NOVELTY - Hydrogel comprises amphiphilic peptides and/or peptoids capable of self-assembling into three-dimensional macromolecular nanofibrous networks, which entrap water and form the hydrogel. The amphiphilic peptides and/or peptoids have a structure (I), where at least a portion of the amphiphilic peptides and/or peptoids is chemically cross-linked.    USE - The hydrogel is useful: as a cell culture substrate, preferably a cell culture substrate for three-dimensional cell culture, as a device for drug or gene delivery, preferably for sustained or controlled release drug delivery, as a wound dressing, as an implant or as an injectable agent that gels in situ; in regenerative medicine or in tissue engineering and tissue regeneration, e.g. regeneration of adipose and cartilage tissue, in the treatment of wounds and degenerative diseases of the skeletal system, e.g. degenerative disc disease and urinary incontinence and in an electronic device including a fuel cell, a solar cell, an electronic cell or a biosensing device; and for cosmetic use, where the tissue comprises skin tissue, nucleus pulposus in the intervertebral disc, cartilage tissue, synovial fluid and submucosal connective tissue in the bladder neck (all claimed). No biological data given.    ADVANTAGE - The hydrogel: has high mechanical strength than collagen or its hydrolyzed form (gelatin) and stability at physiological conditions, even at elevated temperatures and excellent biocompatibility; and provides the scaffold for the regenerating skin layers.    DETAILED DESCRIPTION - Hydrogel comprises amphiphilic peptides and/or peptoids capable of self-assembling into three-dimensional macromolecular nanofibrous networks, which entrap water and form the hydrogel. The amphiphilic peptides and/or peptoids have a structure of formula (Zp-(X)n-(Y1)m-AAthiolZ1aq) (I), where at least a portion of the amphiphilic peptides and/or peptoids is chemically cross-linked.    Z = N-terminal protecting group;    X = aliphatic amino acid;    Y1 = hydrophilic amino acid;    AAthiol = amino acid comprising thiol group;    Z1a = C-terminal protecting group;    n = 2-6, preferably 2-5;    m = 0-2, preferably 0-1; and    p, q = 0-1, where preferably p is 1.    INDEPENDENT CLAIMS are included for:    (1) a method-I of preparing the hydrogel, comprising dissolving amphiphilic peptides and/or peptoids in an aqueous solution comprising an oxidizing agent or exposing the ready-made hydrogel to a solution of an oxidizing agent;    (2) a cell culture substrate, preferably a cell culture substrate for 3-D cell culture, comprising the hydrogel;    (3) a device for drug or gene delivery, preferably sustained or controlled release drug delivery, comprising the hydrogel;    (4) an implant or injectable agent or wound dressing comprising the hydrogel;    (5) a pharmaceutical or cosmetic composition comprising the hydrogel;    (6) a method-II of tissue regeneration or tissue replacement comprising providing the hydrogel, exposing the hydrogel to cells, which are to form regenerated tissue, and allowing the cells to grow on or in the hydrogel; and    (7) a thin layer obtained from the hydrogel, preferably by glass plate casting, or casting with stain-less steel, inert metals, non-reactive polymeric material.