Dendrimer-based hydrogels for biomedical applications

Dendrimers as building blocks for hydrogels

Unlike low-molecular-weight crosslinkers, dendrimers are precisely defined macromolecular objects that combine a large molecular volume with a high and controllable density of reactive terminal groups. Their incorporation into hydrogel precursor mixtures can therefore alter not only the number of network junctions, but also their spatial distribution, local functionality, chain mobility and nanoscale heterogeneity^[29]. Depending on dendrimer generation, concentration, peripheral chemistry, functionality conversion and the nature of the polymer matrix, dendritic crosslinkers can regulate hydrogel stiffness, viscoelasticity, gelation kinetics, swelling, pore architecture and biological ligand presentation. Thus, dendrimers should be regarded as architectural regulators of hydrogel networks rather than simply as multifunctional crosslinkers.

Several classes of dendritic architectures have been integrated into hydrogel networks to address specific functional requirements [Figure 1]. Poly(amidoamine) (PAMAM) and 2,2-bis(hydroxymethyl)propionic acid-based dendrimers (bis-MPA) polyester dendrimers take advantage of their controllable generation, multivalent surface and ability to engage in electrostatic, hydrogen-bonding or host-guest interactions. Poly(L-lysine) dendrigrafts (DGL) and poly(L-lysine)-based dendrons provide protein-like, positively charged backbones that can serve as covalent crosslinkers for poly(ethylene glycol) (PEG) or hyaluronic acid matrices while enhancing cell adhesion and osteogenic responses, thus enabling mechanically tunable scaffolds for bone and soft-tissue regeneration. Carbosilane and phosphorus dendrimers, with robust inorganic or heteroorganic cores and functional peripheries, have been exploited to construct self-assembled physical gels and self-immolative networks in which pH-, redox- or light-triggered degradation is coupled to the release of hydrophobic drugs or nucleic acids. Finally, dendronized polymers and bis-dendron PEG architectures illustrate how dendritic motifs can be used to introduce multivalent ligand clustering, supramolecular chirality and independently tunable viscoelasticity into hydrogel matrices, opening routes toward synthetic mimics of anisotropic, hierarchically organized tissues^[29-35].

Figure 1. Dendritic architectures used for obtaining functional hydrogels. Second-generation dendritic species are presented as examples. The dendrimer core is drawn in bold; the first generation is presented in red; the second generation is presented in blue, peripheral functional groups, if different from the dendrimer branches, are presented in green. PAMAM: poly(amidoamine) dendrimer; bis-MPA: 2,2-bis(hydroxymethyl)propionic acid-based dendrimers.

Table 1 summarizes principal advantages, limitations, biodegradability, and biological properties of different dendrimer architectures and representative hydrogel applications.

The biological behavior of dendrimers is governed by their size, generation, core and, most importantly, surface chemistry. Surface multivalency can promote cell interaction, ligand binding, cargo complexation and tissue retention; however, highly cationic surfaces may also disrupt negatively charged cell membranes, induce hemolysis, oxidative stress and inflammatory responses^[36]. Neutral, anionic or partially shielded dendrimers generally show improved cytocompatibility^[37], whereas acetylation, hydroxylation, PEGylation, glycosylation and covalent incorporation into hydrogel networks can reduce exposure to free cationic species. Biodistribution and elimination are similarly size- and charge-dependent: smaller dendrimers may undergo renal clearance, while larger or more hydrophobic structures can accumulate in the liver, spleen or other mononuclear-phagocyte-system organs^[38,39]. Consequently, biodegradable dendritic scaffolds and systematic assessment of degradation products, local tissue response, systemic exposure and long-term clearance are essential for safe biomedical translation. A number of dendrimer species have been subjected to clinical trials and already translated into practice^[34].

Dendrimers modulate mechanical properties of hydrogels

Dendritic crosslinkers provide an efficient platform for controlling hydrogel mechanics because each macromolecule presents multiple reactive groups within a confined volume. Increasing the amount of a suitably functionalized dendrimer generally increases the effective crosslink density and reduces polymer-chain mobility, thereby increasing the elastic and viscous components of the mechanical response. However, this relationship depends on the accessibility of terminal groups, stoichiometry with the complementary polymer or crosslinker, steric crowding, dendrimer flexibility and the occurrence of network defects. Dendrimer concentration and molecular architecture can be used as independent formulation variables to access a wide range of mechanical properties within a common chemical platform.

For example, hydrogels formed by crosslinking dithiol-terminated PEG with RGD peptide-functionalized PAMAM G5 dendrimers showed a marked, concentration-dependent increase in complex modulus, G^*, from ca. 45 Pa at 1.2% PAMAM to 5,000 Pa at 5.1% PAMAM^[40]. Similarly, RGD-functionalized PAMAM dendrimers crosslinked with PEG diacrylate (PEGDA) yielded photopolymerized matrices with storage moduli, G′, between 20 and 8,000 Pa, and loss moduli, G′′, of ca. 30-600 Pa, according to precursor composition. In that system, the stiffest formulations supported osteogenic differentiation of mesenchymal stem cells without observable cytotoxicity, illustrating how dendritic crosslinking can be used to establish mechanically instructive cell microenvironments^[41].

The mechanical range accessible with dendritic building blocks is also evident in hydrogels derived from natural polymers. Low-generation multiarm PEG-polyaldehyde dendritic crosslinkers enabled the modulation of carboxymethyl chitosan hydrogels from G′ ≈ 250 Pa and G′′ ≈ 30 Pa to G′ ≈ 11 kPa and G′′ ≈ 5 kPa^[42]. In alginate/oxidized dextran systems crosslinked with PAMAM dendrimers, increasing dendrimer content increased compressive strength continuously from approximately 50 to 650 kPa; the response could be further adjusted through the dextran:alginate ratio^[43]. Together, these examples show that relatively small changes in dendrimer content can tune hydrogel moduli over at least two orders of magnitude.

This capability is particularly relevant for cell-instructive matrices, because material stiffness can influence cell spreading, cytoskeletal tension, mechanotransduction and lineage commitment. Nevertheless, hydrogel mechanics should not be reduced to elastic modulus alone. Dendrimer concentration, generation and topology may simultaneously influence stress relaxation, swelling, ligand density and pore architecture. The mechanobiological interpretation therefore requires these parameters to be measured and, wherever possible, varied independently. Below, this consideration will be illustrated by DGL-based PEG and hyaluronic acid matrices, where both stiffness and viscoelastic dissipation influence osteogenic cell responses^[44,45].

Dendrimers versus conventional crosslinkers

The advantage of dendrimers over conventional low-molecular-weight crosslinkers derives from their ability to create a local excess of reactive groups while maintaining a macromolecular junction size. A small bifunctional or multifunctional linker creates relatively localized junctions between adjacent polymer chains. By contrast, a dendrimer can connect multiple chains over a larger molecular volume and can establish a highly multivalent, spatially organized crosslinking node. This topology can increase network connectivity and rigidity even when the parent polymer alone would form only a weak or soft hydrogel.

A representative comparison was reported for collagen matrices crosslinked using carbodiimide, glutaraldehyde or PAMAM dendrimers. Carbodiimide, a zero-length crosslinker, and glutaraldehyde, a short molecular linker, produced collagen materials with Young’s moduli of approximately 50-100 kPa. In contrast, the macromolecular PAMAM crosslinker yielded a substantially more rigid collagen network with a Young’s modulus of approximately 1.4 MPa^[46]. Beyond mechanical reinforcement, the dendrimer-crosslinked collagen displayed improved optical transparency relative to thermally gelled collagen and to collagen networks crosslinked with 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) or glutaraldehyde. It also showed glucose permeability exceeding that of native human cornea, supported human corneal epithelial-cell attachment and growth, and did not exhibit the cytotoxicity associated with glutaraldehyde-crosslinked controls.

An additional advantage is that crosslinking need not consume all dendrimer surface groups. In PEGDA hydrogels formed through aza-Michael addition with amino-terminated PAMAM G5 dendrimers, partial acetylation of the peripheral amines altered gelation time, network structure, rheological behavior, swelling and degradation without completely abolishing network formation^[47]. Compared with unmodified PAMAM, 50% acetylation reduced network rigidity, whereas further acetylation up to 90% produced more modest changes. The corresponding gel-state storage modulus ranged from approximately 1 Pa to 10 kPa, and swelling increased to approximately 300% in dendrimer-containing systems. This result demonstrates that a proportion of terminal groups can be reserved for orthogonal functionalization with peptides, proteins, drugs, nucleic acids or imaging probes while retaining sufficient functionality for hydrogel crosslinking^[41,48].

Dendrimer crosslinking controls hydrogel porosity

Because dendrimers modify the density, distribution and connectivity of hydrogel junctions, they can strongly influence pore size and pore-size distribution. This is a critical design parameter for hydrogel applications because porosity regulates diffusion, swelling, nutrient transport, cell infiltration, vascularization and the accessibility of matrix-bound signals. The direction and magnitude of the porosity change depend on the composition of the hydrogel, total solid content, dendrimer-to-polymer ratio, crosslinking kinetics and the physical state in which the material is formed or dried.

In hydrogels based on natural polymers, dendritic crosslinking frequently yields smaller but more uniform pores, consistent with formation of a denser and more regularly connected network. For instance, gelatin methacrylate hydrogels exhibited a pore diameter of 310 ± 80 µm, whereas incorporation of methacrylated PAMAM reduced the mean pore diameter to 80 ± 20 µm. This structural refinement was accompanied by an increase in compressive modulus from approximately 2.5 to 8 kPa^[49]. Similar trends have been described for oxidized carboxymethylcellulose hydrogels crosslinked using PEG-poly(L-lysine) bis-dendrons^[50]. Such materials may be advantageous when structural integrity and controlled molecular transport are prioritized over rapid cell migration.

In synthetic-polymer networks, the effect of dendritic components can be more complex and may be exploited to tune pore interconnectivity rather than simply reduce mean pore size. In PEG hydrogels containing lysine dendrigrafts, variation of total component concentration and dendrimer-to-polymer ratio shifted the pore-size distribution from a monomodal population centered near 100 µm to a bimodal distribution with maxima near 150 and 450 µm^[51,52]. This type of hierarchical pore architecture may be favorable for cell culture and tissue formation because smaller pores can improve surface area and local cell-matrix interactions, whereas larger interconnected pores facilitate nutrient diffusion, waste removal, cell migration and vascular ingrowth.

The relationship between dendrimer incorporation and porosity should therefore be considered alongside mechanics rather than as an independent variable. Denser dendritic crosslinking may increase modulus and reduce average pore size, but formulation strategies that modify dendrimer content, functionality or crosslinking rate can generate mechanically robust networks while retaining macroporosity and transport pathways. Dendrimer-based hydrogels are consequently well suited to approaches in which pore structure and mechanical performance must be optimized simultaneously for a specific biomedical application.

Manifestation of the dendritic effect

The dendritic effect refers to the generation-dependent and often non-linear changes in macromolecular behavior that arise from increasing branching, terminal-group number, molecular size and steric organization. In hydrogel systems, this effect can manifest through altered crosslinking efficiency, terminal-group accessibility, local functionality, chain packing, polymer-dendrimer interactions and the number of effective network junctions. Importantly, increasing dendrimer generation does not necessarily produce a monotonic increase in mechanical strength. The outcome reflects the balance between multivalency, which can increase effective network connectivity, and steric shielding or reduced flexibility, which may limit the accessibility of functional groups.

A positive generation-dependent mechanical effect was observed in a peptide-dendrimer-based bioink prepared from hyaluronic acid and poly(L-lysine) (PLL) dendrimers. Increasing the PLL dendrimer generation from G1 to G3 increased G′ from 1 to 7 kPa and G′′ from 100 to 400 Pa^[53]. The higher-generation dendritic component thus produced a mechanically more robust bioink while preserving the cytocompatibility needed for three-dimensional bioprinting of hepatic cells. The printed constructs containing HepG2-C3A hepatic epithelial-like cells, LX-2 hepatic stellate cells and EA.hy.926 endothelial cells recapitulated key liver-associated functions, including endothelial-barrier behavior, hepatic activity and enhanced drug-metabolizing-enzyme activity.

By contrast, PAMAM generation can have the opposite effect in some network chemistries. In hydrogels formed by thiol-ene coupling of methacrylated hyaluronic acid with thiol-modified PAMAM dendrimers, the complex modulus decreased from 1,240 Pa for PAMAM G2 to 583 Pa for PAMAM G3^[52]. Similarly, ionic nanofibrous bioinks prepared from PAMAM dendrimers and poly(L-lactic acid) showed a decrease in Young’s modulus from approximately 95 to 70 kPa as PAMAM generation increased from G1 to G5^[54]. These results suggest that in higher-generation PAMAM dendrimers, steric congestion, reduced peripheral-group accessibility, altered molecular flexibility or less efficient packing may outweigh the theoretical benefit of a higher number of terminal groups.

Generation-dependent effects are thus not merely synthetic curiosities. They provide a methodology to tailor hydrogel properties through dendrimer topology. In practice, generation should be selected according to the intended role of the dendrimer: low-generation structures may offer greater functional-group accessibility and more flexible network formation, whereas higher-generation architectures may provide greater local multivalency, larger molecular volume and enhanced capacity for ligand clustering or cargo binding. A systematic assessment of generation, surface conversion, dendrimer concentration and polymer stoichiometry is required to establish structure-property relationships and to distinguish true dendritic effects from changes caused by precursor composition or incomplete crosslinking.

Antioxidant and reactive oxygen species-scavenging dressings

Oxidative stress is a major driver of impaired healing in chronic wounds, particularly in diabetic patients, where excess reactive oxygen species (ROS) delay re-epithelialization and collagen deposition. Islam et al. tackled this problem by conjugating gallic acid onto a fourth-generation PAMAM dendrimer and incorporating the resulting antioxidant macromolecule into a ternary hydrogel with polyvinyl alcohol and silk fibroin, crosslinked by ionizing gamma radiation (20-35 kGy). The macroporous architecture (compressive strength 1.4 MPa at 56% strain) achieved 70% H₂O₂ scavenging within 24 h in vitro, while in a streptozotocin-induced diabetic mouse excision model the wound area was reduced to 30% of its original size by day 10 and reached near-complete contraction by day 16. Hemolysis remained below 5%, and cell viability was significantly boosted relative to controls. The residue-free gamma-crosslinking ensures high material purity, and the synergy between the silk scaffold and the dendrimer antioxidant is a key design advantage; the only technical constraint noted is that the radiation dose must be carefully optimized for each blend composition^[55].

Multifunctional hemostatic and antibiotic hydrogels

Beyond oxidative damage, acute and infected wounds require simultaneous control of bleeding and microbial colonization. Jia et al. addressed both needs with a chemical hydrogel of sodium alginate and γ-polyglutamic acid (γ-PGA) cross-linked with a third-generation PAMAM dendrimer upon EDC/N-hydroxysuccinimide (NHS) activation. Amoxicillin (AMX) was taken as antibiotic cargo. The resulting self-healing (88% recovery) injectable network, with 200-400 µm interconnected pores, reduced hemostatic time to approximately 0.6-0.7 min (vs. over 5 min in controls), released 43% of AMX over 72 h, and achieved bactericidal rates above 96% against both E. coli and S. aureus. Applied to scald wounds in rodent models, the healing rate exceeded 98.9% after 20 days. An additional practical asset is the material's adhesion to heterogeneous substrates including pigskin, internal organs, and metal surfaces, making it suitable for emergency use in complex anatomical sites. The principal limitation is the need to optimize component ratios for wound types of varying complexity^[56].

Gupta et al. took a complementary drug-delivery approach by loading hesperidin, a bioflavonoid with documented wound-healing properties but poor aqueous solubility, into G3/G4 PAMAM dendrimers physically incorporated into a chitosan-sodium alginate matrix and lyophilized into a flexible bandage. The ~12 nm dendrimer particles achieved 20% entrapment efficiency and released 86.4% of hesperidin over 24 h. In a Wistar rat full-thickness excision model, the bandage produced 98.9% wound contraction after 14 days with measurable improvements in collagen synthesis and re-epithelialization; hemolysis was below 1%. The main bottleneck is the relatively modest drug-loading capacity of the dendrimer cavities^[57].

Antibiotic-free antimicrobial hydrogels

A recurring theme in recent literature is the desire to achieve effective bacterial killing without conventional antibiotics, thereby reducing resistance risk. Biscari et al. prepared hybrid hydrogels by complexing a second-generation cationic bis-MPA polyester dendrimer bearing twelve β-alanine surface groups with dopamine-functionalized gellan gum. Three crosslinking modes were exploited: physical polyelectrolyte complexation, optional ionotropic reinforcement with CaCl₂ for solid gels, and dynamic covalent Schiff base/Michael addition for injectable self-healing versions. Storage moduli ranged from 0.5 (injectable) to 21.0 kPa (solid), swelling capacity exceeded 1,700%, and solid formats achieved complete (100%) bacterial killing of S. aureus and E. coli within 4 h. Injectable versions demonstrated 100% self-healing efficiency. The trade-off is a shorter functional lifetime for injectable gels (under 2 days) versus solid ones (~7 days)^[58].

The same group subsequently introduced near-infrared (NIR) responsiveness by replacing the surface chemistry with cysteamine hydrochloride groups on G1 and G2 bis-MPA dendrimers, and by incorporating in situ-synthesized polydopamine (PDA) into an ethylenediamine-functionalized gellan gum matrix. The freeze-dried microporous sponge rehydrates to a bulk hydrogel, swells above 1,500%, and retains a storage modulus of ~657 Pa up to 50 °C. Against S. aureus and P. aeruginosa, G1 dendrimers eradicated bacteria even without irradiation, while G2 systems required NIR stimulation at 810 nm to loosen the hydrogel mesh. The material is non-hemolytic and shows low cytotoxicity in HaCaT keratinocytes. The dependence of G2 on external light stimulation is both its key functional feature and its primary practical constraint^[59].

Fan et al. took the antibiotic-free concept further by demonstrating that hydrogels based on amino-functional hyperbranched dendritic-linear-dendritic (DLD) copolymers, a linear PEG core with G5/G6 bis-MPA-derived blocks bearing β-alanine surface groups, can not only kill bacteria directly but also modulate the host innate immune response. Covalently crosslinked DLD polymer and NHS-activated PEG cross-linkers, the porous adhesive bandages (storage moduli 638-2,969 Pa) achieved 100% killing of E. coli and P. aeruginosa and were equally active against clinical methicillin-resistant S. aureus, S. pyogenes, and P. aeruginosa strains. Uniquely, the materials upregulated expression of the endogenous antimicrobial peptides RNase 7 and psoriasin in HaCaT keratinocytes while reducing pro-inflammatory interleukin-1 beta (IL-1β) and mitochondrial ROS. Rapid degradation within 24 h prevents accumulation and resistance development, and the material adheres strongly to porcine skin^[60].

Ye et al. introduced a structurally distinct concept by preparing covalently stabilized peptide nanoparticles formed via dendritic polymerization of AB2-type peptide monomers through azide-alkyne or thiol-maleimide click chemistry. These nanoparticles were used as rigid multifunctional crosslinkers within a 4-arm-PEG-azide network assembled by CuAAC click reaction. Cationic nanoparticles (zeta potential +23.1 mV) provided inherent antibacterial activity, and the resulting hydrogel (storage modulus ~4 kPa) exhibited remarkable resistance to swelling (volume expansion ~2%), achieved 100% killing of S. aureus, and drove near-complete wound closure by day 12 in a murine infected full-thickness skin defect model, accompanied by reduced IL-6 levels and promoted neovascularization (CD31 staining). The covalent assembly strategy prevents the premature disassembly that commonly limits supramolecular peptide systems, and the sequence-independent platform can be readily reformulated with different bioactive peptides^[61].

Tissue sealants

Achieving reliable tissue adhesion under the wet, dynamic conditions of surgical fields or traumatic wounds requires materials combining covalent bonding chemistry with mechanical toughness.

Zhu et al. constructed a dual-bioinspired double-network hydrogel adhesive from a barbell-like dendritic lysine scaffold modified with catechol groups (53.9% substitution degree) to mimic mussel wet adhesion, combined with a noncovalent network of chitosan and carboxymethyl cellulose inspired by the energy-dissipating mucus of slugs. The covalent network was formed by HRP/H₂O₂-mediated π-π coupling, yielding an injectable, self-healing hydrogel (300% stretch recovery after 10 min) with a storage modulus of 2 MPa and adhesion energies of 200-900 J/m² against porcine skin. These values substantially exceed the parameters of commercial sealants Tisseel and BioGlue. In a rabbit femoral artery damage model, hemostasis was achieved in under 30 s. Intrinsic antimicrobial activity against E. coli and S. aureus was additionally demonstrated^[62].

Sanz del Olmo et al. reported a complementary on-demand-curing strategy using G2-to-G5 DLD block copolymers based on PEG and bis-MPA, with a heterofunctional surface carrying allyl groups for crosslinking and quaternary ammonium groups for antibacterial activity. Visible light-induced thiol-ene reaction cured the hydrogel in under 20 s. Storage moduli ranged from 270 to 7,024 Pa, and tensile adhesion to pig skin and bone patches reached up to 61.2 kPa, with 100% killing of Gram-negative bacteria by the optimized formulation. The technology targets wound closure adhesives, antibacterial coatings on medical devices, and surgical site infection prevention. A noted limitation is that high crosslinking density in stoichiometric formulations can sterically mask ammonium groups, reducing antibacterial efficacy^[63].

Muñoz Taboada et al. demonstrated that dendrimer hydrogels can be extended to the demanding application of vascular anastomosis sealing. A two-component sprayable system was formulated by combining oxidized dextran and oxidized alginate (polyaldehyde components) with a surface-modified G5 PAMAM dendrimer (75% hydroxyl, 25% amine) that crosslinks through instantaneous covalent imine bond formation upon mixing. Delivered via an airless syringe, the hydrogel withstood supraphysiological burst pressures of ~300 mmHg, maintained cell viability above 90%, and passed genotoxicity and sensitization assessments. Crucially, unlike the rigid commercial sealant BioGlue which risks vascular stenosis, this pliable hydrogel allows the vessel to restore its natural luminal diameter after application. The material retained sealing performance after 20 kGy gamma sterilization, and efficacy was confirmed in rabbit aorta puncture and pig carotid end-to-side graft models^[43].

A notable translational case of a hydrogel for topical use is VivaGel® (SPL7013), a topically administered formulation in which the dendrimer itself is the active antimicrobial agent rather than a passive crosslinker or carrier. SPL7013 is a fourth-generation poly(L-lysine) dendrimer bearing 32 terminal naphthalene disulfonate groups, which confer a highly multivalent polyanionic surface. This architecture was designed to promote local interactions with pathogens while limiting systemic exposure. VivaGel® has been evaluated clinically as a 3% vaginal microbicide for human immunodeficiency virus 1 (HIV-1) and herper simplex virus 2 (HSV-2) prevention, including phase I studies of repeated vaginal dosing and antiviral retention (NCT00331032 and NCT00740584), and as a 1% formulation for bacterial-vaginosis treatment and recurrence prevention, including phase III studies (NCT01577537 and NCT02236156). In addition, SPL7013 has been incorporated into condom lubricants marketed in several jurisdictions.

Although VivaGel® is not a dendrimer-crosslinked bulk hydrogel, it provides clinical proof that precisely defined dendritic macromolecules can be formulated into locally retained gels or device coatings and can advance through clinical development when their charge, multivalency, local retention and safety profile are matched to a specific medical indication.

Cartilage repair

Osteoarthritis (OA) is characterized by progressive degradation of articular cartilage driven by mechanical stress and inflammatory mediators, including elevated matrix metalloproteinases (MMPs). A central challenge for intra-articular therapy is achieving adequate drug penetration into the dense, avascular cartilage matrix while restricting release to diseased tissue [Figure 3].

Figure 3. Dendrimer-based hydrogels for cartilage repair. Dendrimer-containing matrices provide local delivery of anti-inflammatory and regenerative agents while supporting cartilage cells and matrix restoration. ECM: Extracellular matrix; MMP: matrix metalloprotease; MSC: mesenchymal stromal cells; GAG: glycosaminoglycans; M1, M2: macrophages type 1 or 2; IL-1β: interleukin-1 beta.

Zhou et al. addressed this with a dual-responsive composite nanohydrogel in which a fifth-generation PAMAM dendrimer was conjugated to an MMP-13-responsive peptide linker and loaded with the pro-chondrogenic small molecule kartogenin. Hydrogel nanoparticles were encapsulated within a thermosensitive DLD hydrogel that gels at body temperature, enabling single-step intra-articular injection. The cationic PAMAM surface (+18.9 mV) exploited electrostatic attraction to anionic cartilage proteoglycans, achieving 67.2% cartilage penetration at 500 µm depth within 3 days. Kartogenin release reached 73% within 72 h in high-MMP-13 environments. In a rat ACLT+DMM OA model, the system achieved a 3.8-fold increase in Collagen II expression and significant reductions in IL-1β and IL-6. Future steps include large-animal validation and long-term assessment of PAMAM biodegradation in vivo^[64].

Extending the temporal dimension of cartilage therapy, Cheng et al. developed a gelatin methacrylate (GelMA)-based composite hydrogel incorporating G5 PAMAM dendrimers that carry covalently bound diclofenac on their surface and strontium ions in their interior cavities. UV photo-polymerization of the GelMA matrix provided the structural bulk, while the nanoparticles enabled sequential release: diclofenac during the initial 9 days to suppress inflammation, followed by strontium from days 3 to 15 to drive chondrogenesis. Rabbit in vivo models demonstrated significantly reduced inflammation and enhanced extracellular matrix (ECM) deposition [Collagen II and glycosaminoglycans (GAG)] at 6 weeks. The sequential release of anti-inflammatory priming and pro-regenerative signaling represents a conceptual advance over co-delivery systems, and bone marrow stem cells were identified as the preferred cellular cargo^[65].

Wang et al. approached cartilage repair from a different angle, targeting concurrent treatment of bone joint tuberculosis with a multicomponent biomimetic gel formed by amine-epoxy click crosslinking between G3 PAMAM dendrimers, dendrimer-templated silver nanoparticles, amine-functionalized mesoporous silica nanoparticles, and PEG diglycidyl ether. Inclusion of silica nanoparticles and silver nanoparticles raised the tensile modulus from 360 kPa to 2.1 MPa thus meeting the stiffness requirements of human joint cartilage, while the dual-drug payload delivered isoniazid with a burst release (50% in 4 h) and rifampicin by zero-order kinetics over 9 days. The gel demonstrated negligible mass loss over 14 weeks and effective antimicrobial activity against E. coli^[66].

Rheumatoid arthritis (RA) is a systemic autoimmune condition driving synovial inflammation and progressive joint destruction. Two complementary platforms illustrate how this immunological complexity can be addressed with dendrimer hydrogels.

Zhu et al. designed an ECM-inspired injectable hydrogel formed by reversible Schiff base crosslinking between a third-generation polylysine dendrimer and oxidized hyaluronic acid. The dynamic imine bonds conferred shear-thinning and self-healing behavior for minimally invasive intra-articular injection, and the polycationic dendrimer surface scavenged negatively charged inflammatory cytokines and cell debris. Adipose-derived stem cells encapsulated within the 3D porous network (storage modulus up to ~104.5 Pa; elastic moduli 400-1,100 kPa) showed prolonged in vivo retention of 7 days compared to bare cell injections. In a collagen-induced arthritis rat model, the system successfully reversed macrophage polarization from M1 to M2 and significantly improved bone mineral density and cartilage integrity, with no systemic organ toxicity^[67].

Oliveira et al. integrated nanotechnology with organ-on-chip engineering by loading anti-TNFα monoclonal antibodies into chondroitin sulfate-modified PAMAM dendrimer nanoparticles embedded within a tyramine-functionalized gellan gum hydrogel (enzymatically crosslinked by HRP/H₂O₂), incorporated into a cartilage-on-a-chip microfluidic device co-culturing human monocytes and primary chondrocytes. Over 14 days, the system maintained high Collagen II expression, reduced chondrocyte death induced by inflamed macrophages, and demonstrated sustained anti-inflammatory capacity. This study was the first cartilage-on-chip model to integrate dendrimer nanotechnology and microfluidics. The use of normoxic culture conditions, while the RA joint is typically hypoxic, is identified as the principal limitation; hypoxic modeling is a stated future direction^[68].

Ma et al. developed a triplex injectable composite in which siRNA targeting the stress-response gene DDIT4 was complexed with a G5 amino-terminal PAMAM dendrimer and coated with hyaluronic acid to form 100-200 nm particles, then embedded in an injectable hydrogel matrix for intradiscal delivery. In a rat needle-puncture intravertebral disc disease model, DDIT4 siRNA fluorescence persisted in discs for 35 days (vs. 21 days for naked siRNA), inhibiting nuclear pore complex-associated pyroptosis via the ROS/TXNIP/NLRP3 axis and significantly improving the disc height index. The study establishes DDIT4 as a validated therapeutic target for intravertebral disc disease and identifies biodegradable PAMAM variants as a necessary development to avoid long-term intradiscal accumulation^[69].

Liu et al. extended the cartilage engineering toolkit to ear reconstruction (microtia) using a double-network hydrogel scaffold combining reversible Schiff base crosslinks (oxidized chondroitin sulfate/gelatin) and permanent methacrylate photo-polymerization, with PEG as a porogen. A G5 PAMAM dendrimer modified with guanidinobenzoic acid delivered a Runx1-expressing plasmid (pRunx1) to dedifferentiated chondrocytes. Scaffolds cast in 3D-printed ear-shaped molds and tested subcutaneously in nude mice produced mature cartilaginous tissue with a Young's modulus exceeding 8 MPa (twice that of controls), low swelling, and ~25% degradation over 60 days. The non-viral gene delivery approach avoids the immunogenicity risks of viral vectors^[70].

The vocal fold lamina propria must sustain millions of phonation cycles while exhibiting non-linear, anisotropic, and viscoelastic behavior. Carrancá et al. constructed a fiber-reinforced composite hydrogel based on DGL cross-linked with a PEG-NHS polymer^[71]. This hydrogel matrix served as an analog of the elastin-ground substance component while jet-sprayed polycaprolactone microfibers mimicked the collagen fiber network. By varying the fiber volume fraction (3%-11%) and PEG molecular weight, the tangent modulus and strength were tuned to match native vocal-fold stress-strain responses in both longitudinal tension and transverse compression. The inherently cell-interactive DGL surface eliminated the need for surface coating. The principal limitation is that jet-spraying produces straight polycaprolactone (PCL) fibers rather than the native wavy collagen architecture at the microscale^[72].

Volumetric muscle loss exceeds the intrinsic regenerative capacity of skeletal muscle, leaving permanent functional deficits. Two studies from the same group developed and applied effervescent DGL/PEG hydrogels to this challenge. Griveau et al. established the foundational platform: G3 DGL was covalently crosslinked with bis-NHS-PEG by amide bonding, and during syringe injection a concurrent effervescent reaction of K₂CO₃ and acetic acid generated a highly interconnected macroporous bulk network in situ, stabilized by Pluronic F-68. The resulting hydrogels achieved 75%-80% porosity with ~100-130 µm pore interconnections and storage moduli between 12.7 and 29.9 kPa. Subcutaneous implantation in SKH1 hairless mice confirmed extensive cellular infiltration, neovascularization within 3 weeks, and only a mild inflammatory reaction. This study was the first to report a hydrogel in which macroporosity is generated concomitantly with injection. Pore size reduction in vivo relative to in vitro conditions, owing to external tissue pressure, is the noted limitation^[51].

Griveau et al. then applied this platform specifically to volumetric muscle loss (VML) repair, tuning stiffness from 12 to 160 kPa by varying the DGL/PEG ratio, and showing that ~300 µm interconnected pores support contractile myotube formation by C2C12 myoblasts and primary human muscle stem cells in vitro. In a large tibialis anterior defect model in rats, injected scaffolds filled the defect, promoted neovascularization, and facilitated aligned muscle fiber regeneration at the injury periphery within 21 days. The cell-adhesive DGL surface eliminated the need for external fibronectin or laminin coatings. Limitations include restricted myotube fusion in deeper pores and the absence of functional contractility measurements; incorporation of growth factors (insulin-like growth factor and fibroblast growth factor) is identified as the key future direction^[73].

Bone regeneration

Bone regeneration requires biomaterials that combine mechanical support with cues that promote stem-cell recruitment, osteogenic differentiation and vascular ingrowth. Dendrimer-based hydrogels offer a modular platform in which matrix stiffness, viscoelasticity, pore architecture and delivery of osteoinductive drugs, genes or bioactive signals can be independently tailored to support bone healing [Figure 4].

Figure 4. Dendrimer-based hydrogel for bone regeneration. Dendritic crosslinkers regulate hydrogel mechanics, porosity and the presentation or release of osteogenic cues. These properties can support stem cell recruitment and differentiation, vascularization and bone formation. YAP: Yes-associated protein; hMSC: human mesenchymal stromal cells; ROS: reactive oxygen species; BMP: bone morphogenetic protein; ALP: alkaline phosphatase; OPN: osteopontin; OCN: osteocalcin; GIT1: G protein-coupled receptor kinase-interacting protein 1.

Valeo et al. reported the first use of G5 DGL as covalent crosslinkers in PEG hydrogels for bone tissue engineering. EDC-mediated amide bonding between DGL terminal amines and dicarboxylic acid-PEG yielded bulk hydrogels with Young’s modulus tunable from 8 to over 30 kPa [15-100 kPa by atomic force microscopy (AFM)] by varying the NH₂/COOH stoichiometric ratio. Dual surface functionalization with RGD and bone morphogenetic protein 2 (BMP-2) biomimetic peptides promoted human mesenchymal stromal cells (hMSC) adhesion and osteogenic differentiation: on stiffer gels (22-30 kPa), a two-fold upregulation of osteopontin was observed after two weeks. No leachable DGL cytotoxicity was detected^[45].

Apartsin et al. extended this work using hyaluronic acid as the matrix component, demonstrating that in DGL G5/hyalurobic acid hydrogels, stiffness and stress relaxation timescales can be independently controlled. Lower-stiffness formulations with higher viscoelastic dissipation drove a 3-fold upregulation of the early osteocyte marker E11/podoplanin, and Yes-associated protein (YAP) nuclear localization was governed more by viscoelastic dissipation than by nominal stiffness thus providing evidence that viscoelastic properties, rather than elastic modulus alone, should be a primary design parameter. The platform enables orthogonal tuning of stiffness and viscous dissipation within a single chemical system^[44].

Roumani et al. showed that DGL/PEG-NHS microspheres (G3 DGL; 22,000 g/mol; 10-1,600 µm diameter; water-in-oil emulsion fabrication) possess intrinsic osteogenic activity without cargo loading. In co-culture with human umbilical vein endothelial cells (HUVEC), the microspheres triggered a 5-fold increase in transforming growth factor β1 (TGF-β1) and a 3-fold increase in Complement C5a, driving a 2.5-fold increase in hMSC recruitment and a 3-fold increase in alkaline phosphatase (ALP) activity and BMP-2 secretion. The injectable microsphere format conforms to irregular defect geometries; elucidation of the precise molecular mechanism underlying the intrinsic osteoinductive effect is identified as a future direction^[74].

Kurian et al. integrated G3 PAMAM dendrimer-functionalized nanoceria into photo-crosslinked GelMA to address oxidative stress in critical-sized bone defects. The nanoparticles provided enzymatic-like ROS scavenging [superoxide dismutase (SOD) activity], protecting MSCs from oxidative stress, while supramolecular interactions between dendrimer amines and GelMA carboxyl groups raised the compressive modulus to ~16.1 kPa. In a rat calvaria defect model at 12 weeks, mature bone formed with high Collagen I, osteopontin (OPN), osteocalcin, and CD31 expression through canonical Wnt pathway activation, with excellent tissue integration and minimal inflammatory response^[75].

Yesbeck et al. confirmed the feasibility of G5 PAMAM/PEGDA hydrogels for sustained cefazolin release in periodontal bone regeneration, retaining ~75% of the antibiotic at 72 h and demonstrating compatibility with co-applied particulate bone allografts. Longer monitoring periods and osteoblast cytotoxicity assessment are identified as priorities^[76]. Attik et al. further applied the effervescent DGL/PEG platform combined with aluminum-free borosilicate glass particles to dental tissue regeneration, achieving ~79% porosity (313 µm average pore size), enhanced calcium deposition, and cell colonization to a depth of 200 µm in human gingival fibroblasts^[77].

Cheng et al. used an injectable thermoresponsive dendronized chitosan/PEGDA hydrogel to deliver G protein-coupled receptor kinase-interacting protein 1 (GIT1) plasmids for gene therapy of bone defects. The dendronized chitosan backbone provided both mechanical stability via hydrophobic interactions and DNA condensation via cationic surface charge, achieving in vivo transfection efficiency more than 3000-fold above lipoplex controls at day 3 and significant improvements in trabecular bone volume at four weeks through Notch-pathway-driven neovascularization^[78].

Shrestha et al. used G2 PAMAM dendrimers to coat porous silicon nanoparticles, enabling loading of three pro-osteogenic miRNAs (miR-29b-3p, miR-101-3p, miR-125b-5p) within a norbornene-modified gelatin/PEG-dithiol visible-light photo-crosslinked hydrogel. Transfection efficiency in the 3D hydrogel reached 97.9%, which is substantially higher and more spatially uniform than 2D conditions, thus driving a 2.7-fold increase in hBMSC mineralization over seven days. The degradation of nanoparticles to orthosilicic acid provided an additional direct stimulus for mineralization. In vivo validation remains to be completed^[79].

Dendrimer-based hydrogels as defined alternatives to Matrigel for organoid culture

3D organoid culture relies heavily on Matrigel and related basement-membrane extracts that contain a complex, variable mixture of basement-membrane proteins, growth factors and other bioactive constituents. Their composition, mechanical properties and growth-factor content may vary both within and between batches, limiting reproducibility and preventing independent control of biochemical and biophysical variables^[97-99].

Dendrimer-based hydrogels offer a potentially valuable route towards chemically defined synthetic ECMs. Their generation-defined molecular architecture, controlled number of terminal groups and modular surface chemistry enable the preparation of reproducible matrices in which network connectivity, ligand density and local multivalency can be rationally designed.

Apartsin et al. designed adaptive PEG bis-dendron hydrogels in which PEG chains of 2, 4, or 10 kDa carry first-generation branching units (dimethyl 5-hydroxyisophthalate) decorated with norbornene groups, covalently crosslinked with 4-arm-PEG-thiol via UV-induced thiol-ene reaction. The bis-dendron topology clusters bioactive cues at branch points, promoting multivalent integrin engagement, a feature unavailable in linear or branched PEG systems. Stiffness was tunable from G' = 30 Pa to 3.3 kPa, stress relaxation half-lives from 20 to 673 s, and pore size from 1.2 to 10.5 µm, all independently addressable through PEG molecular weight and solid content. RGD peptide clusters were immobilized as adhesion cues, and an automated algorithm for assessing peptide cauterization using confocal microscopy data has been proposed. The study establishes a versatile organoid culture platform^[100].

Peptide-dendrimer-reinforced bioinks for 3D bioprinting

Bioprinting of functional tissue models requires hydrogel inks that are simultaneously processable, mechanically stable after deposition, cytocompatible, and capable of sustaining multiple cell types in distinct spatial zones. Zhou et al. developed a dual-network bioink based on lysine-derived peptide dendrimers G1-G3 grafted onto a PEG backbone and end-modified with norbornene groups, crosslinked via thiol-ene photoclick chemistry with cysteamine-modified hyaluronic acid and DTT under 405 nm visible light. Storage modulus scaled with dendrimer generation, reaching ~6.4 kPa for G3, and HC-PDN showed a significant reduction in ROS accumulation compared to standard hyaluronic acid methacrylate bioinks. Used as a support bath for 3D embedded bioprinting of heterogeneous hepatic models co-encapsulating HepG2-C3A hepatocytes, LX-2 stellate cells, and EA.hy.926 endothelial cells, the system reproduced functional endothelium barrier properties, glycogen storage, and albumin and urea secretion. A key design advantage is that the fully degradable network offers a route to future in vivo translation; the main limitation is the mechanical weakness of standard natural bioinks that the dendronized system overcomes, widening the biofabrication window^[53].

Self-immolative dendron hydrogels

A fundamental limitation of diffusion-controlled hydrogel release is that payload liberation continues even when the therapeutic need is absent. Self-immolative architectures, in which a single stimulus triggers complete network disassembly via a cascade fragmentation mechanism, offer a conceptually distinct solution.

Gill et al. reported the first self-immolative dendron hydrogels, in which G1 and G2 polycarbamate dendrons bearing a photocleavable o-nitrobenzyl carbamate trigger at their focal point and alkyne groups on their periphery were covalently crosslinked with 4-arm-PEG-azide via CuAAC. UV irradiation at 365 nm cleaved the focal-point trigger, initiating the “one trigger, many bonds” cascade that dismantled the entire network: G1 gels degraded more than 40% within one day of irradiation, while G2 gels were slower (18%) owing to higher crosslinking density. Gel content exceeded 88%, G2 moduli reached 144 kPa, and no cytotoxic leachable species were detected in C2C12 myoblast cultures. The principal limitations are the slow complete fragmentation timescale (10-18 days) and restricted UV penetration in thick bulk samples, which together constrain use to near-surface or thin-geometry applications^[101].

Dynamic and supramolecular dendritic hydrogels

Beyond covalently crosslinked networks, dendritic building blocks enable hydrogel formation through reversible covalent and non-covalent interactions, including hydrogen bonding, electrostatic association, dynamic imine or disulfide linkages, etc. Because dendrimers present multiple interacting groups within a confined, generation-defined architecture, they can amplify weak molecular interactions into stable three-dimensional networks while retaining reversibility at the individual junction level. This combination can impart shear-thinning, self-healing, injectable and stimulus-responsive behavior that is difficult to achieve using conventional linear polymers alone. The following examples illustrate how dendritic topology has been exploited to create self-healing, physically assembled, chiral and stimuli-responsive hydrogel networks for biomedical and bioinspired applications.

Li et al. built a self-healing hydrogel from a thiol-rich glutamic acid-cysteine dendrimer and oxidized sodium alginate, crosslinked through dual dynamic linkages: Schiff base formation between dendrimer amines and alginate aldehydes (pH-responsive), and disulfide bond formation between dendrimer thiols (redox-responsive via GSH). The combination of these two reversible chemistries provided autonomous self-healing and pH/GSH dual-stimuli-triggered doxorubicin release: 76% of DOX was liberated at pH 5.5 with 10 mM GSH, matching the tumor microenvironment, while release was substantially suppressed at physiological conditions. Water retention capacity reached 25 times the hydrogel's original mass. Cell viability in normal L929 fibroblasts remained high while HepG-2 hepatocellular carcinoma cells showed comparable cytotoxicity to free DOX. The multi-dynamic crosslinking approach, which confers structural robustness alongside stimuli-responsiveness, is the platform’s defining conceptual contribution^[102].

Apartsin et al. synthesized cyclotriphosphazene-core phosphorus dendrimers G1-G3 bearing peripheral trimethylammonium or pyridinium acetohydrazone groups. These polycationic dendrimers self-assembled into physical hydrogels through hydrogen bonding between surface hydrazone groups upon incubation at 65 °C in the presence of biocompatible additives (glucose, glycine, PEG), with gelation kinetics and gel rigidity depending on dendrimer generation, cation type, and biocompatible additive. Owing to their strong cationic surface charge, the hydrogels efficiently bound a model fluorescein-labeled oligonucleotide, achieving loading capacities of 1.5-3 µmol/g depending on dendrimer type and additive, but cargo release studied across pH 4.5-7.0 was slow and pH-dependent (higher below pH 6). The authors conclude that these biocompatible-additive-based phosphorus dendrimer hydrogels represent a novel, well-characterized nanomaterial platform for nucleic acid loading, and suggest that reducing dendrimer surface charge density could improve control over cargo release kinetics for future drug- or gene-delivery applications^[103].

These authors have also developed another hydrogel platform using phosphorus dendrimers. They obtained neutral, biocompatible agarose hydrogels impregnated with polyelectrolyte complexes (dendriplexes) formed between anticancer Mcl-1 siRNA and polycationic G3 phosphorus dendrimers bearing piperidinium, trimethylammonium acetohydrazone, or pyridinium acetohydrazone peripheral groups. These dendrimers and dendriplexes have been shown to possess anti-tumor activity^[104,105]. Dendriplexes were uniformly round, roughly 100 nm particles regardless of dendrimer composition, and they were embedded into 2% agarose hydrogels. Release kinetics from the hydrogels depended strongly on dendrimer surface chemistry: complexes of siRNA with acetohydrazone-terminated dendriplexes were retained in a hydrogel due to hydrogen bonding between the hydrazone moieties and the agarose scaffold. By mixing dendrimers in different ratios, the authors demonstrated that the dendriplexes release rate can be finely tuned to achieve programmed, sustained local delivery of therapeutic nucleic acids for applications such as tumor treatment, wound healing, or tissue engineering as the hydrogel bioresorbs over time^[106].

Phan et al. used asymmetric polyglycerol dendrimers G1-G3 as multi-functional initiators for N-carboxyanhydride ring-opening polymerization of lysine to create star-shaped poly(L-lysine) architectures with 6, 12, and 24 arms, whose side chains were subsequently grafted with indole or phenyl groups. Gelation occurred through non-covalent hydrogen bonding, π-π stacking, and hydrophobic interactions among the grafted moieties, producing shear-thinning, rapidly recovering physical networks. The 24-armed indole-grafted variant exhibited the strongest mechanics and the lowest critical gelation concentration (2.9 wt%), with polypeptide chains adopting β-sheet/β-turn conformations (50%-60%) that drove network formation. The key design insight is that asymmetric topology (more arms, greater steric diversity) amplifies the gelation tendency^[107].

The introduction of chirality and helical order into hydrogel matrices opens pathways toward chiral recognition, asymmetric catalysis, and biomimetic scaffolds that replicate the structural anisotropy of native cartilage and muscle. Two studies establish the principles using dendronized polymer systems. Mei et al. reported that G1 dendronized amphiphiles - three-fold dendritic oligoethylene glycol units bridged by a phenylalanine-glycine dipeptide and terminating in diacetylene groups - self-assembled in water into thermoresponsive helical fibers whose supramolecular chirality was controllable by stirring direction (vortex-dependent chirality). UV irradiation at 254 nm triggered topochemical polymerization of the diacetylene segments, covalently locking the helical conformation and converting the physical gel into a robust material: storage modulus rose from ~20 Pa to >10 kPa post-polymerization. The combination of programmable supramolecular assembly and covalent fixation enables hierarchical structural organization. A limitation is the low mechanical strength of the prefixation network^[108].

Shen et al. extended the principle to helical poly(phenylacetylene) copolymers carrying dendritic oligoethylene glycol pendants, crosslinked by dynamic covalent arylhydrazone linkages. Gelation temperature determined network architecture: room-temperature gelation produced homogeneous gels, above-cloud-point gelation yielded heterogeneous networks, and cryo-gelation at -20°C via ice-templating generated macroporous lamellar structures with G' reaching 30 kPa. The lamellar gels exhibited sponge-like compressive behavior: extruding 80% of their water under load and recovering to 90% strain over 50 fatigue cycles. This feature positions them as synthetic mimetics of cartilage or muscle. Crucially, chirality was fixed and stabilized after gelation, preventing the dynamic helical inversion seen in precursor solutions. Precise temperature control during fabrication is the process constraint^[109].