## 4 SSHies: An Era of Research
### Blockchain-Based Techniques in HIE Systems: A Background  
In [58], the authors identified blockchain features such as distributed storage and authentication as well as applications like smart contracts and identity verification. It also highlighted limitations such as lack of standardization, decentralized storage and privacy issues, key management, scalability, and IoT overhead. The study analyzed a set of 70 papers and presented an overview of the blockchain in the healthcare domain, comparing each blockchain by describing its advantages and limitations. The study in [59] investigated the use of blockchain technology in healthcare, focusing on its limitations and potential future developments. The methodology involved analyzing and classifying selected papers into five categories using the PRISMA statement: electronic medical records, health data security and management, medical research and diagnosis, IoT architectures for healthcare, and other applications. The findings indicated that the research predominantly centers on leveraging blockchain features, such as security and immutability, to safeguard and oversee sensitive patient information. The paper [43] presents a survey on the challenges and issues of using blockchain and smart contracts for healthcare access control. It focuses on smart contract mechanisms, blockchain-based smart contract architecture, and platforms like Ethereum and Hyperledger. The paper also discussed permission-less and permissioned blockchain-based EHR access control methods, their taxonomy, consensus protocols, and storage types. The paper also discussed the identification of smart contracts, authentication/authorization methods, and storage types for healthcare information systems (HERs). Study [60] aimed to understand the role of patients in patient-centric healthcare information exchange (HIE). It identified two groups of antecedents: patient-related factors and healthcare system factors. The study also connects attitudes towards patient engagement to willingness to participate in HIE and perceived privacy concerns. The findings revealed that patient-related elements notably influence patient inclinations towards care management involvement, with the connection between patient engagement and readiness to engage in HIE being more pronounced among those who perceived lower levels of privacy and security apprehensions. The authors of [61] presented a review concerning the secure sharing of healthcare data based on blockchain technology. The proposed review classified the studied papers into three categories: blockchain-based data security [46; 62; 63; 64; 65; 66; 67], blockchain with IOMET [68; 69; 70; 71; 72], and blockchain with medical federal learning. The study showed that federated learning has emerged as a novel AI method designed to safeguard data privacy, allowing multiple nodes to collectively learn a model while only transmitting gradients and losses between nodes. Consequently, blockchain and smart contracts (SCs) hold inherent advantages in managing medical data due to their tamper-proof and traceable nature. Study [41] aimed to conduct a systematic review of research papers exploring the application of blockchain technology in healthcare and to analyze its attributes. The findings from the selected papers were analyzed, and the quality of the publications was assessed. The primary motivations behind the adoption of blockchain technology in the healthcare industry were identified as ensuring data integrity, controlling access, logging data, versioning data, and providing non-repudiation. These findings contribute to a better understanding within the scientific community of the implementation aspects of blockchain technology and its potential applications in the healthcare sector. In [42], the authors conducted a survey of research on blockchain technology in patient care, identifying challenges and providing a research agenda for future studies.