A Review of Recent Developments in Pectin Formulation to Improve its Bioavailability and Systematic Efficacy with Future Outputs

1.1. Pectin structure and occurrence

Pectin is an anionic, high molecular weight, linear chain hetero polysaccharide. It is considered the most structurally complex polysaccharide found in planta, making up as much as 35% of the cell wall in dicots and non-gramineous monocots.^[1] While present in all higher plant cell walls, it is particularly abundant in certain fruits like citrus, apples, pears, guava, and plums, however is less abundant in others like grapes, strawberries, and cherries.^[2] Apple pomace, orange, and lemon peels are considered the major sources of commercial pectin at an industrial level.

The average molecular weight (MW) of pectin ranges from 50-150 kDa.^[3-5] Pectin is composed primarily of a minimum of 70-100 α-D (1→4)-covalently linked galacturonic acid units (= α-D-homogalacturonan), which comprise around 65% of pectin’s MW. The galacturonic acids carboxyl groups are esterified to various degrees to form methoxy groups and could also be acylated with acetic (O-2/O-3) or ferulic acids, as in spinach and sugar beet. According to its degree of methoxylation (DM), pectin is classified into high-methoxy (≥ 50% esterification) and low-methoxy (≤ 50% esterification). Neutral sugars such as L-rhamnose, D-xylose or D-apiose can combine with galacturonic acid to form various polysaccharides like rhamnogalacturonan (I & II), xylogalacturonan or apiogalacturonan, respectively.^[3,5,6]

During the ripening process of fruits, pectin changes from a water-insoluble substance in the unripe stage (protopectin) into water-soluble gel-forming polysaccharides in ripe fruits.^[6] Their viscosity is inversely proportional to the degree of esterification. In low‐methoxy pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups. In contrast, in high‐methoxy pectin, the cross‐linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions. In aqueous solutions, pectin is most stable at a pH of 4.0, whereas it undergoes de-esterification and depolymerisation concurrently at higher or lower pH values.^[3-5]

1.2. Pectin in food and drug formulations

Pectin plays an important role in food^[7] and drug formulations^[8] especially for colon-targeted release. It can resist gastric and small intestinal enzymes, protecting the drug-loaded formulation until it reaches the colon, where it is degraded by colonic microflora.^[9] Moreover, pectin possesses mucoadhesive properties (determined by the degree of esterification) which extend the drug contact with biological membranes, hence improving the bioavailability of drugs.^[10] Nevertheless, it is difficult for natural pectin to meet all requirements for various uses. Therefore, pectin modification has become an effective approach to maximise its applications. In addition, a study of the relationship between the properties of pectin and its active function can provide a basis for these modifications. The environmental pH greatly affects pectin’s stability due to the large number of anionic groups present on the pectin molecule. Studies have shown that the most stable pectin casein nanoparticles can be produced at pH= 4,^[11] while another study has shown that pectin particles’ ability to load insulin increases three-fold when pH changes from 2 to 3.^[12] The degree of esterification can affect the binding capacity of pectin to the intestinal mucosa,^[13] and the degree of methylation can affect the texture of jelly.^[14] This study attempted to explore the relationship between pectin properties, structure and its interaction with other substances while discussing different approaches to enhance its applications. Metabolic effects are discussed in context to pectin structural features, i.e., MW, DM, degree of esterification (DE), distribution of free- and esterified carboxyl groups, degree of acetylation (DAc) to dissect structural motifs critical for each effect to aid design more effective analogues in the future.

1.3. Pectin fermentation mediated by intestinal microbiota

Pectin is a complex, plant-derived polysaccharide that evades digestion by human endogenous enzymes and reaches the colon largely intact. In the large intestine, pectin is fermented under the action of gut microbiota, producing bioactive metabolites that play a pivotal role in mediating its systemic effects. Recently, pectin’s fermentation dynamics have progressed significantly, shedding light on involved microbes, fermentation pathways, and metabolic outcomes as explained in the next subsections. Figure 1 illustrates the sources, structure and key properties of pectin.

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Figure 1:

Pectin fundamentals; sources, structure and key properties.

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3.1. Modification and property improvement of nano-sized pectin

Due to its excellent biocompatibility and biosafety, pectin is considered as one of the best choices for drug carriers or formulation research. However, pectin has some defects due to its natural physical and chemical properties, such as tendency to form gels in solution and low stability in an alkaline environment,^[15] limiting its use in the preparation of some drugs. Consequently, modification or property processing has been attempted and to be discussed in that section mainly targeting the improvement of its extraction yield, purity and carrier particle properties. Azhar et al. prepared alginate-pectin beads using an electrospray technique with voltage application where alginate-pectin concentration was the most prominent factor in producing spherical beads. Spherical beads were prepared at a size of 2.97 mm and a spheric coefficient of 0.776 using the optimal process conditions of 3.5% material concentration and 2.4kV applied voltage by response surface analysis.^[16] Another study used response surface methodology to analyse the effects of pH and polymer concentration on pectin particles. At pH of 4.1 the most stable pectin-caseinate nanoparticles with a diameter of 100 nm could be prepared.^[11] Pectin with a high esterification degree (82%) was obtained by enzymatic extraction while maintaining an extraction rate of (23% w/w) compared with the classically acid-extracted method (67-74%).^[17] The pectin polymer extracted by the enzyme (Laminex CK2) was found not sensitive to the presence of Ca²⁺ ions rich in dairy matrices forming a gel at low pH in the presence of sugar employed in stabilising acidified milk drinks. To improve pectin quality, a purification step should be carried out. A stepwise purification process to reduce impurities during pectin extraction from pineapple fleshes and banana peels was proposed.^[18] In general, initial acid extraction produced pectin rich in glucuronic acid, arabinose, and xylose, which are undesirable impurities. Purification involves treating dialyzed pectin with 78–85% acidified methanol which can effectively reduce these neutral sugars. Glucuronic acid decreased from 4.1% to 0.5%, arabinose from 12.9% to 5.6%, and xylose from 5.1% to 2.7%.^[18]

In addition to the processing technology, the physical properties of pectin itself are also known to affect its applications. Cheng et al. evaluated pectin molecular weight and pH on insulin loading capacity of pectin.^[19] Increasing the pH from 2 to 3 enhanced insulin association efficiency by three-fold, from 32.7% to 93.31%, at an insulin loading concentration of 80 U/mL, which correlated to the charge density on pectin molecules as a function of pH. In contrast, reducing pectin molecular weight by mechanical milling did not significantly affect insulin association efficiency. In another study, Liu et al. observed the binding of pectin to colonic mucosal surface of pigs to assess the interaction of various pectin formulations with porcine colonic tissues.^[13] Scanning electron microscope (SEM) results showed that pectin with higher net charge was more mucoadhesive than other pectin, with pectin uptake to be further enhanced either by lowering the degree of esterification or by replacing side chain carboxyl groups with primary amine groups.

Pectin’s properties influence its food applications. Sobrino et al. assessed the use of pectin and Ca²⁺ ions in diet jelly.^[14] The study stated that increasing pectin’s methoxylation degree from 31% to 36% did not affect the jelly’s colour, flavour, sweetness, or acidity while enhancing the jelly strength. This change in texture and mechanical strength may be due to the prolonged cooking time of jellies made with higher methoxylation pectin, leading to a higher content of soluble solids and thus increased texture.^[14]

3.2. Pectin as a drug carrier to promote drugs’ metabolism

Pectin is widely used in drug formulations targeting the gastrointestinal tract (GIT) tract, since it is poorly absorbed in the intestine, but is readily metabolized in the colon by the resident microflora.^[9,15] The preparation of pectin nanoparticles has been shown to improve the biological activity of several drugs justifying its inclusion in drug formulations. In a recent study, curcumin-loaded micelles self-assembled from disodium glycyrrhizin (Na₂GA) were coated with pectin and tannic acid to construct a core-shell solid dispersion (SD-CUR) with an average nanoparticles size of 146 nm. Such formulation improved drug solubility and release in the gastrointestinal environment.^[20] Pharmacokinetic studies showed that the bioavailability was increased by 10-fold, due to the increased uptake of the drug carrier by intestinal cells by the nanomodified layer containing pectin; and this assumption is further confirmed using intestinal in situ absorption assay. Yener et al. showed similar results in another study with the active ingredient melatonin.^[21] The melatonin-loaded pectin-based nanoparticles with particle size of 75.3 nm were prepared and assessed for their anti-inflammatory effect in the rat bowel disease model. The obtained nanoparticles reduced the damage score by 73.2% and 67.1% in oral and intracolonic routes, respectively. In a third study, a kind of gastrointestinal-resistant nanoparticle matrix obtained by pectin-nano chitin-nano lignocellulose^[22] was used to coat the probiotic Bacillus coagulans. Such formulation resulted in an enhanced viability for Bacillus coagulans, with 68% of its cells remaining viable after five weeks, compared to 53% in non-coated control.^[22]

Beyond its usage in formulations targeting the GIT, pectin carriers have also been used as efficient delivery system for enhancing cellular uptake of flavonoids. Neohesperidin (NH) is a flavanone glycoside with multiple pharmacological activities, but is relatively unstable in the physiological environment such as temperature, pH, salt, oxidative, UV, enzymes, and serum.^[23] To overcome this drawback, NH-loaded pectin-chitosan decorated liposomes (365 nm in size) was prepared and compared to the NH-loaded liposomes without modification (66 nm in size). After adding 0.15 mM palmitic acid (PA) into L02 cells, cell viability was reduced to 53.16% compared with normal cells, and the NH-loaded decorated liposomes were more efficient in recovering the cell viability compared to non-modified liposomes.^[24] Another study aiming at improving flavonoid delivery involved nanoparticle fabrication with zein and pectin-loaded naringenin (Smruthi, Nallamuthu, & Anand, 2022) in Wistar rats to assess the in vivo bioavailability of the flavonoid; naringenin. Results illustrated that the maximum plasma concentration of nanoparticles (12.7 µg/mL) was observed one hour after administration, however the free drug reached its peak earlier at 0.5 h with a lower concentration (4.6 µg/mL). Therefore, pectin carriers not only improved drugs’ bioavailability in vivo, but also extended the metabolic time, which positively improved drug efficacy. In a third study, Souza et al. loaded quercetin with pectin and casein to form 20-500 μm microparticles.^[25] Although the particles were not nano-sized, quercetin was also efficiently encapsulated inside the polymeric matrix, creating a solid amorphous solution and alleviating oxidative stress in arthritic rats.

Pectin formulations can also be used to promote in vivo bioavailability of insulin. Meneguin et al. prepared a microparticles-based formulation using retrograded starch and pectin coated with gellan gum to assess insulin in vivo bioavailability.^[12] The results of ex vivo insulin permeability on rat intestinal tissues suggested that pectin coating of the carrier increased intestinal insulin availability from 57% to 73-86%. This enhanced osmosis of the intestinal surface may be due to pectin effect on opening tight junctions, along with the excellent mucoadhesive properties of the gellan gum, which prolonged the contact time of the insulin with the mucosa, leading to increased local concentration gradient of the drug.

In addition to improved drug absorption, pectin formulations could also be used in formulations aiming at reducing cellular, tissues, or organs damage. To examine whether pectin formulations could reduce lung damage caused by the herbicide paraquat (PQ), nanoparticles of 520 nm were assembled using pectin/chitosan/tripolyphosphate to load PQ.^[26] The Sprague-Dawley rats inhaled and nebulized different paraquat formulation for 30 min in various experimental groups and were subsequently assessed for lung injuries. Rats treated with nanoparticle-loaded PQ showed a lower degree of pulmonary fibrosis and cell apoptosis markers, concurrent with reduced oxidative stress. Reduction in toxicity was attributed to the nanoparticles exerting their inhibitory effects on PQ-induced lung fibrosis via reduction in epithelial-mesenchymal transition and further apoptotic markers.^[26]

Due to its excellent film-forming properties, pectin has been widely used in membrane preparation, in addition to the preparation of water-soluble carriers, as another potential drug delivery tool. Pectin nanogels fabricated with norbornene group functionalized pectin, dithiol crosslinker, and thiolated ovalbumin (OVA) were used to design a novel transcutaneous antigen-delivery carrier.^[27] In this study, OVA-loaded pectin nanogels penetrated the cutaneous barrier. At the same time, soluble OVA could not penetrate the stratum corneum layer, confirming pectin’s role in the stratum corneum and was deposited in both the epidermis and dermis. To observe the promoting effect of pectin gels on drug penetration, fluorescence microscopy was used to monitor fluorescence reaction of THP-1 cells incubated with different drugs. Results showed that the fluorescence intensity of cells co-treated with modified pectin-modified nanoparticles was higher than that of free-drug medications. In addition, reverse transcription quantitative polymerase chain reaction (RT-qPCR) results indicated that mRNA expression levels of dendritic cells maturation markers in cells treated with pectin nanogel for 24 h showed a two-fold increase in CD80 and CD83 mRNA levels compared with free drug control. Thus, nanogels were further internalized by dendritic cells derived from THP-1 monocytes, inducing the upregulation of maturation markers.^[27]

Silver nanoparticles have unique properties to treat several cancers; however, as the silver ion is inherently cytotoxic; it is essential to deliver it to cancer cells accurately to avoid toxicity. In the research of Wang et al., pectin was used as a natural reducing and stabilising agent for the synthesis of Ag nanoparticles.^[28] Compared with silver used alone, nanoparticles with pectin enhanced the inhibitory effect on colorectal cancer cells, with IC₅₀ of pectin/Ag nanoparticles against Ramos.2G6.4C10, HCT-8 [HRT-18], HCT 116, and HT-29 at 485, 393, 236, and 262 µg/mL respectively. In contrast, higher cell viability, more than 50% was observed in case of AgNO₃ at similar dose level. To better evaluate the biosafety, normal cells (HUVEC) were treated with AgNO₃ and pectin/Ag nanoparticles, while the dose of nanoparticles was less than 125 µg/mL, it showed nearly no effect compared with normal cells, with increase in dose up to 1000 µg/mL, the cell viability of nanoparticles (NPs) treated cells exceed 70% versus 50% in case of AgNO₃. The results showed that pectin-based nanoparticles reduced oxidative stress in cells and further protected normal cells, proving its safety. Ellagic acid (EA) is a common phenolic in several dietary sources used to prevent cancer and treat viral and bacterial infections.^[29] Nevertheless, it is difficult to use efficiently in vivo owing to its short transient time inside the GIT; Ortenzi et al. overcame this problem with a pectin film which could not only control EA in vitro release but also improved the stability of EA in the gastrointestinal tract. Release based assays showed that the quantity of EA released after 120 min was ca. 15% with pectin gel in phosphate buffer saline (PBS) solution and maintained release without change in 24 h, which proved that gels could control EA release. In addition, to assess EA release from pectin gels inside the digestive tract, it was treated with simulated gastric and intestinal environments. Results showed that ca. 4%-12% of the overall EA content was released after gel incubation in gastric pH, and 64% of the overall content EA was released after two-hour incubation, which proved that pectin gel could control the release of the loaded drugs in different gastric conditions.^[30]

4.1. Cancer treatment

Pectin is considered one of the promising materials which can be used in the development of different anticancer nanoformulations. Pectin can suppress cancer progression.^[38,39] Moreover, pectin contains β-galactose units which can target the galectin-3 adhesive molecule overexpressed in several kinds of cancers.^[40,41] The literature is rich in different studies showing the use of pectin in the fabrication of anticancer nanoformulations either alone or combined with drugs.

One study investigated the preparation of magnetic nanoparticles inside the pectin matrix. One pot synthesis technique was conducted to prepare orange pectin/Fe₃O₄ nanoparticles. The anticancer activity of pectin/Fe₃O₄ nanoparticles was examined applying 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for 48 h on liver cancer cell lines like pleomorphic hepatocellular carcinoma and novikoff hepatoma. The cells’ viability decreased in a dose-dependent manner after applying pectin/Fe₃O₄ nanoparticles. The calculated IC₅₀ were 8 and 7 µg/mL against the afore-mentioned cell lines, respectively. While the IC₅₀ for the anticancer drug; Lenvatinib (positive control) was 7 µg/mL for both cell lines.^[42] The obtained findings indicated the potential of using pectin/Fe₃O₄ nanoparticles to treat liver cancer, nevertheless, more clinical investigations are required to ascertain their anticancer activity.

Another study investigated the combination between pectin and silver nanoparticles. Silver nanoparticles are known to have unique properties against several cancers. Wang et al., used pectin as a natural reducing and stabilising agent for the synthesis of silver nanoparticles.^[28] The bio-application of pectin/silver nanoparticles on colorectal cancer cells; Ramos.2G6.4C10, HCT-8 [HRT-18], HCT 116, and HT-29, enhanced the inhibitory effect where the calculated IC₅₀ values were 485, 393, 236, and 262 µg/mL, respectively. In contrast, higher cell viability, more than 50% was observed in case of AgNO₃ at similar dose level. To better evaluate the biosafety of the fabricated nanoparticles, normal cells (HUVEC) were treated with AgNO₃ and pectin/silver nanoparticles separately. No effect was observed on the treated cells when the dose of nanoparticles was less than 125 µg/mL, while an enhancement in cell viability above 70% was observed in case of pectin/silver nanoparticles when the dose was increased up to 1000 µg/mL versus only 50% in case of AgNO₃. The results showed that pectin/silver nanoparticles reduced oxidative stress in cells and further protected normal cells, proving its safety.

The combination between pectin and guar gum along with ZnO was exploited in one research article to develop a nanocomposite with enhanced anticancer efficacy on human lung carcinoma (A549). The nanocomposite possessed a polygonal shape with particle size ranging between 50 and 70 nm.^[43] The developed nanocomposite overcame one of the marks of cancer which is the uncontrolled cell division through the induction of S phase arrest, mitochondrial dysfunction and reactive oxygen species (ROS) mediated death leading to apoptosis.^[44-47] The synergism between the three components of the nanocomposite was clear when calculating the produced ROS levels, where a 12-fold increase in ROS production was observed with the nanocomposite versus 2-fold and 1.8-fold increase with pectin and guar gum when used individually, in that order.^[43]

The success of pectin nanoformulations in treating cancers can extend also to overcoming the associated problems with the administration of chemotherapy. Pectin nanoformulations can improve the penetration and targeting of anticancer drugs which in turn will enhance the therapeutic efficacy and reduce the severe side effects associated with chemotherapy administration.^[48]

One study developed a modified pectin/tannic acid nanocomplex as a carrier for different chemotherapeutic agents. Tannic acid was added as a crosslinker. The particle size ranged between 378 and 541 nm with a low polydispersity index between 0.12 and 0.26. The nanocomplex uptake by cancer cell lines HPAF-II and PANC-1 cells was tested using 6-coumarin green dye. The results obtained from the fluorescence microscopy indicated the accumulation of the dye-loaded nanocomplexes in a concentration dependent manner from 2.5 to 10 µg of dye equivalent nanocomplex. To examine the ability of nanocomplexes to facilitate the delivery of drugs and enhance their therapeutic efficacy, hence MTT assay on HPAF-II and PANC-1 cell lines was conducted. Both cell lines were treated with 5-flurouracil-loaded modified pectin/tannic acid nanocomplexes and drug solution separately. The obtained IC₅₀ values were 88.8 and > 150 µM with HPAF-II cells as well as 44.9 and 121 µM with PANC-1 for the afore-mentioned samples, in that order. The obtained results confirmed the synergism between the loaded drug and modified pectin/tannic acid nanocomplexes to deliver the drugs compared to the free drug against cancer cells.^[49]

Another study highlighted the preparation of doxorubicin loaded pH-responsive hydrogel using zein protein nanoparticles and pectin, where the gelation occurred without using crosslinkers. The spherical shape of zein nanoparticles (80-120 nm in size) aided in drug encapsulation, adsorption of pectin layer on their surfaces which in turn assisted the gel formation. Doxorubicin-loaded hydrogels showed excellent cytotoxicity against cervical cancer cell lines by inducing intracellular antioxidative stress-based apoptosis. The fabricated hydrogels could release the drug specifically in a pH-dependent manner in the cytosolic acid environment of HeLa cells with minimal side effects on normal cells.^[50]

The combination between curcumin (known for its anticancer effect), pectin and skimmed milk powder (emulsifying agent) was investigated to prepare curcumin-loaded double layered solid lipid nanoparticles via the hot homogenisation technique. The double layer was formed by the complexation between pectin and skimmed milk powder via superficial electrodeposition process. Pectin was added for several reasons including protecting the loaded drug from being released in the acid medium hence targeting drug release at the colon (site of action), improving the drug stability inside the coated core of the solid lipid nanoparticles and finally improving its cytotoxic activity. Results revealed the fulfilment of these goals, where the drug release in the acid medium (pH 1.2 and 4.5) was less than 4%, while the release of drug was > 90% at pH 7.4 at 72 h time point, confirming the acid-resistant properties of the coated nanoparticles. Regarding assessing the cytotoxicity, it was evident from MTT assay results that the prepared double layered solid lipid nanoparticles showed enhanced cytotoxicity against SW480 cell lines where the IC₅₀ values were 31 and 132 μM. mL^–1 for the nanoparticles and free drug, respectively. This enhanced cytotoxicity might be attributed to the enhanced cellular uptake by active targeting. Pharmacokinetic studies revealed the superiority of the fabricated solid nanoparticles over free curcumin regarding C_max, where the developed nanoparticles showed a 2.07-fold increase in C_max values. The obtained results indicated elevated systemic bioavailability.^[51]

4.2. Diabetes treatment

As previously mentioned under Section 2.4., pectin possesses excellent anti-diabetic efficacy. Besides its anti-diabetic activity, one study exploited its unique physicochemical properties in enhancing the therapeutic performance of metformin HCl; an anti-diabetic drug. Metformin HCl can cause unfavourable gastrointestinal symptoms due to its frequent administration. Hence, this study aimed at preparing metformin HCl-loaded nanoparticles with extended release to reduce the associated side effects. Pectin/tri-polyphosphate nanoparticles were fabricated by ionic gelation method due to the covalent bonding between the hydroxyl groups of pectin with the crosslinker; tri-polyphosphate. The formed nanoparticles were characterized by high entrapment efficiency of 68% as well as particle size value of 482.7 nm. The cumulative drug release after 12 h ranged between 74 and 98%, indicating prolonged drug release being obtained. By assessing the drug uptake by L6 myotubes, it was manifested that the drug uptake from the developed nanoparticles was 1.3-fold more than from the free drug, which confirmed the synergistic activity between pectin and metformin HCl regarding glucose-lowering effect.^[35]

Another study investigated the combination between three types of polysaccharides; chitosan, pectin and dextran for loading insulin.^[33] Insulin-loaded chitosan nanoparticles improve the penetration rate of insulin into the bloodstream by paracellular route.^[52] In the same context, pectin nanoparticles can reduce insulin resistance and glucose tolerance.^[53] On the other hand, dextran resists the digestion by amylases and instead can be digested by dextranase present in the large intestine, liver, spleen and kidney. Hence, dextran containing carriers can guard drug against degradation in the GIT, hence improving oral bioavailability.^[54] Briefly, insulin-loaded chitosan/tripolyphosphate nanoparticles were prepared following ionic gelation technique and using pectin/dextrin as a coat. The coated nanoparticles were spherical in shape with a particle size of 90 nm as well as entrapment efficiency and insulin-loading values around 69 and 26%, respectively. The calculated entrapment efficiency and drug loading indicated the successful loading of insulin inside the coated nanoparticles. The developed nanoparticles were administered orally to streptozotocin-induced diabetes in male Wistar Albino rats compared to subcutaneous free insulin administration. The administration was daily for 4 weeks. Results revealed that the insulin-loaded coated nanoparticles and subcutaneously administered free insulin succeeded in reducing blood glucose levels, increased antioxidant capabilities and, hence lessening the oxidative stress. The obtained results elaborate the possibility of using the developed nanoparticles for treating diabetes evading the disadvantages of subcutaneous insulin administration.^[33] Extensive clinical studies should be done to determine the efficacy of the developed nanoparticles on diabetic patients.

4.3. Antimicrobial activity

Pectin is one of the biopolymers which has intrinsic antimicrobial activities. Several researches investigated its antimicrobial properties.^[55,56] Besides, pectin can induce crystal nucleation and growth required for the stabilisation of nanoparticles.^[57] Ibraheem et al.,^[58] exploited these properties for the synthesis of pectin-stabilized silver nanoparticles to serve as antimicrobial formulation against E. coli. The developed preparation method is a green, ecofriendly approach. In brief, the functional groups in pectin like hydroxyl and carboxylic groups can reduce Ag⁺ to Ag⁰. The reduction step continued for some time leading to the growth of nanoparticles. The produced nanoparticles were also stabilized by the formation of pectin coats around the nanoparticles, hence avoiding aggregation and agglomeration. By examining the morphology and particle size under transmission electron microscope, it was evident that the pectin-stabilized silver nanoparticles were spherical in shape, well-dispersed with particle size between 10 to 60 nm. The antimicrobial activity of the synthesized pectin-stabilized nanoparticles was assessed using agar well diffusion method. The obtained results showed that the degree of antimicrobial activity was directly dependent on the amount of the nanoparticles used, where the inhibition zones were 16, 25 and from 25 to 30 mm with 1, 5 and 10 mM nanoparticles. The amplified antibacterial activity with 10 mM nanoparticles might be attributed to the higher concentration of phytochemicals in pectin along with the higher concentration of silver ions resulting in the formation of more nanoparticles. Table 1 summarizes the scientific usefulness of pectin in fabricating different drug delivery systems.

4.4. Tissue engineering

To avoid the immune system’s rejection of the transplanted tissues, the field of tissue engineering emerged in 1993. This approach combines the principles of life sciences and engineering aiming at restoring the damaged tissues to reestablish their normal function.^[59] Pectin played an important role in the field of tissue engineering either for the regeneration of soft tissues like retina and skin or hard tissues like bone.

5.1. 3D printing

3D printing technique shared in the development of biomedical and pharmaceutical fields assuring the manufacture of high-quality medical devices or pharmaceutical dosage forms.^[72,73] Natural and synthetic polymers were used extensively for the preparation of the 3D prints like collagen, fibrin and pectin (natural polymers)^[74] and polylactic acid, polyvinyl alcohol and polycaprolactone (synthetic polymers).^[75]

Lidocaine HCl-loaded chitosan-pectin hydrogel scaffolds (mesh-shaped) were successfully prepared using BioBot1 3D printer for wound healing purposes. The obtained scaffolds were lyophilized later. The in vitro release studies in phosphate buffer saline revealed that the developed scaffolds possessed biphasic release with an initial burst within 1 h which is essential for the rapid pain management and the rest of drug dose was released in a controlled manner over 6 h. The initial flush might be attributed to the porous structure of the developed mesh-shaped scaffolds while the controlled release of the rest of drug dose might be endorsed to the sponge-like structure of the wet hydrogel scaffolds.^[76] The proposed hydrogel scaffold offered a promising dosage form capable of tuning the drug release by controlling the mesh shape and size.

Another study highlighted the application of 3D printed pectin hydrogels for the musculoskeletal tissue restoration. Confluent chondrocytes-laden pectin hydrogels were utilized to prepare the bioinks required using Regemat3D Extrusion-based bioprinter. Hydrogel scaffolds were printed then soaked in 100 mM CaCl₂ solution for a total time of 80 min from both sides to properly crosslink. The cellular proliferation was tested applying alamarBlue™ assay, which indicated the ability of 3D printed pectin hydrogels to improve chondrocyte proliferation and maturation, where the metabolic activity reached highest value after 14 days. The obtained results suggested a promising formulation for soft tissues engineering.^[77] Drug-loaded formulations should be prepared to examine the capability of the developed formulation to deliver the loaded drugs. More clinical investigations should be carried out to examine the efficacy of the developed formulation in the human body.

Although using pectin as a useful pharmaceutical additive for fabricating 3D printed delivery systems, however most results remain in the in vitro or animal stage, as human clinical trials are currently inadequate.