Nanotechnology for Regenerative Medicine
The changing lifestyle of society, an ageing population and the high expectations for a better quality of life call for improved, more efficient and affordable health care (1). Use of nanotechnology in regenerative medicine can offer new treatment modalities, when applied to major medical challenges (2). Regenerative medicine is the method of creating living and functional tissues to repair or replace tissue or organ function lost due to congenital defects, damage, disease, or age (3). This field holds promise for regenerating damaged tissues and organs in the body by stimulating previously irreparable organs to heal intrinsically (4). Regenerative medicine also permits scientists to grow tissues and organs in the laboratory and to safely implant them when the body cannot heal itself (4). Most importantly, regenerative medicine has the potential to solve the problem of the shortage of organs available for life-saving organ transplantation (5; 6).
Regenerative medicine has become a multidisciplinary field (7). Application of nanotechnology in regenerative medicine can radically change the way some diseases are treated in the future. In the last few decades, nanomedicines have started coming onto the market (8). Regenerative medicine can be used to restore, maintain or enhance tissues and hence organ functions. Regeneration of tissues can be achieved by the combination of living cells, which will provide biological functionality, and materials, which act as scaffolds to support cell proliferation (8; 7; 9). In vivo mammalian cells respond to the biological signals they receive from the surrounding environment. These signals are controlled by nanometer-scaled components, so it is very important that the material used produces the correct signal to guide cell growth and functionality appropriately (10). The application of nanotechnology to regenerative medicine is a wide area (11). Nanotechnology is an excellent tool for producing scaffolds that mimic the biological structures. This technology also offers efficient drug delivery system.
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In this study, we focused on three different applications of regenerative medicine. Our first aim was to develop an anodization technique to produce surface modified nanoporous titanium that can be used as potential system for engineering a distinctive biomaterial for bone tissue engineering. Our second aim was to fabricate a halloysite-PCL (poly-Æ-caprolactone) scaffold and assess its ability to support cell growth, differentiation, and fucntionality. The final aim was to examine the effect of different drug loaded halloysite-PCL scaffold as potential antibacterial, antiseptic and disinfectant material.
Nanoparticles and Nanotubes for Regenerative Medicine
Extensive libraries of nanoparticles, composed of an assortment of different sizes, shapes, and materials, and with various chemical and surface properties, have already been constructed. The field ofÂ nanotechnologyÂ is under constant and rapid growth and new additions continue to supplement these libraries. Examples of nanoparticles are buckyballs, liquid crystals, liposomes, nanoshells, quantum dots and supramegnetic nanoparticles. Carbon nanotubes and halloysite nanotubes are example of nanotubes.
Liquid crystal pharmaceuticals are composed of organic liquid crystal materials that mimic naturally-occuring biomolecules like proteins or lipids. They are considered a very safe method for drug delivery and can target specific areas of the body where tissues are inflamed, or where tumors are found.
Liposomes are lipid-basedÂ liquid crystals, used extensively in the pharmaceutical and cosmetic industries because of their capacity for breaking down inside cells once their delivery function has been met. Liposomes were the first engineered nanoparticles used for drug delivery but problems such as their propensity to fuse together in aqueous environments and payload release, have led to replacement, or stabilization using newer alternative nanoparticles.
Also referred to as core-shells, nanoshells are spherical cores of a particular compound surrounded by a shell or outer coating of another, which is a few nanometers in thickness.
Also known as nanocrystals, quantum dots are nanosized semiconductors that, depending on their size, can emit light in all colors of the rainbow. These nanostructures confine conduction band electrons, valence band holes, or excitons in all three spacial directions. Examples of quantum dots are semiconductor nanocrystals and core-shell nanocrystals, where there is an interface between different semiconductor materials. They have been applied in biotechnology for cell labeling and imaging, particularly in cancer imaging studies.
Superparamagnetic molecules are those that are attracted to a magnetic field but do not retain residual magnetism after the field is removed. Nanoparticles of iron oxide with diameters in the 5-100 nm range, have been used for selective magnetic bioseparations. Typical techniques involve coating the particles with antibodies to cell-specific antigens, for separation from the surrounding matrix. Used in membrane transport studies, superparamagenetic iron oxide nanoparticles (SPION) are applied for drug delivery and gene transfection. Targeted delivery of drugs, bioactive molecules or DNA vectors is dependent on the application of an external magnetic force that accelerates and directs their progress towards the target tissue. They are also useful as MRI contrast agents.
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Dendrimers are highly branched structures gaining wide use in nanomedicine because of the multiple molecular "hooks" on their surfaces that can be used to attach cell-identification tags, fluorescent dyes, enzymes and other molecules. The first dendritic molecules were produced around 1980, but interest in them has blossomed more recently as their biotechnological uses were discovered.
Typically 1-100 nm in length, nanotubes are most often made from semiconducting materials and used in nanomedicine as imaging and contrast agents. Nanotubes can be made by generating small cylinders of silicon, gold or inorganic phosphate, among other materials.
Nanosized tubes of carbon known as carbon nanotubes possess optical transitions in the near-infrared that can be utilized for tracking cells. The infrared spectrum between 900 and 1,300nm is an important optical window for biomedical applications because of the lower optical window for biomedical applications because of the lower optical absorption and small auto-fluorescent background. Like QD, carbon nanotubes possess good photostabillity and can be imaged over long periods of time using Raman scattering and fluorescence microscopy. However, unlike QD, which are typically composed of heavy metals such as cadmium, carbon nanotubes are made of carbon, an abundant element in nature. Carbon nanotubes possess large aspect ratios with nanometer diameters and length ranging from submicron to millimeters. These tubes can contain a single wall of carbon (SWNT) or multiple walls of carbon nanotubes (MWNT). The small size of the SWNT makes it possible for 70,000 nanotubes to be ingested where they can remain stable for weeks inside 3T3 fibroblasts and murine myoblast stem cells. Having such a high concentration of carbon nanotubes within a cell differentiation, even though. While such nanomaterials have yet to reach clinical application, it does show the potential for non-invasive optical imaging.
An ideal scaffold for tissue regeneration should have similarity to native extra cellular matrices in terms of both chemical composition and physical nanostructure. Recently, nanostructured biomaterials having physical nanofeatures such as nanocrystals, nanofibers nanosurfaces, nanocomposites, etc. gained much interest in regenerative medicine. This is mainly because of their resemblance of physical nanofeatures to natural ECM. There are many different type of scaffold: nanocrystalline bioresorbable bioceramic scaffolds and nanofibrous polymeric scaffolds for tissue regeneration. Fabrication of porous bioceramics based on HA and other calcium phosphates with interconnected pore structure can be done by the replication of polymer foam. The advantage of this technique is the control over porosity, pore geometry and pore size of the fabricated scaffolds. Electrospinning is a versatile technique to fabricate nanofibrous polymeric matrices for use in regenerative medicine. The recent developments in electrospun scaffolds with a special emphasis on FDA approved biodegradable polymers such as PCL, PLA, PLGA, collagens, etc have been extensively studied. Special attention has been given to the mechanical properties and cell interaction of the electrospun fiber mats. Electrostatic cospinning of polymers with nanohydroxyapatite to fabricate hybrid nanocomposite scaffolds as potential scaffolds mimicking the complex nanostructured architecture of bone has been suggested for hard tissue regeneration.
Advanced techniques for the preparation of nanofibers, core shell fibers, hollow fibers, and rods and tubes from natural and synthetic polymers with diameters down to a few nanometers have recently been established. These techniques, among them electro- and coelectrospinning and specific template methods, allow the incorporation not only of semiconductor or catalytic nanoparticles or chromophores but also enzymes, proteins, microorganism, etc., directly during the preparation process into these nanostructures in a very gentle way. One particular advantage is that biological objects such as, for instance, proteins can be immobilized in a fluid environment within these polymer-based nano-objects in such a way that they keep their native conformation and the corresponding functions. The range of applications of such biohybrid nanosystems is extremely broad, for instance, in the areas of biosensors, catalysis, drug delivery, or optoelectronic
Nanostructures promote formation of blood vessels; bolster cardiovascular function after heart attack - Injecting nanoparticles into the hearts of mice that suffered heart attacks helped restore cardiovascular function in these animals. The self-assembling nanoparticles - made from naturally occurring polysaccharides and molecules known as peptide amphiphiles - boost chemical signals to nearby cells that induce formation of new blood vessels and this may be the mechanism through which they restore cardiovascular function. One month later, the hearts of the treated mice were capable of contracting and pumping blood almost as well as healthy mice. In contrast, the hearts of untreated mice contracted about 50 percent less than normal. In other recent studies using a similar technique, Stupp and his colleagues found nanoparticles hastened wound healing in rabbits and, after islet transplantation, cured diabetes in mice. Nanoparticles with other chemical compositions accelerate bone repair in rats and promote the growth of neurons in mice and rats with spinal cord injuries.
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The recent advances in the preparation of some nanomaterials, growing awareness of material science and tissue engineering researchers regarding the potential of stem cells for regenerative medicine, and advances in stem cell biology have contributed towards the boost of this research field in the last few years. Nanoparticles have several potential applications such as intracellular drug carriers to control stem cell differentiation and biosensors to monitor in real time the intracellular levels of relevant biomolecules/enzymes.
Cell-based therapies have produced significant enthusiasm and study and are one of the most active areas of research in regenerative medicine. The creation of multi-functional tools, which allow the improved monitoring and modifying of cell behavior is one method of accelerating the pace of research. While cell-based a therapy in cancer is a huge part of the nanomedicine effort for regenerative medicine. Improving non-invasive monitoring methods is particularly desirable since current methods of evaluating cell treatment typically involve destructive or invasive techniques such as tissue biopsies. Traditional non-invasive methods such as magnetic resonance imaging (MRI) and positron emission tomography (PET), which rely heavily on contrast agents, lack the specificity or resident time to be a viable option for cell tracking. However, in vitro and in vivo visualization of nanoscale systems can be carried out using a variety of clinically relevant modalities such as fluoresce microscopy, single photon emission computed tomography (SPECT), PET, MRI, ultrasound, and radiotracing such as gamma scintigraphy. Nanoparticulate imaging probes include semi-conductor quantum dots (QD), magnetic and magnetofluorescent nanoparticles, gold nanoparticles, and nanoshells among others, While there are currently few examples of nanotechnologies being applied to the understanding of important process in tissue regeneration, relevant uses of nanoparticles for regenerative medicine such as monitoring angiogensis and apoptosis are appearing.
Tissue Engineering in Dental and Orthopedic
It is predicted that tissue engineering will have a considerableÂ effect on dental practice during the next 25 years. The greatestÂ effects will likely be related to the repair and replacementÂ of mineralized tissues, the promotion of oral wound healingÂ and the use of gene transfer adjunctively. Tissue engineering buildsÂ on the interface between materials science and biocompatibility,Â and integrates cells, natural or synthetic scaffolds, and specificÂ signals to create new tissues.Â This field is increasingly beingÂ viewed as having enormous clinical potential.
Clinical problems relating to the loss and/or failure of tissuesÂ extend beyond dentistry to all fields of medicine, and are estimatedÂ to account for approximately one-half of all medical-relatedÂ problems in the United States each year. Currently, the replacementÂ of lost or deficient tissues involves prosthetic materials,Â drug therapies, and tissue and organ transplantation. However,Â all of these have limitations, including the inability of syntheticÂ prostheses to replace any but the simplest structural functionsÂ of a tissue. An extreme shortage of organs and tissues for transplantationÂ exists. Fewer than 10,000 organs are available for transplantationÂ each year in the United States, while more than 50,000 patientsÂ are registered on transplantation waiting lists.Â Such problemsÂ have motivated the development of tissue engineering, whichÂ can be defined as a "combination of the principles and methodsÂ of the life sciences with those of engineering to develop materialsÂ and methods to repair damaged or diseased tissues, and to createÂ entire tissue replacements."
Many strategies have evolved to engineer new tissues and organs,Â but virtually all combine a material with either bioactive moleculesÂ that induce tissue formation or cells grown in the laboratory.Â The bioactive molecules are frequently growth factor proteinsÂ that are involved in natural tissue formation and remodeling.Â The basic hypothesis underlying this approach is that the localÂ delivery of an appropriate factor at a correct dose for a definedÂ period of time can lead to the recruitment, proliferation andÂ differentiation of a patient's cells from adjacent sites.Â These cells can then participate in tissue repair and/or regenerationÂ at the required anatomic locale.
The second general strategy uses cells grown in the laboratoryÂ and placed in a matrix at the site where new tissue or organÂ formation is desired. These transplanted cells usually are derivedÂ from a small tissue biopsy specimen and have been expanded inÂ the laboratory to allow a large organ or tissue mass to be engineered.Â Typically, the new tissue will be formed in part from theseÂ transplanted cells.
With both approaches, specific materials deliver the moleculesÂ or cells to the appropriate anatomic site and provide mechanicalÂ support to the forming tissue by acting as a scaffold to guideÂ new tissue formation.Â Currently, most tissue engineering effortsÂ use biomaterials already approved for medical indications byÂ the U.S. Food and Drug Administration, or FDA. The most widelyÂ used synthetic materials are polymers of lactide and glycolideÂ , since these are commonly used forÂ biodegradable sutures. Both polymers have a long track recordÂ for human use and are considered biocompatible, and their physicalÂ properties (for example, degradation rate, mechanical strength)Â can be readily manipulated. A natural polymer-type 1 collagen-isÂ often used because of its relative biocompatibility and abilityÂ to be remodeled by cells. Other polymers familiar to dentistry, including alginate, are also being used.
Bone and cartilage generation by autogenous cell/tissue transplantation is one of the most promising techniques in orthopedic surgery and biomedical engineering . Treatment concepts based on those techniques would eliminate problems of donor site scarcity, immune rejection and pathogen transfer . Osteoblasts, chondrocytes and mesenchymal stem cells obtained from the patient's hard and soft tissues can be expanded in culture and seeded onto a scaffold that will slowly degrade and resorb as the tissue structures grow in vitro and/or vivo . scaffold or three-dimensional (3-D) construct
provides the necessary support for cells to proliferate and maintain their di!erentiated function, and its architecture the ultimate shape of the new bone and cartilage. Several scaffold materials have been investigated for tissue engineering bone and cartilage including hydroxyapatite (HA), poly(a-hydroxyesters), and natural polymers such as collagen and chitin. Several reviews have been published on the general properties
and design features of biodegradable and bioresorbable polymers and scaffolds [4,12].
In the United States each year, over half a million people undergo total joint replacement (14). The average lifespan of a reconstructive joint implant is approximately 15 years. In all likelihood this means that each patient will have to undergo a second surgery to maintain functionality (15). There are many drawbacks with replacement surgeries such as inferior recovery compared to the initial surgery, postsurgical complications and pain (16). The most common explanation for implant failure is improper growth on the implant surface (17). Currently vanadium, cobalt, chromium and smooth titanium are used in dental and orthopedic implants. Out of all these metals, titanium is most frequently used due to its tensile strength and corrosion resistance (13; 18; 19). But the problem with titanium implants is that it does not mimic the natural bone structure. So there are higher chances of implant failure (20). Natural bone is nanoporous at the surface. So if we modify the surface of titanium such that it becomes nanoporus, this may help in increasing the life span of the implant. So the first objective is to produce nanoporus titanium by the process of anodization.
Nanotechnology for Bioactive Molecule and Drug Release
Controlled drug delivery is one of the most promising biomedical applications of nanotechnology. The use of nanomaterials as nanocarriers for improving delivery methods has shown to be advantageous technically and viable economically. Controlled release of antibiotics and antiseptic drug from halloysite PCL scaffold can be used for wound healing. The basic unit of healing in any tissue type (for example bone or skin) is the same. The second objective, of this project is to electrospin PCL-halloysite scaffold, find the best concentration and the exact location of halloysite in the PCL-halloysite scaffold by Fluorescein isothiocyanateÂ (FITC) labeling of halloysite and check its biocompatibility. The third objective of this project is to produce drug loaded halloysite-PCL scaffold and test it effectiveness on bacteria.
1. To find out the best parameter of anodization to produce nanoporous titanium. Compare osteoblast cell proliferation and differentiation on smooth versus nanoporous titanium surfaces. Nanoporous surfaces should lead to better cell proliferation and differentiation leading to enhanced implant durability and osteointegration for patients with degenerative joint problems, as it is similar to natural bone surface.
2. To electro-spin halloysite-PCL scaffold and find the best concentration and the exact location of halloysite in the halloysite-PCL scaffold by Fluorescein isothiocyanateÂ (FITC) labeling of the halloysite, compare osteoblast cell proliferation and differentiation on PCL and halloysite-PCL scaffolds.
3. To load halloysite nanotubes with drugs, for example antibiotics and antiseptic, measure the drug released from the halloysite and document the effect of the drug released from the halloysite-PCL scaffold on bacteria.