Biomedical Applications of Aerogels

30Biomedical Applications of Aerogels

Wei Yin and David A. Rubenstein

Abstract This section highlights a few applications of aerogels in a biological context, as

a biomaterial. Some aerogel formulations have been shown to have compatibility with

the cardiovascular system and others have been able to induce apatite formation for potential

bone growth. Others have provided proof that proteins can be embedded within aerogel

samples maintaining their biological functionality, therefore aerogels may be used in a drug

delivery system. At this point, more work is needed to determine how aerogels can be

applied to the biological systems; however, with the improvements in aerogel processing

along with a better understanding of biomaterials the use of aerogels in biological applica-

tions will be significant in the future.

30.1. Introduction

Synthetic materials have been used in biological environments for approximately 3,000

years. As newmaterials are developed and newmaterial processing methods are designed, the

biological effect of materials has been continually investigated to determine whether or not the

material has any potential to be used in the human body. Over the past 100 years, our

understanding of biological processes combined with our ability to precisely fabricate materi-

als has led to the fast growing field of biomaterials. It was estimated that in the year 2000, about

20million individuals hadmedical devices implanted, incurring an approximate annual cost of

$300 billion (including hospitalization and surgical costs) [1]. The use of novel biomaterials in

medical applications has significantly enhanced the longevity of patients. However, the failure

of biomaterials can lead to symptoms, diseases, side effects, or sudden patient death, which

leaves room for improvement in the current biomaterial properties and applications.

Silica aerogel is a well-known lightweight solid. Even though it was invented in

1931, it only started to draw interest from materials scientists about 15 years ago, due to the

improvements in the use of sol-gel processes to expedite the synthesis time (Chap. 1).

However, traditional aerogels have never been used as a biomaterial. Along with the

significant improvement in the mechanical strength, modern aerogels have demonstrated

W. Yin (*) and D. A. Rubenstein l School of Mechanical and Aerospace Engineering, Oklahoma State

University, Stillwater, OK 74078, USA

e-mail: [email protected]; [email protected]

M.A. Aegerter et al. (eds.), Aerogels Handbook, Advances in Sol-Gel Derived

Materials and Technologies, DOI 10.1007/978-1-4419-7589-8_30,# Springer Science+Business Media, LLC 2011

683

certain properties required for biomedical applications. Thus, investigations on the

biocompatibility of aerogels have been recently initiated. This contribution highlights

some of the current work being carried out to extend aerogel applications in the biomate-

rials field (Chap. 31).

Cardiovascular diseases are currently the number one killer in the Western world and

there is a significant need for new devices to augment these conditions. Tissue engineering is

currently hindered by the design of new porous but strong biocompatible materials that can

be used to promote cell growth throughout the material. These new materials can act as a

template for new cell growth. New materials are also needed to design targeted-controlled

release systems that can be used to treat various diseases, including genetic diseases. In the

following sections, the use of various aerogel materials as cardiovascular implantable

devices, as tissue engineering scaffolds, and as drug delivery vehicles is described.

Before we get into the details of the above-mentioned applications, we need to keep in

mind that for any implantable device, there can be unwanted biological responses, which can

be initiated by the device itself, and unwanted material responses, which can be initiated by

the biological system. In general, there are four common biological changes that occur in

response to foreign material implantation. These include the inflammatory response, coagu-

lation/hemolysis, the allergic response, and the carcinogenic response. Inflammation is a

nonspecific response to tissue trauma, infection, local cell death, or intrusion of a foreign

material. Inflammation is typically characterized by redness, swelling, pain, and heat.

Coagulation and hemolysis are nonspecific responses that occur when there is damage to

blood vessels or when blood comes in contact with a foreign material. Coagulation is the

activation and aggregation of platelets, and hemolysis is the destruction of red blood cells.

The allergic response is a specific response carried out by the immune system when there is a

recognized foreign particle within the body. This particle is typically attacked by white

blood cells, T-cells, B-cells, and antibodies to be removed. Certain implantable materials

could express or degrade into compounds that are recognized by this system. The last

response occurs when an implantable material causes damage to a host cell’s DNA that

induces cancer formation. Cancer is characterized by the uncontrollable cell growth and

spreading throughout the body. Material responses can include swelling or leaching, corro-

sion, wear, deformations, and the formation of new biological compounds (i.e., organo-

metallic compounds, which are a combination of a metal with an organic part). To investi-

gate the potential applications of aerogels in the biomedical field, all the responses discussed

earlier need to be considered.

30.2. Aerogels Used for Cardiovascular Implantable Devices

Cardiovascular diseases and complications are the leading cause of death in the United

States, which creates a large demand for biomaterials suitable for cardiovascular implant-

able devices. In general, in order for a biomaterial to be usable in a certain organ system in

the human body, the material must be compatible with that system over the device’s entire

service life period. For a cardiovascular system, this includes compatibility with the

patient’s blood, especially with respect to immune responses and hemostatic/thrombotic

responses and compatibility with blood vessels, if the device is in contact with them.

When in contact with blood, a foreign material of the implantable device may induce a

rapid deposition or adsorption of plasma proteins onto the surface, followed by the adhesion

and activation of platelets [2]. Plasma protein deposition onto a material may trigger acute

684 Wei Yin and David A. Rubenstein

immune responses, characterized by the attack of leukocytes [3]. Platelet activation and

coagulation can lead to clot formation or thrombosis. A clot that forms on the surface of a

blood implantable device can severely affect the performance of the device. Furthermore,

inflammation may also be triggered by foreign material–blood contact [4]. An ideal blood

implantable polymeric material should not induce plasma protein adhesion/adsorption or

trigger an acute immune response or platelet activation. It should also not initiate cell death

for those cells that it is in contact with.

As one of the most commonly known blood implantable devices, artificial heart valves

are used to replace diseased or damaged heart valves. There are approximately 300,000

artificial heart valves implanted every year, about 60% of which being mechanical heart

valves. Tissue valves are the most common alternative to mechanical heart valves, account-

ing for the remaining prosthetic heart valve market. Polymeric heart valves have been

investigated for more than 10 years, though their performance is far from satisfactory.

They are usually made of polyurethane and in the shape of a native heart valve (with soft

leaflets). Their overall success rate is fairly low due to numerous problems, including

material degradation and poor mechanical strength.

The popularity of mechanical heart valves is closely related to their mechanical

strength, durability, and good hemodynamic performance. However, valve-induced cavita-tion (vaporous bubble formation due to a transient pressure drop below the liquid vapor

pressure) may curb the performance of mechanical heart valves. Cavitation occurs during

valve closure when the fluid mass is squeezed through the valve opening. The fluid reaches

very high velocities and is subjected to a large pressure drop over a small distance. When

vaporous bubbles inside the fluid collapse near the blood vessel wall, the wall boundary is

impacted with very high local pressures, which can result in elevated shear stress and lead to

platelet activation. The transvalvular pressure gradient is critical to cavitation and is directlyrelated to the leaflet inertia [5]. Employing a low density material for leaflets may be the

potential solution to cavitation problems. In summary, materials suitable for mechanical

heart valves must be blood compatible, blood vessel wall endothelial cell compatible, strong,

durable, and light. With a significantly improved mechanical strength, new aerogels may be

considered as candidate materials for artificial heart valve leaflets, where high mechanical

strength and low inertia are required to enhance valve durability and minimize the occur-

rence of cavitation. Furthermore, aerogels are generally inexpensive to formulate, which

may benefit many potential prosthetic heart valve recipients.

Recent work started by Yin and Rubenstein at Oklahoma State University has aimed

to investigate the compatibility of various formulations of aerogels within the cardio-

vascular system. The type of aerogel used in their initial studies was a surfactant-templated

polyurea-nanoencapsulated macroporous silica aerogel (referred to as cross-linked aerogel:

X-MP4-T045) [6] (Chap. 13). X-MP4-T045was made using tetramethylorthosilicate (TMOS)and tri-block copolymer PEO20PPO70PEO20 (Pluronic P123) following the Leventis

approach [7]. It had a mass density of 0.66 g/cm3 and a porosity of 50.0%. The average pore

size is approximately 5 mm. Its effects on plasma anaphylatoxin generation (C3a is a very

important plasma inflammation marker), plasma protein adsorption, platelet activation, coag-

ulation, and vascular endothelial cell normal functions were investigated.

First, it was determined whether or not aerogel samples would induce platelet

activation upon contact. To investigate this, washed platelets were incubated with aerogel

samples for up to 6 h. The expression of phosphatidylserine (PS) and P-selectin (CD-62P)was measured to determine how platelets responded to aerogel contact. Platelets are a

critical component of the hemostatic system and play a salient role in clot formation.

Biomedical Applications of Aerogels 685

Platelets undergo two parallel processes within the body: activation and aggregation.

Platelet activation involves the expression of the negative phospholipid, phosphatidy-

lserine, along with the release of multiple procoagulant proteins. Active platelets partici-

pate in the coagulation cascade, which results in stable fibrin formation. Platelet

aggregation involves the expression of many adhesion molecules and the end product is

stable platelet–platelet adhesion or platelet–endothelial cell adhesion. The results demon-

strated that contact with aerogel under static conditions did not trigger platelet activation

and was reduced as compared to calcium ionophore (A23187) activated platelets

(Figure 30.1). This indicates that this particular aerogel formulation (X-MP4-T045) wascompatible with platelets.

To answer the question if platelet normal functions are altered by this particular

aerogel, platelet activation and aggregation were monitored after aerogel contact using

the modified prothrombinase assay and optical platelet aggregation. For aggregation

Figure 30.1. There was no significant difference in CD62P A. and phosphatidylserin (PS) B. expression on

untreated and X-aerogel treated platelets after 6-h incubation, while A23187 treatment induced a much higher

CD62P and PS expression on washed platelets.


experiments, platelets were incubated with aerogel samples and then antagonized with

thrombin receptor agonist peptide 6 (TRAP6) or ADP. Within 6 h, aerogel incubation did

not enhance or impair the normal aggregation process (Figure 30.2A). Using the modified

prothrombinase assay [8], aerogel incubation did not enhance or inhibit platelet participation

in the coagulation cascade (Figure 30.2B) measured through thrombin generation. Com-

bined, these data suggest that surfactant-templated polyurea-nanoencapsulated macroporous

silica aerogel is compatible with platelets [6].

0 0.5 1 2 4 6 240.000.050.100.150.200.250.300.350.400.450.500.550.60

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Aerogel - TRAP6

Control - ADP Aerogel - ADP

0 15 30 45 60 75 90 105 120 135 1501.0

1.5

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Platelets @ 100,000/µL Platelets @ 100,000/µL + X-Aerogel Platelets @ 250,000/µL Platelets @ 250,000/µL + X-Aerogel

A

B

Figure 30.2. A. The effect of X-aerogel on platelet aggregation rate towards TRAP6 and ADP (Data presented as

mean + standard error of the mean). B. The effect of X-aerogel on platelet participation within the coagulation

cascade, as measured by thrombin generation (Data presented as mean � standard error of the mean). Different

platelet concentrations were used to determine if enhanced platelet–platelet contact affects the biocompatibility.


The complement system is an important contributor in inflammation, whose activation

may be triggered after foreign material contact with blood. Complement activation can lead

to the generation of physiologically relevant levels of anaphylatoxins, C3a and C5a, whichsupport the recruitment of leukocytes and can enhance vascular wall permeability. As the

major complement proteins involved in inflammation, C3a and C5a can induce production

and release of cytokines and cause cell death. They are usually considered biomarkers for

inflammatory conditions. To determine if cross-linked aerogel X-MP4-T045 would trigger

immune responses, the aerogel samples were incubated with normal human plasma at room

temperature for up to 24 h. The aerogel induced plasma anaphylatoxin level was measured.

The results indicated that aerogels, as a foreign material, induced acute inflammatory

responses and led to C3a level increase. However, this increase was not statistically

significant, compared to that observed with control plasma (plasma that was not treated

with aerogels) (Figure 30.3).

To further investigate the compatibility of cross-linked aerogel X-MP4-T045 with the

cardiovascular system, human bone marrow microvascular endothelial cells and human

umbilical vein endothelial cells were cultured in the presence of aerogel samples. Endothe-

lial cells are the cell type that lines the interior of all blood vessels and any blood implantable

device would come into contact with these cells. It is required for a material used in blood

implantable device that after its incubation with endothelial cells, there should be no change

in endothelial cell function, growth, viability, or migration. Endothelial cell culture para-

meters were investigated using a live/dead cell cytotoxicity assay, which consists of calcein

and ethidium. After 5 days of endothelial cell culture with aerogel, there were no differences

in cell culture parameters (Figure 30.4). Combining all the data regarding cardiovascular

compatibility, it has been shown that crosslinked aerogel X-MP4-T045 is compatible with

the inflammatory system, platelets, and endothelial cells [6]. Current work is being carried

out on whether or not this type of aerogel is compatible with red blood cells.

0

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1200

1400

2 hr 4 hr 6 hr 24 hr

C3a

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cent

ratio

n (n

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l)

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Control

X-aerogel

Figure 30.3. Generation (ng/ml) after plasma incubation with X-aerogel for 2, 4, 6, and 24 h. All data were

presented as mean + standard error of the mean (n ¼ 6). No significant difference was detected between X-aerogel

treated and untreated plasma.


However, with all materials, slight changes in the material composition and/or the

processing of the material can drastically affect the compatibility of the material within a

biological system of interest. For instance, a chitosan–silica hybrid aerogel is not compatible

with red blood cells and induces a significant amount of hemolysis [9] (Chap. 18). This is

interesting because silica aerogels are compatible within the cardiovascular system and

chitosan, processed in other forms, is a common biomaterial for cardiovascular devices.

Therefore, it is important to classify the compatibility of individual aerogel formulations

within the biological system. There are a number of research groups currently interested in

determining the compatibility of various aerogels (silica, polymeric) within the cardiovas-

cular system with the long-term goal of fabricating cardiovascular implantable devices, with

the majority of the current work focused on determining the compatibility of different

aerogel samples within the vascular system.

Our main interest is the formation of novel mechanical heart valve leaflets composed

of a functionalized cross-linked silica aerogel. As discussed previously, the silica aerogel of

interest has a very low bulk density combined with a high mechanical stiffness, which makes

it ideal for a heart valve leaflet. These properties would minimize cavitation formation and

would increase the working life time of the valve. Current work is focused on designing

and fabricating leaflets and leaflet housing for future use in cardiovascular implant system.

Figure 30.5 depicts a flow chamber with two prototype aerogel monoleaflet heart valves

installed. The two valves are located on the opposite sides of the flow chamber and are

placed in opposing directions to control the flow direction under dynamic conditions.

The flow chamber (made of Teflon) is connected to a peristaltic pump which can generate

Figure 30.4. Digital images of bone marrow microvascular endothelial cells (Panel A/B) or human umbilical

vein endothelial cells (Panel C/D) cultured without X-aerogel samples (Panel A/C) or with X-aerogel samples

(Panel B/D). Cells were stained with calcein (green, live) or ethidium (red, dead). All scale bars are 100 mm.


physiological flow conditions, mimicking that of the heart. The interaction between the

prototype aerogel heart valve and blood/plasma under dynamic conditions will be tested in

this flow chamber. Preliminary studies indicated that neither the prototype aerogel valves

nor the flow chamber itself activate or damage blood cells under static conditions.

30.3. Aerogels as Tissue Engineering Substrates

Tissue engineering is concerned with the design and manufacturing of replacement

tissues and organs. In order to successfully tissue engineer an organ, it is required that the

tissue that is being fabricated be housed within a biocompatible scaffold. These scaffolds actto support and promote the tissue growth. There are two major approaches in tissue

engineering scaffolds. The first one is to have the scaffold mimic the native extracellular

matrix of the tissue that is being formed. With this approach, the forming tissue would

recognize native topographies and the tissue would not need to form its own extracellular

matrix. The scaffold provided would be used during the entire lifetime of the engineered

tissue and hence would need to be compatible over the entire lifetime. The second approach

is to fabricate a scaffold which promotes cell infiltration but is also degradable. Using this

Figure 30.5. Proengineering drawing of a flow chamber with two prototype aerogel monoleaflet heart valves.

A picture of the prototype monoleaflet valve is shown in the left top corner.


approach, cell growth into tissues would be promoted within the scaffold but then the cells

would need to degrade this scaffold and fabricate their own extracellular matrix. Both

approaches have distinct advantages and disadvantages and it has recently become clear

that the choice of approach is dictated by the type of tissue which is being fabricated.

Aerogels have various physical properties which make them ideal candidates as tissue

engineering scaffolds. The first is a high porosity. The native extracellular matrix is on the

order of 80% porous and this is difficult to mimic with many biomaterials. The second

property is good mechanical strength (Chap. 22). Most biomaterials that are highly porous

are very weak mechanically (i.e., electrospun scaffolds). This typically hinders cell growth

and migration throughout the tissue engineered scaffolds because the mechanical stiffness of

the native extracellular matrix is on the order of 100 MPa. Most aerogel formulations can

easily match this property. The last critical parameter is the chemical composition. With a

better understanding of materials science, it has become easy to fabricate aerogel samples

from various materials. Many of these materials have acceptable biocompatibilities in their

polymer form, which would suggest that in the form of an aerogel the compatibility should

be acceptable as well, since biocompatibility is typically determined by chemical composi-

tion and degradation products. However, the compatibility testing of these materials must be

conducted one by one.

Surfactant-templated polyurea-nanoencapsulated macroporous silica aerogels

(X-MP4-T045) are compatible with endothelial cells, suggesting they may be used as a

scaffold for vascular tissue engineering. However, the formulation of the scaffold would

need to be changed to allow for the migration of endothelial cells throughout the scaffolds.The chitosan–silica hybrid aerogel, which showed a high value of hemolysis, also showed

a low value for cytotoxicity [9]. While it was not reported which cell type was investigated,

it suggests that if cytotoxicity is the primary concern for biomaterial scaffolding, this

chitosan–silica aerogel may be considered as a suitable tissue engineering substrate.

Bone replacements are currently one of the most investigated tissue engineered

product. These replacements can be used for patients with severe osteoporosis or a com-

pound break of one of the load bearing bones. Bone has a very high mechanical stiffness in

compression (Chap. 22) but is also highly porous, which demonstrates two important

analogies to aerogels. Bone is also a very dynamic tissue which is constantly undergoing

remodeling. Therefore, any scaffold to be used for bone tissue engineering needs to replicate

this property. Recently, the group of Toledo-Fernandez has investigated the bioactivity of

wollastonite aerogels (composites), which matches bone in mechanical properties and

porosity, within simulated body fluid [10]. After 25 days of incubation within such a fluid,

a uniform apatite layer is formed on the surface of the aerogel. This layer is the most

common additive to bone implantable devices (i.e., cobalt–chromium–molybdenum

implants) to promote bone cell growth into the scaffold. Due to the formation of this layer

on the aerogel surface, it makes it an ideal candidate for bone tissue engineered scaffolds.

The next steps for real bone tissue growth would be to determine whether or not bone cells

(osteocytes, osteoblasts, and osteoclasts) are compatible with the apatite-coated aerogel

samples. Also, it would need to be determined whether or not the bone cells could then

remodel the aerogel and incorporate into this material. If this were the case, it would be

possible for the bone cell remodeled aerogel to be implanted into a patient.

It is also important to note that highly porous scaffolds are very desirable in tissue

engineering to promote cell migration. Although the tissue compatibility of most aerogels

has not been extensively studied, it is worthwhile to mention that highly porous (>95%)

aerogel scaffolds can be formed [11]. These scaffolds had a relatively low pore diameter


(<1 mm), but with different process parameters, these scaffolds may be able to be fine tuned

to be useful for tissue engineered applications, especially if the pore size could be increased.

At a pore diameter of less than 1 mm, cells would not be able to permeate the aerogel sample.

However, with increasing pore size, on the order of a 5–10 mm diameter, cells would begin to

be able to invade the scaffold and potentially use it as a template for cell growth.

30.4. Aerogels as Drug Delivery Systems

The last major biomedical field that aerogels have been applied to is drug delivery

systems. Not much work has been done yet within this field, but what has been investigated

shows promising uses of aerogels as drug delivery systems (Chap. 31). Drug delivery is

primarily concerned with administering a drug to a targeted region within the body. As an

example, aspirin is very effective as a pain reliever but there are many unwanted side effects

associated with aspirin treatment. A perfect drug delivery system would locate the region of

the body which needs the drug, would deliver the drug to that region, and would not affect

any other locations within the body. In this way, side effects will be significantly reduced.

There are a few principles that need to be discussed regarding drug delivery systems

before we will show how aerogels can be used as a drug delivery system. When designing a

drug delivery system, the first critical parameter to consider is the desired release profile of

the drug. In general, there are three types of release profiles: a bolus release, a sustained

release, and a controlled release. The bolus release is the easiest system to design and this

would include the complete release of the entire drug payload within a short amount of time

(<30 min). Any prescription that states, “take x pills every y hours and not to exceed z pillsin 24 h” is an example of a bolus release system. Sustained release systems, generally have

one dose that lasts for at least 4 h. An example of this medication is the melatonin release

system that aids in sleeping. One dose of this medication lasts for approximately 8 h, so that

the patient can sleep throughout the entire night. The last system is a controlled release drug

delivery system and this is some combination of a bolus release system and a sustained

release system. These systems are also known as smart release systems, because they can

recognize that a dose is needed and the delivery system releases an appropriate dose within a

short amount of time. An example of this type of system would be the smart insulin delivery

systems that sense the levels of insulin within the blood stream and release insulin accord-

ingly. The second critical parameter for drug delivery systems is the type of release

mechanism used. For instance, a pill can be designed that completely dissolves within the

body (can be bolus or sustained) or the pill can make use of an osmotic pump to eject

the drug from its reservoir. Differences in these systems would arise due to different

polymers that the drug can be embedded in.

There has been some work documenting that aerogel samples can be prepared with a

protein payload encapsulated within the aerogel [12]. In this work, a red fluorescent protein

was loaded into a silica aerogel. On 5 subsequent days after the aerogel preparation, the

stability of the encapsulated protein was examined by quantifying the fluorescence intensity.

After 24 h in the aerogel formulation, there was a drop in intensity (to ~85%), which then

remained constant for the remaining of the observation time. Although there was no

compatibility testing associated with this work and the protein investigated has no immedi-

ate biological applications, this study was a proof of principle that a protein can be

embedded within aerogel samples and more importantly, the protein was viable after


material processing. Using a similar method, there is a high potential to employ aerogels in

drug delivery systems.

A second study investigated the immobilization of lipase (a protein that breaks down

lipids) onto methyl-modified silica aerogels [13]. This work showed that a protein can be

placed on the surface of aerogel samples and that this protein remains partially active after

immobilization (there was an approximate 50% reduction in enzyme activity). While this is

a significant reduction in activity, it suggests that functional groups can be placed onto

aerogel samples and these groups can retain some biological activity (perhaps due to the

random nature of this adsorption). In drug delivery devices, this would be critical for

targeted delivery systems. In these types of systems, a functional group is added to a

delivery system which typically prevents drug release until some condition is met.

For instance, such a functional group could be sensitive to pH and would prevent an oral

drug from being released within the stomach where the drug could potentially be degraded.

More work is needed within this research field, but again, this report acts as a proof of

principle for protein immobilization onto aerogels, which can later be released in a

controlled manner.

The TAASI Corporation (Delaware, OH, USA) has begun to investigate the devel-

opment of their PristinaTM aerogels for targeted controlled release of cancer pharmaceu-

ticals for the potential application of a drug delivery system to treat cancer. In their system,

aerogel particles were coated with ligands that would target cancerous cells. Upon

ligand–receptor binding, pharmaceutical agents (melitin) loaded within the aerogel parti-

cles would be released through a specific pore structure within the aerogel. In two cell

culture experiments, these loaded aerogel particles were able to kill 97% of the targeted

cells and only 1% of the nontargeted cells, which did not express the specific ligands

receptor. The efficacy of this product needs to undergo more testing, such as a coculture

system where there are two (or more) cell types that either do or do not express the

receptor of interest.

30.5. The Future of Aerogels in Biomedical Applications

This contribution has discussed the few reports that have investigated aerogels in a

biological context. Some aerogel formulations have demonstrated good compatibility with

the cardiovascular system and others have been able to induce apatite formation for potential

bone growth. Others have provided evidence that proteins can be embedded within aerogel

samples and maintain their functionality after protein removal. At this point, more work is

needed to determine how aerogels can be applied to various biological systems, however,

with the improvements in aerogel processing along with our better understanding of

biomaterials; it is believed that the use of aerogels in biological applications will be

significant in the future. As discussed earlier, there is a direct link for silica aerogels to

be used as a cardiovascular implantable device. The potential for aerogels as a tissue

engineering scaffold and a drug delivery system was also discussed. There is also a potential

to adapt aerogels to be used as filters in extracorporeal devices, due to their high porosity,

nonfouling behavior, and ability to be functionalized. Aerogel samples can potentially be

used as dental substitutes and can be used as components in many other implantable systems.

However, before that step is taken, the compatibility of aerogel samples must be confirmed

under application relevant conditions.


30.6. Conclusion

Modern cross-linked aerogels have significantly improved mechanical properties.

They are strong and more durable, while they maintain their traditional characteristics of

being light and porous. The findings discussed here indicated that by adjusting chemical

components and manufacturing procedure, aerogels can be made suitable for many biomed-

ical applications. More is about to be explored and we believe aerogels will have a promising

future in the biomaterials market.

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