Limits...
Tissue Engineering the Cornea: The Evolution of RAFT.

Levis HJ, Kureshi AK, Massie I, Morgan L, Vernon AJ, Daniels JT - J Funct Biomater (2015)

Bottom Line: This review will detail how we have refined the simple engineering technique of plastic compression of collagen to a process we now call Real Architecture for 3D Tissues (RAFT).The RAFT production process has been standardised, and steps have been taken to consider Good Manufacturing Practice compliance.The evolution of this process has allowed us to create biomimetic epithelial and endothelial tissue equivalents suitable for transplantation and ideal for studying cell-cell interactions in vitro.

View Article: PubMed Central - PubMed

Affiliation: Department of Ocular Biology and Therapeutics, UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, UK. h.levis@ucl.ac.uk.

ABSTRACT
Corneal blindness affects over 10 million people worldwide and current treatment strategies often involve replacement of the defective layer with healthy tissue. Due to a worldwide donor cornea shortage and the absence of suitable biological scaffolds, recent research has focused on the development of tissue engineering techniques to create alternative therapies. This review will detail how we have refined the simple engineering technique of plastic compression of collagen to a process we now call Real Architecture for 3D Tissues (RAFT). The RAFT production process has been standardised, and steps have been taken to consider Good Manufacturing Practice compliance. The evolution of this process has allowed us to create biomimetic epithelial and endothelial tissue equivalents suitable for transplantation and ideal for studying cell-cell interactions in vitro.

No MeSH data available.


Related in: MedlinePlus

Evolution of the RAFT tissue engineering procedure. (A) Schematic diagram of original plastic compression process with application of a load for unconfined compression and downward fluid flow; (B) Confined compression in a well plate with upward flow on application of a load; (C) Current RAFT process with gentle wicking of fluid into HPAs in a confined manner with no addition of a significant load.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4384100&req=5

jfb-06-00050-f002: Evolution of the RAFT tissue engineering procedure. (A) Schematic diagram of original plastic compression process with application of a load for unconfined compression and downward fluid flow; (B) Confined compression in a well plate with upward flow on application of a load; (C) Current RAFT process with gentle wicking of fluid into HPAs in a confined manner with no addition of a significant load.

Mentions: Cellular type I collagen hydrogels have previously been used as 3D substrates for cell culture and creation of corneal models. However, because they are composed of a high proportion of water they are intrinsically weak unless modified with chemical crosslinking or blended with other polymers to create collagen composites, preventing direct seeding of cells within the scaffold [17,18,19]. To overcome this problem, Brown and colleagues developed a novel method of plastic compression of type I collagen hydrogels by applying simple engineering techniques such as external mechanical loading and capillary fluid flow (Patent number WO2012004564) [20,21]. Hyperhydrated collagen gels are composed of a mesh of collagen fibrils supporting a large volume of excess fluid (99%). Hydrogels were produced by neutralising a mix of acetic acid based rat-tail type I collagen and 10× minimum essential medium (included as an indicator of pH and to ensure physiological ionic strength for cell compatibility and standardised collagen fibril formation) with sodium hydroxide. Liquid was then cast into moulds and set/stabilized at 37 °C. In their method, hydrogels were subjected to an unconfined compression by placing the gel on top of a series of nylon and stainless steel meshes and blotting filter papers with addition of a load (Figure 2A). The key feature of this process is that the expulsion of this liquid does not return on the removal of the load, hence the hydrogel undergoes plastic compression (PC) in an unconfined manner. One major advantage of this method is that cells can be seeded into the body of the hydrogel before compression and therefore production of a cell seeded scaffold is ultrarapid, taking just minutes and without loss of cell viability. The use of plastic compressed collagen as a substrate/scaffold has been proposed for many tissue engineering applications, including bone [22], skin [23], nerve [24], bladder [25], and microvascular endothelium [26].


Tissue Engineering the Cornea: The Evolution of RAFT.

Levis HJ, Kureshi AK, Massie I, Morgan L, Vernon AJ, Daniels JT - J Funct Biomater (2015)

Evolution of the RAFT tissue engineering procedure. (A) Schematic diagram of original plastic compression process with application of a load for unconfined compression and downward fluid flow; (B) Confined compression in a well plate with upward flow on application of a load; (C) Current RAFT process with gentle wicking of fluid into HPAs in a confined manner with no addition of a significant load.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4384100&req=5

jfb-06-00050-f002: Evolution of the RAFT tissue engineering procedure. (A) Schematic diagram of original plastic compression process with application of a load for unconfined compression and downward fluid flow; (B) Confined compression in a well plate with upward flow on application of a load; (C) Current RAFT process with gentle wicking of fluid into HPAs in a confined manner with no addition of a significant load.
Mentions: Cellular type I collagen hydrogels have previously been used as 3D substrates for cell culture and creation of corneal models. However, because they are composed of a high proportion of water they are intrinsically weak unless modified with chemical crosslinking or blended with other polymers to create collagen composites, preventing direct seeding of cells within the scaffold [17,18,19]. To overcome this problem, Brown and colleagues developed a novel method of plastic compression of type I collagen hydrogels by applying simple engineering techniques such as external mechanical loading and capillary fluid flow (Patent number WO2012004564) [20,21]. Hyperhydrated collagen gels are composed of a mesh of collagen fibrils supporting a large volume of excess fluid (99%). Hydrogels were produced by neutralising a mix of acetic acid based rat-tail type I collagen and 10× minimum essential medium (included as an indicator of pH and to ensure physiological ionic strength for cell compatibility and standardised collagen fibril formation) with sodium hydroxide. Liquid was then cast into moulds and set/stabilized at 37 °C. In their method, hydrogels were subjected to an unconfined compression by placing the gel on top of a series of nylon and stainless steel meshes and blotting filter papers with addition of a load (Figure 2A). The key feature of this process is that the expulsion of this liquid does not return on the removal of the load, hence the hydrogel undergoes plastic compression (PC) in an unconfined manner. One major advantage of this method is that cells can be seeded into the body of the hydrogel before compression and therefore production of a cell seeded scaffold is ultrarapid, taking just minutes and without loss of cell viability. The use of plastic compressed collagen as a substrate/scaffold has been proposed for many tissue engineering applications, including bone [22], skin [23], nerve [24], bladder [25], and microvascular endothelium [26].

Bottom Line: This review will detail how we have refined the simple engineering technique of plastic compression of collagen to a process we now call Real Architecture for 3D Tissues (RAFT).The RAFT production process has been standardised, and steps have been taken to consider Good Manufacturing Practice compliance.The evolution of this process has allowed us to create biomimetic epithelial and endothelial tissue equivalents suitable for transplantation and ideal for studying cell-cell interactions in vitro.

View Article: PubMed Central - PubMed

Affiliation: Department of Ocular Biology and Therapeutics, UCL Institute of Ophthalmology, 11-43 Bath Street, London, EC1V 9EL, UK. h.levis@ucl.ac.uk.

ABSTRACT
Corneal blindness affects over 10 million people worldwide and current treatment strategies often involve replacement of the defective layer with healthy tissue. Due to a worldwide donor cornea shortage and the absence of suitable biological scaffolds, recent research has focused on the development of tissue engineering techniques to create alternative therapies. This review will detail how we have refined the simple engineering technique of plastic compression of collagen to a process we now call Real Architecture for 3D Tissues (RAFT). The RAFT production process has been standardised, and steps have been taken to consider Good Manufacturing Practice compliance. The evolution of this process has allowed us to create biomimetic epithelial and endothelial tissue equivalents suitable for transplantation and ideal for studying cell-cell interactions in vitro.

No MeSH data available.


Related in: MedlinePlus