Compositions that reversibly gel and de-gel

1. A modified or isolated composition, comprising:

a gel including:

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.

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 a sequence of at least ten bases in said first nucleic acid sequence is complementary to at least a portion of 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. 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.

7. The composition as recited in claim 1 , wherein at least about 50 percent of bases in said first nucleic acid sequence are complementary to at least a portion of said second nucleic acid sequence.

8. The composition as recited in claim 1 , wherein at least 99 percent of bases in said first nucleic acid sequence are complementary to at least a portion of said second nucleic acid sequence.

9. The composition as recited in claim 1 , wherein internal complementarity within said first nucleic acid sequence and within said second nucleic acid sequence are both less than about 30 percent.

10. The composition as recited in claim 1 , wherein internal complementarity within said first nucleic acid sequence and within said second nucleic acid sequence are both less than about 10 percent.

11. The composition as recited in claim 1 , wherein said gel has a melting temperature of about 55° C.

12. The composition as recited in claim 1 , wherein said first polymer and said second polymer comprise a polymethylmethacrylate.

13. The composition as recited in claim 1 , wherein said first polymer and said second polymer comprise a polymethylmethacrylate.

14. The composition as recited in claim 1 , wherein said first polymer and said second polymer comprise a polyacrylamide.

15. The composition as recited in claim 1 , wherein said first polymer and said second polymer comprise a polyvinyl alcohol.

16. The composition as recited in claim 1 , wherein one of said first polymer or said second polymer comprises a polymethylmethacrylate, a polyacrylamide or a polyvinyl alcohol, and the other of said of said first polymer or said second polymer comprises a different polymer than said one.

17. The composition as recited in claim 16 , wherein said first polymer is a polyacrylamide and said second polymer comprises a different polymer than said one polymer.