*Article* **New Hydrogel Network Based on Alginate and a Spiroaceta Copolymer**

**Alina Elena Sandu, Loredana Elena Nita \*, Aurica P. Chiriac , Nita Tudorachi, Alina Gabriela Rusu and Daniela Pamfil**

> "PetruPoni" Institute of Macromolecular Chemistry, Grigore Ghica Voda Alley 41-A, RO-700487 Iasi, Romania; sandu.alina@icmpp.ro (A.E.S.); achiriac@icmpp.ro (A.P.C.); ntudor@icmpp.ro (N.T.); rusu.alina@icmpp.ro (A.G.R.); dpamfil@icmpp.ro (D.P.)

**\*** Correspondence: lnazare@icmpp.ro

**Abstract:** This study reports a strategy for developing a biohybrid complex based on a natural/synthetic polymer conjugate as a gel-type structure. Coupling synthetic polymers with natural compounds represents an important approach to generating gels with superior properties and with potential for biomedical applications. The study presents the preparation of hybrid gels with tunable characteristics by using a spiroacetal polymer and alginate as co-partners in different ratios. The new network formation was tested, and the structure was confirmed by FTIR and SEM techniques. The physical properties of the new gels, namely their thermal stability and swelling behavior, were investigated. The study showed that the increase in alginate content caused a smooth increase in thermal stability due to the additional crosslinking bridges that appeared. Moreover, increasing the content of the synthetic polymer in the structure of the gel network ensures a slower release of carvacrol, the encapsulated bioactive compound.

**Keywords:** hybrid gel network; natural/synthetic polymer conjugate; alginate; poly(itaconic anhydride-co-3,9-divinyl-2,4,8,10-tetra-oxa-spiro[5.5]undecane); bio-applications
