NOVELTY - A biodegradable, biocompatible crosslinked polymeric matrix (A1) comprises poly- alpha (1-4)glucopyranose polymeric segment and linker segment, where at least a portion of the linker segments is covalently bonded to a portion of the alpha (1-4)glucopyranose polymeric segment.    USE - As a biodegradable, biocompatible crosslinked polymeric matrix used in a system for treating a condition in a subject (claimed); for various applications in the body, including drug delivery and cell therapy; for a medical or therapeutic application; in coating on a surface of an implantable medical device, a three-dimensional implantable medical article formed of the crosslinked material, a cell scaffolding, a sealant, and an embolic composition; in a variety of applications such as to make implantable medical devices (e.g. stents, tubes, aneurysm coils), in situ delivery articles (e.g., cell delivery or bioactive agent delivery articles); as tissue sealants; and to release bioactive agents falling within the following classes e.g. actin inhibitors, analgesics, anesthetics, antipolymerases, antisecretory agents, anti-AIDS substances, antiapoptotic, antibiotics, anticancer substances, anticholinergics, anticoagulants, anticonvulsants, antidepressants, antiemetics, antifungals, antiglaucoma solutes, antihistamines, antihypertensive agents, antiinflammatory agents, antimetabolites, antimitotics, antioxidizing agents, antiparasitic and/or antiParkinson substances or antiproliferatives.    ADVANTAGE - The matrices formed using the polymeric materials and reactive hydrazide chemistries has desirable physical properties for use in vivo, such as durability, limited swellability, in vivo biodegradability, and biocompatibility. Biodegradable matrices for the delivery of polynucleotides, particularly plasmids, can be prepared with minimal degradation of the polynucleotide during their preparation. Also, when placed in vivo, the matrices prevent degradation of polynucleotide within the matrix, and also regulate its release over therapeutically effective periods of time.    DETAILED DESCRIPTION - A biodegradable, biocompatible crosslinked polymeric matrix (A1) comprises poly- alpha (1-4)glucopyranose polymeric segment and linker segment including a formula selected from =(NNHC(O))- (I) or -(NHNHC(O))- (II), where at least a portion of the linker segments is covalently bonded to a portion of the alpha (1-4)glucopyranose polymeric segment.    INDEPENDENT CLAIMS are included for:    (1) a system for forming a biodegradable, biocompatible crosslinked polymeric matrix comprising an alpha (1-4)glucopyranose polymer (P1) and that comprises pendent first reactive groups; and second polymer (P2) that comprises pendent second reactive groups that are reactive with the first reactive groups, where either the first or second reactive groups comprise hydrazide groups, and the hydrazide groups or the second reactive groups have a degree of substitution on the alpha (1-4)glucopyranose polymer of 0.05-1, and the first or second reactive groups that do not comprise hydrazide group comprise hydrazide-reactive groups, and the second component comprises alpha (1-4)glucopyranose polymer or a component that is different that alpha (1-4)glucopyranose polymer;    (2) method (M1) for forming a biodegradable, biocompatible crosslinked polymeric matrix the system by contacting alpha (1-4)glucopyranose polymer (P1) with (P2); and    (3) method for treating a condition in a subject by placing or forming a biodegradable, biocompatible crosslinked polymeric matrix (A1) at a target location of a body, where the matrix degrades over a period of time at the target location and the presence of the polymeric matrix at the target location is able to treat the condition.