Gelatin nanoparticles: a potential candidate for medical applications

1.1 Gelatin and gelatin nanoparticles

Gelatin is a natural versatile biopolymer; it has several important applications due to its low cost, easy availability, biodegradable and biocompatible nature as well as the presence of abundant active groups [10]. Gelatin is poly-ampholyte in nature because it contains both cationic and anionic groups. Gelatin polypeptide is composed of repeating triplets of alanine, glycine and proline residues, responsible for typical triple helical structure of gelatin [11]. Gelatin is a protein obtained from the hydrolysis of collagen. The type of gelatin obtained (type A or type B) is governed by the process of collagen hydrolysis (i.e. acidic and basic hydrolysis, respectively). Types A and B have different IEPs [12]. Type A has IEP 7–9 while type B has IEP 4–5. Each type of gelatin has different drug release potential for different kinds of NPs. It is shown that type B gelatine nanoparticles (GNPs) show better potential in terms of drug delivery than type A [13]. Moreover, gelatin type B physically captures DNA molecule, thus increasing the transfection efficiency of the carriers. Commercially available gelatin is a heterogeneous mixture of polypeptides, presented in varying molecular weights in different ranges, e.g. thousand to million Daltons [14].

The GNPs are nontoxic, biodegradable, bioactive, and inexpensive and are very promising in terms of drug delivery and controlled drug release. Different mechanical properties of GNPs like thermal range and swelling behavior are dependent on the amphetatic interactions on gelatin. Different desired GNPs can be prepared by exploiting the physical and chemical properties of gelatin [15], [16]. Gelatin-based materials need to be cross-linked with glutaraldehyde (GA) or other bifunctional cross-linker such as genipin, carbodiimide/N-hydroxysuccinimide, aldehyde groups, and transglutaminase [10] to render insolubility at high temperatures, reduced swelling in water, and hence drug release from NPs [17]. Drug release was suggested to be dependent on the cross-linking density of gelatin [18].

1.2 Preparation of gelatin nanoparticles

The GNPs can be prepared by several different techniques, including desolvation, coacervation-phase separation, emulsification-solvent evaporation, reverse phase microemulsion, and nanoprecipitation. The preparation methods of GNPs have been elaborated in a recently published review article [10]. Briefly, we describe here some of the main methods for the preparation of GNPs.

1.2.5 Nanoprecipitation/solvent displacement method

In this technique water is used as a solvent phase in which gelatin and drug molecules are dissolved. This aqueous phase is then added to ethanol as the nonsolvent phase containing poloxamer as a stabilizer. GNPs are formed on the junction of water and ethanol because of interfacial turbulence generated during solvent displacement [27] and are subsequently cross-linked using GA (schematically shown in Figure 1).

Figure 1:

Schematic illustration of nanoprecipitation technique for the formation of GNPs [28].

1.3 Mechanisms of drug release from GNPs and GNPs clearance

The GNPs should ideally have improved loading capacity in order to deliver desired amount of drug. Drug can be loaded onto GNPs, either by soaking the particles in drug solution after preparation, or by dissolving the drug in the polymer solution before NPs preparation. With regard to drug loading outcomes, various behaviors of loading efficiency were observed for different drugs (given in Table 2).

There are several possible mechanisms of drug release from gelatin (protein) NPs: (a) liberation due to polymer erosion or degradation; (b) self-diffusion through pores; (c) release via surface erosion of the polymer; and (d) pulsed delivery initiated by the application of an oscillating magnetic or sonic field [29]. In most of the drug release pattern, biphasic release is most common, it includes two stages – an initial phase of burst release of immediate discharge surface associated drugs (weakly interacted) from GNPs and then a second phase of covalently bound (tightly bonded) drugs releases in slow diffusion from the matrix, exhibiting prolonged and sustained release [30]. The initial burst release occurs due to weak adsorption of drugs onto NPs surface [31]. The efficacy of drug release is dependent on the size and loading efficiency of the GNPs as well as drug solubility. Smaller particle tends to achieve big burst effect while larger particles show sustained release thoroughly. Apart from the size, density of gelatin cross-linking is also known to have effect on swelling ratio and drug release pattern from the matrix [10]. pH is another factor which contributes to drug release from GNPs. Proteolytic enzymes also accelerates drug release by GNPs, as shown in Figure 2 [28]. The different mechanism of drug release from gelatin NPs is shown schematically in Figure 3. In the case of gelatin nano-spheres, drug is uniformly distributed in the NP matrix and release occurs by diffusion or erosion of the matrix. If diffusion of the drug is faster than matrix degradation, then the mechanism of drug release occurs mainly by diffusion, otherwise it depends upon degradation. Different methods for in vitro drug quantification are also suggested such as: (i) side-by-side diffusion; (ii) equilibrium dialysis technique; (iii) reverse dialysis sac technique; (iv) ultracentrifugation; (v) ultrafiltration; or (vi) centrifugal ultrafiltration technique [32]. Drug release profiles of GNPs can be deployed by manipulating the size, cross-linker density, and IEPs of the particle [33]. Sustained and targeted release of drug from GNPs inside biological fluids can be accomplished by modifying GNPs surface with site-specific ligands, polyethyl glycols coating, and surface cationization with amine derivatives [34]. GNPs are biodegradable and are cleared easily from the body. Hence no hematological toxicity and nephrotoxcity were observed with GNPs [35]. Moreover, the cells adhesion capacity and cytoskeleton organization were unaffected by GNPs, which depicts the nontoxic nature of GNPs [26].

Figure 2:

Model drug (FITC-dextran) release from GNPs after tryptic digestion [28].

Figure 3:

Drug release patterns from gelatin nanoparticles: (A) Simple diffusion of drug particles; (B) Degradation release; (C) Cleavage of the gelatin matrix by proteolytic enzymes.

2.1 Targeting human malignancies with nanoparticles

When tumor cells multiply and reach a size of 2–3 mm, the demand for high nutrition and oxygen in the blood increases. A tumor tissue also exhibits distinctive pathophysiological properties that are different from normal tissues or organs. They have defective and leaky vascular architecture, extensive angiogenesis leading to hyper-vasculature, impaired lymphatic drainage, and overproduction of various permeability mediators. This anatomical defectiveness, along with functional abnormalities, results in extensive leakage of blood plasma components, such as macromolecules, NPs and lipidic particles, into the tumor tissue. The poor lymphatic clearance results macromolecules to retain in the tumor for longer time. This process of enhanced particles movement and their retention there for longer duration is called enhanced permeability and retention (EPR) effect as explained by Maeda et al. [41]. The NPs with long circulatory half-life were suggested to be more suitable as a cargo to deliver encapsulated drugs/genes to the target tumors passively by exploiting the EPR effect of the tumor vasculature. Administration of tumor suppressor genes, e.g. p53 (wt-p53), is the main focus of anti-tumor gene therapies, which can help cell to potentially restore its pro-apoptotic function [42]. Cancer cells have the ability to develop resistance against anticancer drugs similar to that of microbial pathogens. This resistance is more commonly seen in solid tumors [43]. Inside experimental models of human tumors transplanted to nude mice, the efficacy of the conjugated cytostatic drugs such as 5-fluorouracil, paclitaxel [44], and doxorubicin [23] with albumin or GNPs were not only shown to be enhanced significantly in comparison to free drug but also reduced cytotoxicity of these drugs substantially.

Ellagitannins, derived from pomegranate have been claimed to prevent cardiovascular diseases and cancer. Gelatin and pomegranate ellagitannins can bind together and assemble into NPs. Ellagitannins encapsulated in GNPs had decreased apoptotic effects on leukemia cells HL-60 [45]. The GNPs conjugated with biotinylated CD3 specific antibodies showed great specificity in cellular uptake in leukemic T lymphocytes (CD3 expressing) [46]. Among the drugs used for treatment of acute leukemia, the effective one is cytarabine (ara-C), which actually affects replication of DNA [47]. Cross-linked GNPs form a swelling controlled drug release system, which effectively delivers cytarabine via diffusion controlled pathway [13]. Lung cancer kills around 25% of the patients each year, and is one of the major cause of cancer leading to mortality in underdeveloped and developed countries [48]. Non-small cell lung cancer constitutes 75–80% of all lung cancers and is the most frequent tumor found in the elders [49]. Administration of chemotherapeutic drugs directly into the lungs not only increases the drug exposure to lung cancers but also causes cytotoxicity to normal cells. Ligand-targeted nano-particulate system could be very effective in the treatment of the lung cancer. A study suggested that epidermal growth factor-modified gelatin nanoparticles could be administered directly to lungs via inhalation and could improve the therapeutic options in lung cancer therapy [50]. Resveratrol (RSV) is a naturally occurring polyphenolic phytoalexin having valuable effects against many diseases including cancer [51] and inflammatory diseases [52]. The prepared RSV-GNPs were reported to exhibit very rapid and more efficient cellular uptake than free RSV. Free RSV treatment shows less anti-proliferative properties than RSV-GNPs treatment in NCI-H460 cells accompanied with more ROS production, DNA damage apoptotic incidence, least toxic response, more bioavailability, and longer half-life [53]. Similarly, Rubus Coreanus Miquel (black raspberry) is known to have anti-oxidative and anticancer properties [54], [55]. Rubus Coreanus Miquel-GNPs were suggested as amazing transport vehicle to immune cells, which activates immune system by enhancing antibody and cytokine production along with inducing proliferation of immunity-related cells [56]. Similarly, Lu et al., has reported the effectiveness of paclitaxel-loaded GNPs against human RT4 bladder transitional cancer cells. Using paclitaxel-loaded NPs, the concentration of drug in the regions of Ta and T1 tumors (i.e. urothelium and lamina propria tissue layers, respectively) was 2.6 times higher than free drug in solution [44]. Beside this, other anticancer drugs such as cycloheximide [15], cyclosporine-A8 [57], and cytarabine [13] have also been loaded into GNPs for potential anticancer therapy. All these attempts give an insight that NPs prepared from gelatin can promise better to enhance therapeutic index of partially water-soluble drugs.

2.2 Crossing the blood-brain barrier

The blood-brain barrier (BBB) is a complex physiological structure in central nervous system (CNS) that inhibits free diffusion of circulating molecules from the blood into the brain. Because of this strong barrier across the entire CNS majority of the brain disorders remain untreatable. Nanoparticluate system has the ability to overcome this barrier [58]. The drugs administered through intravenous injection can be transported across BBB with the help of NPs drug delivery system more efficiently, especially using soluble protein NPs. Drugs like hexapeptide, dalargin, endorphin, dipeptide, kyotorphin, loperamide, doxorubicin, and tubocurarine could be loaded onto these nano-protein particles. Also protein NPs systems are now well known for efficient delivery of several other drugs, e.g. loperamide [59], temozolomide [60] and doxorubicin [61], which, normally prone resistant to cross the BBB. NPs have the ability to easily flow through capillaries and can penetrate their walls to reach their site of action due to their small size and perfect surface functionalization [62], [63]. A study reported that SynB-PEG-GS NPs can effectively cross BBB and can transport drugs across the membrane. SynB-PEG-GS NPs have suitable size distribution, morphology, and show less cytotoxicity. Moreover, the SynB-PEG-GS NPs cross the BBB more efficiently along with improved endothelial uptake [64] (Figure 4).

Figure 4:

Diagrammatic representation elaborating the gelatin nanoparticles crossing the blood brain barrier, owing to their small size readily move towards brain tissues.

Inactivation via short living, Si-RNAs are the recently discovered advanced technique used in gene silencing. However, this technique lacks the desired penetration of small RNA in to the membrane [65], [66]. GNPs provide an efficient vehicle for delivery of these RNAs to the cell, provide safety against degradation, and also have nontoxic degradation products [67]. NO is viewed as an important therapeutic target. Therapeutic efficacy of iNOSsiRNA/GNPs is reported to be significantly higher and long sustainable, and also show neuroprotective effect, which is not the case when treated with the bare drug [68] (Figure 5).

Figure 5:

NO-SiRNA-GNPs internalization to neuronal cells and their subsequent release of SiRNA and NO after degradation.

2.3 Macrophages targeting; chasing HIV by GNPs

Mannose-PEG modified GNPs have shown increased drug loading and double cellular uptake in contrast to unmodified GNPs. This shows that coupling of mannose with GNPs enhances the cellular uptake of drug to different organs [69]. Coupling of the GNPs with mannose (MN-GNPs) significantly enhances the lung, liver, and lymph nodes uptake of the drugs [70]. These surface-modified NPs can effectively deliver biopharmaceuticals to macrophages during macrophage targeting therapies [71]. Biotinylated peptide nucleic acid is reported to be effectively complexed by the avidin-conjugated GNPs. Avidin-conjugated GNPs were suggested as potential carrier system for biotinylated drug derivatives in antisense therapy particularly for HIV treatment [72]. The surface-modified GNPs using novel ligand 4-sulfated N-acetyl galactosamine (4-SO4GalNAc) assures for targeting resident macrophages specifically [73]. In a recent study macrophage cell-line was shown to exhibit two-fold greater internalization of anti-HIV drug, stavudine conjugated with mannosylated GNPs through macrophage mannose-receptor, far better than unconjugated GNP. Thus mannosylated GNPs could be useful as a carrier system in the treatment of macrophage-mediated intracellular infections [74]. Mannan-coated GNPs were also claimed to efficiently target macrophage with didanosine (an anti-HIV drug), with the help of mannosyl receptor mediated endocytosis [75]. Macrophages represent a key target for HIV in addition to CD4 positive lymphocyte cells (CD4+). Mannan-coated didanosine GNPs are reported to be highly accumulated inside spleen, lymph nodes, and brain in comparison to free didanosine injections [75].

2.4 GNPs as DNA carrier

Nanoparticulate systems hold promising importance among the approaches used to deliver DNA due to their easy preparation, versatility, and protection of plasmid DNA via encapsulation [4]. A good gene delivery system should be stable inside plasma and resist reticulo-endothelial system (RES) uptake in order to get its target, e.g. solid tumor. This is achieved by surface modification of NPs with PEG which inhibit macrophages uptake due to steric repulsion of proteins of complement system [76]. GNPs have been studied by many researchers as boat for gene delivery [77]. Gene expression in mice subsequent to intramuscular injection of DNA-gelatin nanospheres was greater and more prolonged compared to an equal amount of naked DNA or DNA complexed with lipofectamine [78]. Human CFTR-gene has been transported to human tracheal epithelial cells for expression using nanospheres composed of gelatin and DNA [79]. The PEG-modified gelatin NPs were also used in BT/20 human breast cancer cells for intracellular absorption [80]. Surface modification of thiolated GNPs with PEG increases their circulation and retention time inside plasma and tumor [81]. Another study also claimed that PEGylated GNPs were absorbed in sufficient number inside the cells (murine embryo fibroblast cell line) by nonspecific endocytosis, remains in the cytoplasm for longer duration and shows good transfection efficiency [82]. Expression of β-galactosidase was also reported in vivo after transformation with respective reporter plasmid DNA-loaded PEGylated GNPs inside Lewis lung carcinoma (LLC) in mice. The in vitro and in vivo results of this study clearly showed that the long-circulating, biocompatible and biodegradable, DNA-encapsulated PEGylated GNPs efficiently transfects LLC cells [83]. Inside pancreatic cancer, p53 mutations are the most common abnormalities [84], which correlate with progression of cancer, apoptotic halt, and chemo-resistance [85], [86]. The combination of gene/drug treatment shows better therapeutic performance of the delivery system, rather than treatment alone with free drug or gene. Thiolated gelatin loaded wt-p53 plasmid or gemcitabine-based therapy of pancreatic cancer was also reported to cause cell apoptosis leading to over-expression of apoptotic transcription factors, protein apoptotic biomarker expression, and under expression of anti-apoptotic transcription factors [87]. Over-expression of the epidermal growth factor receptor (EGFR) on panc-1 human pancreatic adenocarcinoma cells was also previously documented [88]. Another study showed that EGFR-targeted thiolated GNPs could be used as a treatment option for pancreatic cancer, where it served as safe DNA delivery system for gene therapy [89]. The PEG-modified thiolated GNPs as nano-particulate vector system can efficiently deliver DNA to tumorous tissues, containing high glutathione concentration at the tumor site [69]. Cerebral vasospasm is also well known as a major cause of morbidity and death in patients after subarachnoid haemorrhage. An essential vasodilator gene, calcitonin gene-related peptide (CGRP) is in clinical trials in therapy of vasospasm. An important technique used for vasospasm prevention is the injection of recombinant adenovirus, carrying CGRP gene into the cisterna magna, after subarachnoid hemorrhage in rabbits and dogs [90], [91]. Reduction in vasospasm was reported inside rat model of subarachnoid haemorrhage with the over-expression of CGRP along with other neurological improvements. Therefore, the use of Tat-GS NP mediated CGRP gene delivery is thought to have potential for treatment of cerebral vasospasm after subarachnoid hemorrhage [92] (Figure 6). Other bioactive hybrid compounds like siloxane conjugated with gelatin were also reported as efficient and safe novel nonviral vector for gene delivery [93], [94].

Figure 6:

Gelatin nanoparticles carry CGRP to hemorrhaged vessels. The expression of CGRP inside the vessel eventually relaxes vasospasm.

2.5 Gelatin-CpG nucleotide complexes as DNA vaccines

Immune system of a vertebrate recognizes foreign DNA by specific nucleotide sequences carried by the invader DNA. Especially, CpG islands, which are CpG-rich regions, are particularly detected as danger signal. Inside animal models, the innate immune response amplification is achieved by using synthetic oligodeoxy-nucleotides containing CpG motifs (CpG-ODN), complimentary to Toll-like receptor [95]. Clinical studies elaborated that CpG-ODN have a strong potential as adjuvant in antiviral vaccination, treatment of asthma, allergic diseases, and cancer [95]. Inside murine system, CpG-ODN show better uptake and immune-stimulation when administered in the form of CpG-ODN-loaded cationized gelatin NPs (CpG-GNPs) both in vivo and in vitro. Increased production of cytokines like IFN-α in primary human plasmacytoid dendritic cells (DCs), after transformation with cat-ionized GNPs of CpG-ODN suggest that CpG-ODN can be delivered to the cell with the help of GNPs to activate and boost-up the immune system. The same perception was suggested to act better as novel adjuvant for antitumoral and antiviral vaccines [96]. GNPs have been used in immunotherapy, to target lymph nodes with CpG-oligonucleotides to activate antitumoral immunity [96]. Powerful immune-stimulation was reported due to cationized GNPs CpG-oligonucleotides complex [96].

2.6 Management of infectious tuberculosis via GNPs

Tuberculosis (TB), a bacterial infectious disease is also included as a major killer worldwide, infecting both youth and adults. TB stands second to acquired immunodeficiency syndrome (AIDS) in terms of mortality. Although complete treatment of TB is possible, but nowadays a serious negative set back in chemotherapy is rising, due to emergence of multiple drug therapy, longer duration of treatment, and quality of available drugs to common folk [97].

New strategies like nanotechnology are in dire need to enhance drug availability and control release to the infected cells for an extended period of time with the help of an efficient delivery system [98]. The cytotoxicity studies revealed that rifampicin (RIF)-loaded GNPs do much less harm to normal cells than free drug. RIF-GNPs conjugates have been found to accumulate highly in various organs in vivo, while plain RIF lack the desired biodistribution profile. Inside TB-infected mice, administration of RIF-GNPs resulted in reduced bacterial counts in the lungs and spleen. Unlike plain drug, the NPs drug delivery system possibly improves pharmacokinetics of drugs along with sustained plasma level, by increasing mean residence time and area under the curve. GNPs is an attractive option for efficient management of tuberculosis not only because it is expected to have great potential for increasing drug targetability, but also due to reduced dose requirement, which ultimately minimizes side effects associated with multiple use of the drug [99].

2.7 GNPs targeting Leishmaniasis

Leishmaniasis is a microbial disease, caused by intracellular protozoan parasite Leishmania donovanianLeishmania infantum (Leishmania infantum chagasi). In leishmaniasis, the parasite invades and uses macrophages and RES for their replication. Leishmaniasis can be cutaneous or visceral, but the visceral becomes deadly if not treated properly. Macrophages readily engulf NPs and this makes the NPs a more promising carrier for drug delivery to target diseased tissues especially where macrophages are involved [100]. Amphoteracin-B (AmB) is a potent polyene antibiotic, used for the treatment of visceral leishmaniasis (VL) and some other systemic fungal infections like candidiasis. AmB is highly potent against VL which is a protozoan infection disseminated by the parasite called Leishmania donovani, transmitted by sand-fly bite. In VL the macrophages of the lymph node, spleen, liver, and bone marrow are preferentially parasitized and support intracellular replication of the parasite [101]. A study indicated that surface functionalized GNPs (f-GNPs) could be a promising carrier for specific delivery of AmB to macrophages for effective treatment of VL. Furthermore, f-GNPs show reduced cytotoxicity and increased uptake by macrophages [71]. A recent study was conducted to monitor the 1, 2-diacyl-sn-glycero-3-phospho-l-serine-coated GNPs carrying amphotericin B (AmB) for specific targeting to the macrophages in VL. The in vitro and in vivo results of this study show high accumulations of AmB in liver and spleen and resultantly enhanced anti-leishmanial activity [102].

2.8 GNPs as bactericidal bodies

Silver ions or silver NPs have long been known to show antimicrobial activity and can be effectively used for curing infectious wounds [103]. Gelatin fiber mats containing silver NPs are reported to possess higher antibacterial activity against Pseudomonas aeroginosa, Staphylococcus aureus, Escherichia coli, and methicillin-resistant S. aureus [104]. The silver NPs (nAg)-loaded gelatin hydrogel pads were also found to be effective in elimination of E. coli, P. aeruginosa, and S. aureus with about 100% inhibition rate. But these hydrogels have toxic effects on normal skin. However, gelatin hydrogels that contained AgNO₃ at lower concentrations (0.75, 1.0 wt%) were considered to be more safe for the skin cells [105]. Similarly, gelatin-based sponge incorporated with silver NPs (AgNPs) was prepared by a solution plasma process. It was shown that the gelatin/AgNP solutions and sponges exhibited excellent bactericidal activity against two bacteria, i.e. E. coli and S. aureus [106]. Gelatin NPs were also suggested as immunological adjuvant to activate and boost immunity against antigen, either cellular or humoral [107].

2.9 GNPs monitoring restenosis (vascular malady)

Restenosis is a term referred to lumen narrowing of arterial vessels after injury caused by multiple factors including surgical procedures such as arterial angioplasty and possess a permanent threat to the failure of the procedure [108], [109]. Nitric oxide (NO) has been found to have an important role in regulation of vascular smooth muscle cells proliferation; therefore, it has been considered as an effective agent for relaxing restenosis. Endogenous production of NO badly suffers from injuries during surgical interventions [110], and supply of exogenous NO is harmful due to its highly reactive nature. Different carrier systems have been proposed to deliver NO to the injured points. Among these, NPs are more advantageous, not only because they can conjugate with different products but also due to potential of controlled release of NO. GS-NO NPs have great potential of NO delivery to the targeted region, to regulate vascular restenosis, and can be administered as restenosis prevention agent after surgery [111] (Figure 7).

Figure 7:

Gelatin nanoparticles transport can supply NO in plenty of amount, a vasodilator, to narrowed vessels in order to eliminate the deposited plaque.

2.10 The role and potential of gelatin in tissue engineering

Tissue engineering is one the most interesting fields of nano-biotechnology. Tissue engineering focuses on the generation of biocompatible tissues in vitro. The use of nano-composites scaffolds in tissue engineering has attracted broad research interest in recent years due to their biological origin [112]. Presently various types of nanocomposites are tried in tissue engineering strategies, to make porous scaffolds. Nano-composite scaffolds have been used in reconstruction of tissues like muscles, bone, tendons, cartilage, ligaments, other multi-tissue organs, and tissues interfaces [113]. Composite systems synergistically combine two or more materials in order to produce a new system with novel properties. Gelatin-based composite systems provide new options for tissue engineering. As gelatin is a denatured biopolymer, the selection of gelatin as a scaffolding material can circumvent the concerns of immunogenicity and pathogen transmission associated with collagen [114]. Most of the work is based on the use of gelatin nano-composite focus in bone defects. Wound infection and bone nonunion are the two most well-known challenges of bone defects. Production and application of gelatin-based ceramics for drug delivery and bone regeneration are in active progression. Gelatin nano-composites can be formed with different types of polymers, both natural and synthetic, according to the purpose of their use. The insulin like growth factor-1 (IGF-1) is reported to get five times increase in quantity inside the cells, when treated with the cationized GNPs containing the IGF-1 plasmid compared with the unmodified particles [115].

It was found that calcium phosphate composites (PCL)/hydroxyapatite (Hap)/gelatin composite fibrous scaffolds are very elastic and let the bone cells (osteoblasts) to penetrate inside them [116]. Synthetic polymers are always surface modified in order to make them more biological, biocompatible, and safe to cells. The porous scaffolds imitate bone extracellular matrix not only in structure and composition but also in function. It is claimed that the preosteoblastic MC3T3-E1 cells attached, spread, and proliferated well with a flat morphology on the mineralized scaffolds, which clearly indicates that scaffolds composed of poly(ε-caprolactone), gelatin, and calcium phosphate are biomimetic and could serve as worthy scaffolds for bone tissue engineering [117]. Gelatin is composed of a unique sequence of amino acids such as glycine, proline, and hydroxyproline which promotes cell adhesion [118]. However, because of its weak mechanical strength it lacks the desired properties. Surface modification with other supportive materials such as hydroxyapatite, aluminosilicate (geopolymers), BaG ceramic was used to improve its strength before using it for scaffold construction. BaG is well known to bind with hard and soft tissues and to boost the bone cells growth [119]. Therefore, it is preferentially used in engineering bone repair scaffolds [120], [121]. Novel, three-dimensional (3D) porous nanocomposites formed by inter-connected microstructure is formatted by fusion of BaG with gelatin which showed great biocompatibility with SaOS-2 cell line in vitro [122].

Commonly alveolar bone loss is strongly linked to periodontal degeneration [123]. Bioactive glasses are osteoconductive and biodegradable biomaterial utilized in bone repair [124]. Bioactive glass ceramic scaffolds containing chitosan-gelatin can attach and spread cells more efficiently. Therefore, gelatine-conjugated nanocomposite scaffolds are thought to be a better option for regeneration of alveolar bone in tissue engineering [125]. The proliferation rate of the cells on the mineralized scaffolds [poly (ε-caprolactone) fibers with gelatin and calcium phosphate] is reported significantly higher than that on the pristine fibrous scaffolds. Different gelatin nano-composites and their use in tissue engineering is enlisted in Table 3.

2.11 Gelatin lowers quantum dots related toxicity

In recent years nanomolecules, especially quantum dots (QDs) are mainly focused as potential tumor diagnostic and drug delivery system [145], [146], [147]. Although QDs are considered as striking tool both in diagnostics and therapeutics, they are inherently cytotoxic which limits their use in various fields of research and diagnostics [148], [149]. Their toxicity can be reduced in vivo for short time by coating them with certain biocompatible polymers [150]. Coating QDs with gelatin has been reported to effectively reduce its cytotoxic effects on cells. Gelatin coating on QDs surface works as a barrier, which prevent toxic ion leakage from the core of QDs for longer duration inside differentiated pheochromocytoma 12 (PC12) cells [151].

In the field of diagnostics, gelatin-coated TGA-CdTe quantum dots have shown good potential for in vitro diagnosis of cancer [152]. Along with lowering cytotoxicity gelatin coating of QDs has been shown to provide substantially improved biocompatibility to QDs [150], [151]. Theranostics is a blend of diagnostics and therapy. NPs, including QDs, have been investigated for their theranostical potential especially in cell tracking and drug delivery [153], [154]. Recently CdSe/ZnS quantum dots (QDs)-fluorescent gelatin nanospheres (GNs) conjugated with anti-human immunoglobulin-G Fab (QDs-GNs-anti-IgG Fab) were found to be an effective theranostic tool for direct imaging and targeted drug delivery in human osteosarcoma [155] (as shown in Figure 8).

Figure 8:

Imaging of QDs and IGg decorated GNPs in the bone tumor site.