Since you are using chitosan, I suggest you make a solution of the extract and add it (to the slurry) in the process of making the film. 

You will have to test the adsorption process of your synthesided biopolymer onto film by do an isotherm. You will need to test diferents concentrations and media condictions (pH, temperature, salts, time of adsorption...). After you achieved the isotherm profile, you will need to evaluate what kind of behavior it have for you fit. For example, langmuir, freundlich...

What kind of films are you intend to adsorb?

Dear Cleverton, i am trying to synthesized chitosan based films with plant extracts to enhance its inherent antimicrobial activities. Any other suggestion, please

Dear Siimon

Thank you for your valuable suggestion. 

If the biopolymer film is able to swell in protonic or aprotic solvent, then you can apply the swelling phenomena to incoporate the extract into the films.

the structure of extract is so important, check it

Depending on the polymer you are using. For water soluble polymers can incorporate the extract as a solvent of the polymer.

Since you are using chitosan, I suggest you make a solution of the extract and add it (to the slurry) in the process of making the film. 

First you have to solubilizing the chitosan and then add your plant extract under slow stirring. before that you have to check the drug binding efficiency of your composites the same. then only you know the appropriate concentration of drug. 

if you are using also a plasticizer, you can consider to blend previously the active agent with the plasticizer and after having an homogeneous dispersion incorporate them into the polymer matrix. However if you need temperature you have to take ino account that most of a plant extracts are volatile.

Mariana Patricia Arrieta:  Thank you for your valuable suggestion

 You can please download the pdf of the file attached herewith to obtain certain valuable informations.

Sandeep chakrabotry..Thanks for your valuable assistance

due to the bio compatibility of your base polymer (CHITOSAN) you may directly added to the mixture during preparation.