NOVELTY - Producing nanocrystalline cellulose from biomass, by extracting hemi-cellulose from the biomass to produce first biomass portion and first extract, extracting lignin from the first biomass portion to produce cellulose portion and second extract, processing the cellulose portion into cellulose nanofibrils, hydrolyzing amorphous cellulose in the nanofibrils to produce solution of nanocrystalline cellulose and glucose, separating the nanocrystalline cellulose from the glucose, and recycling at least one of first and second extracts and glucose.    USE - The method (M1) is useful for producing nanocrystalline cellulose from biomass. The method (M2) is useful for producing fibrin-nanocrystalline cellulose composite. The nanocrystalline cellulose composite is useful in nanocomposite matrix material used in graft for replacement or repair of a blood vessel (all claimed), preferably damaged or clogged blood vessels.    ADVANTAGE - The method enables production of the nanocrystalline cellulose having better quality at a reduced cost-effective and with less waste. The nanocrystalline cellulose enables preparation of synthetic material with improved properties for use as graft material. The presence of higher nanocrystalline cellulose to fibrin ratio in the graft provides increased strength, and lower nanocrystalline cellulose to fibrin ratio provides increased elasticity to the graft. The graft is biocompatible with tissue being repaired.    DETAILED DESCRIPTION - Method (M1) for producing nanocrystalline cellulose from biomass, involves extracting hemi-cellulose from the biomass to produce a first biomass portion and a first extract, extracting lignin from the first biomass portion to produce a cellulose portion and a second extract, processing the cellulose portion into cellulose nanofibrils, where the nanofibrils comprises nanocrystalline cellulose separated by regions of amorphous cellulose, hydrolyzing the amorphous cellulose in the nanofibrils to produce a solution of nanocrystalline cellulose and glucose, separating the nanocrystalline cellulose from the glucose, and recycling at least one of the first extract, the second extract and the glucose. INDEPENDENT CLAIMS are included for the following:    (1) method (M2) for producing fibrin-nanocrystalline cellulose composite, involves mixing an aqueous solution of nanocrystalline cellulose, fibrinogen and thrombin to produce a reactive mixture, and incubating the reactive mixture to convert fibrinogen to fibrin and produce a composite material of cross-linked nanocrystalline cellulose and fibrin;    (2) nanocomposite matrix material comprising a fibrin matrix reinforced with oxidized nanocrystalline cellulose through cross-linking;    (3) nanocomposite material comprising a fibrin matrix reinforced with nanocrystalline cellulose through cross-linking; and    (4) graft for replacement or repair of a blood vessel comprising a formed tubular matrix comprising a nanocomposite of cross-linked nanocrystalline cellulose and fibrin.