3D Printed Biomimetic Bioglass-Gradient Matrices for ACL Reconstruction - Project Summary
Anterior cruciate ligament (ACL) is a band of connective tissue that connects the femur and the tibia and
plays a crucial role in stabilizing the knee joint. ACL ruptures are very serious musculoskeletal injuries with poor
self-healing capability and often mandate surgical intervention to restore normal joint function. Over 175,000
ACL reconstruction (ACLR) surgeries are performed in the US each year with over 17 billion dollars in lifetime
healthcare costs. While viable graft choices are available, graft failure is reported in 10% of cases. In addition, 1
in 5 teenage athletes reinjure their ACL. Long-term consequences of ACLR include limited mobility of the affected
joint and early onset of osteoarthritis in up to 80% of patients. Further, sex-based differences in healing outcomes
have been reported with females more susceptible to ACL re-tear compared to males. Poor integration of the
ACL graft at the bone-ligament interface (i.e., enthesis) is reported to be the main reason for suboptimal graft
performance and high graft failure rates. Tissue engineering of the graft-tissue interface is a promising alternative
solution to overcome the limitations of existing graft choices and improve the clinical outcome post ACLR. In this
realm, recreating the heterogeneity in composition, architecture and cell phenotype of the native enthesis post
ACLR is deemed to be critically important for improving graft-bone integration, facilitating reliable load transfer,
and restoring long-term normal ACL function. Towards this goal, we propose to develop a novel continuous
gradient-based construct that combines multiple biophysical and biochemical cues on a single platform to guide
functional regeneration of the ACL enthesis. We hypothesize that spatial presentation of tissue-specific cues will
promote cell migration, stimulate multilineage differentiation and matrix remodeling, improve graft integration,
and enable functional healing of enthesis post ACLR. Using support from the first period of this R15 project, we
delivered a continuous biomimetic Bioglass-gradient integrated collagen matrix (BioGIM) that emulates the
composition of the mineralized gradient of the native enthesis. This renewal application has three specific aims.
In Aim 1 studies, 3D printing will be combined with a magnetic alignment approach in a 4D printing scheme to
orient collagen fibers and achieve > 90% collagen alignment index in BioGIMs. Aligned collagen can provide
topographical cues to guide ligamentous differentiation on pure collagen side of the BioGIM. In Aim 2 studies,
TGF-β1 dosage and delivery strategy will be optimized to attain reliable fibrocartilaginous matrix formation on
the BioGIM interface. In addition, multi-lineage cell differentiation and matrix remodeling along the BioGIM will
be assessed. In Aim 3 studies, 4D printed BioGIM flaps will be integrated onto ends of a tendon autograft and
implanted in rabbits. Autograft without BioGIM will serve as clinical control and unoperated healthy rabbits will
be the positive control. Three weeks post implantation, outcomes measured will include mechanical strength of
the bone-ligament interface, typification of de novo matrix remodeling, and inflammatory response. Successful
completion of proposed studies is critical for clinical translation of the novel BioGIM flap for ACL reconstruction.
