Collagen-Enriched Immunomodulatory Hydrogel for Tendon Regeneration

Rotator cuff tendon injury (RCTI) is aggravated by the pro-inflammatory milieu elicited by TLR4 and TREM1 signaling. Hence, tendon tissue engineering approaches require considerations that address these inflammatory episodes to benefit active regenerative responses. The objective of this study was to engineer and evaluate the immunocompatibility of a tendon-mimetic hydrogel composed of a chitosan-polyvinyl alcohol (PVA) blend incorporated with Collagen-I and to assess LR12 delivery for addressing TREM1-driven inflammation in RCTI management. A chitosan-PVA-HEMA-Acrylic acid (CPHA) hydrogel was synthesized by blending the linear natural polysaccharide chitosan and linear synthetic polymer PVA in an aqueous phase, followed by incorporation and redox chain growth with HEMA using acrylic acid (AA). Interpenetration of Collagen-I in CPHA yielded the CPHA-C hydrogel. CPHA and CPHA-C hydrogels displayed ample surface functional moieties provided by the co-polymers, exhibited excellent porosity as revealed by SEM imaging (28.65 ± 6.85 and 41.56 ± 18.00, respectively, for CPHA and CPHA-C), and were amphiphilic, as evident by contact angle analysis (~70 for CPHA and CPHA-C). Both hydrogels displayed a progressive release profile for the TREM1-inhibitory peptide LR12 for 7 days, whereas the LR12-loaded CPHA hydrogel exhibited increased TREM1 inhibition in LPS-challenged RAW264.7 macrophages. CPHA and CPHA-C hydrogels were immunocompatible and masked the oxidative damage in RAW264.7 macrophages, as evident by decreased levels of mitochondrial superoxide and ROS. Additionally, the CPHA hydrogel displayed an increased TGFβ/TLR4 ratio (0.24), whereas the CPHA-C (-0.52) system showed a decreased ratio upon exposure to tenocytes and macrophages. Overall, the findings highlight the potential of CPHA and CPHA-C hydrogels as candidates for tendon regenerative applications.