Nerve regeneration »
Microfab Technologies and Wake Forest Institute of Regenerative Medicine have developed a skin engineering 3D bioprinter to significantly advance the fabrication of anatomically and functionally improved skin substitutes. This instrument will be used in research to fabricate 3 dimensional skin substitute repair constructs for treating skin wounds, as a result of thermal injury, mechanical trauma, disease, cancer and genetic disorders. The Dermal Repair Construct Printer (DRCP) can also be used to fabricate functional skin substitutes for cosmetology and pharmaceutical testing and skin research in vitro studies. The DRCP is capable of large volume global deposition of tissue engineering construct materials and epidermal / dermal cells for high throughput fabrication combined with low volume high precision inkjet deposition to spatially define patterns of functional cells, growth factors and acellular matrices. This will enable the potential for the in situ delivery of skin substitute materials to provide for rapid skin restoration directly on the patient. An important feature is the capacity to deposit subconfluent autologous cells, thus reducing the time required for dermal repair treatment in comparison to the conventional confluent cell methods (from 2-3 weeks to 5-7 days). The volume and ratio of cells, matrices and growth factors, as well as the thickness of the skin substitute layers can be more precisely controlled via the drop-on-demand inkjet based bioprinting when compared to traditional bolus application methods. The approach under development will advance the treatment of burn patients by reducing morbidity and mortality rates, while improving the outcome of patient recovery with more rapid healing, improved functionally and less pain and suffering.
The DRCP shown in figures below display the 3D bioprinter self-contained in a HEPA class 100 positive pressure laminar flow cabinet fitted with a UV germicidal lamp to provide for a sterile work area. The printhead is mounted on a gantry style X, Y, Z motion stage and is comprised of two valvejet dispensers for higher throughput nanoliter drop volume dispensing of viscous hydrogels and four inkjet dispensers with heated stirring reservoirs for the precision picoliter (50-100pL) volume dispensing of cells, growth regulators and other allied reagents. Crosslinking of the chemical reactive and UV photoreactive hydrogels is achieved either by using the on-the-fly crosslinker nebulizer or fiber optic UV light. The interchangeable heated substrate holder can accommodate SBS format microwell plates (6, 12, 24, 48, 96 wells), 100mm petri dishes and small live animals (lab mice and rats). The user can create printing patterns via a scriptwriter program to specify the number of drops to be deposited per location (volumes via drop accretion), drop pitch, sequence of layers to be deposited and the type and duration of crosslinking. Under development is the free form printing matching curvilinear surfaces, such as on a mouse. This will be achieved by importing CAD files obtained from 3D scanner surface metrology into the jetlab™ printing software.
Printheads for 3D biofabrication are currently in design for incorporation onto existing Jetlab printing stations. Ancillaries for chemical or UV light crosslinking can also be added. Printing programming upgrades to existing machines for 3D biofabrication as well as 3D scanning capability are in the design phase and will soon be available.
Of the many challenges daunting clinicians today, the most vital is the perpetual shortage of implantable tissues for major tissue repair. Acute, chronic or congenital injuries often require treatment with replacement tissues and organs to insure patient survival. However, transplant waiting lists are extensive and many people die waiting for a new organ. Beyond whole organ replacement, the need for tissues to treat acute trauma is also vital. Reconstructive surgeries following cancer resection and tissue loss from traumatic injury can require extensive amounts of tissue, often with the patient as the sole source for autologous materials. Creating artificial means to generate supplement tissue has many significant process barriers. In order to generate physiologically correct tissue scaffolds, bioabsorbable polymer substrates must be created in 3-D, which is very difficult using current fabrication methods and the limits these processes place on selecting a process compatible material. This is where MicroFab’s ink-jet printing technology creates an advantage. This technology is best integrated in our printing platform family. These platforms enable the end user to precisely deposit materials onto a number of substrates in a non-contact format in a cleanroom, sterile environment.
Sterile tissue culture hood with integrated JetLabR II.
Thermal controllers in the printing device and substrate allow for printing at either hot or cold temperatures depending on the specific needs.
An array of dispensing devices are available for this family of printing platforms, that allow a user to print materials ranging from polymers and sensitive protein solutions to tissue extracts and live cells. The printing devices can be heat-sterilized or gamma irradiated without changing their functional characteristics.
The printing process can be scaled-up through the use of multiple printing devices, array print-heads or multiple substrates simultaneously.
Integrated array print-heads. Left - printhead with 10 individual fluid supplies. Right - integrated array printhead dispensing simultaneously with multiple channels.
If a traumatic injury takes place causing a loss of nerve tissue, the clinician only has the option of taking nerve from another portion of the patient’s body to replace the “more important” nerve deficit. While up to 80% successful, autologous nerve grafts create further trauma to the patient. Tissue engineers have recognized the need for an artificial means to facilitate nerve regeneration and have pursued bioabsorbable nerve guidance conduits as a solution. Bioabsorbable nerve conduits are designed to facilitate nerve regeneration by optimizing growth conditions at the wound site in a number of ways. When a peripheral nerve guidance conduit is surgically implanted, the proximal and distal nerve stumps are sutured into the conduit. This allows the conduit to act as a physical guiding pathway for nerve growth, as well as a reservoir that sequesters important growth factors that further guide the sprouting daughter axons in the proximal nerve stump. Finally, by building the conduits with bioabsorbable polymers, the conduit is absorbed by the body within the time required to complete the repair process and thus, there is no need for surgery to remove them.
The technology allows:
Furthermore, the high precision nature of ink-jet method enables one to create and control protein amount or gradients within conduit material, and conduit surface texture and physical dimensions.
While peripheral nerve regeneration has been our main focus to date, we are currently exploring other tissue engineering fields such as cardiovascular and esophageal stents.
3D polymer structure mimicking blood vessel network (120µm wide branches).