Tissue Engineering and Organ Fabrication Laboratory

Engineered Vascular Networks

For over 10 years, the laboratory has had an active program to understand and recreate vascular networks similar to those found in the body. General and tissue specific criteria have been compiled that are key to mimicking blood flow in the body. Following these principles, we have developed computational fluid dynamic (CFD) models and translated them to microfluidic devices. Platelet deposition in these models is minimized so that negligible clotting is observed during in vitro and in vivo tests. Tissue specific vascular networks have been developed and are being optimized for use in engineered lung and liver tissues.

Tissue-Engineered Scaffold Design, Manufacture & Testing

Our tissue-engineered scaffolds have been developed using a variety of computational and manufacturing tools. Prior to manufacture, the vascular networks in the scaffold are modeled and optimized using 3D computer modeling and simulated using computational fluid dynamics. These scaffolds are manufactured in-house using soft-lithography or 3D printing and then tested. Precision tools and process control enable us to quickly identify and correct process issues, extending the boundaries of state-of-the-art engineered scaffolds.

Liver Tissue Engineering

Extensive work has been devoted to developing a tissue engineered liver. This liver is comprised of an engineered biomimetic vascular network and parenchymal chamber separated by a semi-permeable membrane and utilizes our engineered vascular network technology. This model is being tailored to develop a bridge to liver transplantation, a full replacement engineered liver and to model liver pathology such as liver fibrosis.

Lung Tissue Engineering

Efforts to develop a tissue engineered lung have only recently begun to gain momentum despite a significant clinical need for patients of all ages. Ongoing research focuses on creating an artificial lung by applying biomimetic principles. This artificial lung is comprised of an engineered biomimetic vascular network and a gas chamber, separated by an ultra-thin and highly gas permeable membrane. While blood continuously flows through the vascular network, oxygen and carbon dioxide are exchanged by diffusion across the membrane. Current work is focused on optimizing the components to maximize gas transfer and oxygenation within the system.

Vascularized Bone

Bone grafting is required to correct deficits arising from congenital defects, trauma and disease. Synthetic and decellularized allogeneic grafts seeded with autologous bone marrow aspirate are used in spinal fusion applications and to repair nonunion long bone fractures. However, a central zone of necrosis frequently occurs as the core relies upon mass transport for oxygen and metabolic requirements; extensive necrosis results in only a shell of ossification. A clinically relevant model has been developed, based on seeded endothelial cells and mesenchymal stem cells, to produce vascularized bone grafts which eliminate hypoxia in the core. Parameters are being identified that impact the rate and quality of vascular network formation. These parameters will be applied to the development of a protocol that permits efficient blood perfusion throughout the scaffold. Incorporation of these vascular networks will greatly increase the quality of bone grafts.

In Vitro Model of Drug Metabolism

In collaboration with the Draper Laboratories, a microfabricated, microfluidic bi-layer liver device has been developed based on our engineered vascular networks to model liver drug metabolism. Hepatocytes seeded into the device are exposed to drugs flowing through the vascular side of the device. The effluent can be easily assayed for applicable markers of hepatocyte metabolism and function. This model is scalable, maintains long-term cellular viability and is designed to mimic liver tissue phenotype and function.

Drug-induced Vascular Injury

Drug-induced vascular injury (DIVI) is a major cause of failure of phase I (safety) clinical trials of pharmaceuticals. This vascular injury is characterized by extravasation of red blood cells through the endothelium into the smooth muscle cell layer that surrounds blood vessel endothelium. The mechanisms of this pathology are not currently understood. In addition, the formation and progression of these vascular lesions cannot be monitored in vivo in living animals or humans.

In collaboration with the Draper Laboratory, an in vitro model of DIVI is being developed that builds on our engineered vascular networks. Endothelial cells and smooth muscle cells are cultured on either side of a semi-permeable membrane in a configuration of similar size to lesion-prone blood vessels. When optimized, this model will be utilized to assess the potential of pharmaceutical compounds to induce DIVI as well as to identify DIVI markers and mechanisms.

Muscle

A primary focus of the laboratory is engineering replacement skeletal muscles to treat severe facial muscle injuries. Our engineered muscle is a self-assembled 3D muscle that exhibits the physiologic morphology of immature skeletal muscle and its development mimics native muscle maturation. We are currently engineering a vascular network in vitro that will anastomose with the host vasculature upon implantation. The vascularized, engineered muscle will also contain a neuronal system that will facilitate the innervation between the construct and the host. In addition to optimizing the implantation conditions to support vascularization and innervation of the implanted engineered muscle, we are developing scaffold strategies to scale up our muscle tissue to a full-sized facial muscle.

Ear

A significant challenge remains to maintain the 3D shape of engineered cartilage avoiding its distortion and shrinkage when the supporting scaffold framework is resorbed and the cartilage tissue matures. Our approach is to engineer ear-shaped autologous cartilage with an embedded framework to define the ear shape utilizing materials previously approved by the FDA. Fabricated using 3D process technology, the supporting framework will be customizable to the patient. In support of this effort, a clinically relevant approach is being developed to acquire massive populations of autologous chondrocytes from a limited initial source for engineering full sized human ear-shaped cartilage. Extensive cell expansion in vitro leads to cell de-differentiation and the inability to form cartilage; our work looks to explore methods to promote re-differentiation or to hinder de-differentiation of chondrocytes.

Kensey Nash Collaboration

The laboratory has an extensive collaboration with Kensey Nash Corp., a medical device company with broad experience in clinical applications of resorbable and collagen-based materials. Together we are developing and testing resorbable scaffolds for lung and liver applications and for engineering ear cartilage. Kensey Nash is leveraging their collagen fabrication experience to create simple and patterned thin collagen films for lung and liver applications. Our ear replacement scaffold is a composite scaffold which primarily consists of Kensey Nash's fibrous collagen.

Poly (Glycerol Sebacate): In collaboration with Peter Masiakos, MD

Poly (glycerol sebacate) (PGS) is a novel resorbable bioelastomer designed to mimic the properties of collagen and elastin in soft tissue engineering applications. It is unique in its ability to sustain and recover from deformation in mechanically dynamic environments while maintaining remarkable biocompatibility.

We have tested PGS for use in applications that have challenged clinical medicine. For example, PGS plugs have been tested as a possible tympanic membrane plug. Each year, more than 500,000 tympanostomy tubes are placed in children chronically suffering from otitis media. In 2-19% of these cases, the tympanic membrane perforations fail to close after tube removal. In response to this medical challenge, we developed novel processing to manufacture small tympanic membrane plugs. In collaboration with Christopher Hartnick, MD, these plugs were implanted into chronic tympanic membrane perforations of chinchillas; perforation closure was observed at a statistically higher rate than the standard of care.

PGS has also been tested as a potential barrier to abdominal adhesion formation. Adhesions are a common post-operative complication of abdominal surgery in which scar tissue deposits at the surgical site and binds to other parts of the bowel or peritoneum; adhesions often result in disruption of normal bowel function with significant morbidity and mortality. Thin films of PGS were manufactured and implanted in the rat model of abdominal injury. PGS films were found to be highly effective in preventing adhesion formation. Currently, we are testing the ability of thin PGS tubes to prevent adhesion formation following small bowel resection and reconnection surgery.

In collaboration with Jeffery Karp, PhD, PGS surfaces are being modified to include nanopatterning and surface coatings to promote biocompatible PGS-tissue adhesion. This work is being developed for applications like sealant of lung damage and closure of pathological fistulas and patent foramina.