Steven P. Walsh

Decellularized human valve allografts.

BACKGROUND Variable performance of allograft tissues in children and some adults may be linked to an immune response and could be mitigated by reducing implant antigenicity. METHODS As endothelial and fibroblast cells are the likely source of valve antigenicity, human (CryoValve SG) and sheep pulmonary valves were decellularized using the SynerGraft treatment process. Treated valves were evaluated in vitro using histochemical, biomechanical, and hydrodynamic methods, and compared with standard cryopreserved valves. Four SynerGraft-treated and two cryopreserved sheep pulmonary valves were implanted as root replacements in the right ventricular outflow tract of growing sheep and monitored echocardiographically and histologically at 3 and 6 months. CryoValve SG human pulmonary valves were implanted in 36 patients. RESULTS SynerGraft treatment reduced tissue antigen expression but did not alter human valve biomechanics or strength. Decellularized sheep allograft valves were functional during the implantation period, and, they became progressively recellularized with recipient cells. In humans, CryoValve SG pulmonary valves did not provoke a panel reactive antibody response. CONCLUSIONS SynerGraft decellularization leaves the physical properties of valves unaltered and substantially diminishes antigen content. Reduction in implant cellularity enables host recellularization of the matrix, which should favorably impact long-term graft durability.

Transpecies heart valve transplant: advanced studies of a bioengineered xeno-autograft

BACKGROUND Tissue engineering approaches utilizing biomechanically suitable cell-conductive matrixes should extend xenograft heart valve performance, durability, and growth potential to an extent presently attained only by the pulmonary autograft. To test this hypothesis, we developed an acellular, unfixed porcine aortic valve-based construct. The performance of this valve has been evaluated in vitro under simulated aortic conditions, as a pulmonary valve replacement in sheep, and in aortic and pulmonary valve replacement in humans. METHODS SynerGraft porcine heart valves (CryoLife Inc, Kennesaw, GA) were constructed from porcine noncoronary aortic valve cusp units consisting of aorta, noncoronary aortic leaflet, and attached anterior mitral leaflet (AML). After treatment to remove all histologically demonstrable leaflet cells and substantially reduce porcine cell-related immunoreactivity, three valve cusps were matched and sewn to form a symmetrical root utilizing the AML remnants as the inflow conduit. SynerGraft valves were evaluated by in vitro hydrodynamics, and by in vivo implants in the right ventricular outflow tract of weanling sheep for up to 336 days. Cryopreserved allograft valves served as control valves in both in vitro and in vivo evaluations. Valves were also implanted as aortic valve replacements in humans. RESULTS In vitro pulsatile flow testing of the SynerGraft porcine valves demonstrated excellent valve function with large effective orifice areas and low gradients equivalent to a normal human aortic valve. Implants in sheep right ventricular outflow tracts showed stable leaflets with up to 80% of matrix recellularization with host fibroblasts and/or myofibroblasts, and with no leaflet calcification over 150 days, and minimal deposition at 336 days. Echocardiography studies showed normal hemodynamic performance during the implantation period. The human implants have proven functional for over 9 months. CONCLUSIONS A unique heart valve construct has been engineered to achieve the equivalent of an autograft. Short-term durability of these novel implants demonstrates for the first time the possibility of an engineered autograft.

Fatigue durabiity of a novel disc nucleus repair system

Abstract Purpose of study: It has been repeatedly demonstrated that disc denucleation ultimately results in segment destabilization and progressive collapse of disc space. Microdiscectomy alone for the treatment of primary herniated nucleus pulposus (HNP) has been only partially effective because of clinically relevant recurrence. To provide stabilization to the denucleated disc, while eliminating the potential for recurrent herniations, we propose the use of an in situ polymerizable protein hydrogel device (BioDisc). When introduced as a liquid into the denucleated disc space, the implant cross-links to form a durable hydrogel that maintains disc height and segmental stability while preserving motion. Methods used: Fresh calf lumbar segments (single bone-disc-bone [BDB] segment) were modeled as a worst-case stability scenario by full removal of the posterior spinal segments. Baseline compressive properties were obtained by cyclically loading 300 to 1,200 N for 1,000 cycles, and recording compressibility and overall segment height over each cycle. The disc of each BDB segment was then thoroughly denucleated with spinal rongeurs, following an anterior, posterior of posterolateral approach, and re-evaluated under identical test conditions to assess loss of height and segmental stability. The denucleation was then repaired with BioDisc, whereupon the segment was evaluated as above. Subsequently, each BDB segment was cyclically loaded to the equivalent of 1,200 N through 10 million cycles with interval evaluations. of findings: After the removal of the disc nuclear material, BDB segments exhibited an immediate loss in disc height. Repair of the disc denucleation with BioDisc preserved the initial (predenucleation) disc height. During monotonic loading through 10 million cycles, the repaired BDB segment demonstrated a minimal reduction in overall height and retained the axial compressibility of the motion segment. Upon completion of each test, all samples were grossly inspected (by sectioning through the repaired region) and the implanted BioDisc material was observed to be intact within the nuclear space. Relationship between findings and existing knowledge: The BioDisc implant has been shown to possess suitable biomechanical properties to stabilize a denucleated intervertebral disc. Mechanical durability of the implant in a severe model construct was demonstrated through 10 million compressive loading cycles. Overall significance of findings: These data demonstrate the potential utility of BioDisc for the repair of denucleated intervertebral discs in the treatment of HNP. Disclosures: No disclosures. Conflict of interest: Umit Yuksel, and; Steven Walsh: employees of Cryolife Inc.