## 4 Antibacterial Nanotheranostics
### Theranostic Antibacterial Star-Shaped Polymers  
The synthesis of star-shaped polymers is an increasingly important area in diagnosis and polymer therapeutics (e.g., drug delivery, antibacterial, and anti-biofilm agents) because of their featured structural (physical and chemical) properties, encapsulation capabilities (because of their 3D structure), functionalities (internal and peripheral), and heightened stimuli-responsiveness [211]. Star polymers can be classified into two types: (i) regular or symmetric star polymers that possess identical arm segments; and (ii) mikotaorm star polymers, which are also defined as asymmetric star polymers or heteroarm star polymers, possessing diverse chemical structures, topologies, molecular weights, and functional groups. On the one hand, such heterogeneity of mikotaorm star polymers provides the potential to synthesize novel morphological nanostructures and self-assemblies in aqueous media, which is promising for biomedical applications (i.e., drug delivery). On the other hand, the main challenge facing mikotaorm star polymer synthesis is the complicated process to prepare architectures with various precisely designed arms [211; 212]. As far as antibacterial properties are intended, the much denser functionalities of star polymers excel in the antibacterial functionalized star polymers over linear polymers' antibacterial effects [211]. The combinations of properties of star polymers provide means for their efficient use for diagnosis in different forms, including fluorescent probes, contrast agents, and in vitro diagnostics [211]. [PERSON] et al. [213] have shown the thermo-responsive phase transitions of star conjugated copolymers (with different poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) chain lengths prepared from the hyperbranched conjugated polymer (HCP)) with adjustable lower critical solution temperature (LCST) according to the pH of the copolymeric solution. By exceeding the LCST, the arms of PDMAEMA were collapsed, and the emission of HCP-star-PDMAEMAs was enhanced, detecting _E. coli_ with high sensitivity. [PERSON] et al. [214] fabricated water-soluble fluorescent Ag nanoclusters (i.e., bioimaging labels) from multiarm star poly(acrylic acid) (PAA), which are characterized by strong binding of the protonated acrylic acid groups with Ag\({}^{+}\). The fluorescence of Ag nanoclusters diminished after 100 min of illumination (i.e., the formation of large Ag NPs). [PERSON] et al. [215] have explored the therapeutic area of star polymers via preparing (in a one-pot approach using amino acid building blocks, N-carboxyanhydrides), a highly functionalized water-soluble and degradable core cross-linked star (CCS) polymers. The therapeutic CCS could release its drug cargo upon degradation. Investigators have recently examined the multimodal antibacterial therapeutic effects of star-shaped peptide polymeric nanoparticles, namely structurally nanoengineered antimicrobial peptide polymers (SNAPPs). SNAPS combatted multidrug-resistant superbugs via the physical disruption of bacterial cell membranes, dysregulation of ion efflux/influx, and induction of apoptotic-like death [216]. [PERSON] et al. [217] identified the antibacterial effects of star-shaped polymers against _S. aureus_ and _E. coli_, retaining their antibacterial properties even after 20 water flush treatments. More therapeutic applications of star polymers have also been reported [218], using star-shaped-brush polymers in electrospinning. The electrospunmicrofibers (100 mg) killed _E. coli_ (99%) within 2 h of contact. [PERSON] et al. [219] have shown that furanone containing the star-shaped PAA (as shown in Figure 5) decreased the viability of _Streptococcus mutans_, which was unchanged after 30 days of aging in water, suggesting its potential application as long-lasting antibacterial cement. Bone repair tissue engineering represents a specific application of biodegradable star polymers due to the ease of tuning the mechanical properties and degradation time of star polymers.