Benz, M. A. | bioRxiv Science

bioRxiv2025

Melt Electrowritten Scaffold-Reinforced Affibody-Conjugated Hydrogels for Controlled Bone Morphogenetic Protein-2 Delivery

Bone morphogenetic protein-2 (BMP-2) is clinically used to promote bone regeneration but suffers from uncontrolled release when delivered from collagen sponges, necessitating high doses that can cause adverse effects. Hydrogels offer tunable protein release but are limited by weak mechanics and poor stability during storage and handling. Here, we introduce a two-part protein delivery platform that integrates mechanical reinforcement with affinity-controlled protein release. We developed a melt electrowritten (MEW) scaffold-reinforced, affibody-conjugated polyethylene glycol maleimide (PEG-mal) hydrogel for affinity-controlled BMP-2 delivery. MEW scaffolds improved hydrogel handling, compressive resistance, and stability during lyophilization and rehydration, without altering bulk stiffness. Engineered BMP-2-specific affibodies provided affinity-based control over BMP-2 release. This ability to control BMP-2 release was preserved after lyophilization and rehydration of the hydrogels. In vivo, affibody conjugation of high-affinity affibodies to the hydrogels significantly enhanced BMP-2 retention in subcutaneous implants, while MEW reinforcement significantly increased bone volume and defect bridging in rat femoral bone defects. This affibody-conjugated, MEW scaffold-reinforced hydrogel system effectively integrates mechanical reinforcement with tunable protein-material affinity interactions, advancing hydrogel-based delivery strategies for BMP-2 and other protein therapeutics in musculoskeletal repair.

bioengineering↗

bioRxiv2024

Recombinant and synthetic affibodies function comparably for modulating protein release

PurposeAffibodies are a class of versatile affinity proteins with a wide variety of therapeutic applications, ranging from guided contrast agents for imaging to cell-targeting therapeutics. We have identified several affibodies specific to bone morphogenetic protein-2 (BMP-2) with a range of binding affinities and demonstrated the ability to tune release rate of BMP-2 from affibody-conjugated poly(ethylene glycol) (PEG) hydrogels based on affibody affinity strength. In this work, we compare the purity, structure, and activity of recombinant, bacterially-expressed BMP-2-specific affibodies with affibodies synthesized via solid-phase peptide synthesis. MethodsHigh- and low-affinity BMP-2-specific affibodies were recombinantly expressed using BL21(DE3) E. coli and chemically synthesized using microwave-assisted solid-phase peptide synthesis with Fmoc-Gly-Wang resin. The secondary structures of the affibodies and dissociation constants of affibody-BMP-2 binding were characterized by circular dichroism and biolayer interferometry, respectively. Endotoxin levels were measured using chromogenic limulus amebocyte lysate (LAL) assays. Affibody-conjugated PEG-mal hydrogels were fabricated and loaded with BMP-2 to evaluate hydrogel capacity for controlled release, quantified by enzyme-linked immunosorbent assays (ELISA). ResultsSynthetic and recombinant affibodies were determined to be -helical by circular dichroism. The synthetic high- and low-affinity BMP-2-specific affibodies demonstrated comparable BMP-2-binding dissociation constants to their recombinant counterparts. Recombinant affibodies retained some endotoxins after purification, while endotoxins were not detected in the synthetic affibodies. High-affinity affibody-conjugated hydrogels reduced cumulative BMP-2 release compared to the low-affinity affibody-conjugated hydrogels and hydrogels without affibodies. ConclusionsSynthetic affibodies demonstrate comparable structure and function to recombinant affibodies, while reducing endotoxin contamination and increasing product yield, indicating that solid-phase peptide synthesis is a viable method of producing affibodies for controlled protein release and other applications.

bioengineering↗