Supramolecular polymer hydrogels have emerged as a promising class of biomaterials in biomedical applications due to their unique combination of self-healing properties, tunable mechanical strength, and thermoplastic behavior. These characteristics stem from dynamic physical interactions within the hydrogel network, including hydrogen bonding, host-guest interactions, metal-ligand coordination, and hydrophobic associations. Among these, hydrogen bonding is particularly significant because it is abundant in biological systems and can generate strong synergistic effects even though individual bonds are weak. This makes hydrogen-bonded networks ideal candidates for constructing tough yet flexible hydrogels. However, traditional supramolecular hydrogels based on single amide hydrogen bonding often suffer from instability in aqueous environments due to competitive solvation by water molecules, which disrupts the hydrogen-bonding network.
To overcome this limitation, we previously developed a poly(N-acryloyl glycinamide) (PNAGA) hydrogel with dual amide motifs in its side chain. The presence of two amide groups enabled the formation of robust hydrogen-bonded microdomains that effectively shielded against water penetration, resulting in high mechanical strength and excellent resistance to swelling. By employing Type II photoinitiated self-condensing vinyl polymerization, hyperbranched PNAGA hydrogels were synthesized with higher crosslinking density, leading to superior mechanical performance compared to linear analogs. Furthermore, copolymerization with other monomers allowed fine-tuning of mechanical properties across a wide range—from rigid to soft injectable forms—enabling applications such as 3D-printed osteochondral scaffolds, artificial vitreous bodies, and antiadhesion barriers.
In our recent work, we discovered that introducing a single methyl group into the double bond of NAGA significantly reduced mechanical strength while enhancing autonomous self-healing at room temperature, due to steric interference with hydrogen bonding. Inspired by this finding and the structural features of protein secondary structures, we hypothesized that modifying the spacer length between dual amide motifs could further modulate the hydrogen-bonding network and thus tailor the physicochemical properties of the resulting hydrogel.ATP2A1 ProteinSource Specifically, we introduced an additional methylene spacer between the two amides in the side chain of N-acryloyl glycinamide (NAGA), yielding a new monomer: N-acryloyl alaninamide (NAAA). This subtle structural change was expected to weaken intermolecular hydrogen bonding while simultaneously strengthening hydrogen bonding between the polymer chains and surrounding water molecules—a balance that could lead to ultrasoft, highly swollen, and antifouling hydrogels.
Polymerization of NAAA in aqueous solution produced a novel supramolecular hydrogel, poly(N-acryloyl alaninamide) (PNAAA), without requiring any chemical cross-linkers. Fourier transform infrared spectroscopy (FTIR) and variable-temperature FTIR analysis confirmed a reduction in hydrogen-bonding strength, evidenced by shifts in NH bending and C=O stretching frequencies upon heating. Simulation calculations using DFT-D3(BJ) revealed that the dimer-dimer intermolecular hydrogen bonding energy decreased significantly in PNAAA compared to PNAGA, while intramolecular and polymer-water hydrogen bonding energies increased. This shift indicated weakened cross-linking between polymer chains and enhanced hydration capacity, explaining the pronounced swelling behavior observed in PNAAA hydrogels.
Rheological studies demonstrated that PNAAA hydrogels exhibited fluid-like behavior at low frequencies but transitioned into elastic-like states at higher frequencies, indicating dynamic network reorganization. Notably, hydrogels with lower NAAA content (20% and 25%) showed rapid recovery after deformation, confirming their ability to self-fuse and heal through reversible hydrogen bonding. In contrast, higher concentration samples (30% and 35%) displayed irreversible damage during extrusion, attributed to limited chain mobility in dense networks. After repeated syringe extrusion, fragments of PNAAA-25 hydrogel readily merged back into a continuous gel—demonstrating true self-fusion capability.
The antifouling properties of PNAAA hydrogels were evaluated through protein adsorption and cell adhesion assays. Compared to PNAGA-25, PNAAA-25 showed dramatically reduced bovine serum albumin (BSA) and fibrin adsorption (2.98 vs. 13.02 µg/cm²; 5.85 vs. 20.57 µg/cm²), indicating superior resistance to nonspecific protein deposition. This effect was linked to a tightly bound hydration layer formed via strong hydrogen bonding between water and amide groups, creating a physical barrier that prevents protein and cell attachment. Moreover, L929 fibroblasts barely adhered to PNAAA surfaces, and all formulations maintained over 86% cell viability, demonstrating excellent cytocompatibility. Hemolysis tests further confirmed negligible red blood cell lysis (<5%), highlighting favorable hemocompatibility. In vivo evaluation in rat models revealed the exceptional efficacy of PNAAA hydrogel in preventing postoperative abdominal adhesions. In both primary adhesion and recurrent adhesion models following adhesiolysis, the PNAAA-treated group achieved nearly complete prevention of adhesion formation (average score: 0.2), outperforming commercial hyaluronic acid (HA) hydrogel (score: 2–2.8). Histopathological analysis showed minimal inflammation, no collagen deposition, and intact mesothelial layers in the PNAAA group, whereas control groups exhibited severe fibrosis and inflammatory infiltration.CD33 Antibody Biological Activity Molecular studies revealed that PNAAA hydrogel suppressed pro-inflammatory cytokines (TNF-α, IL-1, IL-6), inhibited NF-κB activation, and restored balance in the fibrinolytic system by upregulating t-PA and downregulating PAI-1.PMID:34718095 Additionally, PNAAA significantly attenuated TGF-β1 expression and modulated Smad3/Smad7 signaling, thereby suppressing fibrotic pathways.
Importantly, the PNAAA hydrogel demonstrated appropriate in vivo retention time—visible fluorescence persisted for over 14 days, covering the critical window for adhesion formation (days 3–14)—before fully dissociating and being excreted. No signs of organ toxicity were observed in histological evaluations of heart, liver, spleen, lung, and kidney tissues. These findings collectively establish PNAAA as a transient, biodegradable, self-fusing, antifouling hydrogel with transformative potential for clinical antiadhesion therapy.
This study presents a rational design strategy for tuning supramolecular hydrogels through precise manipulation of molecular architecture. By introducing a simple methylene spacer, we achieved a dramatic shift in material behavior—from rigid to ultrasoft, from static to self-fusing, and from prone to fouling to highly resistant. The resulting PNAAA hydrogel not only prevents tissue adhesion effectively but also promotes healing by modulating key biological pathways. Its biocompatible, transient nature and ease of delivery make it a highly viable candidate for translation into clinical practice. Future work will focus on large-animal trials and optimization of dosage and formulation for human application.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com