Polymeric nanoparticles are minuscule particles composed of either synthetic or natural polymers, with dimensions ranging from 1 to 1000 nm [[1], [2], [3], [4], [5], [6]]. These nanoparticulate structures are specifically created to enclose pharmaceuticals, genetic material, or substances used for medical imaging. They have several uses in the field of biomedicine, including delivering medications, facilitating imaging procedures, and aiding in diagnostics [[7], [8], [9], [10], [11], [12], [13], [14]]. Biocompatible materials may be used to create polymeric nanoparticles, which can then be delivered in vivo without the danger of immune reactions or toxicity [15]. Some examples of commonly used biocompatible polymers include poly(lactic-co-glycolic acid) (PLGA), polyethylene glycol (PEG), chitosan, and gelatin [16]. Further, polymeric nanoparticles provide a flexible platform for enclosing both hydrophobic and hydrophilic drugs inside their polymeric matrix [17]. This process of encapsulation provides a protective barrier for the medicine, shielding it from degradation and enhancing its solubility, stability, and bioavailability [18]. By manipulating the polymer composition, nanoparticle size, and surface features, one may customize and regulate the release of pharmaceuticals from polymeric nanoparticles [19]. The regulated release kinetics of this mechanism allow for the gradual and prolonged release of drugs, resulting in a decrease in the frequency of administration and a reduction in the occurrence of adverse effects [20]. Moreover, the process of attaching targeting ligands to polymeric nanoparticles enables the precise delivery of drugs to desired tissues, such as tumors. Notably, precision distribution improves medication concentration at the intended location while minimizing overall exposure and unintended side effects [21]. Further, polymeric nanoparticles provide protection for medications or genetic material that is enclosed inside them, preventing enzymatic breakdown and clearance by the immune system [22]. This leads to enhanced stability and a longer duration of circulation. Polymeric nanoparticles can include imaging contrast agents, such as fluorescent dyes, magnetic nanoparticles, or radioactive tracers. This allows for the non-invasive imaging of tissues or disease biomarkers [23]. In addition, they may be modified with targeting agents to enable specialized molecular imaging applications. Notably, theranostic platforms are created by certain polymeric nanoparticles, which combine diagnostic and therapeutic capabilities inside a single nanoparticle system. They provide continuous tracking of drug distribution, pharmacokinetics, and treatment response, aiding in the customization of therapeutic choices [24]. Biodegradable polymeric nanoparticles degrade into harmless substances inside the body, making it easier for them to be eliminated and lowering the potential for long-term buildup or toxicity [[25], [29], [30]].

Polymeric nanoparticles have gained considerable interest in the realm of breast cancer therapy because of their capacity for precise drug administration, improved therapeutic effectiveness, and fewer adverse reactions [1,[26], [27], [28], [29], [30]]. (Fig. 1, Table 1). They can be designed to selectively bind to certain receptors, such as HER2 receptors, that are overly present on breast cancer cells [[31], [32], [33], [34], [35], [36], [37], [38], [39]]. This focused delivery strategy improves the concentration of drugs at the specific tumor location while reducing the potential harm to the rest of the body [21,[40], [41], [42], [43], [44], [45], [46]]. Current studies have concentrated on the creation of versatile polymeric nanoparticles that can transport numerous therapeutic substances at the same time from a single delivery vehicle [[47], [48], [49], [50], [51], [52], [53], [54]]. This strategy enables the use of combination therapy, which can improve treatment outcomes and overcome drug resistance by leveraging synergistic effects between diverse medications [[28], [39]]. This enables the development of tailored treatment approaches and the tracking of treatment effectiveness. Furthermore polymeric nanoparticles can be engineered to respond to specific stimuli in the tumor microenvironment, like pH, temperature, or enzyme activity and release drugs as per the stimuli [[54], [55]]. This drug release patterns allows for precise and continuous delivery of drugs specifically at the tumor's location, which improves treatment effectiveness and minimizes any unintended effects on other parts of the body [56]. Notably, certain polymeric nanoparticles can regulate the immune response in the tumor microenvironment. This helps stimulate the body's immune system to fight against the tumor and improves the effectiveness of immunotherapy in treating breast cancer [57]. Formulation scientist has investigated the application of polymeric nanoparticles as a method to overcome drug resistance in breast cancer. At present, they are using nanoparticles to enclose drugs and target specific cellular pathways that contribute to drug resistance [58]. The goal is to increase the effectiveness of chemotherapy and other treatments on cancer cells. Nevertheless, several polymeric nanoparticle formulations have progressed to clinical trials for breast cancer treatment [59]. These studies aimed to evaluate the safety, effectiveness, and pharmacokinetics of polymeric nanoparticle formulations in breast cancer patients, thereby advancing the use of this technology in clinical practice and have yielded the favorable results [1]. Micro environmental variations in tumors include pH levels, the presence of reactive oxidative species, low oxygen levels (hypoxia), the quantity of glutathione, and the overexpression of enzymes like hyaluronidase and metalloproteinase [60]. The variations in the microenvironment may be exploited to guarantee the targeted release of the medication, thereby minimizing the overall exposure to chemotherapeutic agents throughout the body. The outer layer of polymeric nanoparticles is hydrophilic, which stops non-specific absorption and increases the length of circulation inside the body. The small size of the polymeric nanoparticles enables these nanoparticles to easily migrate to the tumor site in response to a particular stimulation [61]. To create polymeric nanoparticles, researchers have studied various polymers that attract water (hydrophilic) and repel it (hydrophobic). Hydrophilic polymers, such as polyethylene glycol, polysaccharides, and poly[N-(2-hydroxypropyl) methacrylamide] (pHPMA), have the benefit of being non-toxic and biocompatible [2,19]. Consequently, this enables them to flow through the bloodstream, selectively interact with certain tissues, and diminish inflammatory reactions. On the other hand, polyethylene glycol can't be broken down by living things, but polysaccharides can at high temperatures, and making pHPMA is a complicated process [62,63]. Polyacrylic acid and polyglutamic acid exhibit pH sensitivity, biodegradability, and biocompatibility. However, they also suffer from drawbacks such as inadequate mechanical stability and high manufacturing costs [64]. Also, different types of polyethylene glycol and β-cyclodextrin have been used to make polymeric nanoparticles that target tissues that have a lot of reactive oxidative species [65]. Another example is the use of enzyme-responsive nanoparticles made up of polyethylene glycol and glucose conjugates, as well as polyamidoamine dendrimers, which exhibit a reaction in response to the excessive presence of metalloproteinases [66,67]. Notably, there are thermosensitive nanoparticles that are made from different polymers, like poly(N-isopropyl acrylamide), and they release drugs at the tumor site when the temperature changes around the tumor.

This review article will provide an in-depth examination of the many types of polymeric materials used in the manufacturing of innovative polymeric nanoparticles for targeted medication delivery in breast cancer treatment (Fig. 1). Additionally, it evaluates both the favorable and unfavourable characteristics of these drug delivery vehicles, including the results of clinical trials that have investigated the efficacy of these vehicles.