Physical characterization
According to the literature, the success of film formation is proved by the fact that the prepared films are smooth in texture, translucent and uniform without any visible cracks or imperfections (
16,
17). Regarding this, all prepared films were visually inspected. With exception of group A formulations (containing less than 1:10 drug: polymer) which were very soft and sticky, the rest of the films were homogeneous, translucent and flexible. Futhermore, their homogeneous and continuous surface without any crack or phase separation between the matrix and drug was achieved. This indicates the uniform distribution of the drug and polymers.
Uniformity of weight
The weight of ocular films in each batch was found to be uniform and in the range (
Table 2). The weight uniformity of the films indicates the good distribution of the polymer, drug and plasticizer.
Uniformity of thickness
The thickness of ocular films in each batch varied in the range as expected (
Table 2). The formulations had low standard deviation values which indicated the uniformity of the films.
Drug content determination
The drug content of ocular films has been presented in
Table 2. As evident, the drug content varied from 96.9 ± 0.96 % to 102.10 ± 0.76% and was consistent in different formulations which indicated the fact that the drug was uniformly distributed in the polymeric matrix and the preparation method gave reproducible results.
Swelling index
As can be seen in
Table 2 and as expected, formulations with HPMC had more swelling index. In group B formulations, cellulose derivatives, especially Na CMC had great effect on swellability (11 times increase in film weight), and Eudragits resulted in less swelling index. By applying Eudragit RS PO, it is even more decrease due to difference in chemical structure of applied Eudragits. The least amount of swelling index is achieved in group D (4 times weight increase in film). Increasing Drug: polymer ratio resulted in less swellability which can be justified by thickness increase and less water accessibility.
Mucoadhesion study
The mucoadhesion time of ocular films (in triplicate) on a freshly cut sheep eyelid was studied and it was proved that in all formulations with glycerin as plasticizer, mucoadhesion time was 10 hours. However, formulations with PEG 400 had no mucoadhesion. Meanwhile, utilizing TEC single resulted in a 3-5 hour mucoadhesion and when it was combined with glycerin (1:1), the time reached to 7 hours.
| Formulation | Weight (mg) | Thickness (µm) | Drug content (%) | Swelling index (%) |
|---|
| A1 | 10.33 ± 0.76 | 75 ± 5 | 100.63 ± 0.65 | 705 ± 11.4 |
| A2 | 11.60 ± 0.37 | 85 ± 5 | 98.5 ± 0.54 | 598 ± 6.1 |
| A3 | 12.36 ± 0.55 | 93 ± 5.77 | 101. 90 ± 0.80 | 412 ± 5.67 |
| B1a | 20.96 ± 0.15 | 148. 33 ± 2.88 | 99.00 ± 0.59 | 750 ± 8.9 |
| B1b | 21.36 ± 1.48 | 175.00 ± 8.02 | 98.75 ± 0.67 | 1110 ± 13.4 |
| B1c | 11.93 ± 0.40 | 126. 00 ± 3.73 | 100.06 ± 0.70 | 1117 ±14.2 |
| B2a | 18.93 ± 1.33 | 133.00 ± 5.77 | 98.12 ± 0.80 | 610 ± 7.9 |
| B2b | 14.26 ± 1.10 | 116 ± 4.32 | 99.96 ± 0.49 | 1580 ± 16.8 |
| C1a | 13.55 ± 0.25 | 100.00 ± 5.5 | 96.9 ± 0.96 | 799 ± 6.8 |
| C1b | 14.23 ± 0.02 | 105.00 ± 8.66 | 98.63 ± 0.84 | 761 ± 5.9 |
| C1c | 14.5 ± 1.85 | 113.00 ± 10.40 | 98.97 ± 0.99 | 520 ± 4.6 |
| C1d | 16.76 ± 1.26 | 118.00 ± 7.63 | 102.10 ± 0.76 | 601 ± 5.1 |
| C2a | 11.46 ± 1.10 | 95.50 ± 5.00 | 98.55 ± 0.27 | 608 ± 6.2 |
| C2b | 16.52 ± 0.56 | 120.00 ± 0.01 | 99.99 ± 0.76 | 592 ± 6.9 |
| C2c | 13.83 ± 0.20 | 113.30 ± 2.80 | 99.97 ± 0.89 | 589 ± 4.9 |
| C3a | 10.20 ± 0.41 | 88.33 ± 5.77 | 98.43 ± 0.07 | 445 ± 5.5 |
| C3b | 14.76 ± 0.65 | 115.00 ± 5.00 | 97.56 ± 0.55 | 454 ± 4.8 |
| D1a | 10.00 ± 0.95 | 85.00 ± 10.00 | 98.50 ± 0.11 | 690 ± 7.9 |
| D1b | 11.20 ± 1.05 | 91.66 ± 2.88 | 98.86 ± 0.49 | 601 ± 6.8 |
| D1c | 12.46 ± 1.07 | 98.33 ± 7.63 | 99.80 ± 0.98 | 580 ± 5.8 |
| D2a | 17.20 ± 0.84 | 115.00 ± 5.00 | 102.05 ± 0.87 | 501 ± 4.9 |
| D2b | 17.76 ± 0.59 | 141.00 ± 4.18 | 99.12 ± 0.15 | 578 ± 5.1 |
| D2c | 18.66 ± 1.15 | 150.00 ± 0.00 | 98.98 ± 0.23 | 703 ± 5.6 |
| D3a | 13.33 ± 0.61 | 160.00 ± 8.66 | 98.95 ± 0.89 | 402 ± 3.7 |
| D3b | 14.16 ± 1.30 | 160.00± 10.00 | 99.43 ± 0.64 | 410 ± 3.4 |
| D3c | 17.43 ± 1.75 | 171.66 ± 10.27 | 97.97 ± 0.22 | 421 ± 3.6 |
| D3d | 13.95 ± 0.87 | 165.00 ± 5.77 | 97.99 ± 0.46 | 427 ± 4.1 |
In-vitro drug release studies
In polymeric matrices, drug release is elicited by water accessibility into the matrix, breaking the polymer–polymer bonds and simultaneously leading to the formation of water–polymer bonds, which separates polymer chains, and swells to form a gel. The drug diffuses from gel network to the medium with a diffusion rate which is dependent on its diffusion ability through the gel and its concentration gradient. Concurrently, the rate of gel matrix erosion depends on medium hydrodynamics and molecular weight of polymer. Therefore, the drug release profile mainly depends on relative rates of these processes (
13,
14, and
17).
In this study, all of the successfull ocular film formulations, with proper texture and thickness were subjected to
in-vitro drug release studies (A1-D3). In
Table 3, cumulative drug release percent of diclofenac sodium in groups A and B have been summarized. As it has been depicted, group A formulations which were prepared by utilizing HPMC 4000 cps and PVP 30K released more than 50% of the drug from their matrices within 1 hour and the remaining drug was delivered in less than 4 h of the experiment. It is quite evident that both HPMC and PVP 30K were not able to effectively modulate diclofenac sodium release. In group B formulations, HPMC polymers and Na CMC, as single or combination polymers were applied and as can be seen in
Table 3, these formulations were not efficient enough to contorl the drug release. This can be explained by rapid water uptake which is followed by the rapid erosion and dissolution of hydrated matrices due to the high solubility of the polymer which caused relaxation and disentanglement of polymer chains and the formation of loose network, therefore diclofenac rapidly diffused to the release medium. On the other hand, the release from HPMC 100K formulations was fast at first due to the late hydration of heavy chains of high viscosity grade of HPMC. It resulted in more freedom of drug molecules to diffuse from the outer surface/layers of the film. The release was incomplete later due to the more chain entanglement and a thicker gel formation after hydration and drug molecules entrapped in gel network and lost the ability to diffuse. Furthermore, Na CMC entraps the drug more, decreases the drug diffusivity and finally releases the drug less due to its ionic structure and ionic interction with diclofenac ions.
| Formulation | % CR at different time intervals (h)
|
|---|
| 0 | 0.5 | 1 | 2 | 3 | 4 | 5 |
|---|
| A1 | 0 | 40.63± 2.55 | 78.44 ± 4.58 | 98.93 ± 1.66 | - | - | - |
| A2 | 0 | 71.28± 5.11 | 90.38 ± 9.49 | 106.2 ± 5.79 | - | - | - |
| A3 | 0 | 37.08± 3.75 | 55.73 ± 4.40 | 78.80 ± 4.67 | 92.38± 9.18 | 99.70 ± 1.87 | - |
| B1a | 0 | 40.63± 2.55 | 78.44 ± 4.58 | 98.93 ± 1.66 | 100.02±4.30 | 102.66 ±1.93 | - |
| B1b | 0 | 34.67± 4.39 | 56.44 ± 8.37 | 86.81 ± 4.01 | 102.86±2.30 | 103.04±1.79 | - |
| B1c | 0 | 30.99± 0.55 | 53.46±4.23 | 68.07±2.67 | 75.63 ± 3.03 | 79.67 ± 2.67 | - |
| B2a | 0 | 41.21± 2.13 | 77.43 ± 4.58 | 97.97 ± 1.64 | 101.23±3.40 | 101.41±3.21 | - |
| B2b | 0 | 36.95± 3.26 | 47.80 ±0.00 | 58.19 ± 0.32 | 61.43 ± 0.64 | 62.70 ± 1.47 | 63.13±2.44 |
Drug release studies in Group C and D formulations are presented in
Figures 1 and
2. As mentioned, group C formulations were prepared by utilizing HPMC 4K and RL PO, with different ratios (HPMC : EU RL PO, 3:1, 1:1 and 1:3) categorizing in 3 different subgroups (C1, C2 and C3). As shown in
Figure 1, in these formulations, increasing drug to polymer ratio resulted in slower drug release. Furthermore, drug release rate was decreased by increasing EU RL PO, as in 1:3 ratio, t
50% has been achieved in 4 hours and in ratio 1:1, t
50% has increased to 5 hours and in ratio 3:1, this time has extended to 9 hours. Finally, the total amount of released drug was not more than 34% and even did not reach 50%. This can be explained by the hydrophobic nature of Eudragit comparing HPMC and is proved by swelling studies, entrapment of drug molecules in polymeric network and less accesibilty to water channels which lead to slower release rate. In Group D formulations (
Figure 2), almost the same manner of drug release can be seen. However, in 1:3 Eudragit RS PO: HPMC ratio comparing Eudragit RL PO, Eudragit RS PO resulted in faster drug release due to less quarterny amonium groups in its chemical structure and in polymer network as well as less ionic interaction with drug molecules. In 3:1 Eudragit RS PO: HPMC ratio, the behaviour is vice versa, as it lead to slower and incomplete release,
i.e, releasing 25% in 7 hours and not more because of less wetability when it is the majority of polymer matrix (
18-
20).
Diclofenac sodium release pattern from ocular films of formulation C in simulated tear fluid (pH 7.4) at 37±1 °C (n=3, mean ± SD).
Diclofenac sodium release pattern from ocular films of formulation D in simulated tear fluid (pH 7.4) at 37±1 °C (n=3, mean ± SD).
Plasticizer influence
In order to study the plasticizer influence on physicochemical characteristics and drug release, Glycerin, PEG 400 and TEC were utilized as single or combination plasticizers with equal ratios in group D formulations. The ocular films prepared by TEC had more clarity in comparison with Glycerin. However, TEC films lost their flexibility in dissolution medium and it had negative effect on drug release, which can be due to the insolubility of TEC comparing Glycerin solubility in water. Formulations diclofenac PEG400 had more clarity in comparison with Glycerin, but showed much less mucoadhesion property. Therefore, glycerin was chosen as the plasticizer in this study.
Drug release kinetics
In order to investigate drug release kinetics, the release constants were calculated from the slope of the respective plots and the results of formulations D2b and D2c were summarized in
Table 4 because these formulations were superior to others considering the physicochemical characteristics and release behaviour as can be seen in
Figure 3. In these 2 ocular film formulations perfoming regression analysis, higher correlation was observed with respect to zero order plots (
r2 > 0.99). It was confirmed by zero order plots that the drug diffused slowly from ocular fims. In planar geometry by applying Korsmeyer-Peppas model, the value of n = 0.5 implies a Fickian diffusion, 0.5 < n < 1.0 indicates anomalous (non-Fickian) transport, and n = 1 indicates case II (relaxation controlled) transport. In the present films, this value was found in the range of 0.8473–1.0092 which implied that the release mechanisms followed anomalous (non-Fickian) transport and zero order release (case II transport) (
9,
21).
Diclofenac sodium release pattern from ocular films of formulation C2 and D2 in simulated tear fluid (pH 7.4) at 37±1 °C (n=3, mean ± SD).
| F | Zero order
| First order
| Higuchi
| Hixon-crowell
| Korsmeyer-peppas model
|
|---|
| R2 | R2 | n | Order of release |
| D2b | 0.9960 | 0.8450 | 0.9780 | 0.9720 | 0.9975 | 1.0092 | Super case- II transport |
| D2c | 0.9970 | 0.8620 | 0.9750 | 0.9500 | 0.9978 | 0.8473 | non-Fickian diffusion |