Bacterial infections are one of the major threats to human health due to the raising crisis of antibiotic resistance. Herein, second generation antibacterial heterofunctional dendrimers based on 2,2-bis(methylol)propionic acid were synthesized. The dendrimers possessed six alkenes and 12 ammonium end-groups per molecule and were used to fabricate antibacterial hydrogels together with dithiol-functional polyethylene glycol (mol wt of 2, 6 and 10 kDa) as crosslinkers via thiol-ene chemistry. The network formation can be completed within 10 s upon UV-irradiation as determined by the stabilization of the storage modulus in a rheometer. The hydrogels swelled in aqueous media and could be functionalized with the N-hydroxysuccinimide ester of the dye disperse red 13, which allowed for visually studying the degradation of the hydrogels through the hydrolysis of the ester bonds of the dendritic component. The maximum swelling ratio of the gels was recorded within 4–8 h and the swelling ratios increased with higher molecular weight of the polyethylene glycol crosslinker. The gel formed with 10 kDa polyethylene glycol crosslinker showed the highest swelling ratio of 40 and good mechanical properties, with a storage modulus of 8 kPa. In addition, the hydrogels exhibited good biocompatibility towards both human fibroblasts and mouse monocytes, while showing strong antibacterial activity against both gram-positive and gram-negative bacteria.

Cationic dendrimers are intriguing materials that can be used as antibacterial materials; however, they display significant cytotoxicity towards diverse cell lines at high generations or high doses, which limits their applications in biomedical fields. In order to decrease the cytotoxicity, a series of biocompatible hybrid hydrogels based on cationic dendrimers and carboxylated cellulose nanofibrils were easily synthesized by non-covalent self-assembly under physiological conditions without external stimuli. The cationic dendrimers from generation 2 (G2) to generation 4 (G4) based on trimethylolpronane (TMP) and 2,2-bis (methylol)propionic acid (bis-MPA) were synthesized through fluoride promoted esterification chemistry (FPE chemistry). FTIR was used to show the presence of the cationic dendrimers within the hybrid hydrogels, and the distribution of the cationic dendrimers was even verified using elemental analysis of nitrogen content. The hybrid hydrogels formed from G3 and G4 showed 100% killing efficiency towards Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) with bacterial concentrations ranging from 10(5) CFU/mL to 10(7) CFU/mL. Remarkably, the hybrid hydrogels also showed good biocompatibility most probably due to the incorporation of the biocompatible CNFs that slowed down the release of the cationic dendrimers from the hybrid hydrogels, hence showing great promise as an antibacterial material for biomedical applications.

Microbial infections caused by antibiotic-resistant bacteria are a major threat to humans, associated with a high mortality and for the society increased economic burden. To address this, a series of cationic hydrogels based on amino-functional hyperbranched dendritic−linear−dendritic copolymers (HBDLDs) were formed easily within 1 min through interactions between the amino-terminated HBDLDs and di(N-hydroxysuccinimide ester) functionalized polyethylene glycol (PEG). The hydrogels exhibited excellent inherent antimicrobial activity towards a wide range of Gram-positive and Gram-negative clinical bacteria including drug-resistant strains, isolated from wounds. In vitro cell infection assays showed that the hydrogels were able to significantly reduce cell infections caused by different strains, with the highest killing efficacy of 96% towards S. aureus. The hydrogels also inhibited the initiation of E. coli biofilm formation. Remarkably, the hydrogels induced the expression of the antimicrobial peptides, RNase 7 and psoriasin, in keratinocytes (HaCaT) which suggests that the hydrogels are likely able to promote host-mediated bacterial killing. The expression of pro-inflammatory cytokine IL-1β, reactive nitrogen species (NO) and mitochondrial reactive oxygen species (ROS) in S. aureus-infected HaCaT cells were reduced after the treatment with the hydrogels. The hydrogels degraded within 24 h, showing great promise for treating skin infections and reducing inflammation.

Biocompatible and degradable dual-delivery gel systems based on hyperbrancheddendritic−linear−dendritic copolymers (HBDLDs) is herein conceptualizedand accomplished via thiol-ene click chemistry. The elasticity of thehydrogels is tunable by varying the lengths of PEG (2, 6, 10 kDa) or the dryweight percentages (20, 30, 40 wt%), and are found to be between 2–14.7 kPa,comparable to human skin. The co-delivery of antibiotics is achieved, wherethe hydrophilic drug novobiocin sodium salt (NB) is entrapped within thehydrophilic hydrogel, while the hydrophobic antibiotic ciprofloxacin (CIP) isencapsulated within the dendritic nanogels (DNGs) with hydrophobic cores(DNGs-CIP). The DNGs-CIP with drug loading capacity of 2.83 wt% are thenphysically entrapped within the hybrid hydrogels through UV curing. Thehybrid hydrogels enabled the quick release of NB and prolonged released ofCIP. In vitro cell infection assays showed that the antibiotic-loaded hybridhydrogels are able to treat bacterial infections with significant bacterialreduction. Hybrid hydrogel band aids are fabricated and exhibited betterantibacterial activity compared with commercial antimicrobial band aids.Remarkably, most hydrogels and hybrid hydrogels showed enhanced humandermal cell proliferation and could be degraded into non-toxic constituents,showing great promise as wound dressing materials.

Nanomaterials, with various shapes and specific physicochemical properties, have attracted a lot of interest in the biomedical fields. Fluorescent silicon nanoparticles (SiNPs) have shown promise as immunofluorescent cellular imaging agents. In this study, SiNPs were synthesized to explore their potential as bacterial imaging agents. Silicon nanoparticles with amino groups on the surface were prepared using microwave-assisted synthesis method using trisodium citrate as the reducing agent. The obtained SiNPs were characterized using dynamic light scattering (DLS), UV−vis absorption spectroscopy and fluorescence spectrophotometer. And SiNPs were used to study their interactions with both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). The interactions between the prepared SiNPs and bacteria were monitored by the fluorescence microscope, and SiNPs showed a strong interaction with S. aureus. SEM was used to study the morphological changes of S. aureus, and we found that the cell membranes of S. aureus became damaged after the interaction with SiNPs. The amino groups on the surfaces of SiNPs could also be functionalized with other functional groups for other applications.