Tissue engineering is an emerging area of tissue-regenerative medicine that can offer an effective treatment for a wide variety of conditions and injuries as well as become a valid substitute to currently available treatment methods (Rana et al. 2015). The potential of three-dimensional (3D) scaffolds to control cell functions and provide temporary support for the growth of cells during the process of tissue development allows for their use in tissue engineering. The scaffold also is known as a synthetic extracellular matrix (ECM) promotes the formation of new cells by stimulating seeded cells to produce their own ECMs (Rana et al. 2015).
ECM facilitates the development of tissues by localizing the cells, creating adhesion, migration, proliferation, and differentiation cues as well as assembling “the propagated cells and secreted matrices into functional tissues and organs” (Hoshiba et al. 2012, p. 1718). Even though ECM can be made from numerous materials, such as polymers, bioceramics, and proteins, among others, the ideal scaffold should have a high degree of biocompatibility and biodegradability (Rana et al. 2015). Therefore, ECM derived from the tissues or organs through decellularization are among the best biomaterials for tissue engineering. This paper aims to explore the development of decellularized scaffolds and their potential use in tissue engineering.
Literature Analysis
Old Applications of Decellularized Scaffolds
The article titled “Decellularized matrices for tissue engineering” by Hoshiba et al. (2012) explores advances in the development of decellularized ECM scaffolds as well as the promises of their application in the field of tissue engineering. The authors review the advantages and challenges of decellularized matrices and highlight their promised potential.
The ECM is a complex structure of different types of polysaccharides and proteins that allow it to “maintain tissue architecture in vivo” (Hoshiba et al. 2012, p. 1718). However, it is also capable of controlling cellular functions by either directly or indirectly activating intercellular signaling pathways (Hoshiba et al. 2012). The authors note that decellularized ECM molecules and their networks could potentially create an environment that would be identical or at least very similar to that of ECMs in vivo. Hoshiba et al. (2012) state that ECMs existing in vivo are constructed of proteins that have extremely complex biomechanical properties; therefore, the use of physicochemical methods existing at the time of the writing of the article makes it difficult to mimic the composition of a natural ECM. For this reason, scientists use in vitro ECMs that have undergone decellularized treatment (Hoshiba et al. 2012).
The authors state that decellularized matrices formed from stem cells could be potentially applied not only in the field of tissue engineering but also in biological research (Hoshiba et al. 2012). Moreover, the use of “protein knocked-down animals” and “surfaces coated with ECM proteins” (Hoshiba et al. 2012, p. 1724) makes it possible to further explore how ECM influences the process of tissue development. However, they note that animal-derived ECM-mimicking scaffolds are not perfectly suitable for this purpose; therefore, there is a need for good in vitro ECM models that replicate natural ECMs.
According to Hoshiba et al. (2012), the recent development of advanced decellularization techniques makes possible the application of matrices derived from decellularized tissues and organs in the fields of “tissue engineering and stem cell manipulation (p. 1725). New methods of decellularization also allow for substituting isolated ECM proteins with “an extract of basement membrane secreted from Engelbreth-Holm-Swarm sarcoma cells” (Hoshiba et al. 2012, p. 1725) called Matrigel. Even though the use of Matrigel shows promising results, it is necessary to use the complete composition of ECM. It should be noted that ECM structure varies to a significant degree with the type of cells and tissues; therefore, to exert maximal cellular functions, matrices should be identical to natural ones. Taking into consideration extremely complex biomechanical properties of proteins composing in vivo ECMs, decellularized matrices are the most suitable for both tissue engineering and ECM research (Hoshiba et al. 2012).
According to Hoshiba et al. (2012), unlike previous generations of decellularization methods that were used for the isolation of ECM of tissues, like intestinal submucosa, amniotic membrane, and skin, among others, the recent advances in the technology allow for its use for whole organs. New methods of decellularization will allow for substituting airway trees in lungs and complex networks of blood vessels in a heart that cannot be created by other techniques (Hoshiba et al. 2012). The authors argue that the trend of using decellularized matrices for tissue engineering organ transplantation will continue. They note that ECMs are not fully suitable for observing the process of tissue development. However, they state that in the future, the use of pluripotent or embryonic stem cells will allow for the creation of matrices capable of copying the development process (Hoshiba et al. 2012).
It should be noted that even though decellularized ECM scaffolds have numerous advantages, the technology is also associated with some drawbacks. One of its major challenges has to do with the fact that matrices from different donors vary significantly (Hoshiba et al. 2012). The authors argue that the use of synthetic ECMs can help to eliminate this problem. To this end, scientists might utilize synthetic peptides or proteins (Hoshiba et al. 2012). However, it should be noted that such substitutes will not allow for the exerting of maximal cellular functions. Scientists believe that substituting intricate molecular networks of natural ECMs and proteins with extremely complex biomechanical properties with synthetic matrices will make it impossible to achieve full synergistic effects (Hoshiba et al. 2012).
Another challenge that has to be solved to make decellularized ECM technology cheaper is the restricted access to and limited availability of tissues and organs donated for transplantation. Even though xenogeneic and allogeneic materials could be used as a substitute for organs and tissues derived naturally, there is always a risk of immunological and inflammatory reactions that could lead to rejection of transplanted tissues (Hoshiba et al. 2012). However, the future developments of decellularization technology will make it possible to extract cellular components completely, thereby preventing the rejection of transplanted materials by xenogeneic recipients (Hoshiba et al. 2012). The authors state that autologous ECM scaffolds could become a viable solution for this problem. Hoshiba et al. (2012) note that the process of decellularization of autologous tissues is extremely complicated; therefore, it is better to use cultured cells for preparation of scaffolds derived from autologous materials.
The authors argue that even though, unlike scaffolds derived from organs and tissues, cell-formed matrices are easily available, their composition might have critical differences that have to be taken into account during their use. According to Hoshiba et al. (2012), application of decellularized scaffolds is an extremely promising trend in the field of tissue engineering and organ transplantation. However, there are still many regulatory issues that have to be addressed before the start of commercialization of the technology. Some of the most pressing problems that have to be solved first are “regulation of production, management of donor tissues and organs, effectiveness and safety evaluation, quality control, application protocols and guidelines, and ethics” (Hoshiba et al. 2012, p. 1727).
New Applications of Decellularized Scaffolds
The article titled “Tissue engineering and regenerative medicine 2015: A year in review” by Wobma and Vunjak-Novakovic (2016) discusses the progress in the field of Tissue Engineering and Regenerative Medicine (TERM) that was achieved over 2015. This part of the paper will focus on the major advances and promises of decellularized scaffolds for whole organ engineering and biological research reported in the recent articles.
According to Wobma and Vunjak-Novakovic (2016), there was not a dramatic change in the use of decellularized scaffolds, meaning that it is not possible to engineer whole organs at this point of scientific development. Substituting airway trees in a long and complex network of blood vessels in a heart or intricate tissues of a liver is still beyond the capabilities of the TERM field (Hoshiba et al. 2012; Wobma & Vunjak-Novakovic 2016). However, the properties of ECM scaffolds derived with the help of decellularization make possible their use for tissue engineering.
Even though decellularized scaffolds are less adjustable than those derived with the help of synthetic peptides or proteins, “they benefit from having a structural, mechanical, and biochemical composition that resembles native tissue and displays low immunogenicity following removal of cells” (Wobma & Vunjak-Novakovic 2016). Another advantage of tissue-specific ECM scaffolds has to do with the fact that they maintain biochemical and mechanical properties of native tissues and do not provoke a significant immune response in a host body. Moreover, structural cues retained by decellularized ECM scaffolds are known to guide stem cells in the process of the differentiation into the “appropriate mature cell fates” (Wobma & Vunjak-Novakovic 2016, p. 107).
A recent article written by Hussein et al. (2016) examines the biocompatibility of decellularized scaffolds. The authors focus on the “different methodology involved in cytotoxicity pathogenicity, immunogenicity and biodegradability testing” (Hussein et al. 2016, p. 766) for assessment of biocompatible properties of matrices derived from both human and animal tissues and organs. Hussein et al. (2016) state that the modern methods of decellularization could be roughly divided into three categories: physical, chemical, and enzymatic. The choice of treatment category and method depends on “the tissue or organ of interest” (Hussein et al. 2016, p. 770).
After testing cytocompatibility, immunogenicity, pathogenicity, and biodegradability, the authors concluded that in vivo data received with the help of laboratory rodents is not sufficient for adequately assessing the efficiency of decellularized scaffolds (Hussein et al. 2016). They argue that computer simulation will be used in the future to provide human models for conducting screening tests. The article indicates that scientists are not yet able to measure the effect of chemical residue in decellularized scaffolds on “growth factors, structure, and retention” (Hussein et al. 2016, p. 777).
Hussein et al. (2016) argue that there is a pressing need for a higher level of collaboration between researchers as well as a multidisciplinary approach to the development of decellularized scaffolds. It will help to develop a better understanding of the processes involved in the determination of biocompatibility of synthetic biomaterials, thereby leading to commercialization of the technology. The authors note that there is also a need for standardization of the laboratory results “evaluating the biocompatibility of decellularized matrices” (Hussein et al. 2016, p. 777) for all organs and tissues.
Hoganson et al. (2016) discussed another application of ECM scaffolds in their article, “Decellularized extracellular matrix microparticles as a vehicle for cellular delivery in a model of anastomosis healing.” These materials are characterized by “exposed proteins for avid cell attachment, biologic activity, and high surface area” (Hoganson et al. 2016, p. 1732); therefore, they can be potentially used for cell delivery. The researchers claim that microparticles of decellularized ECM materials can be seeded in approximately an hour. After exploring the potential use of microparticles for cell delivery, Hoganson et al. (2016) discovered that they can be placed in collagen gel as a simple delivery system with extremely promising results.
Moreover, there is another potential application of migrating quality of these decellularized materials: “paracrine therapy from cytokines released from cells on the microparticles or a combination thereof” (Hoganson et al. 2016, p. 1732). Furthermore, the delivery of paracrine factors could significantly reduce the risk of breakdown of cardiac, vascular, biliary, and other anastomoses that could lead to bleeding and sepsis (Hoganson et al. 2016). For example, the use of microparticles of decellularized ECM materials for placing endothelial cells in the region of a vascular anastomosis is known to almost eliminate the risk of anastomotic breakdown. The authors argue that the future development of the technology will allow for the use of fibrin or hyaluronic acid gel as a carrier for transporting seeded cells and paracrine factors. Hoganson et al. (2016) note that there are regulatory challenges that have to be solved before the commercialization of this method of cellular delivery.
An article by Zia et al. (2016) discusses the recent advances in the whole organ and tissue engineering focusing on whole-heart decellularization. The article makes it clear that even though the current state of tissue and organ engineering technology has significantly changed over the last five years, it still does not allow for the elimination of the problem of organ shortage (Zia et al. 2016). However, the rapid pace of advances in the use of decellularized scaffolds promises to drastically change the situation shortly.
Zia et al. (2016) state that in recent years, new methods of assessing the rate of cell removal have emerged. The following are the most popular methods for verification of efficiency of cell removal: DNA purification, polymerase chain reaction (PCR) analysis, histological analysis, and SEM (Zia et al. 2016). DNA purification allows the confirmation of the successful cell extraction at a genomic level by analysing the content of decellularized scaffolds. PCR analysis makes possible amplification of small amounts of DNA to detect the presence of trace DNA on decellularized organs or tissues (Zia et al. 2016). The histological analysis allows for the use of a histological stain for verifying the rate of cell removal (Zia et al. 2016). SEM is another method that is capable of visually confirming cell removal. It is associated with assessing the microstructure of tissues and organs after the process of decellularization with the help of high-resolution images.
Conclusion
The analysis of the current state of development of the field of tissue engineering and the use of decellularized scaffolds showed that they can provide an effective treatment for a wide variety of conditions and injuries as well as become a valid substitute for currently available treatment methods. ECM scaffolds can be used to control cellular functions by activating signalling pathways between different cells, thereby creating an environment that would be identical or at least very similar to that of ECMs in vivo. This means that decellularized scaffolds could potentially be used for tissue engineering but also in the field of biological research. It should be noted that while the current methods of decellularization are not fully suitable for observing the process of tissue development, the use of pluripotent or embryonic stem cells should eliminate this problem in the future.
The most promising potential use of decellularized scaffolds is the creation of whole organs, which will eliminate the problem of availability of donors. It has to do with the fact that new methods of decellularization will allow for substituting airway trees in lungs and complex networks of blood vessels in a heart that cannot be created by other techniques (Hoshiba et al. 2012). Structural and mechanic composition of scaffolds derived with the help of modern methods of decellularization will push further the current capabilities of the TERM field, making it possible to create intricate tissues of organs such as the heart, liver, and lungs. Taking into consideration the fact that decellularized scaffolds maintain biochemical and mechanical properties of native tissues, they will not provoke a significant immune response in a host body. Another potential use of decellularized scaffolds is a cell delivery that can significantly reduce the risk of breakdown of cardiac, vascular, biliary, and other anastomoses.
Reference List
Hoganson, D, Owens, G, Meppelink, A, Bassett, E, Bowley, C & Hinkel, C 2016, ‘Decellularized extracellular matrix microparticles as a vehicle for cellular delivery in a model of anastomosis healing’, Journal of Biomedical Materials Research vol. 104, no. 7, pp. 1728-1735.
Hoshiba, T, Lu, H, Kawazoe, N & Chen, G 2012, ‘Decellularized matrices for tissue engineering’, Expert Opinion on Biological Therapy, vol. 10, no. 12, pp. 1717-1728.
Hussein, K, Park, K, Kang, K & Woo, H 2016, ‘Biocompatibility evaluation of tissue-engineered decellularized scaffolds for biomedical application’, Materials Science and Engineering vol. 67, no. 1, 766-778.
Rana, D, Zreiqat, H, Benkirane-Jessel, N, Ramakrishna, S & Ramalingam, M 2015, ‘Development of decellularized scaffolds for stem cell-driven tissue engineering’, Journal of Tissue Engineering and Regenerative Medicine vol. 10, no. 1, pp. 32-39.
Wobma, H & Vunjak-Novakovic, G 2016, ‘Tissue engineering and regenerative medicine 2015: A year in review’, Tissue Engineering, vol. 22, no. 2, pp. 101-113.
Zia, S, Mozafari, M, Tan, A, Zhanfeng, C & Seifalian, A 2016 ‘Hearts beating through decellularized scaffolds: whole-organ engineering for cardiac regeneration and transplantation’, Critical Reviews in Biotechnology vol. 21, no. 1, pp 1-11.