Compositions that reversibly gel and de-gel

1. A modified or isolated composition, comprising:

a plurality of first polymers, each of said first polymers having first functional groups comprising a first nucleic acid sequence attached as side-chains thereto; and

a plurality of second polymers, each of said second polymers having second functional groups comprising a second nucleic acid sequence attached as side-chains thereto, said first and said second functional groups forming a reversible cross-link between said first and said second polymers, wherein said cross-link comprises a plurality of hydrogen bonds between complementary base portions of said first and said second nucleic acid sequences, and

wherein said composition is used as a prosthetic device capable of changing shape and elastic modulus as a function of an extent of said cross-links formed between said first and said second polymers and wherein said prosthetic device is selected from the group consisting of:

artificial spinal disk fluid;

artificial ligaments;

artificial bone;

artificial valves;

artificial skin; and

dental prostheses.

2. The composition as recited in claim 1 , wherein said first and said second nucleic acid sequences are separately selected from the group consisting of:

deoxyribonucleic acid;

ribonucleic acid;

peptide nucleic acids; and

phosphorothioate analogues of DNA.

3. The composition as recited in claim 1 , wherein at least ten bases in said first nucleic acid sequence form a sequence complementary to a base sequence in said second nucleic acid sequence.

4. The composition as recited in claim 1 , wherein said first nucleic acid sequence and said second nucleic acid sequence each comprise between about 5 and about 100 nucleotide bases.

5. The composition as recited in claim 1 , wherein said first functional groups comprises at least two first nucleic acid sequences having at least one difference in a base sequence between said first nucleic acid sequences, and wherein said second functional groups comprises at least two second nucleic acid sequences having at least one difference in a base sequence between said second nucleic acid sequences.

6. A modified or isolated composition, comprising:

a plurality of first polymers, each of said first polymers having first functional groups comprising a first nucleic acid sequence attached as side-chains thereto;

a plurality of second polymers, each of said second polymers having second functional groups comprising a second nucleic acid sequence attached as side-chains thereto, said first and said second functional groups capable of reversibly forming a reversible cross-link between said first and said second polymers wherein said cross-link comprises a plurality of hydrogen bonds between complementary base portions of said first and said second nucleic acid sequences; and

a third nucleic acid sequence, wherein at least one of said first nucleic acid sequence or said second nucleic acid sequence further comprise a nucleic acid sequence that is sufficiently complementary to said third nucleic acid sequence that said third nucleic acid sequence facilitates a dissociation of said cross-link.

7. The composition as recited in claim 1 , further including a third nucleic acid sequence capable of attaching to said first and said second nucleic acid sequences to facilitate formation of said cross-link.

8. A modified or isolated composition, comprising:

a plurality of first polymers, each of said first polymers having first functional groups comprising a first nucleic acid sequence attached as side-chains thereto;

a plurality of second polymers, each of said second polymers having second functional groups comprising a second nucleic acid sequence attached as side-chains thereto, said first and said second functional groups forming a reversible cross-link between said first and said second polymers, wherein said cross-link comprises a plurality of hydrogen bonds between complementary base portions of said first and said second nucleic acid sequences;

a third nucleic acid sequence capable of attaching to said first and said second nucleic acid sequences to facilitate formation of said cross-link; and

a fourth nucleic acid sequence, wherein said third nucleic acid sequence further comprises a nucleic acid sequence that is sufficiently complementary to said fourth nucleic acid sequence that said fourth nucleic acid sequence facilitates a dissociation of said cross-link.