Biomimetic proteoglycans as a tool to engineer the structure and mechanics of porcine bioprosthetic heart valves

The utility of bioprosthetic heart valves (BHVs) is limited to certain patient populations because of their poor durability compared to mechanical prosthetic valves. Histological analysis of failed porcine BHVs suggests that degeneration of the tissue extracellular matrix (ECM), specifically the loss of proteoglycans and their glycosaminoglycans (GAGs), may lead to impaired mechanical performance, resulting in nucleation and propagation of tears and ultimately failure of the prosthetic. Several strategies have been proposed to address this deterioration, including novel chemical fixatives to stabilize ECM constituents and incorporation of small molecule inhibitors of catabolic enzymes implicated in the degeneration of the BHV ECM. Here, biomimetic proteoglycans (BPGs) were introduced into porcine aortic valves ex vivo and were shown to distribute throughout the valve leaflets. Incorporation of BPGs into the heart valve leaflet increased tissue overall GAG content. The presence of BPGs also significantly increased the micromodulus of the spongiosa layer within the BHV without compromising the chemical fixation process used to sterilize and strengthen the tissue prior to implantation. These findings suggest that a targeted approach for molecularly engineering valve leaflet ECM through the use of BPGs may be a viable way to improve the mechanical behavior and potential durability of BHVs.

Biomimetic proteoglycans can molecularly engineer early osteoarthritic cartilage in vivo

Biomimetic proteoglycans (BPGs) have the potential to treat osteoarthritis (OA) given that these molecules mimic the structure and properties of natural proteoglycans, which are significantly reduced in OA. We examined the effects of BPGs injected into the intra-articular space in an in vivo OA rabbit knee model and evaluated the effect on histological response, joint friction, and BPG distribution and retention. Rabbits underwent ACL transection to create an arthritic state after 5 weeks. OA rabbits were treated with BPGs or Euflexxa® (hyaluronic acid) intra-articular injections. Non-OA rabbits were injected similarly with BPGs; contralateral joints served as controls. The progression of OA and response to injections were evaluated using Mankin and gross grading systems indicating that mild OA was achieved in operated joints. The coefficient of friction (COF) of the intact knee joints were measured using a custom pendulum friction apparatus, showing that OA joints and OA + Euflexxa® joints demonstrated increased COF than non-operated controls, while BPG-injected non-OA and OA + BPGs were not significantly different from non-OA controls. Injected fluorescently labeled BPGs demonstrated that BPGs diffused into cartilage with localization in the pericellular region. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:403-411, 2019.