temperature and non-physiological conditions, in contrast to

biosilica structures in animals and plants. Here, we show for

the first time the use of recombinant silicatein-α, the most

abundant subunit of sponge proteins catalyzing

biosilicification reactions, to direct the formation of

optical waveguides in-vitro through soft microlithography. The

artificial biosilica fibres mimic the natural sponge spicules,

exhibiting refractive index values suitable for confinement of

light within waveguides, with optical losses in the range of

5–10 cm−1, suitable for application in lab-on-chips systems.

This method extends biosilicification to the controlled

fabrication of optical components by physiological processing

conditions, hardly addressed by conventional technologies.

Sol-gel

The term sol-gel is a compound of the abbreviation sol for

solution and the word gel , describ- ing a dense network of


fine particles dispersed in a solvent. Modern products of the

sol-gel technique are ceramics and glasses in form of ultra-

fine powders, monosized powders, particles, monolithic

solids, aerogels, coatings and membranes. Technical

applications are planar devices such as sensors for heat and

pressure, structured materials, e.g. photonic crystals,

chemical sensors and biomedical applications as entrapment of

molecules for biosensors. In addition, complex geometry such

as multi-core fibers or micro- structured fibers with

gradients in the dopant concentration or even mixed or

multiple doping conditions can easily be produced. Sol-gel

technique offers the flexibility of dopant content, any H 2O

or ethanol soluble dopant can be incorporated, homogeneity of

the dissolved parts, and adjustable processing temperatures

(200 °C – 2000 °C). The sol-gel route is generally very cost-

effective.

Chemistry

In today’s sol-gel technique, the colloidal particles usually

are produced via the chemical route. The two involved

reactions are the hydrolysis and condensation, as presented in

the following.

The sol-gel processing involves the synthesis of an inorganic

network by a chemical reaction in solution not far above room

temperature, e.g. at 40°C – 50°C. Basically, a solution is

prepared that is led to react in a process called gelation.

The reactions leading to gelation are hydrolysis and

condensation of metal organic compounds in a solution. In this


work, the formation of a silica sol-gel from the alkoxide

tetraethyl-orthosilicate (TEOS) in ethanol (EtOH, C2H5OH) and

H2O was performed.

The two reaction steps are the hydrolysis,

Si(OC 2H5)4 + H 2O → Si(OC 2H5)4-x(OH) x + x ⋅C2H5OH

With subsequent and parallel polymerization to build siloxane

bonds (...-Si-O-Si-...) through condensation reactions

Si(OC 2H5)4-x(OH)x+Si(OC 2H5)4 → (HO) x-1(OC 2H5)4-xSi-O-Si(OC

2H5)3+C 2H5OH,

Leading to a polymeric solution with increased viscosity. The

condensation can also occur between partly or fully hydrolyzed

precursor molecules, leading to the condensation also of

water.

The hydrolysis can be accelerated by adding a catalyst to the

solution, typically - and also used in this work - is

hydrochloric acid (HCl). This transformation leads to a

colloidal solution, a sol. Colloids are a stable intermediate

state between solution and suspension. Sols with particles up

to 500 nm are generally long time stable.

The sols in this work were used within several days after

production and were shaken before application. The two

reactions are presented more detailed in the following, and

the most important stages are summarized at the end. sol-gel

polymerization occurs in three stages:

1. Polymerization of monomers to form particles.

2. Growth of particles.


3. Linking of particles into chains, then networks that

extend throughout the liquid medium, thickening into a gel.

In general sol-gel derived silicon oxide networks under acid-

catalyzed conditions yield primarily linear or randomly

branched polymers which entangle and form additional branches

resulting in gelation. Silicon oxide networks derived under

base-catalyzed conditions yield more highly branched clusters

which do not interpenetrate prior to gelation and thus behave

as discrete clusters.

Silica aerogels are particularly easy to functionalize—that

is, attach chemicals to the surface of their skeletons—because

of all the silanol groups (Si-OH) on their surfaces. Think of

these silanol groups as being molecular electrical outlets

that we can plug useful molecular appliances into! During the

formation or purification steps of silica gel production (and

even during supercritical drying), chemicals can be introduced


into the pores of the gel which will react with the gel’s

silanol groups, resulting in the attachment of other chemical

groups to the gel’s surface. When the gel is dried to make an

aerogel, these groups stick around and coat the surface of the

skeleton of the resulting aerogel.

This is where chemists and materials scientists get to have

some fun! You could replace the silanol groups with a non-

polar group, such as trimethylsilyl -Si(CH3)3, which would make

the resulting silica aerogel water-proof! Or you could add a

fluorophore, which would make the resulting silica aerogel

glow under a UV lamp! All sorts of neat things can be attached

to silica aerogels to make useful aerogel materials. One

interesting example is the attachment of molecules which

fluoresce when exposed to oxygen, resulting in silica aerogel

that can act like an oxygen sensor!

Waterproofing Silica Aerogel

Water-proofing aerogels is useful especially when using silica

aerogels in an application where they need to be transparent,

such as in window insulation or a Cherenkov radiation

detector. One chemical used to water-proof silica aerogels is

hexamethyldisilazane, a compound used to water-proof other

materials, which plants those trimethylsilyl groups mentioned

earlier over the surface of the gel.

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P (L/D, L) LA composite

New nanocomposite membranes with high bioactivity were

fabricated using the electrospinning. These nanocomposites

combine a degradable polymer poly(l/dl)-lactide and bone cell

signaling carbonate nano-hydroxyapatite (n-HAp). The

incorporation of the n-HAp into the structure increased

significantly the mineralization of the membrane in vitro. In

vitro experiments demonstrated that the incorporation of n-HAp

significantly improved cell attachment, upregulated cells

proliferation and stimulated cell differentiation quantified

using Alkaline Phosphatase and OsteoImage tests. the addition

of n-HAp provided chemical cues that were a key factor that

regulated osteoblastic differentiation.

The effective regeneration of fully functional body tissues

including bone structures is one of the major challenges in

regenerative medicine. Current approaches include surgical

reconstruction using autografts or allografts. These methods

have some limitations that are associated with the


availability of autografts, the risk of immunogenicity and

infection. To address these issues tissues can be engineered

ex vivo, which allows ‘manufacturing’ a tissue substitute that

match specifically the implantation site. Therefore tissue

engineering approaches hold great promise for regenerative

medicine. Main requirements for materials used as scaffolds

for bone tissue engineering are:

(i) biocompatibility,

(ii) biodegradability with a controllable degradation time,

(iii) suitable surface chemistry to regulate cell

attachment, proliferation and differentiation,

(iv) adequate mechanical properties that match those of

tissue at the site of implantation and

(v) bioactivity attributed to the formation of a biological

carbonated apatite layer on the surface of the

scaffold, which leads to better osteo integration and

the enhanced formation of new bone tissue within a

short period

Natural extracellular matrix (ECM) provides physical

environment for cells to attach, grow, migrate, respond to

signals and also gives the tissue its structural and therefore

mechanical properties, such as rigidity and elasticity that is

associated with the tissue functions. Ideally the scaffold

should mimic the structure of the fibrous component of the

ECM. Many extracellular proteins have a fibrous structure with

diameters on the nanometer or micrometer scales, surrounded

and infiltrated by nano-sized crystals of apatite. Nano-


structured scaffold can improve the cell–matrix interaction by

adsorption of cell adhesion-mediating molecules from

biological fluids. One of the techniques to manufacture

nanofibrous scaffolds for tissue regeneration is

electrospinning. This technique enables the fabrication of

scaffolds with different topographies and porosities (at nano

to microscale) inspired by ECM that are capable of controlling

cellular responses. Electrospun scaffold have high surface

area and interconnected pore network, providing a facile

transport of metabolic nutrients and waste through the

nanometer-sized pores, whereas the efficient cell implantation

and blood vessel invasion can be expected through the

micrometer-sized pores.

Poly(lactic acid) (PLA) has been frequently used in many

orthopaedic applications. It can be easily processed into

shapes such as screws, pins and plates for tissue fixation,

sutures and surgical staples for wound closure and fabricated

into scaffolds or devices for controlled delivery of

biomolecules. The success of PLA in biomedical applications is

strictly connected with its tuneable degradation, which occurs

by hydrolysis and sufficient mechanical properties. Co-

polymers including poly(l/dl lactide) are clinically used

materials for fracture fixation. The ratio of l and dl

isomeric forms can vary and subsequently impact of material

characteristic due to different level of crystallinity. For

example greater level of crystllinity is observed for l/dl

ratio is higher. Thus the use of amorphous poly(l/dl)-lactide


70:30 has a significant benefit because it prevents from the

generation of undesired degradation products in the form of

highly crystalline debris. It is also expected that by using

this co-polymer the tissue reaction to the material will be

milder. Implants produced from poly(l/dl-lactide) 70:30 are in

clinical use for fracture fixation in regions of limited

mechanical load and are well suited for the fabrication of

scaffold for the regeneration of the bone tissue. Also the

degradation time is suitable for such application as well as

it characterises with good formability into the fibers.

Hydroxyapatite is calcium phosphate mineral naturally

occurring in human tissues, which is commonly used as a bone

graft. One of the current approaches to improve biological

properties of synthetic HAp is to adjust more closely its

chemical composition and morphology to that of cancellous bone

through incorporation of carbonate ions into the HAp structure

(cHAp). Carbonate ions improve the solubility of HAp, thus its

release on Ca and P ions that encourage bone regeneration.

Hydroxyapatite is also often used as filler in polymer based

composites to enhance their integration in bodily environment,

buffer (when poorly crystalline HAp is used) degradation

products and modify mechanical properties. Therefore, the

incorporation of carbonate HAp particles into electrospun

membranes could regulate osteoinductivity of the membranes,

thus stimulate de nove bone tissue formation.

Material and Methods


Carbonate nano-hydroxyapatite was synthesized by a wet

precipitation method as previously described. An average size

of the n-HAp particles was 23 nm and the specific surface area

of the n-HAp powder was 79.9 m2/g. Co-polymer of l-lactide and

dl-lactide (PLDL Acetone was used as a solvent.

The electrospinning solutions were prepared by dissolving 1 g

of PLDL copolymer in 50 ml of acetone at room temperature

under magnetic stirring. For the composite scaffold the PLDL–

acetone solution was mixed with 20 wt% of n-HAp. Stable

dispersion of n-HAp colloidal suspension was achieved by

sonication of the solution.

Fabrication of the membrane by electrospinning

To fabricate the membranes electrospinning was used. Polymer

solutions were loaded into a plastic syringe (20 mL) and

injected through a stainless steel needle (diameter 0.7 mm) at

injection rate of 1.5 mL/h. The needle was connected to a high

voltage supply (30 kV). Rotating metal drum was place at a

distance of 20 cm from the needle tip. Membranes were

collected on silica coated paper attached to drum collector.

Two types of nonwoven membranes were formed: PLDL without

ceramic additives (PLDL) and PLDL modified with n-HAp (PLDL/n-

HAp).


Fig: Microstructure of electrospun scaffolds: a PLDL; b

PLDL/n-HAp

Electrospun PLDL and PLDL/n-HAp membranes are composed of

smooth and uniform fibers with minimal bead formation.

The distribution of n-HAp particles in the PLDL matrix is

nonhomogeneous and agglomerates of HAp particles were

observed on the surface of PLDL/n-HAp fibers.

n-HAp crystals at higher concentrations (at and above 20

wt %) have a tendency to form agglomerate (do not form

homogenous colloidal suspension), thus subsequently are

incorporated within the fiber structure during

electrospinning.

The fiber diameter of PLDL membranes is in the range from

0.40 μm to 3.2 μm (the average fiber diameter is

1.7 ± 0.5 μm), while PLDL/n-HAp fibers showed has

diameter from 0.40 μm to 5.0 μm (the average diameter:

2.8 ± 1.4 μm).

The membranes are porous and pores are interconnected.

The main pore fraction for PLDL membrane is in the range


of 6.5–7.5 μm, and the PLDL/n-HAp scaffold showed narrow

distribution of pore size centered at 4.8 μm.

The decrease in porosity of the composite PLDL/n-HAp

membranes can be attributed to the effective charge

dissipation by HAp particles, preventing inter-fiber

repulsion.

Fig: a–b PLDL and c–d PLDL/n-HAp scaffold after 7 days

immersion in SBF solution

BiomineralizationMineralization was assessed in vitro using two concurrent

methods:

(1) simulated body fluid (SBF)

(2) cell based assays.

Novel PLDL/n-HAp composite membranes for bone tissue

engineering were successfully produced by electrospinning. The


incorporation of the n-HAp into the structure increased

significantly the mineralization of the membrane in in vitro

conditions. It has been demonstrated that after a 3 day

incubation in SBF a continuous compact apatite layer was

formed on the surface of the composite membrane. The membrane

microstructure and chemical composition were found to have

positive effect on cells attachment, proliferation and

morphology. In vitro experiments using NHOst cells showed that

the addition of n-HAp provided chemical cues that was a key

factor that regulated osteoblastic differentiation. In

summary, preliminary studies have shown that PLDL/n-HAp

electrospun scaffold can direct HAp mineralization both in SBF

and in cell culture. This study formed a strong foundation to

design osteogenic scaffolds for bone tissue regeneration.

*************


A spider silk supportive matrix used for cartilage

regeneration

Silk fibers spun by several species of arthropods have

existed naturally for hundreds of millions of years. The

ecological functions of the silk fibers are closely related

to their properties. orb-weaving spiders produce a variety

of different silks with diverse properties, each tailored to

achieve a certain task. It is Stronger and more flexible

than steel, spider silk offers a lightweight alternative to

carbon fibre. Up to now it has been impossible to produce

"spider fibre" on a commercial scale. Unlike silk worms,

spiders are too anti-social to farm successfully. Naturally

occurring spider silk is widely recognized as the strongest,

toughest fibre known to man. Most arthropod species produce

silks used for building structures to capture prey and

protect their offspring against environmental hazards. The


most investigated categories that have piqued the greatest

amount of interest are spider silk and dragline silk in

particular, produced by major ampullate glands and the

cocoon silk of Bombyx mori (B. mori). The ongoing

evolutionary optimization of silks from silkworms and

spiders exhibit outstanding mechanical properties, such as

strength and extensibility, as well as toughness, which

outperform most other natural and man-made silk fibers

These crystalline and non-crystalline domains are organised

in nanofibrils, which are embedded in an amorphous protein

matrix. A spider-web’s ability to catch insects is due to

the silk’s unique combination of mechanical properties:

strength, extensibility (up to 30%) and, most importantly,

toughness, or resistance to breakage. Spider silk may be six

times stronger than steel by weight, but it is its toughness

that makes it so special, as it allows it to absorb a large

amount of energy without breaking. Man-made materials such


as Kevlar are strong, but lack this specificity. Moreover,

unlike Kevlar, spider silk is biodegradable and recyclable:

when repairing their webs, spiders frequently eat damaged

parts of the web and absorb the nutrients.

Types

Different specialized silks have evolved with properties

suitable for different uses. These include, major ampullate

silk also known as the 'dragline silk' which is used as a

lifeline and for the web's outer rim and spokes; it can be as

strong per unit weight as steel, but much tougher.

Minor ampullate silk is used for temporary scaffolding

during web construction.

Flagelli form silk is the other major web component and

is used for the typically circumferential capturing lines

of the web, and is tough and extremely stretchy. The high

elasticity, around 300%, is used to dissipate the impact

energy of prey striking the web. The stickiness of


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flagelli form silk varies between species, and a

primitive format included the use of an additional

cribellate silk for stickiness.

Piri form silk is used to form bonds between separate

threads in the web and for attachment points.

Acini form silk is used to wrap and secure freshly

captured prey; it is typically two to three times as

tough as the other silks, including dragline silk.

Tubuli form silk, also called cylindri form silk is used

as an egg cocoon silk and for protective egg sacs; it is

the stiffest silk.

Aggregate silk is a glue formed as sticky globules. Of

these, the dragline silk and the flagelli form silks have

been the most studied.

Morphological Structure

The morphological structure of B. mori silk and spider

dragline silk are very similar, as both possess a core-shell

structure. The silk thread diameter varies across types and

species. For example, coating the two core brins of B. mori

silk fiber with sericin yields fibers about 20 μm width.

Spider dragline silks have a diameter of 3-5 μm and to date,

have been described to contain only one protein monofilament.


Spider dragline silk is remarkably strong. It is five times

stronger by weight than steel, three times tougher than

Kevlar, although dragline silks from different species show

different properties. Nevertheless, it is these remarkable

mechanical properties that make it attractive for many

applications, not just as a biomedical material. All dragline

silks have a high MW, 250–320 kDa which on its own provides

difficulties for recombinant expression. Dragline silks are

typically composed of two main proteins, the major ampulate

spidroins, MaSp1 and MaSp2 also called ADF3 and ADF4

spidroins for A. diadematus . Spidroins have highly repetitive

structures; they are modular, and contain hundreds of tandem

repeats of distinct consensus motifs.


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These structures have shown little change for over 150 million

years. MaSp1 spidroins generally comprise two motifs,

polyalanine and GlyGlyXaa, where Xaa is frequently Leu, Tyr,

Gln or Ala. MaSp2 spidroins also contain polyalanine, as well

as GlyProGlyXaaXaa repeats, where Xaa is frequently Gly, Gln

or Tyr. The polyalanine or poly(glycyl-alanine) sequences form

into tightly packed β-sheet crystallites, while other Gly-rich

repeats, such as GlyProGlyXaaXaa, can fold into other

structures including 31-helices and coils giving an amorphous,

elastic matrix into which the β-sheets crystallites are

embedded. It is suggested that the high MW of the spidroins is

an integral part of their function and mechanical properties,

with the numerous repeating elements allowing extensive inter-

and intra-chain interactions. These repeats enable formation

of numerous self-assembled antiparallel β-sheet crystalline

segments. These segments are believed to provide the key high

strength element of the fibre, providing a tightly knit

structure, with many H-bonds while absence of water adds large

number of hydrophobic interactions. In addition, at the N- and

C-terminal are non-repetitive domains. The C-terminal domain

is around 100 amino acids, and can form disulfide linked

dimers; it is conserved between species. Similarly, the N-

terminal domain of 130 amino acids is highly conserved and is

also present in flagelliform and cylindriform spider silks.

For biomedical applications, recombinant silk can be

fabricated into various formats. Included in these is

fabrication of a natural fibre. For wide spread application of


recombinant spider silk as an artificial fibre, it is

important that the fibre essentially matches the mechanical

properties of the natural fibre. This had proved difficult to

achieve. The spinning process in vivo is a very sophisticated

assembly process. Silking in vivo is about control of water

content to produce a high concentration dope while still

retaining water as a protein plasticizer that helps improve

tensile strength and stiffness by promoting silk protein

crystallization. In vitro, silk properties are modulated by the

spinning conditions, such as temperature, reeling and drawing

rates and silk type. It has been shown clearly that for

recombinant constructs higher molecular weight gives better,

stronger fibres and that better mechanical properties can be

obtained from post-spin stretching . In particular, it has

been shown using a range of recombinant products from 100 to

285 kDa that performance increases with molecular weight. The

largest product, which has a molecular weight similar to that

of native silk showed mechanical properties, an elongation of

15% and a Young's modulus of 21 GPa, that are comparable to

native silk . Other approaches to fibre formation include the

use of microfluidics, which can be achieved without the use of

harsh solvents and electrospinning .

In addition to fibres, recombinant spider silks can be made

into other formats useful for tissue engineering. Thus,

hydrogels can be formed, using connectivity through either

physical or chemical crosslinking. For example, the

recombinant construct eADF4(C16), with 16 copies of a 35 amino


acid repeating module, can self-assemble into stable

hydrogels, via nucleation aggregation followed by

concentration-dependent gelation. Gels of reproducible

properties can be made by dialysis of low concentration

protein solutions in 6 M guanidinium isothiocyanate solution

into 10 mM Tris/HCl, pH 7.5, followed by further dialysis

against high MW (20 kDa) polyethylene glycol.

Fig: Grooved channels produce microfibers similar to the

grooved silk that encapsulates spider eggs. The grooves

enhance alignment of neuron dendrites and axons.

A mini-spidroin for E. australis has been produced, comprising

four poly-alanine/glycine repeat blocks and the C-terminal

domain from the silk, plus a fusion partner to enhance

solubility on expression. Protease release of the fusion

partner leads to spontaneous formation of metre-long fibres.

These fibres have a strength equivalent to those spun from

dissolved cocoon silk. The presence of the C-terminal domain

is essential for this rapid fibre formation. The N-terminal

domain when added to the mini-spidroin construct provides a

pH-dependent system that mediates the spidroin assembly at pH


6.3 or lower, possibly through structural changes within this

domain. The mini-spidroins can be purified through several

steps, including an endotoxin removal step, without

aggregation occurring. These low pyrogen-containing fibres can

be sterilized by autoclaving, retaining their morphology,

structure and mechanical properties. In addition to fibres,

the mini-spidroin material can be fabricated into a range of

formats, including films, meshes and sponges. These materials

are suitable for cell culture, indicating their applicability

to act as tissue engineering scaffolds. Thus, for example,

primary human fibroblasts attached and grew well, including in

the absence of serum and animal-derived additives, and

produced and deposited type I collagen onto the silk matrix.

Spider eggs are encapsulated with grooved silk, which was also

reproduced in the spider-card with grooved channels. When

embryonic neurons were placed on the grooved silk, their axons

and dendrites ended up more aligned than those found on smooth

microfibers. This might be a vital component in tissue

regeneration after spinal cord or nerve damage. The

researchers also demonstrated their ability to encapsulate gas

bubbles within the fibers at different frequencies and bubble

sizes. Gas bubbles within the microfiber might provide a

temporary source of oxygen for cells encapsulated cells within

the microfiber. Finally, Lee et al. encapsulated fibroblasts

and hepatocytes and measured their viability. Unfortunately

they only investigated cell viability for 5 days, which isn’t

long enough to determine its practicality. They also encoded a


microfiber with a chemoattractant and put it in a cell

culture. The migration of cells toward the chemoattractant is

evident, showing that a spatially encoded fiber could be

useful in cell culture organization.

(a) The hierarchical structure of spider dragline and

silkworm silk fiber. Both spider dragline and fibroin are

composed of numerous minute fibrils, which are separated

into crystalline and amorphous segments. (b) The minute

fibrils in silkworm B. mori silk as revealed in an AFM

image (scale bar: 150 nm). The silk fiber direction is

indicated by the arrow.

Physical (Mechanical) Properties of Silk Fibers

Spider silk and B. mori silk feature unique physical

properties – such as superior mechanical properties in terms

of toughness (the amount of energy absorbed before breakage).

So far, the maximum strength of spider dragline silk (dragline

of Caerostris darwini) up to 1.7 GPa, which exceeds that of


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steel (1.5 GPa), is in the range of high-tech materials. Due

to its great extensibility, spider dragline silks have three

times of toughness of man-made synthetic fibers like Kevlar

49. Typical B. mori silk is presumed to be weaker and less

extensible than spider dragline silk. However, when forcibly

silking from immobilized silkworms artificially at certain

spinning speed, the mechanical properties of the specific B.

mori silk have greatly improved to a level that is comparable

the toughest spider silk .

Fig: A schematic model demonstrating how the silkworm and

spider dragline fibers respond when they are subjected to

stretching. There are two components in the alanine-rich


http://www.intechopen.com/source/html/46460/media/image6_w.jpg

regions of spider dragline silk: β-crystallites and

intramolecular β-sheets.

The mechanical properties of silk fibers can be described by

stress-strain curve profiles, which are generated by

stretching the fibers at a specific strain rate. The stress is

expressed as force per cross-sectional area and the strain is

defined as a normalized extensibility. Typical stress-strain

curves for B. mori silkworm silk and spider dragline silk show

both elastic behavior followed by plastic deformation. The

linear portion of the curve, up to the yield point, is the

elastic region. The slope is defined as Young’s modulus, a

measure of the stiffness of the fiber. After the yield point,

the fiber buffers the plastic deformation and the stress-

strain profiles are subjected to sudden slope changes. This

behavior indicates that major structural transition from

rubberlike to glassy state occurs in the fiber. These

characteristics have driven scientists to explore the

structural origin of the high-performance silk fiber, with the

goal of obtaining templates for designing novel materials with

comparable properties.

Fibers Stiffn

ess

Streng

th

Extensibilit

y (%)

Toughne

ss

(GPa) (GPa) (MJ∙m-3)

B. mori cocoon silk 7 0.6 18 70

B. mori reeled silk 15 0.7 28 150


A. Diadematus silk

(dragline)

10 1.1 27 180

A. Diadematus silk

(flagelliform)

0.003 0.5 270 150

Wool (at 100% RH[b]) 0.5 0.2 5 60

Elastin 0.001 0.002 15 2

Nylon fiber 5 0.95 18 80

Kevlar 49 fiber 130 306 2.7 50

Carbon fiber 300 4 1.3 25

High-tensile steel 200 1.5 0.8 6

Fig: Schematic formation mechanism of the hierarchical

assembly from molecular silk fibroin to microfibers.



Fig: Possible structure and technical applications of the silk

fibers. The dotted line shows an example of the versatility of

silk and the multiple possible applications.

Tissue Regeneration

The group takes a multi-fold approach to the challenges of

tissue regeneration. Traditional biochemical factors are

utilized to direct stem cell and tissue outcomes in selective

(temporal, regional, interfacial) approaches.

In addition, a major focus is on biophysical factors (membrane

potential Vmem, external electric fields, mechanical forces) on

cell and tissue outcomes. The orchestrated suite of inputs to

cell and tissue functions is considered towards desired

fundamental goals, for building quantitative metabolic modelsGOPALAKRISHNAN D & Dr.T.KARTHIK


of tissue functions and regeneration in vitro, and to generate

useful tissue systems for in vitro study and in vivo utility.

Example tissues under study: bone, cartilage, small diameter

vasculature, neurological tissues, cervical, kidney, adipose,

among others.

Fig: Silk scaffolds can be used to produce tissue engineered

bone. The figure illustrates the generation of tissue

engineered bone using silk scaffolds.

Developing Tissue-Based Disease Models

The two categories above (tissue regeneration, biopolymers)

are exploited to develop human tissue models for relevance to

the study of disease mechanisms as well as for therapeutic

screening. These systems are designed to account for complex

cell mixtures, vascular needs and relevant cell types to

recapitulate structure and functional features of the target

tissue, as well as sustainability of these tissues over


extended time frames (weeks to months) for use in both acute

and chronic drug screens. Example disease systems under study

include: kidney, breast, prostate, obesity, diabetes, among

others.

Fig: Application of tissue engineering to diseases affecting

the eye. The illustration depicts the generation of corneas

using tissue engineering techniques.

Drug Delivery


Fig: Bioengineered silk-based delivery systems. The

illustration depicts silk-based fibers that can be used to

deliver genes to cells.

Silk-based drug delivery systems are studied to exploit the

all-water processing, the ability to regulate beta sheet

(crystalline) content for control of lifetime in vivo (days to

years), to control medical device format (e.g., coating,

fibers, tablets, gels, etc.), to deliver small or large

molecules that are hydrophilic or hydrophobic, and to exploit

the stabilization influence of silk on labile compounds. We

approach the challenge from both a fundamental design approach

(genetically engineered block copolymers) to direct delivery

systems from reprocessed silkworm silk. In vitro and in vivo

studies are conducted to understand and optimize the various

systems.

Biomaterials Engineering & Regenerative MedicineGOPALAKRISHNAN D & Dr.T.KARTHIK

Our focus is on biopolymer engineering to understand

structure-function relationships, with emphasis on studies

related to self-assembly, biomaterials engineering and

regenerative medicine. His lab has extensively studied silk-

based biomaterials in regenerative medicine, starting from

fundamental studies of the biochemistry, molecular biology and

biophysical features of this novel class of fibrous proteins.

These studies have led to inquiries into the impact of silk

biomaterials on stem cell functions and complex tissue

formation. The result has been the emergence of silk as a new

option in the degradable polymer field with biocompatibility,

new fundamental understanding of control of water to regulate

structure and properties, and new tissue-specific outcomes

with silk as scaffolding in gel, fiber, film or sponge

formats. Additional technological directions in optics,

electronics, adhesives and many related areas have emerged

from these studies.


Fig: Bio-mimetic processing of silk protein to produce new

materials and devices.

The image depicts processing of natural materials and

illustrates the various uses of these materials.

Biopolymers

The group has a longstanding interest in the study of

biopolymers (structural proteins, polysaccharides),

particularly the use of biological approaches to the synthesis

and modification of these material systems. Genetic

engineering and metabolic engineering strategies are employed

to control chemistry and thus function, along with selective

chemical modifications. Materials science and engineering

approaches are utilized to explore structure-function

relationships from processing. Questions of self-assembly,

biological interfaces and degradation are studied, along with

utility in cell and tissue systems. Specific polymers of

interest include: silks (silkworm, spider), collagens,

resilin, elastins, bacterial cellulose.


Fig: Fibrous proteins in nature that can be used to

fabricate new materials.

Cartilage

There are three types of cartilage: hyaline, which is the most

common, elastic, which looks a lot like hyaline unless it is

specially stained for elastic fibers, and fibrous, which is

not very common and is difficult to identify. Which should

exhibit a long piece of hyaline cartilage. These cartilaginous

rings circle the trachea and keep it from collapsing.


The matrix of the cartilage is basophilic and will normally

stain blue in most slides. The staining varies, however, and

in some of your slides it may appear light purple to pink.

Sitting in this clear matrix are lacunae (small lakes)

containing the chondrocytes or cartilage cells. The matrix

will stain heavier around lacunae. Usually, the lacunae are

found in small groups called isogenous groups (same genes).

Each isogenous group originated from one chondrocyte that

divided a number of times. Notice that there are no blood

vessels in cartilage.


The elastic fibers have been stained dark purple. Elastic

cartilage looks a lot like hyaline cartilage unless the

elastic fibers in the matrix are specially stained. Elastic

cartilage is flexible but

strong.

Fibrous cartilage appears to be a transition between dense

connective tissue and hyaline cartilage. It is usually not

very well demonstrated.


If the predominant color on slide is blue and there are some

little red things here and there, then look closely at the red

things and you will see that they are lacunae with

chondrocytes in them. The blue stuff is collagen. Try to see

both types of slide by sharing with others. There will also be

demonstration slides.

The diagram below demonstrates the process of using the

photopolymerizable hydrogel for cartilage repair.


Creation of new cartilage will use controlled delivery of

biological signals mentioned above in addition to physical

signals provided by a scaffold to design anisotropic,

organized cartilage tissue. In addition, chondrocytes with

varying morphology and gene expression may be organized during

the encapsulation process. Tissue engineered cartilage with an

organized structure similar to native tissue will have

functionality comparable to native tissue and may potentially

integrate more easily into the heterogenous host tissue whereGOPALAKRISHNAN D & Dr.T.KARTHIK

http://www.datlof.com/8axamal/docs/marketing/jhu/je/schematic1.jpg

it is implanted. This three-dimensionality is expected to

increase the speed and efficacy of tissue regeneration.

Traditionally, silk has been utilized in the construction of

textiles. Current research in silk fibers involves their

innovative trends and advanced applications. Basically, the

rich proportion of essential amino acids in silk fibers

indicates high nutritive value, meaning that silk fibroin can

be used as a dietary additive. Furthermore, the amino acids,

glycine, alanine, serine and tyrosine are of vital for

nourishing the skin.

The crystalline structure of silk protein reflects UV

radiation, acting as protective buffer between the skin and

environment. The extracts of silk protein are used in soap

making, personal care and cosmetic products. The silk protein

is also applied to enhance glossy, brightness, and softness of


products. In addition, the production of advanced man made

super-fibers such as Kevlar involves petrochemical processing,

which contributes to pollution. Interest in silk fibers is

mainly due to the combination of the mechanical properties and

eco friendly way in which they are made. Spider silk fibers

have been envisioned to be applied in a variety of technical

textiles, including parachute cords, protective clothing and

composite materials in aircrafts, which demand high toughness

in combination with sleaziness.***************


advances in medical textiles

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