**1. Introduction**

Biomaterial scaffolds are materials which have been engineered to interact with our biological system in providing three-dimensional structure and mimicking an extracellular matrix (ECM). Therefore, it is crucial to design biologically active scaffolds with well interconnected configuration and surface chemistry to enhance the cellular interactions on the scaffold interface [1,2]. The scaffold interface would enhance and facilitate the cell infiltration, proliferation and differentiation of cell lines, and eventually contribute to the tissue regeneration.

**Citation:** Vigneswari, S.; Gurusamy, T.P.; Khairul, W.M.; H.P.S., A.K.; Ramakrishna, S.; Amirul, A.-A.A. Surface Characterization and Physiochemical Evaluation of P(3HB-*co*-4HB)-Collagen Peptide Scaffolds with Silver Sulfadiazine as Antimicrobial Agent for Potential Infection-Resistance Biomaterial. *Polymers* **2021**, *13*, 2454. https:// doi.org/10.3390/polym13152454

Academic Editors: Ariana Hudita and Bianca Galˇ a¸ˇteanu

Received: 4 July 2021 Accepted: 20 July 2021 Published: 26 July 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Polyhydroxyalkonates (PHAs) are insoluble granules accumulated in cell cytoplasm as carbon and energy storage compounds under stress conditions [3–5]. PHAs are a biodegradable thermoplastic which exhibit similar thermo-mechanical properties to synthetic polymers [6]. Among the variety of PHAs, copolymer P(3HB-*co*-4HB) is widely used in biomedical applications due to the non-toxic biodegradation products, wide range of physical and mechanical properties, non-carcinogenic effects and biocompatibility [7]. It possesses exceptional properties for medical and pharmaceutical fields [8,9]. Moreover, P(3HB-*co*-4HB) has Food and Drug Administration (FDA) clearance for clinical usages among all the other PHAs available [3]. The P(3HB-*co*-4HB) was biosynthesized by bacterium *Cupriavidus necator* (formally *Ralstonia eutropha*) from structurally related sources such as 4-hydroxybutyric acid (4HBA), 4-chlorobutyric and γ-butyrolactone [7].

However, P(3HB-*co*-4HB) lacks active functional sites for cell attachment which limits the applications for regenerative medicine. Many studies have been carried out in this direction to overcome this limitation. Therefore, surface modification is carried out by incorporating natural polymers, such as collagen, gelatin, pullulan and chitosan, in enhancing the hydrophilicity of the scaffolds [10]. Nevertheless, the desirability and wide applicability of collagen is often attributed to its abundance in the human body as the key structural fibrous protein of the ECM [11]. Hence, collagen peptide was used as the biomolecules to enhance the hydrophilicity of the scaffolds fabricated in our study. Collagen peptide is a biomolecule which not only has the ability to improve the hydrophilicity of the scaffold but has the natural ability to interact with host cells [12,13].

Biomaterial scaffold-affiliated microbial infections are an emerging threat in clinical practices, which cause serious infection and impact healing. Therefore, designing scaffolds with antimicrobial efficacy have extensively gained priority in resolving biomaterialassociated infections [14]. Silver sulfadiazine (SSD) is an antibacterial agent that exhibits broad-spectrum antibacterial activity against Gram-positive and Gram-negative bacteria, as well as fungi, even at very low concentrations [15–17]. SSD is a much preferred antibacterial agent of choice due to the ability of SSD to reduce early infections at low concentration. However, currently available formulations of antimicrobial agents lack the ability to control the release of antimicrobial properties [18,19]. There are many scaffolds developed with antimicrobial properties and Table 1 lists common examples of antimicrobial biopolymer incorporated with SSD.


**Table 1.** List of common examples of various antimicrobial scaffolds incorporated with SSD.

Following the aforementioned background, in the present work, the surface architecture of P(3HB-*co*-4HB) was enhanced by incorporating collagen peptides and silver sulfadiazine (SSD) as the antimicrobial mechanism agent. Two different scaffolds, namely SSD coat/collagen peptide coat-P(3HB-*co*-4HB) [SSCC] and SSD blend/collagen peptides coat-P(3HB-*co*-4HB) [SBCC] scaffold, were fabricated by the combination of salt leaching

and freeze-drying techniques which are low cost and apply green technology to fabricate the scaffolds. The study provides evidence for increased hydrophilicity due to the incorporation of collagen peptide. This elucidates surface interface-cell interactions of the modified P(3HB-*co*-4HB) scaffolds and release mechanism of the antimicrobial agent from the scaffolds, thus driving the research effort forward for emerging infection-resisting biomaterials in tissue engineering and regenerative medicine in the future.
