**3.2 Carbon-polymer composites**

*Genetic Engineering - A Glimpse of Techniques and Applications*

system like medicine, agrochemicals, and micronutrients.

ment, treatment of plant disease, and improved growth of the plants.

in various end applications, mainly medicine and agriculture [7].

**3.1 Metal-polymer composites**

In general, polymers encapsulated with various materials including metal nanoparticles, carbon-based nanomaterials, biological molecules, agrochemicals, pesticides, insecticides, etc. with controlled release behaviors enhance the biocompatibility of the materials and are easy for applicability and thereby effectively used

The metal nanomaterials such as Cu, Zn, Fe, titanium dioxide (TiO2), aluminum oxide (Al2O3), silicon dioxide (SiO2), aluminum nitride (AlN), boron nitride (BN), and zinc oxide (ZnO), etc. are extensively used for the plant growth and protection of crops. Usually, nanomaterials are synthesized for providing the controlled release delivery system for agrochemicals that enhanced solubility and protecting biologically active molecules against early degradation, thereby enhancing effectiveness of agrochemicals even at lower doses. However, these metal-based nanomaterials accumulate on the root and translocate less within the shoot and leave. Moreover, agglomeration, instability, and difficulty to use directly in land still remain a concern. In this context, the continuously increasing demands of the hybrid materials provide newer technological breakthrough for various end applications such as medical, environment, sensors, and agriculture. There are various existing materials such as plastics, metals, ceramic, and polymers that cannot achieve technological requirements for different applications. Usually, hybrid nanomaterials containing

Polymers are mainly used for the controlled release of agrochemicals such as insecticides, pesticides, fungicides, germicides, and growth stimulants. There are various factors such as cost, climate condition, controlled release, simple formulation, biocompatibility, and biodegradability involved in alteration in polymers for targeted system or applications. Moreover, thermal stability, thermal plasticity, glass-transition state, nature of polymers, melting point, its compatibility with biologically active molecules, and desired shape and size of the product still remain a concern. On the other hand, these polymers have the potential ability to control the release rate and rate of biodegradability, thereby being effective in various end applications, mainly medicine and agriculture [51]. The control release behavior of the polymeric formulation is one of the most important advantages in the delivery

Usually, the controlled release system is mainly divided into two groups; (1) encapsulation of active molecules/agrochemicals/micronutrients by using polymeric matrix and (2) polymeric matrix and active molecules/agrochemicals/micronutrients enclosed and formation of macromolecular backbones. Several polymers (natural, synthetic, and synthetic elastomers) such as carboxymethyl cellulose [52], cellulose acetate phthalate [53], gelatin [54], chitosan [55], gum Arabic [56], polylactic acid (PLA) [57], poly-butadiene, poly-lactic-glycolic acid (PLGA) [58], polyhydroxyalkanoates (PHAs) [59], polyvinyl alcohol (PVA) [60], polyacrylamide [61, 62], and polystyrene, etc., [63] are extensively used in various delivery systems. Among all of them, natural polymers are extensively used for controlled release of drugs/agrochemicals because of their low cost and being biodegradable. Moreover, controlled release rate might be tuned by using different molecular weight-based polymers and cross-linking of different polymers; therefore, polymeric composites are efficiently used in various biological applications. Recently, nanomaterials have been used as nanofertlizers, nanopesticides, and nanomaterials for genetic advance-

**3. Polymeric composites**

**80**

Carbon-based nanomaterials exhibited various end applications such as environmental remediation, sensors, drug delivery, antibacterial agents, crop protection, and growth regulator of the plants due to unique characteristics, mainly optical, electrical, mechanical, and thermal properties. The significant development has been done in the synthesis of carbon-based nanomaterials such as activated carbon, activated carbon fibers, CNTs, CNFs, graphene, and fullerenes, which have great interest in agriculture due to their possibility as a growth stimulant and protection of crops [66–79]. Moreover, these carbon-based nanomaterials, mainly CNTs, and CNFs, have the potential ability to penetrate seed coat as well as translocation ability within the plants from root to shoot to leaves. Several reports suggested that CNTs and CNFs efficiently translocate within the plants. These studies suggested that carbon-based nanomaterials acted as a growth stimulant with increasing the uptake of water and nutrients. Interestingly, CNFs hold metal nanoparticles and the release of metal nanoparticles in a control manner. These metal nanoparticles like Cu, Zn, and Fe also acted as micronutrients for the plants; therefore CNFs acted as a carrier for micronutrient delivery. Moreover, CNFs increase the water uptake ability, germination rate, and nontoxicity even at higher concentration of dose and therefore are used as a growth stimulant of the plants. In a recent study, Gupta et al. suggested that the CNFs are used as a carrier to deliver acylated-homoserine lactone in chick pea plants [34]. The study suggested that CNF-acylated homoserine lactone-based composite increased the plant growth as well as stress tolerance ability. The CNFs might be new generation fertilizers that enhance growth of the plants and defense regulator, also. However, direct application of the carbon-based nanomaterials still remains a concern. To overcome such issues, carbon-based nanomaterials are encapsulated with polymeric composite for agricultural delivery system. Kumar et al. synthesized bi-metallic (Cu/Zn) nanoparticle-dispersed CNFs encapsulated with PVA-starch composite to produce polymer-bi-metal-carbon (PBMC) composite [33]. The produced PBMC polymeric composite is effectively use as a fertilizer that enhances the growth of the plants. The releases of micronutrient (Cu/Zn) from CNFs, as well as polymeric composite in a controlled manner. The study also suggested that the release of micronutrients from PBMC is relatively slow in comparison with CNFs due to encapsulation of polymers. Moreover, CNFs efficiently translocated with the plants through root to shoot to leaves. The produced biodegradable PBMC-based formulation carrying Cu/Zn-CNFs (micronutrients) unwraps newer approach on the application of nanomaterials in agricultures. **Figure 2** shows the

**Figure 2.**

*A schematic representation of synthesis of Cu/Zn-CNF-dispersed polymeric composite and its agricultural application. Reprinted with permission (Kumar et al.), copyright © 2018, Springer Science Business Media, LLC, part of Springer Nature [33].*

schematic representation of synthesis of Cu/Zn-CNF-dispersed polymeric composite and its agricultural application.
