The limitations of current diagnostic technology mean that some diseases can only be detected when at a very advanced stage. Nanodiagnostics, defined as the use of nanotechnology for clinical diagnostic purposes [10,11], was developed to meet the demand for increased sensitivity in clinical diagnoses and earlier disease detection.

The application of micro and nanobiotechnology in medical diagnostics can be subdivided into two broad categories: In vitro diagnostic devices and in vivo imaging. Research in this field is highly multi-disciplinary and there are close relationships among diagnostics, drug release and regenerative medicine, which are described in the following sections.

One of the most important nanotechnology applications developed over the past decade have been nanovehicles, nanoscale compounds used as a therapeutic tool and designed to specifically accumulate in the sites of the body where they are needed in order to improve pharmacotherapeutic outcomes. The main objective of this application is to increase therapeutic effectiveness while obtaining lower toxicity rates. Hence, nanodrugs and nanodiagnostics have been developed to increase bioavailability profiles, enabling the administration of lower doses and thereby minimizing the adverse reactions found with conventional drugs in clinical practices and increasing the quality of patient health [49]. Table 2 compiles some drugs using nanocarriers and their route of administration.

In the field of cancer therapy there are a lot of clinical applications based on nanotechnologies, with a major development in drug delivery systems. The reason for the rise in nanotechnology applications in medicine is the prospect of improving effectiveness by the biological targeting of drugs in current clinical use [50]. In cancer treatments, nanoparticles are usually administered by intravenous injection, travelling in the blood stream and passing through biological barriers (cell membranes) of the organism in order to reach and activate their molecular targets [51]. One of the main objectives of nanotechnology is overcome the shortcomings of classical chemotherapy, including the multiple drug resistance mechanisms that make this treatment ineffective in a high percentage of cancer cases. The other problem of conventional anticancer therapies is the non-specific action of the drugs, leading them to damage both tumor and non-tumor cells in a state of division.

Nanoparticles can overcome the side effects of conventional therapies by the following means: (1) sustaining drug release over time; (2) so-called “passive enhanced permeability”, targeting the effect to tumor tissue; (3) targeting the cell surface with the use of ligands related to endosomal uptake and membrane disruption; (4) permitting release of the drug in the cell cytoplasm; and (5) protecting the drug from enzymatic degradation [52,53]. The main goals of drug delivery design are: (i) to decrease the side effects of conventional therapy by decreasing drug concentration in normal tissues; (ii) to enhance the pharmacokinetics and pharmacodynamics profiles; (iii) to allow intravenous drug administration by increasing drug solubility; (iv) to minimise drug loss in transit and maximize drug concentration in the tumor; (v) to improve drug stability by avoiding drug degradation; (vi) to achieve optimal cellular uptake and intracellular delivery; and (vii) to ensure biocompatibility and biodegradability [54].

Alternative methods have been developed to increase the effectiveness of drug delivery using the passive or active targeting capacities of nanovehicles. The passive targeting form of drug delivery consists of transporting nanoparticles through leaky tumor capillary fenestrations within the tumor mass to reach cells by convection or passive diffusion. Convection is related to the movement of molecules through organic fluids and is the predominant transport mode for a high percentage of molecules across large pores. However, compounds with a low molecular weight (e.g., oxygen) are most frequently transported by diffusion, in which molecules cross the cell membrane along a concentration gradient, with no energy cost to the cell. In fact, convection through the tumor mass is poor, due to interstitial hypertension; therefore, diffusion is the main type of drug transport used, accumulating nanoparticles with drug by the so-called Enhanced Permeability and Retention (EPR) effect. Nanoparticles are able to achieve an optimal EPR effect if they can evade the immune response, and they remain highly stable in the blood stream until reaching the tumor. The EPR effect is a physiological process based on the capacity of long-circulating nanoparticles to penetrate through the leaky tumor-formed vasculature and degrade within the tumor, releasing the drug and achieving a local concentration in solid tumors that is several-fold higher than that obtained with free drugs [55].

Very high local concentrations of drug-loaded nanoparticles have been obtained within tumors, from 10- to 50-fold higher in comparison to normal tissues in a time period of 1–2 days. The achievement of these drug concentrations in the tumor requires nanoparticles to possess the following characteristics: (a) nanoparticle size between 10 and 100 nm; (b) a neutral or anionic nanoparticle surface charge to prevent elimination by the kidneys; and (c) the ability to avoid opsonization and phagocytosis, which destroy foreign material via the reticuloendothelial system [54,56].

Active targeting using nanoparticles as the delivery system allows a specific area of the body to be targeted, avoiding one of the drawbacks of current chemotherapy, i.e., toxic effects in non-malignant organs [57]. Studies are being carried out on the attachment of targeting ligands on the nanoparticle surface, enabling specific binding of the nanoparticle to receptors on the tumor cell surface. Ligands that bind to specific overexpressed receptors are selected. The types of ligand used include antibodies, antibody fragments or non-antibody (peptidic) ligands. Over the past few years, considerable interest has developed in the numerous antigens present on tumor cells. For instance, HER2 receptor has been proposed as a therapeutic target. HER2 gene, also known as c-erbB2 and neu, encodes a 185-kDa transmembrane glycoprotein receptor that belongs to the ErbB family of growth factor receptors with intrinsic tyrosine kinase activity, whose members exist in homodimer and heterodimer form when activated [58]. Trastuzumab is a humanized antibody designed to specifically recognize the HER-2 receptor and was approved by the FDA in 1998 for the treatment of metastatic breast cancer. Different studies have shown that normal cells can express moderate amounts of HER2 target antigen, while it is overexpressed in tumors in certain patients, and this difference between healthy tissues and tumors allows the effective use of this antibody in patients [59].

Fibroblast growth factor receptors (FGFRs) have also become potential targets for drug delivery and cancer therapy. Fibroblast growth factors (FGFs) are small peptide growth factors that play an important role in tumor growth and angiogenesis because of their high affinity to heparin. FGFRs are upregulated versus normal tissues in numerous tumor cells and tumor neovasculature in situ [60]. One candidate as a targeting ligand for tumor cells is the peptide KRTGQYKLC (bFGFp), which could interact with FGFR1 by binding to bFGF. The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase over-expressed on many human cancer cells surface, making it a target for anticancer drug delivery. Liposomes targeting this receptor promoted the effective intracellular delivery of doxorubicin to tumor cells, yielding superior anti-tumor effects in different in vivo assays. In previous studies, the peptide GE11 was identified as a novel ligand with high affinity towards EGFR and proved effective to mediate targeted liposome delivery to EGFR-positive tumors in vivo [61]. Investigations are ongoing into drug delivery systems based on nanoparticles with different geometry, compositions and surface modifications (Figure 2). They are providing researchers with an enormous collection of nanoparticles with promising applications [62].

Tissue engineering brings together principles and innovations from engineering and the life sciences for the improvement, repair or replacement of tissue/organ function. Since its inception, this multidisciplinary field has been governed by the generic concept of combining cell, scaffold (artificial extracellular matrix) and bioreactor technologies in the design and fabrication of neo-tissues/organs [73]. Every tissue or organ in our body is composed of parenchymal cells (functional cells) and mesenchymal cells (support cells) contained within an extracellular matrix to form a microenvironment, and these microenvironments collectively form our tissues and organs. In terms of the development and maintenance of tissues and organs, our body is the “bioreactor”, exposing the microenvironment of the cell and extracellular matrix to biomechanical forces and biochemical signals. The ultimate goal is to enable the body (cellular components) to heal itself by introducing a tissue engineered scaffold that the body recognizes as “self” and uses to regenerate “neo-native” functional tissues [74]. Furthermore, the demand for organs for transplantation far exceeds the supply, and the construction of organs by regenerative therapy has been presented as a promising option to address this deficit. Nanotechnology has the potential to provide instruments that can accelerate progress in the engineering of organs [75]. Achievement of the more ambitious goals of regenerative medicine requires control over the underlying nanostructures of the cell and extracellular matrix. Cells, typically microns in diameter, are composed of numerous nanosized components that all work together to create a highly organized, self-regulating machine. Cell-based therapies, especially those based on stem cells, have generated considerable excitement in the media and scientific communities and are among the most promising and active areas of research in regenerative medicine [76]. The pace of research could be accelerated by the creation of multi-functional tools to improve the monitoring and modification of cell behavior. While nanomedicine is primarily focused on cancer-related research, the application of nanotechnology has considerable potential in cell-based therapies for regenerative medicine, e.g., in localizing, recruiting and labeling stem cells to begin the regeneration process [75].