Editing Tissue engineering (section)

== Assembly methods ==

A persistent problem within tissue engineering is mass transport limitations. Engineered tissues generally lack an initial blood supply, thus making it difficult for any implanted cells to obtain sufficient oxygen and nutrients to survive, or function properly.{{cn|date=April 2025}}

===Self-assembly===
Self-assembly methods have been shown to be promising methods for tissue engineering. Self-assembly methods have the advantage of allowing tissues to develop their own extracellular matrix, resulting in tissue that better recapitulates biochemical and biomechanical properties of native tissue. Self-assembling engineered articular cartilage was introduced by Jerry Hu and [[Kyriacos A. Athanasiou]] in 2006<ref>{{cite journal | vauthors = Hu JC, Athanasiou KA | title = A self-assembling process in articular cartilage tissue engineering | journal = Tissue Engineering | volume = 12 | issue = 4 | pages = 969–79 | date = April 2006 | pmid = 16674308 | doi = 10.1089/ten.2006.12.969 }}</ref> and applications of the process have resulted in engineered cartilage approaching the strength of native tissue.<ref>{{cite journal | vauthors = Lee JK, Huwe LW, Paschos N, Aryaei A, Gegg CA, Hu JC, Athanasiou KA | title = Tension stimulation drives tissue formation in scaffold-free systems | journal = Nature Materials | volume = 16 | issue = 8 | pages = 864–73 | date = August 2017 | pmid = 28604717 | pmc = 5532069 | doi = 10.1038/nmat4917 | bibcode = 2017NatMa..16..864L }}</ref> Self-assembly is a prime technology to get cells grown in a lab to assemble into three-dimensional shapes. To break down tissues into cells, researchers first have to dissolve the extracellular matrix that normally binds them together. Once cells are isolated, they must form the complex structures that make up our natural tissues.{{cn|date=April 2025}}

===Liquid-based template assembly===
The air-liquid surface established by [[Faraday waves]] is explored as a template to assemble biological entities for bottom-up tissue engineering. This liquid-based template can be dynamically reconfigured in a few seconds, and the assembly on the template can be achieved in a scalable and parallel manner. Assembly of microscale hydrogels, cells, neuron-seeded micro-carrier beads, cell spheroids into various symmetrical and periodic structures was demonstrated with good cell viability. Formation of 3-D neural network was achieved after 14-day tissue culture.<ref>{{cite journal | vauthors = Chen P, Luo Z, Güven S, Tasoglu S, Ganesan AV, Weng A, Demirci U | title = Microscale assembly directed by liquid-based template | journal = Advanced Materials | volume = 26 | issue = 34 | pages = 5936–41 | date = September 2014 | pmid = 24956442 | pmc = 4159433 | doi = 10.1002/adma.201402079 | bibcode = 2014AdM....26.5936C }}</ref>

===Additive manufacturing===
{{main|Organ printing}}
It might be possible to print organs, or possibly entire organisms using [[additive manufacturing]] techniques. A recent innovative method of construction uses an ink-jet mechanism to print precise layers of cells in a matrix of thermo-reversible gel. Endothelial cells, the cells that line blood vessels, have been printed in a set of stacked rings. When incubated, these fused into a tube.<ref name=Elisseeff05/><ref>{{cite journal | vauthors = Mironov V, Boland T, Trusk T, Forgacs G, Markwald RR | title = Organ printing: computer-aided jet-based 3D tissue engineering | journal = Trends in Biotechnology | volume = 21 | issue = 4 | pages = 157–61 | date = April 2003 | pmid = 12679063 | doi = 10.1016/S0167-7799(03)00033-7 }}</ref> This technique has been referred to as "bioprinting" within the field as it involves the printing of biological components in a structure resembling the organ of focus.{{cn|date=April 2025}}

The field of three-dimensional and highly accurate models of biological systems is pioneered by multiple projects and technologies including a rapid method for creating tissues and even whole organs involve a 3-D printer that can bio-print the scaffolding and cells layer by layer into a working tissue sample or organ. The device is presented in a [[TED talk]] by Dr. Anthony Atala, M.D. the Director of the [[Wake Forest University|Wake Forest]] Institute for [[Regenerative Medicine]], and the W.H. Boyce Professor and Chair of the Department of [[Urology]] at Wake Forest University, in which a kidney is printed on stage during the seminar and then presented to the crowd.<ref>{{cite web|url=http://www.ted.com/talks/anthony_atala_printing_a_human_kidney.html|title=Printing a human kidney|date=March 2011|vauthors=Alta A|work=TED|access-date=29 November 2013|archive-date=26 February 2014|archive-url=https://web.archive.org/web/20140226145006/http://www.ted.com/talks/anthony_atala_printing_a_human_kidney.html|url-status=dead}}</ref><ref>{{cite journal | vauthors = Du Y, Han R, Wen F, Ng San San S, Xia L, Wohland T, Leo HL, Yu H | display-authors = 6 | title = Synthetic sandwich culture of 3D hepatocyte monolayer | journal = Biomaterials | volume = 29 | issue = 3 | pages = 290–301 | date = January 2008 | pmid = 17964646 | doi = 10.1016/j.biomaterials.2007.09.016 }}</ref><ref>{{cite journal | vauthors = Kang HW, Lee SJ, Ko IK, Kengla C, Yoo JJ, Atala A | title = A 3D bioprinting system to produce human-scale tissue constructs with structural integrity | journal = Nature Biotechnology | volume = 34 | issue = 3 | pages = 312–19 | date = March 2016 | pmid = 26878319 | doi = 10.1038/nbt.3413 | s2cid = 9073831 }}</ref> It is anticipated that this technology will enable the production of livers in the future for transplantation and theoretically for [[toxicology]] and other biological studies as well.{{cn|date=April 2025}}

In 2015 Multi-Photon Processing (MPP) was employed for in vivo experiments by engineering artificial cartilage constructs. An ex vivo histological examination showed that certain pore geometry and the pre-growing of chondrocytes (Cho) prior to implantation significantly improves the performance of the created 3-D scaffolds. The achieved biocompatibility was comparable to the commercially available collagen membranes. The successful outcome of this study supports the idea that hexagonal-pore-shaped hybrid organic-inorganic micro-structured scaffolds in combination with Cho seeding may be successfully implemented for cartilage tissue engineering.<ref>{{cite journal | vauthors = Mačiulaitis J, Deveikytė M, Rekštytė S, Bratchikov M, Darinskas A, Šimbelytė A, Daunoras G, Laurinavičienė A, Laurinavičius A, Gudas R, Malinauskas M, Mačiulaitis R | display-authors = 6 | title = Preclinical study of SZ2080 material 3D microstructured scaffolds for cartilage tissue engineering made by femtosecond direct laser writing lithography | journal = Biofabrication | volume = 7 | issue = 1 | pages = 015015 | date = March 2015 | pmid = 25797444 | doi = 10.1088/1758-5090/7/1/015015 | bibcode = 2015BioFa...7a5015M | s2cid = 40712319 }}</ref>

Recently, tissue engineering has advanced with a focus on vascularization. Using Two-Photon Polymerization-based additive manufacturing, synthetic 3D microvessel networks are created from tubular hydrogel structures. These networks can perfuse tissues several cubic millimeters in size, enabling long-term viability and cell growth in vitro. This innovation marks a significant step forward in tissue engineering, facilitating the development of complex human tissue models.<ref>{{Cite journal |last1=Grebenyuk |first1=Sergei |last2=Abdel Fattah |first2=Abdel Rahman |last3=Kumar |first3=Manoj |last4=Toprakhisar |first4=Burak |last5=Rustandi |first5=Gregorius |last6=Vananroye |first6=Anja |last7=Salmon |first7=Idris |last8=Verfaillie |first8=Catherine |last9=Grillo |first9=Mark |last10=Ranga |first10=Adrian |date=2023-01-12 |title=Large-scale perfused tissues via synthetic 3D soft microfluidics |journal=Nature Communications |language=en |volume=14 |issue=1 |pages=193 |doi=10.1038/s41467-022-35619-1 |pmid=36635264 |issn=2041-1723|pmc=9837048 |bibcode=2023NatCo..14..193G }}</ref>

===Scaffolding===
In 2013, using a 3-D scaffolding of [[Matrigel]] in various configurations, substantial pancreatic [[organoid]]s was produced in vitro. Clusters of small numbers of cells proliferated into 40,000 cells within one week. The clusters transform into cells that make either digestive [[enzyme]]s or [[hormone]]s like [[insulin]], self-organizing into branched pancreatic organoids that resemble the pancreas.<ref name="Greggio_2013">{{cite journal |vauthors=Greggio C, De Franceschi F, Figueiredo-Larsen M, Gobaa S, Ranga A, Semb H, Lutolf M, Grapin-Botton A |display-authors=6 |title=Artificial three-dimensional niches deconstruct pancreas development in vitro |journal=Development |volume=140 |issue=21 |pages=4452–4462 |date=November 2013 |pmid=24130330 |pmc=4007719 |doi=10.1242/dev.096628 |doi-access=free}}<br />Lay summary: {{cite web |url=http://www.kurzweilai.net/new-3d-method-used-to-grow-miniature-pancreas-model |date=October 17, 2013 |title=New 3D method used to grow miniature pancreas model |website=Kurzweil }}</ref>

The cells are sensitive to the environment, such as gel stiffness and contact with other cells. Individual cells do not thrive; a minimum of four proximate cells was required for subsequent organoid development. Modifications to the medium composition produced either hollow spheres mainly composed of pancreatic progenitors, or complex organoids that spontaneously undergo pancreatic morphogenesis and differentiation. Maintenance and expansion of pancreatic progenitors require active [[Notch signaling|Notch]] and [[Fibroblast growth factor|FGF]] signaling, recapitulating in vivo niche signaling interactions.<ref name="Greggio_2013"/>

The organoids were seen as potentially offering mini-organs for drug testing and for spare insulin-producing cells.<ref name="Greggio_2013"/>

Aside from Matrigel 3-D scaffolds, other collagen gel systems have been developed. Collagen/hyaluronic acid scaffolds have been used for modeling the mammary gland In Vitro while co-coculturing epithelial and adipocyte cells. The HyStem kit is another 3-D platform containing ECM components and hyaluronic acid that has been used for cancer research. Additionally, hydrogel constituents can be chemically modified to assist in crosslinking and enhance their mechanical properties.{{cn|date=April 2025}}